CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[Racecomp Engineering]

Originally Posted by SStratos

Hi Andy,

PM'ed with you last year before I had a chance to purchase my BRZ in November of 2916

In brief I was learning from you about set ups ideal for both daily driving and the occasional track day with a square set up of 17"x8" at that time.

Since then I have done more research on coil overs and wheel fitment and was wanting for more aesthetic reasons wanting to change my above mentioned 17"x8" square set up to a staggered setup of 17"x9" Front/ 17"x10" Rear. I would still be bringing it out to the occasional track day and want to try to maintain as much the neutral handling characteristics of the car as possible, so I have a few other questions about this new wheel set up following your above posted 3 step process.

a) with a budget for coilovers-bushings-strut bracing-steering column bracing trying to keep things, under or near abouts, the $5-6000.00 range using the staggered setup above, with either
-Bridgestone R71 R
https://www.tirerack.com/tires/tires...omCompare1=yes

or

-BFGoodrich g-Force Rival S1.5
https://www.tirerack.com/tires/tires...omCompare1=yes

...and running possibly a dive plane/canard on each front corner, but definitely a duck bill CFD trunk on the back, what would be some of my best options to allow for a good range of setup change between daily street driving vs track set up?

b) with the above setup and your proposed coilovers-bushings-strut bracing-steering column bracing solutions, I would like to understand the physics of how weight distribution affects the above setup; ie. if the above setup will provide under steer, which moves the cornering performance from the OEM neutral to somewhat over steer, would shifting the weight balance by lowering the front and moving the weight balance forward dial away some of the under steer?

c) what other ways can I dial away some of the under steer of the above setup?



Cheers

Originally Posted by cjd

Stick with a square setup for performance driving.

You're asking for some rather technical answers but are ignoring the most fundamental setup mistake you're making. if you absolutely must go staggered, get a separate square setup in a good light/strong wheel for the track (the tires are typically loud on the street anyway, a step down from the 200TW for daily would be good).

Second, for track go RS4. The RE71R is so autocross focused and the wear is likely not worth the grip. The BFG may wear longer (I don't know its lifespan on the track, but I'd be wary given its autocross performance), but everything points to the RS4 being the upgrade a lot of folks hoped for... though not as good for autoxcross.k

As for a setup... a possible starting point:

T2 and good front camber plates (I can't recommend the Raceseng front cascam and rear 1" tophats enough) and the easy to add whiteline inserts/bushings (transmission/shifter/rear subframe/diff/steering rack), no strut-bars. Forget the aero, put the remaining budget (there will be some relative to your stated funds) into that square wheel setup... maybe 949 6UL's or the popular Enkei RPF1. If you really want the aero, rear diffuser and front splitter to start off.

Agree with everything @cjd said here. Skip the bracing, skip the canards. Front splitter and rear diffuser are good. T2s with good top mounts, some key bushings, and a good alignment will go a long way. I would highly recommend 17x9 all around instead of the staggered set-up. If you must get the staggered set up then we would go with slightly stiffer rear springs. But again, it's not recommended.

- Andrew

[Racecomp Engineering]

Originally Posted by Lust

Alright sounds good. What's a good starting point for rebound and damping settings?

http://racecompengineering.com/instr...ingsbrzfrs.pdf

You can definitely go a few clicks softer on both rebound and compression for the street. Softer on rebound makes a large difference in ride.

- Andrew

[SStratos]

Originally Posted by Racecomp Engineering

Agree with everything @cjd said here. Skip the bracing, skip the canards. Front splitter and rear diffuser are good. T2s with good top mounts, some key bushings, and a good alignment will go a long way. I would highly recommend 17x9 all around instead of the staggered set-up. If you must get the staggered set up then we would go with slightly stiffer rear springs. But again, it's not recommended.

- Andrew

Thanks @cjd and Andrew.
For the T2's, would the top mounts be chosen depending on how the car changes due to the rest of the changes to; bushings, splitter-diffuser and grip from the 9" square setup?

[gramicci101]

They would be selected based on how much camber you want. Can you get your desired camber with bolts? Then you don't need top mounts. Beyond that, RCE makes their own, Velox makes great ones, RaceSeng makes the only ones with adjustable caster.

[Tokay444]

Originally Posted by Gforce

So you might think. In the real world, weirdly, it ain't so.

Research tire load v grip at the contact patch.

As load goes up so does grip. That's how aerodynamic downforce finds grip that wasn't there before the aero load. It's not linear though.

Even F1 cars can usefully increase roll resistance such that the inside tire lifts off the road and yet the other three tires deliver more grip than is lost.

Chassis engineering is INCREDIBLY complex.

It's almost something that requires no thought at all.
4 contact patches has the potential for higher level of grip than just 3.

[Gforce]

Originally Posted by Tokay444

It's almost something that requires no thought at all.
4 contact patches has the potential for higher level of grip than just 3.

So you might think. However, suspension gets in the way of your thought experiment.

Your error is in ignoring inertia effects on tire loading which in turn affect total grip available.

Just consider how aerodynamic downforce can seemingly create tire grip out of thin air and that may help.

[Racecomp Engineering]

Originally Posted by SStratos

Thanks @cjd and Andrew.
For the T2's, would the top mounts be chosen depending on how the car changes due to the rest of the changes to; bushings, splitter-diffuser and grip from the 9" square setup?

Originally Posted by gramicci101

They would be selected based on how much camber you want. Can you get your desired camber with bolts? Then you don't need top mounts. Beyond that, RCE makes their own, Velox makes great ones, RaceSeng makes the only ones with adjustable caster.

This.

- andrew

[Tokay444]

Originally Posted by Gforce

So you might think. However, suspension gets in the way of your thought experiment.

Your error is in ignoring inertia effects on tire loading which in turn affect total grip available.

Just consider how aerodynamic downforce can seemingly create tire grip out of thin air and that may help.

I'm not ignoring anything. Load up that 4th tire with even a fraction of the third, and you have more grip.

[Racecomp Engineering]

I believe what Tokay444 is alluding to is this:



Ideally you'd have 4 evenly loaded tires, but then you'd just be driving in a straight line.

- Andrew

[Tokay444]

It is ridiculous to argue that 3 tires have more grip potential than 4 though.

[Gforce]

Originally Posted by Tokay444

It is ridiculous to argue that 3 tires have more grip potential than 4 though.

Where, in your garage or on a real car?

Many successfull cars prove you wrong. VW Golf, Renault Clio, BMW 2002 Tii, Alfa Romeo GTA, the list is endless.

[Gforce]

Originally Posted by Tokay444

I'm not ignoring anything. Load up that 4th tire with even a fraction of the third, and you have more grip.

Yes, but the real world where we all drive won't let you do that.

[Gforce]

Originally Posted by Racecomp Engineering

I believe what Tokay444 is alluding to is this:



Ideally you'd have 4 evenly loaded tires, but then you'd just be driving in a straight line.

- Andrew

I believe the context is driving around bends.

Even if you have an awd car and even in a straight line you cannot achieve equal grip from all four tires. "Weight transfer" (unfortunately named as no weight moves) means it is impossible to obtain usable equal grip from four tires. But you know that, if you're a suspension supplier.

[jamal]

The thing is these are passenger cars, not purpose built race cars. Put on sticky tires and go driving on the track and wheels might come off the ground here and there. It happens because all the weight has been transferred to the other corners. Even if the tire was still on the ground, it couldn't contribute much cornering force because there is no weight on it.

So if you want to keep the tires on the ground, you can go around corners slower. Or, widen the track, lower the car, lighten the car.

And then no, there's not one ideal damping curve for a specific spring rate. or even a specific car. It's always a compromise- a higher damping ratio tends to improve performance on smoother surfaces, a lower damping ratio improves comfort. There's never one set curve that will work for every surface or driver and also it depends on the tire as well. So those adjustment knobs actually are pretty useful.