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

[Racecomp Engineering]

Mods, maybe a sticky for this thread?

[CSG Mike]

Hopefully, this will help everyone get a few different perspectives and solutions to every question and problem. At the least, our collective goal is to educate on the suspension and handling aspect of a platform that is being touted for its prowess around corners.

Ask away!

[Racecomp Engineering]

Originally Posted by aiur55

Thanks for the article. I am interested in learning more.

How would I go about choosing the correct spring rate and damping I want? Are there certain characteristics of the car I should be looking out for?

I would be pretty hard and expensive to test out many set ups. How would I know approximately what kind of setup to go with?

Agreed with @Captain Snooze that establishing a budget is the honest step 1.

Step 2 is deciding what kind and what size tire you plan on using. This plays a big part in step 3, which is deciding how hardcore you want to be. Do you want to set track records with hoosiers? Do you want to drive your car daily? Do you drive on the crappy beat up roads of Baltimore city like me and need something that can handle both that and the track? Again, you can do a lot of things with an excellent shock, but that goes back to step 1...the budget.

There are MANY other factors...wings and aero for example. But budget and tire choice are the main things.

As for damping, that gets a bit more complicated. You'll sometimes see phrases like 65% critically damped thrown around. If that scares you, take a step back. If not...I'd encourage you to do a LOT of reading. It gets fun but nerdy.

- Andy

[Racecomp Engineering]

Originally Posted by Dimman

Do the shim stacks fatigue and stop working over time/use?

ZDan's complaint sounds like a text book example of orifice damping as used on older motorcycle front forks. It's like a squared curve, er... Math squared or exponential or something. Starts horizontal-ish and quickly moves to vertical-ish.

Shims are what modify that curve, right? So they have an oversized orifice that they 'choke back' at low speed with shims that deflect and 'blow open' at high speed, which gets you (a very simplified) digressive curve.

So are shim stacks a part of r and r for an overhaul revalve?

I don't think that new shim stacks are part of "normal" R&R for a regular rebuild. Yes for a "revalve" the shims would be replaced to alter the curve by changing the amount of force before they deflect.

- Andy

[SubaSteve]

Had eibach pro-kit installed still on stock tires. Anything I need to look into upgrading before I get my tires/wheels?

DD but I drive it like a race car.

[Calum]

There's been lots of talk about the camber curve in the front, extended ball joints and tie rod ends, that sort of thing. Is there any reason to worry about the camber curve in the rear? As I understand it, the lower the ride height the more camber is gained for the same amount of tire movement. Can this upset the overall balance once the ride height is too low?

There's also been things like, 20 mm lowered ride height is the lowest we should go before bump steer becomes a worry thrown, around. I'm guessing this was referencing the front suspension. How is the rear for bump steer? Does it become a worry at any ride height?

Finally, what bushings (if any) would your guys recommend to be replaced in the car. Clearly RCE sells some bushings kits, but is there anything else that isn't included that actually benefits handling or helps prevent wheel hop.

Guys, thanks a ton for doing this!

[CSG Mike]

Originally Posted by aiur55

How would I go about choosing the correct spring rate and damping I want? Are there certain characteristics of the car I should be looking out for?

I would be pretty hard and expensive to test out many set ups. How would I know approximately what kind of setup to go with?

First off, determine your budget.

In a black and white world, there is only one "right" damping for any given spring rate, for a given type of damper setup. The best way to really determine the spring rate you want, is to go to a local FR-S/BRZ meet, and ask for rides. Most people will not hesitate if you ask nicely, and offer a few bucks for gas if you want an extended ride.

In our case, we chose our spring rates based on the tires we're using and the effective spring rates at the hubs with setups we've had success with in the past. We chose a rate that gives us flexibility to swap between high performance street tires without overloading them, and also run r-comps without getting excessive roll.

[CSG Mike]

Originally Posted by Dimman

Do the shim stacks fatigue and stop working over time/use?

ZDan's complaint sounds like a text book example of orifice damping as used on older motorcycle front forks. It's like a squared curve, er... Math squared or exponential or something. Starts horizontal-ish and quickly moves to vertical-ish.

Shims are what modify that curve, right? So they have an oversized orifice that they 'choke back' at low speed with shims that deflect and 'blow open' at high speed, which gets you (a very simplified) digressive curve.

So are shim stacks a part of r and r for an overhaul revalve?

Typically not, but they can be changed as part of a revalve. If there was cavitation in the shock, and the shims were damaged, then they may be replaced.

Usually, the oil in the damper is what wears out faster.

[CSG Mike]

Originally Posted by SubaSteve

Had eibach pro-kit installed still on stock tires. Anything I need to look into upgrading before I get my tires/wheels?

DD but I drive it like a race car.

If you drive it like a race car, I'd recommend you get camber bolts for the front. They're super cheap, and will get you more camber in the front so that

- You even out wear under hard cornering
- get a little more front grip
- help prevent chunking if you're tracking

[solidONE]

My question is in regards to roll bars. I know they are there to decrease body roll, but how do roll bars effect the damping of a particular shock? Let's say you have a shock/spring combo that is close to being critically damped. Now let's say you increase the rate on the roll bar. How would this effect the way the shock is damped in relation to the spring(s) since it increases the total roll stiffness in conjunction with the spring? Alternately, would a much smaller anti-roll bar in this set up require less damping?

edit: "sway bars" not "roll bars" I meant. Mike knew what I meant... lol

[CSG Mike]

Originally Posted by Calum

There's been lots of talk about the camber curve in the front, extended ball joints and tie rod ends, that sort of thing. Is there any reason to worry about the camber curve in the rear? As I understand it, the lower the ride height the more camber is gained for the same amount of tire movement. Can this upset the overall balance once the ride height is too low?

There's also been things like, 20 mm lowered ride height is the lowest we should go before bump steer becomes a worry thrown, around. I'm guessing this was referencing the front suspension. How is the rear for bump steer? Does it become a worry at any ride height?

Finally, what bushings (if any) would your guys recommend to be replaced in the car. Clearly RCE sells some bushings kits, but is there anything else that isn't included that actually benefits handling or helps prevent wheel hop.

Guys, thanks a ton for doing this!

The front will initially gain negative camber as it compresses, and then eventually start to lose negative camber (go positive). The rear will always gain negative camber as it compresses, and gain faster as it compresses more.

Once ride height is too low, several things happen:

- You lose negative camber in the front under hard cornering on the loaded tire (compression), and gain it on the unloaded tire. This is the worst of both for grip.
- Roll center adjusts downward, making the car take a lot longer to "settle" (layman's term) when you start cornering. You'll notice it takes a long time for the car to really grip when its turning if you're too low
- The balance of grip is upset, because the rear camber curves and the front camber curves are too different. Effectively, the rear gains negative camber when you turn, while the front loses negative camber.

Bump steer (toe change along the compression curve) on this car, IMO, is not too bad at all. Others may disagree, but I use it to my advantage when cornering. Some people like to have zero bump steer, but my stance is that it's a preference thing.

Bushings will help prevent wheel hop under hard cornering. The CSG BRZ doesn't have any, and it does suffer for it, and we do plan on eventually doing them. However, our concept is to keep the car as simple as possible, and as streetable and tame looking as we can.

[Racecomp Engineering]

Originally Posted by CSG Mike

go to a local FR-S/BRZ meet, and ask for rides. Most people will not hesitate if you ask nicely, and offer a few bucks for gas if you want an extended ride.

This is an awesome suggestion. We had a "suspension" meet once and had almost every single set-up available this side of the pond at our shop on one day with volunteers giving rides. Also burgers, hotdogs, and a Gran Turismo competition (with an ALMS driver!). It was a good day. Need to do that again.

Time for dinner.

- Andy

[CSG Mike]

Originally Posted by solidONE

My question is in regards to roll bars. I know they are there to decrease body roll, but how do roll bars effect the damping of a particular shock? Let's say you have a shock/spring combo that is close to being critically damped. Now let's say you increase the rate on the roll bar. How would this effect the way the shock is damped in relation to the spring(s) since it increases the total roll stiffness in conjunction with the spring? Alternately, would a much smaller anti-roll bar in this set up require less damping?

Depending on how stiff the anti-roll bar/sway bar is, yes, but this is pretty rare. Effectively, you are adding spring to the car, so you may need to re-adjust dampers to be back at critical.

For most situations, damping will not need to be changed.

If you have a highly adjustable blade setup in a race car... well... you're probably not going to be able to change damping in realtime like you can with the sways anyways

[solidONE]

Awesome idea btw. Hope this will become the ultimate go-to thread the the suspension noob and not-so noobs. Cherrio