What coil-overs should I buy? Poll inside

[modernbeat]

... I need a way different setupfor the series I run in.
I need an 18x11 wheel wrapped in 315s. X4 that are rotatable.
Running the thinnest spacer possible* in the front and don't poke out the fenders...

We had a customer insist on the very setup you are asking for even after I heavily advised against it. He ran autocross on his 315s on 18x11 and the vibrations from the spacers he used were enough to convince him to buy another pair (or maybe two pair) of wheels so he could use them without spacers.

What series are you in that requires the same wheel offset front and rear?

 

[JerryZ]

@JerryZ-Since the Vorshlag wheels in that size have been out so long, I didn't think that was classified info any longer. If so, I apologize for asking an inappropriate question. It just seems that other manufacturers have already roughly copied or did their own designing.
I realize that Vorshlag does a lot of testing, and I respect what they do to bring a product to market first and what they do for us in the Mustang community. It's just that I have never actually seen one of these wheels, nor measured one.
Additionally, I am not out to copy this wheel. It won't work for me. I need a way different setupfor the series I run in.
I need an 18x11 wheel wrapped in 315s. X4 that are rotatable.
Running the thinnest spacer possible* in the front and don't poke out the fenders.
I am performing my own calculations to determine the mods I need to do to make this happen. Was just looking for a rough idea of what others were doing, even though it's a narrower tire.

*By thin front spacer, I mean 3/4" or less.

From all the research I have done, Cortex has a front coilover setup that is offset by a decent amount which may allow you to run a square 18X11 setup. I'd recommend giving them a call. Asking for minimal spacer up front and no rear poke is not possible unless you do something for additional strut clearance up front.

 

[DocB]

I run in SCCA GT2, or could run T1, and CP. The series does not "require" that I run the same offset or backspacing front and rear. I am allowed to run up to an 11" wide rim, but must use a DOT tire.
With that being said, I am not a pro race team with an unlimited budget, or an abundance of logistical room/space for storage or transport.
For these reasons, my tires and wheel must be rotatable front to rear.
DOT tires available to me, and that I like, are presently only available in 295 or 315. My car is big and heavy, and the 315s are more appropriate.
In my opinion, 315s, at a minimum, should be mounted on an 11" wide rim (for lots of reasons).
I realize that others run narrower wheels and tires, and it may work out, but I am not others.
Additionally, corners are where I make up my time due to the 75HP defecit of running a 4.6L 3 valve against 5.0L Bosses. For me, every bit of extra traction in the corners helps alot.
I am working on the strut clearance up front, hence the question about backspacing. I have very decent set of front coilovers, and a spare set, and would like to stick with them for now.

Any measurements or advice appreciated. Thanks.

 

[modernbeat]

...Any measurements or advice appreciated. Thanks.

My advice is to run different front and rear offsets and if you are tight on the tire budget, have them flipped on the rim when it's time.

 

[El_Tortuga]

@JerryZ-Since the Vorshlag wheels in that size have been out so long, I didn't think that was classified info any longer. If so, I apologize for asking an inappropriate question. It just seems that other manufacturers have already roughly copied or did their own designing.
I realize that Vorshlag does a lot of testing, and I respect what they do to bring a product to market first and what they do for us in the Mustang community. It's just that I have never actually seen one of these wheels, nor measured one.
Additionally, I am not out to copy this wheel. It won't work for me. I need a way different setupfor the series I run in.
I need an 18x11 wheel wrapped in 315s. X4 that are rotatable.
Running the thinnest spacer possible* in the front and don't poke out the fenders.
I am performing my own calculations to determine the mods I need to do to make this happen. Was just looking for a rough idea of what others were doing, even though it's a narrower tire.

*By thin front spacer, I mean 3/4" or less.

http://www.s197forum.com/forum/showthread.php?t=125304

 

[DocB]

@modernbeat- I hear you, and I understand. But that is not what I am after.

@El Tortuga- again, 18 x 11 with 315, not 305s.

Sure, offset and backspacing is important, but what everyone is forgetting about is "overall section width", of a tire, and futhermore, it changes on differnt rims.

A 315 has a hell of a lot greater OSW than a 305. And it's more than 10 mm btw.

 

[Norm Peterson]

Alternatively to flipping them on the rim could include swapping tires front vs rear on the wheels every once in a while, if the tires have a specified "OUTSIDE".


Norm

 

[El_Tortuga]

@modernbeat- I hear you, and I understand. But that is not what I am after.

@El Tortuga- again, 18 x 11 with 315, not 305s.

Sure, offset and backspacing is important, but what everyone is forgetting about is "overall section width", of a tire, and futhermore, it changes on differnt rims.

A 315 has a hell of a lot greater OSW than a 305. And it's more than 10 mm btw.

Not forgetting anything, just pointing you to very good info.

My 315 Rival S, mounted on 18x11s measure roughly 12-7/16 overall (section) width=316mm. That's spot on. Tire rack lists them as 12.6" actual when mounted on 11" rim.

 

[Mark Aubele]

I have Jongbloeds that are 18x10.5 (actually closer to 10.75) and I run them square with a 3/4" hubcentric spacer up front. 7.75" BS, 315 A7. Going to buy new inners for the rears, have outers for the front. No feasable way to run 11s with a real tire using the same offset without the Cortex offset setup. 10.5s is already pushing it. No issues with the MM spacers I am using so far.

 

[Jack Hidley]

I'd like to address some of the comments in this thread.

Monotube versus twintube.

The issue isn't cavitation versus noncavitation. If the damper gets to the point of cavitation, you have major problems. The issue that needs consideration is damping versus time. The viscosity of the oil in the damper changes with temperature. As temperature goes up, the viscosity goes down. A twintube damper has more thermal resistance from the oil to the external air than a monotube. This means that in a track situation, the twintube is going to lose damping faster, the longer the session is. In an autocross situation this is irrelevant as there is almost zero time for heat buildup.

It is important to note that it is possible to build a monotube damper with just as poor thermal conduction as a twintube damper. An example of this is taking a monotube damper and packaging it inside a strut housing. This has worse conduction to the outside air than a standard twintube.

On the subject of rear spring location.

There is no particular yield or tensile strength issue with mounting the spring on the shock in the S197 chassis. However, there are many other issues with doing this.

The OEM shock bracket on the axle housing was not designed for bump or spring loads. Long term there are likely to be fatigue issues with the shock bracket welded to the axle housing. Short term the issue is that this mounting is much more flexible than simply placing the spring on the top of the axle tube in the stock location. There is no reason to add another undamped compliance to the suspension here. This won't help ride quality or handling.

Locating a rear spring on the shock increases friction in the shock due to increased side loads in the shock shaft and piston. Keeping the spring directly on top of the axle nearly eliminates this friction in the shock and the control arm pivots. Extra friction hurts ride quality and traction.

Rear springs can be changed very quickly when the spring is mounted on top of the axle tube rather than over the shock.

There are fewer potential tire clearance issues when the springs are mounted on top of the axle tube.

Locating the springs on top of the axle tube places them in a location further inboard than springs located on the shocks. This inboard position provides a ratio of wheel rate to roll stiffness that is better for handling. A large number of companies recommend running a poor ratio of front to rear spring rates in the car. This hurts the ride ride quality. When the spring is located on the shock, this ratio must be made even worse.

In short there is no reason to mount the spring on the shock. It is a disadvantage in every way, except possibly in the marketing sense.

With regards to bump travel in the rear.

Since this chassis was originally designed for an IRS, there is reduced clearance between the top of the axle tube and the bottom of the frame rail. Any properly designed shock in the rear suspension should never be the bump travel limitation. This should always be the axle tube to frame rail contact, with a bumpstop between them of course.

It doesn't make sense to lump all JRi dampers into one category. Different companies may use different JRi products. JRi has a lot of different models and options available. In the case of the MM/JRi dampers, most of the parts used are proprietary. You won't find them on any other dampers built by JRi.

 

[Norm Peterson]

Locating the springs on top of the axle tube places them in a location further inboard than springs located on the shocks. This inboard position provides a ratio of wheel rate to roll stiffness that is better for handling.

Can I get you to explain this in a little more detail? Are you trying to separate roll stiffness (mostly to the bar) from ride stiffness (to the springs, obviously) here?

My first thought is that a more inboard spring location ultimately requires either more rear bar stiffness, a higher rear geometric roll center without messing with axle roll steer too badly, or both.


Norm

 

[2Fass240us]

My advice is to run different front and rear offsets and if you are tight on the tire budget, have them flipped on the rim when it's time.

Flipping tires also costs money and you can't do it at the track. Unless you have M&B machines. But those are also money. Or you can get a trackside service to flip them. Money.

And even if you do flip them at the track, that takes time.

@modernbeat- I hear you, and I understand. But that is not what I am after.

@El Tortuga- again, 18 x 11 with 315, not 305s.

I recommend running 20x8s with 235-width, all-season tires.

I'm after the same setup, or at least I was until I gave up and settled on 18x10s with 295s.

 

[Jack Hidley]

This is addressed specifically to answer Norm's question, but it is really directed at everyone.

Springs affect both ride stiffness and roll stiffness. Swaybars (perfect ones with no friction) only affect roll stiffness.

Given this for a target ride behavior, you must adjust the spring rates and rate ratio first. Once you have done this, then you can use swaybars to adjust the total roll stiffness and the roll stiffness distribution to tune the static handling balance.

When this is done on an S197 chassis, if you put the springs on the shocks in the rear, for a given target ride rate, they contribute so much roll stiffness due to their separation distance that when it is time to tune the handling with swaybars, you end up needing tiny bar sizes in the rear that aren't available.

Keeping the rear springs on the axle reduces their roll stiffness contribution, so that the rear swaybar ends up a practical size.

I wouldn't use a roll center height adjustment for tuning the static handling balance since this adjustment is almost completely a transient effect. In an AutoX situation it may end up having nearly the same effect since there is virtually no steady state cornering in an AutoX.

On a semi related note, here is a cool ride behavior video from GM with the worlds cheapest, simplest data logger in action.

https://www.youtube.com/watch?v=1W_J6UhQP6s

 

[ArizonaGT]

This is addressed specifically to answer Norm's question, but it is really directed at everyone.

Springs affect both ride stiffness and roll stiffness. Swaybars (perfect ones with no friction) only affect roll stiffness.

Given this for a target ride behavior, you must adjust the spring rates and rate ratio first. Once you have done this, then you can use swaybars to adjust the total roll stiffness and the roll stiffness distribution to tune the static handling balance.

When this is done on an S197 chassis, if you put the springs on the shocks in the rear, for a given target ride rate, they contribute so much roll stiffness due to their separation distance that when it is time to tune the handling with swaybars, you end up needing tiny bar sizes in the rear that aren't available.

Keeping the rear springs on the axle reduces their roll stiffness contribution, so that the rear swaybar ends up a practical size.

I wouldn't use a roll center height adjustment for tuning the static handling balance since this adjustment is almost completely a transient effect. In an AutoX situation it may end up having nearly the same effect since there is virtually no steady state cornering in an AutoX.

On a semi related note, here is a cool ride behavior video from GM with the worlds cheapest, simplest data logger in action.

https://www.youtube.com/watch?v=1W_J6UhQP6s

Jack: That is very interesting and also helps explain why many of the S197 competition cars that run full rear coil-overs have tiny sway bars (or none at all).

 

[barbaro]

I'd like to address some of the comments in this thread.

On the subject of rear spring location.

There is no particular yield or tensile strength issue with mounting the spring on the shock in the S197 chassis. However, there are many other issues with doing this.

The OEM shock bracket on the axle housing was not designed for bump or spring loads. Long term there are likely to be fatigue issues with the shock bracket welded to the axle housing. Short term the issue is that this mounting is much more flexible than simply placing the spring on the top of the axle tube in the stock location. There is no reason to add another undamped compliance to the suspension here. This won't help ride quality or handling.

Locating a rear spring on the shock increases friction in the shock due to increased side loads in the shock shaft and piston. Keeping the spring directly on top of the axle nearly eliminates this friction in the shock and the control arm pivots. Extra friction hurts ride quality and traction.

Rear springs can be changed very quickly when the spring is mounted on top of the axle tube rather than over the shock.

There are fewer potential tire clearance issues when the springs are mounted on top of the axle tube.

Locating the springs on top of the axle tube places them in a location further inboard than springs located on the shocks. This inboard position provides a ratio of wheel rate to roll stiffness that is better for handling. A large number of companies recommend running a poor ratio of front to rear spring rates in the car. This hurts the ride ride quality. When the spring is located on the shock, this ratio must be made even worse.

In short there is no reason to mount the spring on the shock. It is a disadvantage in every way, except possibly in the marketing sense.

I am aware of your association with MM and your racing. I am aware that MM's JRI package mounts their spring in the original stock location. I am also aware that MM went to JRI after Cortex was using them. But absent the K-member and the caster camber plates MM has not done much with respect to these Chassis. I know because I have both products and am very happy with them. The K-member is especially stout and has had a dramatic effect on my car's handling. However, there is a difference of opinion on the rear coilover issue and your side has not presented any proof at all in support of the notions that you are advancing.

Mr. Hidley, MM is a great company with great products for the PRE- S-197 Chassis but are a bit late to the party on the S197. Both Griggs and Cortex which came to the s-197 party earlier than MM, use true rear coilovers and have tested such on S197 Chassis. True rear coilovers have been used on these cars since 2006. They have been tortured under race conditions and road conditions. There has not been one reported failure despite thousands of vehicles being so equipped. So the facts contradict you unequivocally. Second, ride quality is improved.
http://trackmustangsonline.com/index.php?topic=8761.0

As for using smaller rear sway bars that are unavailable? Not true. they are everywhere? Cortex sells smaller swaybars and I have a couple small sways hanging around in my garage. Also, Strano sells adjustable small rear sways. What exactly is a "practical" size sway bar?

Several race teams use these setups as do entire racing series. So Show evidence they are wrong and you are right. I see no evidence. Just conclusory statements.

Cortex opposes your point of view:

"Failure of the rear upper shock mounting point of the S197 chassis is extremely unlike. We have never seen it happen and there is good reason. The upper mounting pad is tied directly into the rear unibody frame rails with steel that is quite thick. The upper pad that the OEM shock bushings bolt to approximately 0.200" thick and it is surrounded by multi-wall heavy duty vertical reinforcements on all sides. The CorteX Racing upper shock mounts have a large pad area that spreads the loads and feeds them directly into all of the vertical supports surrounding the bushing pad area. Because the shocks are nearly vertical there is essentially no side loads (horizontal). For those that are not convinced, you could always retain the OEM bump stops that are bolted to the top of the axle tube and shorten them as needed to ensure adequate bump travel. We do this on the majority of our installs mainly because it is easier on the shocks over time. If retained, the OEM bump stops would take loads from a large hit such as jumping the car instead of the shock mounts. We have spent a fair amount of time thinking this through and testing our design on daily driver and dedicated race cars of a number of years. The benefits of a much improved motion leads to better ride quality and much improved handling. Properly setup full coil-overs on an S197 are amazing and we highly recommend them for all serious enthusiasts."

Cortex/Filip Trojanek

Now the difference between his statement and yours is that it is based upon evidence. Actual first hand knowledge and experience cited to in the opinion itself. Not supposition, conjecture, or wishful thinking, but ten years of equipping S197 Chassis with true rear coilovers and racing them. As for economic incentive behind the opinion; I should point out that there is no economic incentive in purposefully designing an inferior product that will fail and lose. Nevertheless some people do just that, but can that be said about Bruce Griggs and Filip Trojanek. Are they losers?

Not that it would come even close to proving your point, but show just one example of failure or demonstrably poor performance. Just one. I have challenged everyone on this and noone can come up with even one failure or one case of poor ride quality attributable to spring location, or a history of these cars experiencing a competitive disadvantage on the track. SHOW ONE FAILURE! Because if you cannot show at least one. then the facts do not come close to supporting your opinion.

 

[Pentalab]

I'd like to address some of the comments in this thread.



There are fewer potential tire clearance issues when the springs are mounted on top of the axle tube.


In short there is no reason to mount the spring on the shock. It is a disadvantage in every way, except possibly in the marketing sense.

With regards to bump travel in the rear.

Since this chassis was originally designed for an IRS, there is reduced clearance between the top of the axle tube and the bottom of the frame rail. Any properly designed shock in the rear suspension should never be the bump travel limitation. This should always be the axle tube to frame rail contact, with a bumpstop between them of course.

As shown in a previous post, with the spring at the bottom, and shock at the top, rear tire clearance is not an issue. The spring sits inside the rear wheel barrel. (inverted rear coil over's).

"It is a disadvantage in every way, except possibly in the marketing sense."

Marketing sense? You make it out like they are involved in an engineering scam....merely for profit. Their concept works or doesn't. If they didn't function as advertised, they would not sell. If the mounting location succumbed to metal fatigue, there would be several failures by now. Nobody can hide anything anymore. It would be all over the internet within days. The rear shock locations could easily be re-enforced, and usually are via the cage, or similar. Even the steeda rear STB uses welded brackets, that encompass the top of each rear shock, and part way down the sides... where they are welded. It's a non issue.

"Since this chassis was originally designed for an IRS".

Since when was the S-197 chassis originally designed for IRS ??

 

[B2B]

Since when was the S-197 chassis originally designed for IRS ??

Since 2005... http://www.drivingenthusiast.net/sec-blog/?p=11329

 

[B2B]

I am aware of your association with MM and your racing. <snip>

Are you even referring to the same post by Jack Hidley? I'm pretty sure he was talking about the OEM shock bracket on the axle housing...

 

[Pentalab]

Since 2005... http://www.drivingenthusiast.net/sec-blog/?p=11329

Point well taken..and an excellent read.

 

[Norm Peterson]

Inverting the shock is OK for a pure track toy, but I'd consider doing that a non-starter for cars that see year round DD use in addition to the track time. Especially anywhere in the snow belt.

Race cars and serious track toys get additional reinforcing and better and more frequent inspection than, say, cars whose owners installed coilovers strictly for bragging rights and the bling, called it done, and may never look down there again.


Norm