Torque Arm on an S197

[Whiskey11]

Roll steer (whether under or over) occurs as a result of a difference in the suspension height between the left and the right resulting in a difference in horizontal length of the lower control arms that locate the axle. That difference in horizontal length causes the axle to rotate relative to the chassis.

If you stiffen the rear sway bar, the end result will be less of a difference in the suspension height between the left and right side for a given amount of side loading, and thus less roll steer when taking a given curve at a given speed. I expect you'd have to stiffen the front as well if you wanted to maintain the same understeer/oversteer balance.


Considering the root cause of roll steer, I don't see how changing the sway bar wouldn't have an effect on it.


Cool. Thanks!

So you are advocating for Chapman's law at the expense of the driveability of the car and everything that comes with a stiffer rear swaybar. I'm not sure that is the route I'd want to take. Sam Strano's Hellwigg made 25mm rear bar in it's stiffest setting is only 225lbs/in of deflection. Not enough to really "limit" the motion of the rear of the car and in doing so you are adding a ton of oversteer on top of the roll oversteer. The Ford 25mm on the Boss 302 and the 26mm on the Boss 302 Laguna Seca are stiffer at 250 and 275 lbs/in but again why with the bar? I can't remember what book it was in but there was a video called "Minding your anti's" which is probably worth watching.

One of the many reasons Filip at Cortex designed the Torque Arm setup for the S197 was to allow for greater bite (and %AS) without effecting roll steer so that IS an advantage of the Torque Arm setup over the 3 link but you have to decide if the end results are worth it to you or not because it will change the way you drive the car.

I don't think you will want to go the route you are going either with springs or swaybars with high amounts of roll oversteer. That just sounds like a twitchy headache inducing mess to me.

 

[Norm Peterson]

Okay, but with a suspension geometry that prevents the rear axle from moving relative to the body that way, what it means is that the load on the rear tires will reach a steady state condition more quickly than they would in the case where the suspension is able to move.

I'm not convinced that that is the case here. When more of the load transfer is being taken geometrically, less is available for accelerating the rear of the car upward. The rear of the car is, of course, essentially constant mass. Less force, same mass . . .

The brake hop situation probably involves tire behavior on the back side of your tires' mu-slip curve. Out there you have more grip at lower %slip (analogous to slip angles), which is opposite to what happens when operating on the left side of the peak where you really want to be if you can't be right at the peak. But brake hop has been clearly tied to too much A-S%. The easy fixes are to fix the geometry and/or use less aggressive rear brake pads. Both of those fixes specifically affect the anti-lift, since A-L is the product of A-S and the amount of braking force coming from the rear expressed as a fraction of the total braking force. 50% A-S times 30% rear braking = 15% A-L (typical), and 100% A-S times a 50% in-your-dreams amount of rear braking is still only 50% A-L, so you aren't going to affect rear vertical body motion by a huge amount geometrically.


Even a 3-link with positive A-S% will lift load off the rear tires under braking, just that it's a little harder to visualize. But once you think in terms of the virtual side view swing arm instead of individual links it should become apparent that the UCA and LCAs combine to behave as a virtual beam that pivots about the side view instant center (SVIC) - much like a TA pivots about its physical chassis side pivot. Very much virtual, since the imaginary pivot point moves around quite a lot (several feet!) as the suspension moves in bump/rebound. I suppose you could consider the UCA to be the virtual arm's top flange and the LCAs its bottom flange with no web in between physically tying them together - that is more or less what's happening structurally.

That the SVIC typically moves further forward under braking/tail lift is a 3-link advantage. That it moves rearward during squat - quite possibly to a location rearward of a good TA SVIC location - theoretically hurts its performance on an aggressive launch.

Strictly speaking, a TA-suspended axle does not pivot about the TA's pivot, but a virtual point determined in part by the TA pivot, TA inclination, and LCA inclination. But because the TA's own pivot is at an essentially fixed location, the TA's SVIC cannot migrate very far in any direction. Probably less than an inch.

The S197 A-S% is in the low 30's % range and will depend on the actual ride height. With stock springs, it'll drop about a percent from there when an average-weight driver gets in.


Norm

 

[kcbrown]

KC: I think that you may be focusing on one particular sapling in a FOREST of trees... The "time slice" that you're really dialing into is about 250mS wide (if that) for the transition between straight-line acceleration into braking at the entry to a braking zone, before the suspension "sets" from load transfer. During that period, where you are probably correct in that the grip available is variable, you should be smoothly ramping up the braking forces to ABS threshold, so the variability in loading is immaterial at best.

One would think. I would expect that with a smaller transition time, smooth application of the brakes would be more critical. I can see how it would be a bit more demanding to drive in that you couldn't just stab the brakes to the same degree (note, however, that the load transfer is not just a function of the rear suspension, but also of the front, so even if you had no lift in the rear whatsoever and thus an instantaneous transition back there, the front suspension is still going to compress from the transfer of forces and it'll take some amount of time to reach its steady state).

Probably the biggest variable in that transitional period is the track surface, and it's ability to provide grip, which will NOT be modified by the suspension geometry in any event. In essence, you are "feeling for grip" just as you would in a corner.

While I did bring up roll-steer as an example of a negative effect associated with high A/S, Whiskey and Sheiza are dead on the money about trying to tune that effect out with the rear bar. The more bar you dial in, the less grip you have on that end of the car, which would actually exaggerate the over-steer tendencies of the rear.

I'm skeptical.

Consider, again, the case where you have a car with the springs and shocks replaced by solid arms, and you're driving on a smooth surface. You put this car into a turn. Why would it have any less grip at the limit than a car with springs and shocks and the same size tires in the steady state?

It seems to me that understeer or oversteer are the result of relative grip resulting from corner to corner force transfers. Merely adding more bar in one place or another would not change the total grip of the car in the steady state if you also add more bar in the other location. But stiffening the bars in that way does have an undesirable effect on the behavior of the suspension when going over bumps in the road on one side and not the other, so it's a compromise.

I think what you need to do (other than your stated plan to drive it as-is and see what really needs to be fixed) is separate cause and effect. The S197, even in stock form, certainly isn't "diabolical" under hard braking. Does the rear end lift? Yes. Is there a measure of rear instability under hard braking? Yes, but... It really doesn't show it's head until you've seriously increased grip levels (think slicks and very aggressive race pads) to create enough transfer to really unload the rear.

Well, I'm already noticing a bit of dive in the car merely from normal braking, so I can only imagine what it'll do at the limit (I'm going to have to try that somewhere safe just to see it for myself). Since I don't really want to compromise ride quality, I see no way to reduce that other than by playing with AS%.

I agree, however, that it's immensely important to cleanly separate cause and effect.

If this tendency becomes bothersome, THEN start looking at the car as a whole and figure out what needs fixing on a large scale first. If it's diving too hard, fine. Is it also rolling too much? If so, then increase the spring rates to fix the problem first, before you start doing anything else.

Right. But increasing the spring rates will result in a harder ride unless shock compression is reduced to compensate (and I expect the Koni Sports do not -- but maybe they do. Anyone got test data for the Koni Sports compared with the Brembo package stock shocks?), and the car is already fairly close to my limits on that. I might be able to tolerate the spring rates of the Boss 302, and performing that experiment is insanely cheap ($80 for the springs both front and rear) but I expect that'll be it as far as my limits go.

Once you put "proper" springs on the car, with dampers that can control them properly, you may find that the braking issues are reduced to the point of being a non-issue. IF they're still there, and they actually bother you, then perhaps you should look at front anti-dive.

I would certainly agree with you if stiffening the springs significantly were an option.

All I can say at this point is that without driving the car on the track, there's just no way for me to know how much I'll like how it handles there, so I'm not doing squat until I've got seat time in the car in stock form.

The S197 really isn't a warmed-over FOX body. To track a FOX, you had to do a LOT of things to it just to prevent it from tripping over it's feet in a corner. Not so with the S197. I'm sure you recall Randy Pobst's back-to-back runs in a GT and an M3? Within a couple of tenths... That, right there, tells me that the car is capable in stock form. Yes, the springs are far too soft, and yes the dampers suck, but that would be the MOST I would change on the car until I really had a handle on the idiosyncrasies of the chassis.

The most interesting question is this: what if you simply improve the quality of the dampers? Pobst's main complaint seemed to be that the dampers didn't control the motion very well. I'm curious if anyone's running Koni Sport shocks on the stock Brembo springs and, if so, if there was any notable benefit from it.

Look at the BOSS 302R/S race cars: Very short relocation brackets to compensate for the lowered ride height, but otherwise nothing trick with the rear suspension.

Right, I realize that. It's what drew me to the track pack Mustang GT in the first place, rather than tricking out my Fox body GT (that the current body style looks so good in comparison certainly made it easier!). This is another reason that I'm not inclined to mess with anything right off the bat. What I'm doing in this thread is thinking through the problems that are currently visible to me, and what can be done about them given the constraints I expect I'll be operating under.

 

[kcbrown]

I'm not convinced that that is the case here. When more of the load transfer is being taken geometrically, less is available for accelerating the rear of the car upward. The rear of the car is, of course, essentially constant mass. Less force, same mass . . .

That's a good point, and illustrates the limit of thinking of the suspension as having solid links instead of the springs and shocks...

So it may be that the transition time is about the same (less force, same mass, but the energy absorber is a spring and shock combination). The shock will complicate the picture a bit because it has a nonlinear response if I'm not mistaken.

The brake hop situation probably involves tire behavior on the back side of your tires' mu-slip curve. Out there you have more grip at lower %slip (analogous to slip angles), which is opposite to what happens when operating on the left side of the peak where you really want to be if you can't be right at the peak. But brake hop has been clearly tied to too much A-S%.

So this is essentially independent of how the AS% is achieved? Interesting. If so, then one will be forced to limit AS% for that reason alone.

The easy fixes are to fix the geometry and/or use less aggressive rear brake pads. Both of those fixes specifically affect the anti-lift, since A-L is the product of A-S and the amount of braking force coming from the rear expressed as a fraction of the total braking force. 50% A-S times 30% rear braking = 15% A-L (typical), and 100% A-S times a 50% in-your-dreams amount of rear braking is still only 50% A-L, so you aren't going to affect rear vertical body motion by a huge amount geometrically.

I wouldn't want to use less aggressive rear pads in any case, since what I'd want is maximum braking capability, as long as the rear pads aren't so aggressive that the rears reach the point of breaking traction before the fronts (I'd think you'd want the opposite, actually: you'd want the fronts to reach that point right before the rears do to keep the rear from coming around on you).

Even a 3-link with positive A-S% will lift load off the rear tires under braking, just that it's a little harder to visualize.

Well, yes, that's essentially impossible to avoid. Even if the rear suspension were nailed down, the rear tires would be under less load as the body of the car pivots around the SVIC.

The S197 A-S% is in the low 30's % range and will depend on the actual ride height. With stock springs, it'll drop about a percent from there when an average-weight driver gets in.

So let's say one puts a torque arm on the car. How does one go about tuning the AS% with such as setup?

 

[SoundGuyDave]

One would think. I would expect that with a smaller transition time, smooth application of the brakes would be more critical. I can see how it would be a bit more demanding to drive in that you couldn't just stab the brakes to the same degree (note, however, that the load transfer is not just a function of the rear suspension, but also of the front, so even if you had no lift in the rear whatsoever and thus an instantaneous transition back there, the front suspension is still going to compress from the transfer of forces and it'll take some amount of time to reach its steady state).

First off, you should never "stab" the brakes. It's all about a smooth yet rapid ramp-up in force from 0-100%. Doing that allows the loads to transfer smoothly, without the tendency to "pogo" the front end from momentum.

Consider, again, the case where you have a car with the springs and shocks replaced by solid arms, and you're driving on a smooth surface. You put this car into a turn. Why would it have any less grip at the limit than a car with springs and shocks and the same size tires in the steady state?

As the CG shifts to one side (and it will, even if only from tire carcass deflection), more force is distributed to the outside wheel, and that has to come from someplace, in this case, the inside wheel. In short, you're robbing Peter to pay Paul at that point.

It seems to me that understeer or oversteer are the result of relative grip resulting from corner to corner force transfers. Merely adding more bar in one place or another would not change the total grip of the car in the steady state if you also add more bar in the other location. But stiffening the bars in that way does have an undesirable effect on the behavior of the suspension when going over bumps in the road on one side and not the other, so it's a compromise.

When you add a sta-bar (or stiffen it), it acts as a lever force. In the case of a car in a corner, transitional or steady-state, as the chassis rolls, this lever force acts to redirect force from the unloaded wheel onto the loaded wheel. In essense, it applies force to the axle in an opposite manner to the chassis's motion. This leads to one of two things. If the forces are sufficient, you can overload the outside tire, causing loss of grip, and thus oversteer as the rear end tries to whip around on you. If the forces are NOT sufficient to overload the outside tire, then additional load is placed on the outside tire at the expense of load on the inside tire. Since tire load to grip is not a linear relationship, you have a net loss of tractive capability, and thus oversteer as the rear end tries to whip around on you. It's an old racer's trick that if you need to run in the rain, you pull the rear bar off the car completely. That increases rear grip, putting the car into a (much safer, easily controlled) understeering tendency.

Well, I'm already noticing a bit of dive in the car merely from normal braking, so I can only imagine what it'll do at the limit (I'm going to have to try that somewhere safe just to see it for myself). Since I don't really want to compromise ride quality, I see no way to reduce that other than by playing with AS%.

I agree, however, that it's immensely important to cleanly separate cause and effect.

And I think you'll find that the rear-end lift is an effect, not a cause. In other words, don't treat the symptom...

Right. But increasing the spring rates will result in a harder ride unless shock compression is reduced to compensate (and I expect the Koni Sports do not -- but maybe they do. Anyone got test data for the Koni Sports compared with the Brembo package stock shocks?), and the car is already fairly close to my limits on that. I might be able to tolerate the spring rates of the Boss 302, and performing that experiment is insanely cheap ($80 for the springs both front and rear) but I expect that'll be it as far as my limits go.


I would certainly agree with you if stiffening the springs significantly were an option.

I think you may be surprised at how manageable higher spring rates really are. I'm personally running 350/300, and with the damper rebound dialled way back, they're actually quite comfortable. There are a lot of factors that go into perceived ride quality, and raw spring rate is only one, and arguably not the most important.[/quote]

All I can say at this point is that without driving the car on the track, there's just no way for me to know how much I'll like how it handles there, so I'm not doing squat until I've got seat time in the car in stock form.


The most interesting question is this: what if you simply improve the quality of the dampers? Pobst's main complaint seemed to be that the dampers didn't control the motion very well. I'm curious if anyone's running Koni Sport shocks on the stock Brembo springs and, if so, if there was any notable benefit from it.

I think it might just open your eyes. Also, don't be afraid to play with spring rates as well. When you're done with your first track day or two with the stock chassis, draw up a list of "bitches" about what you experienced, but be selective about how you phrase them. Try to get to the heart of the matter and not get hung up in small details. As an example list:

1) Car pitches too much on braking (not "rear end lifts" or "nose dives")
2) Car understeers at corner entry, but is neutral at mid-corner
3) Car is slow to take a set at turn-in, seems to overcorrect during/after transfer
4) ...

Once you have that list in hand, try to eliminate any "one-time" items, and then work on eliminating any that might have been caused by driving technique errors. If you discover you have a tendency to treat the throttle as an on/off switch, you can pretty much discard "oversteers at corner exit" or "loose under power" if you get my drift.

When you finally pare down that list to what you feel is really "wrong" with the car, THEN start looking for common modalities. If you have "pitches under braking" as well as "rolls too much in corners," then you NEED to up the spring rates, since that's the common modality.

As a final bottom line, you may find yourself in a compromise situation, where the "proper" fix to an issue is one you can't pull the trigger on due to other factors. You'll never get a "Cadillac-soft" suspension to pull 1.2G in a corner, but by the same token, a suspension that WILL carve through a corner may be too harsh to tolerate on a daily-driver. Understanding those limitations will go a long way towards putting together the best possible "package" for your particular needs.

 

[Norm Peterson]

I wouldn't want to use less aggressive rear pads in any case, since what I'd want is maximum braking capability, as long as the rear pads aren't so aggressive that the rears reach the point of breaking traction before the fronts

Sometimes you have to settle for the lesser of two "evils". Here it's either dial back the A-S% (which is apparently very much not a preference) or sacrifice rear braking (even less desirable). You get to pick one or the other, unless there's a "some of each" compromise that works for you individually.

So let's say one puts a torque arm on the car. How does one go about tuning the AS% with such as setup?

Tweaking the LCA side view inclination would be the easiest, though this drags you into an A-S vs axle roll steer compromise (argument?). If you're up for skewing the LCAs in plan view and doing all the necessary fab work including new chassis pickup points of sufficient strength and stiffness, you could then tweak the above compromise such that axle roll steer at least becomes somewhat less sensitive to changes in ride height.

An adjustable-length TA is theoretically another approach.


Norm

 

[kcbrown]

First off, you should never "stab" the brakes. It's all about a smooth yet rapid ramp-up in force from 0-100%. Doing that allows the loads to transfer smoothly, without the tendency to "pogo" the front end from momentum.

Oh, I agree. I'm not saying that stabbing at the brakes is ever a good thing to do, only that a car which transfers the forces more quickly will be more sensitive to braking technique.

As the CG shifts to one side (and it will, even if only from tire carcass deflection), more force is distributed to the outside wheel, and that has to come from someplace, in this case, the inside wheel. In short, you're robbing Peter to pay Paul at that point.

Yes, but that's true even for a car with sticks for the springs and shocks. Which is to say, except for perhaps a slight change in the CG location of the chassis due to body roll, I don't see how there could possibly be any difference at all in the forces on the tires in the steady state condition between the car with springs/shocks and the car with sticks.

When you add a sta-bar (or stiffen it), it acts as a lever force. In the case of a car in a corner, transitional or steady-state, as the chassis rolls, this lever force acts to redirect force from the unloaded wheel onto the loaded wheel. In essense, it applies force to the axle in an opposite manner to the chassis's motion. This leads to one of two things. If the forces are sufficient, you can overload the outside tire, causing loss of grip, and thus oversteer as the rear end tries to whip around on you.

Right, but that's happening because the front suspension isn't lifting the inside wheel by as much, so that wheel gets more contact force during the transition and, because the spring on that side is allowed to extend further, in steady state as well. And as a result, the relative force distribution results in oversteer.

In other words, what I'm saying here is that I can see how this will be an effect if you adjust one end without making a corresponding adjustment to the other. That's exactly why I said that if you increase the bar in the rear to mitigate roll oversteer, you'd have to increase the bar in the front to compensate for the imbalance you'd be creating.

But if you have front versus rear balance, I see no reason that the car with the stiffer bars would achieve any less grip than the one without, because in the steady state condition, all the forces are stabilized, all the weight/force transfer has finalized, and the car can now be analyzed with a static force model.


From the static force model point of view, there is no difference between a car with relatively compliant springs/shocks and very strong sway bars, and a car with very stiff springs/shocks and very weak sway bars. The external forces on the car at all contact patches are the same.

And I think you'll find that the rear-end lift is an effect, not a cause. In other words, don't treat the symptom...

Well, yeah, but treating the root cause would either require geometry changes to the suspension that are not reasonably available (e.g., lengthening the LCAs) or would involve compromising something else (e.g., ride quality).

I think you may be surprised at how manageable higher spring rates really are. I'm personally running 350/300, and with the damper rebound dialled way back, they're actually quite comfortable. There are a lot of factors that go into perceived ride quality, and raw spring rate is only one, and arguably not the most important.

Understood. Unfortunately, stiffer springs are generally also accompanied by shorter suspension travel, so you've no choice but to deal with a harder ride simply because absorbing the same amount of momentum in less distance means greater exerted force which means a harder ride. You can't escape physics here...

I think it might just open your eyes. Also, don't be afraid to play with spring rates as well. When you're done with your first track day or two with the stock chassis, draw up a list of "bitches" about what you experienced, but be selective about how you phrase them. Try to get to the heart of the matter and not get hung up in small details. As an example list:

That's exactly what I plan on doing.

1) Car pitches too much on braking (not "rear end lifts" or "nose dives")

I agree that it's important to cleanly identify the visible symptom, but it's also important to cleanly identify its component symptoms. For instance, pitching too much can be from both nose dive and rear lift, and you'd have to identify the degree to which each is happening in order to know what to address and, as importantly, by how much.

When you finally pare down that list to what you feel is really "wrong" with the car, THEN start looking for common modalities. If you have "pitches under braking" as well as "rolls too much in corners," then you NEED to up the spring rates, since that's the common modality.

Right, I agree for the most part. However, everything depends on what compromises are involved in each modification that would address the issue. What works for many (upping the spring rates) might not work well for others.

As a final bottom line, you may find yourself in a compromise situation, where the "proper" fix to an issue is one you can't pull the trigger on due to other factors. You'll never get a "Cadillac-soft" suspension to pull 1.2G in a corner

Well, you might, but you might have to spend $30k or so on a computer-controlled magnetically-actuated suspension system.

And I suspect that, at the end of the day, the amount of grip you get in the corner is going to be controlled almost exclusively by tire size, compound, and design. The rest of the suspension controls the balance and the transitional behavior (for instance, a car with very soft springs and shocks and which has no sway bars at all might do very well on the skidpad but very badly through a slalom. The transitional responsiveness of the car matters, and a 250 millisecond transition phase seems like it would be a very long time, easily enough to make the car feel sloppy and unresponsive).

, but by the same token, a suspension that WILL carve through a corner may be too harsh to tolerate on a daily-driver. Understanding those limitations will go a long way towards putting together the best possible "package" for your particular needs.

Right. And there's no way to know where those limits really are except through experimentation.

It's why I expect that my approach is going to be "cheap but good first", e.g. switch to Koni Sport dampers while keeping the stock springs, then (maybe) make relatively minor changes to the springs first (e.g., try the Boss 302 springs which are cheap before going with more expensive springs).

 

[SoundGuyDave]

Didn't this forum used to quote through previous posts? I fear that some of the comprehension is being lost without the conversational context...

Oh, I agree. I'm not saying that stabbing at the brakes is ever a good thing to do, only that a car which transfers the forces more quickly will be more sensitive to braking technique.

I'd have to do the math on this, but I don't think that's necessarily the case. More on this later...

Yes, but that's true even for a car with sticks for the springs and shocks. Which is to say, except for perhaps a slight change in the CG location of the chassis due to body roll, I don't see how there could possibly be any difference at all in the forces on the tires in the steady state condition between the car with springs/shocks and the car with sticks.

Which was my description answering your question about force transfer with a rigid suspension... Also, with a rigid-suspension model, there IS no body roll relative to the chassis. As there is no "give" in the suspension, if the body does not remain parallel to the ground, you have lifted the inside tires completely off the ground.

Discussing adding or increasing rear sta-bar stiffness...

Right, but that's happening because the front suspension isn't lifting the inside wheel by as much, so that wheel gets more contact force during the transition and, because the spring on that side is allowed to extend further, in steady state as well. And as a result, the relative force distribution results in oversteer.

In other words, what I'm saying here is that I can see how this will be an effect if you adjust one end without making a corresponding adjustment to the other. That's exactly why I said that if you increase the bar in the rear to mitigate roll oversteer, you'd have to increase the bar in the front to compensate for the imbalance you'd be creating.

But if you have front versus rear balance, I see no reason that the car with the stiffer bars would achieve any less grip than the one without, because in the steady state condition, all the forces are stabilized, all the weight/force transfer has finalized, and the car can now be analyzed with a static force model.


From the static force model point of view, there is no difference between a car with relatively compliant springs/shocks and very strong sway bars, and a car with very stiff springs/shocks and very weak sway bars. The external forces on the car at all contact patches are the same.

Yes, to a point. The difference between the soft-spring/big-bar and hard-spring/soft-bar has been argued for ages. The each have their application. For sake of argument, let's take a look at two theoretical models, one with 150lb/in springs and 350lb/in bars, the other with 350lb/in springs and 150lb/in bars. Assume (for simplicity) a 3000lb car, with 50/50 f/r distribution as well as 50/50 l/r. That equates to 750lbs per corner. In a steady-state cornering condition (skidpad), if you pull 1G laterally, that means you are transferring 750lbs from side to side. In BOTH cases, the outside suspension compresses 1.5", since the wheel rates are identical. No difference at all. Cool. Now, transition those same models from steady-state cornering to steady-state deceleration, also at a rate of 1G. Now, we'll see a bit of a difference, as the sta-bars are no longer part of the equation (assuming frictionless bushings, etc.). The soft/big car will now transfer that 750lb load onto 150lb springs, which will compress the front FIVE INCHES. The hard/small car will transfer the same load, but with 350lb springs, the compression is just a tick over two inches.

Given that disparity in motion relative to rest, which car do you think will be more responsive? Which do you think will be more stable? Think it through in the terms of force, distance, and time...

Well, yeah, but treating the root cause would either require geometry changes to the suspension that are not reasonably available (e.g., lengthening the LCAs) or would involve compromising something else (e.g., ride quality).

Unfortunately, stiffer springs are generally also accompanied by shorter suspension travel, so you've no choice but to deal with a harder ride simply because absorbing the same amount of momentum in less distance means greater exerted force which means a harder ride. You can't escape physics here...

I think it's time to delve into the mysteries of NVH as they're applied to the subjective "ride quality." I honestly don't know enough about NVH engineering to get into the nuts and bolts, but I do know a little bit. A "firm" ride is not necessarily perceived as "poor," as can be evidenced by the massive sales of the BMW 3-series platform. C&D "top 10" for 30 years and all that. The rebound characteristics of the 3-series are considerably stiffer than those present in a stock Mustang, but nobody really complains about them. I *think* the major objection to a "harsh" ride comes from the instantaneous transmission of road irregularities into the chassis, resulting in VERY high transient acceleration rates for the occupants. Perhaps somebody with a background in NVH could chime in here?

I agree that it's important to cleanly identify the visible symptom, but it's also important to cleanly identify its component symptoms. For instance, pitching too much can be from both nose dive and rear lift, and you'd have to identify the degree to which each is happening in order to know what to address and, as importantly, by how much.

Agreed, as far as it goes. If, however, that pitching is part of a larger problem, trying to figure out which end is "off" is wasted time.

And I suspect that, at the end of the day, the amount of grip you get in the corner is going to be controlled almost exclusively by tire size, compound, and design.

I will grant you that those will be the LARGEST factors, but they are hardly the exclusive factors. Another comparison from my archives... On a soft/big suspension (2009), my best time at Putnam Park was 1:26, running with 275 Hoosier R6 tires. In 2010, on a hard/small suspension, running 275 Hoosier R6 tires, my times dropped to 1:21. Granted, the days were not identical, however, both were beautiful, sunny, cooler days. Last event 2009, first event 2010, FWIW. While weather may have been a factor, it certainly wasn't worth five seconds on a 2-mile track! The NASCAR boys use the soft-spring big-bar approach to absolutely dump the nose under braking to A) maximize the effect of the splitter for front downforce, and B) set up a slightly "loose" condition, which is net quicker through the corner. I'm sure there are other things going on, but that's a solid part of it.

The rest of the suspension controls the balance and the transitional behavior (for instance, a car with very soft springs and shocks and which has no sway bars at all might do very well on the skidpad but very badly through a slalom. The transitional responsiveness of the car matters, and a 250 millisecond transition phase seems like it would be a very long time, easily enough to make the car feel sloppy and unresponsive).

Okay, I need to clarify something here. The "250mS time slice" I was referring to was not about the time the car took to "set" in a braking event, it was about the entire time involved from the instant your foot touches the brake pedal to the point where it's at maximum pedal pressure. In amongt that 250mS window, the car transitioned from neutral (assuming right-foot braking) to a compressed, set position, with the relatively slow rate of change in direct response to the driver's foot. Depending on how far the suspension has to travel (spring rate!), the time to the "set" position can be quicker, however if you get too much velocity (spring rate!!) the load transferring can over-shoot the "set" position and momentarily unload as it yo-yos back. That momentary unloading can and will cause braking instability. THAT is what that 250mS jazz was all about. Otherwise, yes, if it took my car 1/4 second to go from neutral to set, I would be pulling my hair out!

Right. And there's no way to know where those limits really are except through experimentation.

It's why I expect that my approach is going to be "cheap but good first", e.g. switch to Koni Sport dampers while keeping the stock springs, then (maybe) make relatively minor changes to the springs first (e.g., try the Boss 302 springs which are cheap before going with more expensive springs).

While I absolutely applaud your progressive approach, I do have one cautionary question: Don't the Koni Sport dampers use shortened cartridges? I'm not positive either way, but IIRC, there was some discussion about them being shortened 1" over the stock pieces. If they are, you will gain some bump travel, but lose some rebound. Just FYI.

 

[sheizasosay]

Oh, I agree. I'm not saying that stabbing at the brakes is ever a good thing to do, only that a car which transfers the forces more quickly will be more sensitive to braking technique.
Changing forces too quickly is not good for traction period. That little "smooth" bit Dave was talking about and also the "overloading" of the tires can't be ignored. You could ignore it, but that wouldn't change the car's reaction much.

Yes, but that's true even for a car with sticks for the springs and shocks. Which is to say, except for perhaps a slight change in the CG location of the chassis due to body roll, I don't see how there could possibly be any difference at all in the forces on the tires in the steady state condition between the car with springs/shocks and the car with sticks.
How do you have body roll when a car has sticks in place of springs? The only "roll" you would get would be however much a bushing compresses, metal chassis bends or however much the tires compress. That would be "it" for body roll.

Right, but that's happening because the front suspension isn't lifting the inside wheel by as much, so that wheel gets more contact force during the transition and, because the spring on that side is allowed to extend further, in steady state as well. And as a result, the relative force distribution results in oversteer.

In other words, what I'm saying here is that I can see how this will be an effect if you adjust one end without making a corresponding adjustment to the other. That's exactly why I said that if you increase the bar in the rear to mitigate roll oversteer, you'd have to increase the bar in the front to compensate for the imbalance you'd be creating.
Just sounds like a terrible way to tune. Why would you want to get X AS% (let's say 100% for now) and then have to fix the rear steer with a big rear bar and then counter it with a big front bar to achieve a neutral handling characteristic, but with less overall grip? Too much spring rate for the tire will overload it and that is less grip. You might be able to tune the over/understeer handling, but you would just be slower around the track.

But if you have front versus rear balance, I see no reason that the car with the stiffer bars would achieve any less grip than the one without, because in the steady state condition, all the forces are stabilized, all the weight/force transfer has finalized, and the car can now be analyzed with a static force model. Looking at it a bid odd IMO. So back to the whole "apply brakes/throttle smoothly" bit....if you didn't do that, you would overload the tires and loose traction right? Without that "smooth" mindset, you would just go into the corner and jerk the hell out of the wheel for turn in.

Given that you are going to try and maximize traction in this scenario, you take a car with way too much spring rate into a corner and it will be slower if you are trying not to lose traction. Slower than a car with the "perfect" spring rate.

So if car B has more traction then it has more resistance and that makes the forces NOT equal between Car A and Car B.


From the static force model point of view, there is no difference between a car with relatively compliant springs/shocks and very strong sway bars, and a car with very stiff springs/shocks and very weak sway bars. The external forces on the car at all contact patches are the same.
See above.
.

Weird computer warning. <--ignore

Edit-Dave's post wasn't up yet when I typed this.

 

[kcbrown]

Didn't this forum used to quote through previous posts? I fear that some of the comprehension is being lost without the conversational context...

As far as I know, when you respond to a message, all you're getting is the previous message's text, and not anything that it quoted. I know how to add those quotes back in manually, but know of no way to have them added in automatically.

I'd have to do the math on this, but I don't think that's necessarily the case. More on this later...

Hmm...well, think of it like this: the springs and shocks spread what would normally be an instantaneous force out over some period of time. The shocks also absorb energy. When you subject the suspension to an instantaneous force, it spreads the application of the force out over time. While we normally think of it applying only to bumps in the road and such, it also does the same thing to the other forces seen by the suspension, such as those generated by acceleration and braking.

If you stiffen the suspension, you decrease its absorption characteristics and trade that for faster transitions. It's obviously much more complex than that as regards handling bumps in the road, but as regards braking and acceleration, it seems to me that it would be relatively straightforward, that it would have to result in faster transitions. Indeed, isn't that precisely why we stiffen the suspension, so that the car responds more quickly to things like steering inputs?

Which was my description answering your question about force transfer with a rigid suspension... Also, with a rigid-suspension model, there IS no body roll relative to the chassis. As there is no "give" in the suspension, if the body does not remain parallel to the ground, you have lifted the inside tires completely off the ground.

I meant the body roll that results from a car on springs and shocks. It is that which is being compared with a car on sticks.

In the steady state, both should have the same amount of grip as long as the contact patches on the tires remain the same. You can't have a terribly different force distribution between them because in the steady state, the car with the springs and shocks is just like a car with sticks of the same lengths as the springs and shocks are in their loaded state.

Let's say, for instance, that you enter a long sweeping curve in a car with springs and shocks, and the end result is 1 inch lift on the inside and 1 inch compression on the outside. Since the car is in a steady state, it is no different than a car with sticks with lengths such that the inside is 1 inch longer than that of the stopped car and, on the outside, 1 inch shorter than that of the stopped car.

So we can then ask ourselves: how much of a difference in the forces seen at the contact patches is there between the car with differing size sticks and the car with same size sticks? Aside from the slight difference due to a slight difference in the location of the CG on each, I expect you'll find that there is no real difference at all.

Yes, to a point. The difference between the soft-spring/big-bar and hard-spring/soft-bar has been argued for ages.

I would expect that the difference is down to the details of the transitional periods rather than the details of the steady state.

The each have their application. For sake of argument, let's take a look at two theoretical models, one with 150lb/in springs and 350lb/in bars, the other with 350lb/in springs and 150lb/in bars. Assume (for simplicity) a 3000lb car, with 50/50 f/r distribution as well as 50/50 l/r. That equates to 750lbs per corner. In a steady-state cornering condition (skidpad), if you pull 1G laterally, that means you are transferring 750lbs from side to side. In BOTH cases, the outside suspension compresses 1.5", since the wheel rates are identical. No difference at all. Cool. Now, transition those same models from steady-state cornering to steady-state deceleration, also at a rate of 1G. Now, we'll see a bit of a difference, as the sta-bars are no longer part of the equation (assuming frictionless bushings, etc.). The soft/big car will now transfer that 750lb load onto 150lb springs, which will compress the front FIVE INCHES. The hard/small car will transfer the same load, but with 350lb springs, the compression is just a tick over two inches.

Oh, most certainly. There's no avoiding front dive under braking and front rise under acceleration. At least, not with the front suspension design as it is. Not unless there's a way to generate anti-dive in the front.

Given that disparity in motion relative to rest, which car do you think will be more responsive? Which do you think will be more stable? Think it through in the terms of force, distance, and time...

Oh, there's no question that the softer car will not be as responsive, but that's basically my point. It's precisely because of what it absorbs, how quickly, etc., that it becomes less responsive.

I think it's time to delve into the mysteries of NVH as they're applied to the subjective "ride quality." I honestly don't know enough about NVH engineering to get into the nuts and bolts, but I do know a little bit. A "firm" ride is not necessarily perceived as "poor," as can be evidenced by the massive sales of the BMW 3-series platform. C&D "top 10" for 30 years and all that. The rebound characteristics of the 3-series are considerably stiffer than those present in a stock Mustang, but nobody really complains about them. I *think* the major objection to a "harsh" ride comes from the instantaneous transmission of road irregularities into the chassis, resulting in VERY high transient acceleration rates for the occupants. Perhaps somebody with a background in NVH could chime in here?

Sounds like a reasonable description of NVH to me.

Agreed, as far as it goes. If, however, that pitching is part of a larger problem, trying to figure out which end is "off" is wasted time.

It depends on whether the solution to the larger problem results in compromises you're willing to make. If you're willing to make those compromises then sure, I agree. But if you're not, then you'll have little choice but to break the problem down into its components and address those individually.

I will grant you that those will be the LARGEST factors, but they are hardly the exclusive factors. Another comparison from my archives... On a soft/big suspension (2009), my best time at Putnam Park was 1:26, running with 275 Hoosier R6 tires. In 2010, on a hard/small suspension, running 275 Hoosier R6 tires, my times dropped to 1:21.

What kind of track is Putnam Park? If it involves a lot of fast transitions then I would expect the more responsive suspension to make a huge difference there. If most of its curves are of the large, sweeping variety then I wouldn't.

I'm certainly not going to argue that a soft suspension can be made as responsive as a firm one! Well, not without the computer-controlled magnetically-actuated suspension I mentioned, at any rate.

I'd prefer the more responsive suspension also, but there is a firmness threshold (as well as a practicality threshold as regards speed bumps, steep driveways, etc.) that I'm not willing to cross in my pursuit of that.

Okay, I need to clarify something here. The "250mS time slice" I was referring to was not about the time the car took to "set" in a braking event, it was about the entire time involved from the instant your foot touches the brake pedal to the point where it's at maximum pedal pressure. In amongt that 250mS window, the car transitioned from neutral (assuming right-foot braking) to a compressed, set position, with the relatively slow rate of change in direct response to the driver's foot. Depending on how far the suspension has to travel (spring rate!), the time to the "set" position can be quicker, however if you get too much velocity (spring rate!!) the load transferring can over-shoot the "set" position and momentarily unload as it yo-yos back. That momentary unloading can and will cause braking instability. THAT is what that 250mS jazz was all about. Otherwise, yes, if it took my car 1/4 second to go from neutral to set, I would be pulling my hair out!

Oh, okay. Well, then my point is made even clearer!

This suggests that perhaps the suspension with the higher AS% will, to a point, be the better one as the larger AS% means that more of the weight transfer is going through the solid links and, thus, that transfer happens instantaneously. While the amount of time it takes to reach steady state may be the same, the amount of weight which is transferred through the rear suspension motion may be reduced enough such that it no longer really matters.

While I absolutely applaud your progressive approach, I do have one cautionary question: Don't the Koni Sport dampers use shortened cartridges? I'm not positive either way, but IIRC, there was some discussion about them being shortened 1" over the stock pieces. If they are, you will gain some bump travel, but lose some rebound. Just FYI.

I thought they were shortened by 1/4" or something, and thus got you a drop of 1/4" relative to the stock struts when you use them. I've no idea about the Koni dampers in the rear, however.


You mentioned the praise the BMW M3 gets for its ride quality. What kind of dampers is it using?

 

[kcbrown]

Just sounds like a terrible way to tune. Why would you want to get X AS% (let's say 100% for now) and then have to fix the rear steer with a big rear bar and then counter it with a big front bar to achieve a neutral handling characteristic, but with less overall grip? Too much spring rate for the tire will overload it and that is less grip. You might be able to tune the over/understeer handling, but you would just be slower around the track.

I am skeptical that this is the case. See my explanation of the steady state cornering case for why.

 

[sheizasosay]

You know on second thought, sticks for springs in steady state would be no different than anything else in steady state. It's that whole "getting to steady state" that is the problem. A person still has to drive the car. The more rate you have, the faster the transfer happens. If you drive by feedback to explore traction, then at some point in the "increased spring rate pursuit" you will outpace yourself and it would be too fast to react to.

 

[Norm Peterson]

I am skeptical that this is the case. See my explanation of the steady state cornering case for why.

I think you are assuming a far more perfect "steady state" than actually exists. Real roads are neither as smooth nor as flat as a 2" thick slab of cold-rolled steel . . . and probably not as rigid against deflection under wheel loads either, given equal subgrade preparation.

If I didn't suggest this before, I meant to - next time you're on a smooth flat road pacing another car at a steady speed, pay attention to the gaps between the tires and the wheel well openings of that other car. If perfect steady state were possible, you'd see zero relative movement (barring the other car's occupants jumping around in their seats to the music). But I'll guarantee that you'll see those gaps vary.

What that means is tire loading is never as constant as it appears you'd like to think, because the suspension does not (in the real world) stay put. Given that, what you want your suspension to do is minimize the force variations away from the average force value that you're assuming corresponds to steady state. That argues for a softer suspension, since force variation equals stiffness times deflection away from the average position. Softer as used here is a rather relative thing, because you still have to satisfy your operating camber and other geometry requirements, fit it all within the available suspension travel and/or ground clearance, etc.


In the end, it's a compromise. If it wasn't, the really smart people who do this stuff for a living would have all ended up with precisely the same answer.


Norm

 

[frank s]

Right. But increasing the spring rates will result in a harder ride unless shock compression is reduced to compensate (and I expect the Koni Sports do not -- but maybe they do. Anyone got test data for the Koni Sports compared with the Brembo package stock shocks?), and the car is already fairly close to my limits on that. I might be able to tolerate the spring rates of the Boss 302, and performing that experiment is insanely cheap ($80 for the springs both front and rear) but I expect that'll be it as far as my limits go.

What is the parts number for this "data" stuff? I think I got ripped off on eVague and my order turned out to be some furrin monstrosity that looks a lot like "testimony":

At street speeds, Koni Sports "ride" a little rougher than stock Brembo-package shocks; that is to say, the effect of encounters with small bumps (jounce) seems to be more sharply transmitted to the butt-dyno and ear-dyno. Magnitude of the deviations from smooth seems unchanged; it must be the rate-of-change that is noticeable.

Rebound is the tunable aspect of Sports shocks. At full "soft", rebound is perceptibly more managed than stock, but not much. Ramping up the rebound setting toward "hard" is, again, perceptible; by the full-hard point, there is plenty of "ride" signal that something is different.

At freeway and higher speeds, "ride" cues at even the full-hard setting are blended into a sense of stability and predictability.

I did a series of adjustments between runs at an autocross practice event. Full-soft at both ends for three runs as a baseline.

First adjustment: full hard on the rear. Result: instant improvement of one second on a seventy-second course. The front end was more responsive, the rear more dependable (enhanced sense of control).

Second adjustment: full hard on both ends. Result: kept the time improvement, lost the sense of control. Might have been learning that kept the time.

Third adjustment: half-hard on the front. Result: edging back toward the sense of control, minor time improvement.

Fourth adjustment: half hard on both ends. Result: backing off from the control sensation, very minor time improvement.

Fifth adjustment: full soft front, full hard rear. Result: sense of control returned, minor time improvement.

I tried several smaller increments between full and half, but was not able to note much change smaller than half (butt-dyno is old and rusty from disuse).


Some months later I did a similar range of adjustments at a practice autocross, a forty-second course, after changing the stock Brembo-kit rear stabilizer bar to a 26mm H&R item. Result: front end was quicker to respond in every configuration, but everything seemed less sensitive to adjustments, with the half-scale changes still perceptible but with lesser effect.

There was a sweeper like one in the first test autocross. My sense in comparing the two in the same car, same tires, different rear stabilizer bar, is that the bar allows a greater ability to steer with the gas pedal, with a lesser tendency to plow. If I had to guess, I'd say the second configuration was definitely more pleasurable, and maybe a little faster.


There is a particular freeway transition ramp that when I have a clear shot at it (like yesterday, praise be) I do at eighty-something. There is a joint bump just past the center. When I hit that pre-Koni-Sports, the car would sit down, then jump up and slide a couple of feet left before settling back and continuing. Post-Sports, bumps down but not jump up, no shift to the left. I like it.


Just for the record: the "Track App" meter showed 1.09 max in right turns, 1.02 left. I have no idea what that measures, but there it is.

 

[kcbrown]

I think you are assuming a far more perfect "steady state" than actually exists. Real roads are neither as smooth nor as flat as a 2" thick slab of cold-rolled steel . . . and probably not as rigid against deflection under wheel loads either, given equal subgrade preparation.

That's true. An uneven surface will greatly complicate the analysis, because it in essence lands you in a perpetual transient state.

What that means is tire loading is never as constant as it appears you'd like to think, because the suspension does not (in the real world) stay put. Given that, what you want your suspension to do is minimize the force variations away from the average force value that you're assuming corresponds to steady state. That argues for a softer suspension, since force variation equals stiffness times deflection away from the average position. Softer as used here is a rather relative thing, because you still have to satisfy your operating camber and other geometry requirements, fit it all within the available suspension travel and/or ground clearance, etc.

Right. And on the other hand, you want to maximize responsiveness, which argues for a stiffer suspension. It makes for a fun compromise.

In the end, I expect that the compromise point is going to be determined by the surface itself. You need to set up the suspension so that it is compliant at and beyond some certain minimum frequency and maximum amplitude combination that is determined by the surface you're driving on, but is relatively rigid beyond that. Street driving involves surfaces that have larger features and thus demand suspensions that are compliant at lower frequencies and higher amplitudes.

Street cars can't (without the magic tech I mentioned before) do as well on the track as purpose-built race cars because the range of surface variation they have to be able to handle is larger.

There are bumps, undulations, etc. on my drive to work which I expect a harder suspension would not handle very well. It's why, of all the lowering springs that are out there, the FRPP "P" springs are the most appealing to me, as they're progressive and lower the car a relatively minimal amount.


I guess I'll drive the car in stock form on the track at least once, but I'm awfully tempted to put Koni Sports on the car (while keeping the stock springs) almost immediately simply because it may result in a more controlled ride on the street.

 

[sheizasosay]

I will grant you that those will be the LARGEST factors, but they are hardly the exclusive factors. Another comparison from my archives... On a soft/big suspension (2009), my best time at Putnam Park was 1:26, running with 275 Hoosier R6 tires. In 2010, on a hard/small suspension, running 275 Hoosier R6 tires, my times dropped to 1:21. Granted, the days were not identical, however, both were beautiful, sunny, cooler days. Last event 2009, first event 2010, FWIW. While weather may have been a factor, it certainly wasn't worth five seconds on a 2-mile track! The NASCAR boys use the soft-spring big-bar approach to absolutely dump the nose under braking to A) maximize the effect of the splitter for front downforce, and B) set up a slightly "loose" condition, which is net quicker through the corner. I'm sure there are other things going on, but that's a solid part of it.

Um...I just had a "holy crap" moment after re-reading that. Dave, from what I gather from you, you don't have much variation in your lap-times from driver skill. Is that correct? Because I'm got my hand up back here and I have a question. 5 seconds going from a soft spring/stiff bar to a stiff spring/soft bar...that is absolutely a monster gain! There has to be something else there right or is that really just the deal?

I have two things that come to mind. Gmitch a while back was preaching "Tires, Tires, Tires" for the #1 suspension mod. Then he referenced and article that either GrassRoots Motorsports done or Tire Rack and I'm about 90% sure it was GRM. Anyway, these testers went through a lot of suspension changes and benchmarked each. The biggest gain of all of it was tires. Coilovers were a close second. Vorshlag is another. They listed a similar trend with their AST's they sell. So damping gets thrown into the mix a little with coilovers, but really, if you look at the big change it's those spring rates. I don't know of any "good" conventional springs that even come remotely close to coilover spring rates. I mean ground control or the koni CO's from Griggs or Cortex start with 400/450 on the front. Vorshlag pushing 550lb on the fronts. KW CS's running 540's on the front. Both Vorshlag and GRM wind up showing where those CO's gain 2 seconds or more.

What I'm getting at is that adding coilovers, damn near, inadvertently, puts you into the "big springs/small bar" category yet they aren't showing a 5 second gain. Maybe I should reconsider what I call "big springs". Is it relative to the total wheel rate? ie...85% of wheel rate comes from springs and we would call that "stiff spring/soft bar" and vice versa? What was your setup change from and to exactly for Putnam?




Also you said " In a steady-state cornering condition (skidpad), if you pull 1G laterally, that means you are transferring 750lbs from side to side. In BOTH cases, the outside suspension compresses 1.5", since the wheel rates are identical. No difference at all. Cool. Now, transition those same models from steady-state cornering to steady-state deceleration, also at a rate of 1G. Now, we'll see a bit of a difference, as the sta-bars are no longer part of the equation (assuming frictionless bushings, etc.). The soft/big car will now transfer that 750lb load onto 150lb springs, which will compress the front FIVE INCHES. The hard/small car will transfer the same load, but with 350lb springs, the compression is just a tick over two inches."

Why would the sta-bars not be providing wheel-rate in steady-state? If the car is leaning, aren't the bars engaged?

ref: http://www.allfordmustangs.com/forums/2005-2010-mustang-gt-tech/262514-s-all-about-tires.html

 

[NoTicket]

5 seconds is almost certainly equal parts grip gained from the suspension improvements, as well as driver confidence from the stability of the new suspension. 5 seconds off of a 1:26 lap time is a giant gain.

 

[csamsh]

.....and properly getting your suspension set up will net those 5 second gains too.

At the first autox I did with 315 V710's, coming from 285 RS3's, I found 4.5 seconds on a 40-something second course from run 1 to run 8, all through shock tuning and tire pressure adjustments.

I'm a believer in the big front spring/less bar combo, just for the record.

 

[SoundGuyDave]

Um...I just had a "holy crap" moment after re-reading that. Dave, from what I gather from you, you don't have much variation in your lap-times from driver skill. Is that correct? Because I'm got my hand up back here and I have a question. 5 seconds going from a soft spring/stiff bar to a stiff spring/soft bar...that is absolutely a monster gain! There has to be something else there right or is that really just the deal?

NASA Midwest finished up it's 2009 season at Putnam Park in Indiana, where we run the "10 turn long course," so 1.766 miles. The terrain is gently rolling, and the layout has a few "technical" sections to it. The Turn 3/4 complex is about as close to a slalom as I've seen on a road course, with the track dropping off-camber past apex of 4. Dead Bear (T8) is a constant-radius carousel with an assortment of camber changes, and the exit of T10 leads directly to hay bales and Aarmco. The main straight drops off a hillcrest right into the braking zone for T1, which is thankfully, ON-camber... Fun, neat track.

I consider myself to be a fairly consistent driver, and am usually within a couple tenths or so per mile at most tracks, and even tighter at others. I will NOT classify myself as a "non-learning driver," however, not by a long stretch. Obviously, this discounts traffic effects...

With all that said, NASA Midwest ended it's 2009 season at Putnam in October, where I turned in the 1:26 best lap in TT. For that outing, I had BMR progressive lowering springs, Tokico D-Spec dampers, BMR bars, and sticker 275/35-18 Hoosier R6 tires. Immediately following that event, the car was pulled into my garage, and then sat for the rest of the callendar year. Over the winter, I swapped out the dampers, springs, and bars, and reset the ride-height to EXACTLY what I had before, not wanting to get into altering geometry with a whole new car to learn to drive. After installing the AST4100s, Hyperco 350 (f) and 300 (r) springs, and Strano's bars, I did an alignment back to my spec, and then went to Gateway in St. Louis for the season opener, sticking to street tires to feel the car out. Gateway is a Roval, so no real opportunity for tuning, particularly since my Ho-Hos were nowhere nearby... In May, I went back to Putnam, and it bears saying that I made NO tuning changes from my initial setup, with the exact same SET of tires from 2009, and promptly ripped off a 1:21.8 in my second TT session. We were back at Putnam again in October of 2010, where my best was a 1:21.7... No other suspension component or specification changes were made between 10/09 and 5/10, and outside of adding a little more negative camber to help with tire shoulder wear, no real changes were made during the 2010 season for me.

No Ticket probably has the right of it: Yes, the suspension WAS faster, notably so, but the confidence in the car certainly let me push harder than I could before. Was it 2sec and 3sec respectively? Dunno. Maybe. The PACKAGE was worth 5 seconds, though, on a fairly short track.

I have two things that come to mind. Gmitch a while back was preaching "Tires, Tires, Tires" for the #1 suspension mod. Then he referenced and article that either GrassRoots Motorsports done or Tire Rack and I'm about 90% sure it was GRM. Anyway, these testers went through a lot of suspension changes and benchmarked each. The biggest gain of all of it was tires. Coilovers were a close second. Vorshlag is another. They listed a similar trend with their AST's they sell.

Absolutely correct. Compound first, width second, then the suspension hardware third.

So damping gets thrown into the mix a little with coilovers, but really, if you look at the big change it's those spring rates. I don't know of any "good" conventional springs that even come remotely close to coilover spring rates. I mean ground control or the koni CO's from Griggs or Cortex start with 400/450 on the front. Vorshlag pushing 550lb on the fronts. KW CS's running 540's on the front. Both Vorshlag and GRM wind up showing where those CO's gain 2 seconds or more.

While I agree that the recommended rates do "skyrocket" when you go to GOOD dampers, it doesn't necessarily have to be so. I was on 350lb fronts, which is lighter than most, but realize that you CAN get 150lb 2.5" or 63mm springs, which is the OE equivalent. Why you would want to is another question.

I'm ABSOLUTELY NOT saying that my results are typical. You know, "your results may vary," "batteries not included," "some assembly required," etc. I am a fairly analytic driver though. I seriously envy those guys that can just hop in anything and make it go fast, but I tend to want certain behaviors out of the car I drive, and when I get the car to do what I want, I find it soooooo much easier to push the limits of the envelope, and my confidence level just skyrockets. 2009 was a LOT of track miles ago, but I wouldn't be surprised if I wasn't leaving quite a bit on the table, wondering when the car would.... or if the car would...

Also you said " In a steady-state cornering condition (skidpad), if you pull 1G laterally, that means you are transferring 750lbs from side to side. In BOTH cases, the outside suspension compresses 1.5", since the wheel rates are identical. No difference at all. Cool. Now, transition those same models from steady-state cornering to steady-state deceleration, also at a rate of 1G. Now, we'll see a bit of a difference, as the sta-bars are no longer part of the equation (assuming frictionless bushings, etc.). The soft/big car will now transfer that 750lb load onto 150lb springs, which will compress the front FIVE INCHES. The hard/small car will transfer the same load, but with 350lb springs, the compression is just a tick over two inches."

Why would the sta-bars not be providing wheel-rate in steady-state? If the car is leaning, aren't the bars engaged?

ref: http://www.allfordmustangs.com/forums/2005-2010-mustang-gt-tech/262514-s-all-about-tires.html

"...from steady-state cornering to steady-state deceleration..." Under decel (braking) the car isn't rolling, it's pitching, and the bars are out of the equation. At that point it's all springs.

 

[sheizasosay]

.....and properly getting your suspension set up will net those 5 second gains too.

At the first autox I did with 315 V710's, coming from 285 RS3's, I found 4.5 seconds on a 40-something second course from run 1 to run 8, all through shock tuning and tire pressure adjustments.

I'm a believer in the big front spring/less bar combo, just for the record.

Yeah I'm wanting details of what he did exactly. Dave is a smart guy, he knows how to get his wheel rate. From the sound of his post, it sounded like he got the wheel rate near the same in both scenarios. It might not have been. But if it was isolated out or isolated within a reasonable manner.... that's pretty damn significant. Maybe I'm late to the game. Maybe this is old news. I'm just trying to learn what he has to offer.

Sam Strano is a heavy bar/ light spring kinda guy I thought. He certainly seems to have made it work for the list of national championships he has. Relevant?

The question is if wheel rate remains the same in this ,swap springs andbars around to the stiff spring/soft bar, is there 5 seconds to be had? If that's the case that needs to be on headlines.

EDIT- again.....Dave's post was not up when I typed this lol. I think that when Dave clicked "quote" to reply it time hacked where his post would be.