Vorshlag 2011 Mustang 5.0 GT - track/autocross/street Project

[2008 V6]

(continued from above)
Leaving the SCCA for 2013 sucks and we're NOT happy about it, but it is a decision we've been discussing since this rule re-write was dumped on us from these committees. Now that the only "legal" Watts Link options we have are to use only a Fays2 or Steeda Watts Link, neither of which I sell (or care to), I opted for Option 2 - leave the class, and leave the sport. By the time this mess is undone, we will have an all new chassis to play with in mid-2014 (see my last section in this post).


(Welcome to the club)
- Been there & got FCKED because of others ego & larger bank roles.- Many, many other groups to run in. I feel your disappointment (Because - I've BEEN THERE & to this day have never gone back.)

 

[Vorshlag-Fair]

They are using adjustable spring perches with probably 2.5" springs. I'm not sure of the rates, probably 600F/225R was the last I heard. The rear springs are NOT spring over shock though.

Yes, we avoided going to coilover rear shock and spring set-up and instead use 2.25" or 2.5" rear springs on AST ride height adjusters and Vorshlag adapters. This all sits in the stock rear spring location. We have done this on our two S197 cars with AST 4150, AST 4200RR and Moton Motorsport 2-way shocks.

We talk a lot of people out of using coilover rear shocks when the factory shock and spring were divorced. This is because, unless the factory had a coilover rear shock/spring set-up, the upper sheet metal shock mounts probably are NOT designed to see full suspension/spring loads, just damping loads.

Of course many folks do go ahead and slap on coilover rear shocks, and in many cases it works without incident, but not always. On BMW chassis it can punch the shock right through the shock tower unless you tie the cage into this area and add some plate steel to reinforce the shock mount opening. And coilover springs mounted to the rear shocks will almost always eat up inside wheel room. There just isn't almost any performance benefit and LOTS of downsides...

Thanks,

 

[SoundGuyDave]

There just isn't almost any performance benefit and LOTS of downsides...

Serious question, not starting anything... What about the differing motion ratios in pitch and roll conditions? In pure pitch, the ratio is roughly 1:1 based on the springs being directly over the axle lateral centerline, but in roll, with the springs offset inboard, it will have a different motion ratio, resulting in a different effective (lower) wheel rate, no? In other words, 300lb springs act like 300lb springs under acceleration, but under cornering loads, they effectively soften. Or am I missing something here?

 

[sheizasosay]

In other words, 300lb springs act like 300lb springs under acceleration, but under cornering loads, they effectively soften. Or am I missing something here?

That would be Agent 47 and Griggs...probably a few more that do that, but don't they usually run a much higher spring rate?....so they could get the wheel rate back up from the same motion ratio differences you're talking about.

 

[Whiskey11]

That would be Agent 47 and Griggs...probably a few more that do that, but don't they usually run a much higher spring rate?....so they could get the wheel rate back up from the same motion ratio differences you're talking about.

They also run full cages that tie into the rear shock mounts. I don't think Ford intended for the spring loads to ever go through the rear shock mounts without first being tied into a cage.

 

[Philostang]

What about the differing motion ratios in pitch and roll conditions? In pure pitch, the ratio is roughly 1:1 based on the springs being directly over the axle lateral centerline, but in roll, with the springs offset inboard, it will have a different motion ratio, resulting in a different effective (lower) wheel rate, no?

That was my understanding as well. I don't think you could call this a real performance advantage to the outboard coilover, just a characteristic of it. If you want X wheel rate, you do as sheizasosay suggested and adjust the spring (wherever it's located) to deliver.

Of course, if you're concern is ride quality, then the advantage seems to go to the outboard set up. To get the same wheel rate in roll with the inboard springs you'll need a stiffer spring (than the coilover alternative) whose full rate you'll feel when going over something like a speed bump or highway expansion joint.

But if it's a pure track car, I don't see a concern with this too much.

Best,
-j

 

[sheizasosay]

They also run full cages that tie into the rear shock mounts. I don't think Ford intended for the spring loads to ever go through the rear shock mounts without first being tied into a cage.

I'm not an engineer, so I'll leave it upto the qualifiied or those have experience with the s197 and outboard coilovers to decide. I have no idea. I do know that Griggs, Cortex and agent 47 offer"street/track" coilovers so using the "they all have cages" logic goes against what they are offering. Are they right or wrong....I don't know. I'm sure that any of them or their customers would be able to elaborate with some kind of history of issues or non-issues.


Sent from my iPhone using Tapatalk

 

[Norm Peterson]

If you move the rear springs outboard without changing their rate, their contribution to rear roll stiffness goes up without increasing ride stiffness. If your roll stiffness distribution was good to begin with, you'd compensate for moving the springs by setting a slightly softer rear sta-bar adjustment. If you then either stiffened or softened the (relocated) springs for any reason, you'd again be back to making a sta-bar adjustment if you weren't happy with the handling balance.


Norm

 

[sheizasosay]

I had the motion ratio/wheel rate reversed.

 

[19COBRA93]

Serious question, not starting anything... What about the differing motion ratios in pitch and roll conditions? In pure pitch, the ratio is roughly 1:1 based on the springs being directly over the axle lateral centerline, but in roll, with the springs offset inboard, it will have a different motion ratio, resulting in a different effective (lower) wheel rate, no? In other words, 300lb springs act like 300lb springs under acceleration, but under cornering loads, they effectively soften. Or am I missing something here?

The rear stabilizer bar will correct for this. In pitch the rear bar contributes nothing. In roll it assists with effective spring rate. Adjust bar accordingly.

 

[SoundGuyDave]

Oh, believe me, I "get" all that was said, but my point still stands... Even leaving aside ride-quality issues (not an issue for me!), you WANT softer spring rates to allow weight transfer to the rear for traction purposes, but those softer spring rates turn the rear end into a noodle in a corner. Assuming (number picked as SWAG) the lateral motion ratio to be 0.6 in the rear, and 0.95 in front (accurate as far as I can find), and assuming the "ultra-stiff" FR500C spring rates of 750F, and 400R, that puts lateral wheel rates at 630, and 144R, which would necessitate an AWFULLY heavy rear bar to make up the balance without having the chassis run into massive understeer. TANSTAAFL, I know, but super-stiff bars have issues unto themselves as well. First, the shocks aren't curved to damp what becomes a giant torsion spring in the suspension system. Second, any sort of one-wheel bump scenario (rough track with frost heaves, or, "perish the thought, hitting a curb*") the bar itself BECOMES the suspension system, transferring load across the car. All of which makes the thing dance around without driver input. Also, the more bar you dial in, the less lateral bite you have as the suspension becomes less and less independent.

(*= Carrol Smith, "Tune To Win," P. 67)

I understand the concept of trade-offs, where you "give a little" in one place to "gain a lot" somewhere else. I'm currently running 300lb rear springs, which seem to be good in terms of rearward weight transfer under acceleration, and to keep the rear body roll SOMEWHAT in check, I'm running the Strano bars in the mid-position, which is considerably stiffer than the stock rear bar. I don't want to increase the bar rate any more, as I'm already dancing on the edge of snap-oversteer as it is, but I still feel like the rear end is rolling over too far under cornering, particularly in the corner-exit phase, where I'm hard on the gas at and just beyond apex.

The FR500S runs 500F/300R (outboard coilovers) with IIRC an 18mm solid bar plus aero, and are balanced, with just a hint of understeer, +/- damper settings.

The FR500C cars, 750F, 400R (outboard coilovers) run no rear bar, no aero, and appear to be pretty well balanced and don't exhibit either excessive rear roll OR huge tendencies towards understeer. Yes, the shock towers are reinforced by the cage, but I can't help but think that in a competition environment, the outboard spring location provides a net performance benefit over the inboard spring pockets, by letting the spring control most (or all) of the chassis roll, and allowing the damper to affect the rate throughout the transfer,without excessive rate increase destroying longitudinal load transfer.

In Terry's case, I'm wondering how much the inboard location is given primacy due to wheelwell space, and whether he'd be doing things differently if he was running in a class with restricted wheel width, where he HAD the space to play in. Or, more finely put, if you HAD the space to run the outboard springs, why wouldn't you?

I'm 99% sure the inboard/outboard location isn't a "one size fits all" scenario.

 

[dontlifttoshift]

Dave, I think the difference in roll center height front to rear has a lot to do with the wheel rates needed in roll. Just guessing here, but there is at least a 10" difference between the two.

I don't think anyone will argue that getting the spring as close to the wheel as possible is the best situation for handling. Wether or not it is the best for this platform is certainly debatable due to stuctural concerns.

 

[Norm Peterson]

Serious question, not starting anything... What about the differing motion ratios in pitch and roll conditions? In pure pitch, the ratio is roughly 1:1 based on the springs being directly over the axle lateral centerline, but in roll, with the springs offset inboard, it will have a different motion ratio, resulting in a different effective (lower) wheel rate, no? In other words, 300lb springs act like 300lb springs under acceleration, but under cornering loads, they effectively soften. Or am I missing something here?

You can look at it that way, and the factor would look something like
{ [spring base] / [track] } ^2

It does seem that the S197 rear springs would be pretty soft in roll, and that small relocations would be significant.


I think there's a better way to determine what's going on, but it looks to be A WHOLE LOT more complex if you don't make a rather crude assumption right at the beginning. If you've read some of Mark Ortiz's "Chassis Newsletters" or other published columns, it's out of his approach. More specifically I'm thinking it's in terms of "anti-roll geometries" and working with the wheel loads themselves rather than with load transfers due to roll stiffnesses and roll center heights.


Norm

 

[Whiskey11]

Just to point out the reason why he started with the stock locations: Current ESP and STX rules do not allow relocation of the springs. This is party of the reason that despite having a power to weight advantage the older SN95 and Fox cars are not that competitive in ESP and STX. Stupid unbearable spring rates to get halfway reasonable wheel rates. Some folks keep trying though, bless their hearts!

 

[DTL]

What are you guys seeing work well in these cars as far as spring rates for a track car that also sees street driving? My chassis guy is recommending 600f / 400r but that seems a little stiff to me, especially the rear. Then again, I'd rather not run monster anti-rolls. Opine away.

 

[Philostang]

DTL, tough question. So much of the answer lies in your own tolerance for harsh ride quality. Those spring rates your guy recommended are definitely on par with a "track-only" mindset. I've been in cars with 350f / 300r and it was pretty uncomfortable but also pretty streetable for my comfort level, and keeping in mind that my need for comfort was restricted to short rides. So how much street driving is also key to consider.

One more thing to keep in mind, lots of guys are running their street cars on track with great success w/o these high rates. By "success" mostly I mean having lots of fun and getting a heck of a lot out of their cars (I'm not talking about competing, etc.). So don't let the focus of dedicated-track-guys lull you into thinking you need to run such high rates to go out and track the car. You do not. For years myself and others have gone out, run circles around the posh-Porsche crowd, and then comfortably driven home on 250f / 200r spring rates (w/aftermarket bars, etc.). I think Steeda's "Competition" springs and H&R "Race" springs are in this general vicinity (H&R may be a bit higher), and I think their name is pure marketing hype, as they're totally streetable for the right set of pants. Those were the rates of my daily driver in a 70 mile round-trip commute. I had lots of fun with that set up. I've moved on since then, but only because the car is retired and I'm trying to extract ever more from it. =)

Best,
-j

 

[JesseW.]

streetablity depends on tire size and damping for me. with 600f/250r springs, strano bars (soft setting front, middle hole in back) it rides a lot better with 255/45-18's up front on the street than the 285/35-18's i autocross on. softening the dampers helps some too.

at really soft spring rates (whatever eibach prokit is) i hated the ride quality of those. it hit the bump stops really easy even after trimming the stops and to get the roll somewhat under control with the front sway on full stiff, the ride quality took a huge nose dive. a bump on the left side would transmit over to the right, so instead of the front acting independent, the car would nose dive... doesn't do that now with the stiff spring rates/ soft bar.

 

[SoundGuyDave]

You can look at it that way, and the factor would look something like
{ [spring base] / [track] } ^2

It does seem that the S197 rear springs would be pretty soft in roll, and that small relocations would be significant.

That's pretty much what I was thinking, and why I wanted to push this topic for discussion. If anybody has access to their car (I don't), can they take center-to-center measurements for the spring mounts? Track width would be a variable, based more on wheel width and offset than anything else, but we can probably assume something close to 73-73.5" in the rear. I know mine is 1.3" narrower in the rear, with identical wheels and tires on all four corners.

I think there's a better way to determine what's going on, but it looks to be A WHOLE LOT more complex if you don't make a rather crude assumption right at the beginning. If you've read some of Mark Ortiz's "Chassis Newsletters" or other published columns, it's out of his approach. More specifically I'm thinking it's in terms of "anti-roll geometries" and working with the wheel loads themselves rather than with load transfers due to roll stiffnesses and roll center heights.


Norm

Um. Yeah. After my eyes de-glaze, maybe I can comment more intelligently, but from what I was able to grasp (10%? 15%?) and looking strictly at the solid rear axle, anti-roll geometry depends strictly on the height of the chassis-side PHB mount. Granted, that was mentioned in context of a NASCAR-style chassis, so presumably taking into account only left-hand corners. I'm still trying to wrap my head around the math, so I'm honestly quite unsure how that would translate to a right-hand corner. Would that require relocating the axle-side? If so, does that imply RC height adjustment becomes the driving force behind anti-roll geometry? Is it even attainable in practice? If it is (attainable, and RC-based), this certainly increases the attractiveness of a Watts link setup with decent RC adjustabiliy! At that point, then, how does the RC slope affect things, as posited by dontlifttoshift? Finally, how would altering the anti-dive angles in the front suspension affect things, if at all?

Time for a couple of aspirin, and maybe a shot of single-malt! This looks to be heading towards a VERY informative and educational (at least for me, anyway) thread drift!

Oh, one other thing I found interesting was the differing shock orientations in Fair's pics. Invert vs. non-invert.

 

[19COBRA93]

If anybody has access to their car (I don't), can they take center-to-center measurements for the spring mounts? Track width would be a variable, based more on wheel width and offset than anything else, but we can probably assume something close to 73-73.5" in the rear. I know mine is 1.3" narrower in the rear, with identical wheels and tires on all four corners.

I have a stock rear end sitting here I just measured. Spring mounts center to center is 38". The total width from axle flange to axle flange (without rotors) is 65.5".

 

[Norm Peterson]

That's pretty much what I was thinking, and why I wanted to push this topic for discussion. If anybody has access to their car (I don't), can they take center-to-center measurements for the spring mounts? Track width would be a variable, based more on wheel width and offset than anything else, but we can probably assume something close to 73-73.5" in the rear. I know mine is 1.3" narrower in the rear, with identical wheels and tires on all four corners.

This is the easy part. The Mustang's rear track - as measured to the tire tread centers - is 62.5" with the 17x8 +45mm offset wheels and 235/55-17 tires. Roughly, as there is probably a ± tolerance on camber.

I got about 34" between spring centers (I can re-check this tomorrow if it isn't raining and the driveway isn't too wet). I don't think I tried to get the distance between the centers of the upper spring seats.

I'm still trying to wrap my head around the math

Same here. It's enough different from the more usual method that your mind kind of fights with itself to make sense out of it. That's why I've still not thrown much time at it. Anti-roll for independent suspensions actually seems easier to grasp.


Did you get his Feb 2013 Newsletter? In there is a hint that sprung CG migration can be considered and some talk about large numbers of simultaneous equations.


Norm