RCE suspension Q&A thread! Ask us anything!
 

Mods, maybe a sticky for this thread?

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!

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

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

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.

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!

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.

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.

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 :)

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

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.

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

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 :)

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

this is a perfect place and time.

So Turbowski and I will be doing our install video on the Ohlins Road and Track. I know Mike does not like it but suspending that for a moment understand the build goal is a near perfect street car that has little compromise for the track. It needs to be almost OEM on the street or better not raising any red flags to casual drivers or the hard core. But when on track can do 80% of what a track prepped car can achieve without changing much of anything.

Impossible right? Thats the goal.

so the road and track on paper is one of the better kits for this purpose. Yes its not double or triple adjustable but it doesnt need to be for a street car.

So onto the questions, pre load do you really want to play with it?
Ride height, they recommend 20mm front 15mm in rear I think it is too much for our area. Would a 15mm 10mm or less hurt that much.
How long to let settle before corner balancing and final alignment?
Damper settings, typically firmer in front than rear?

I would assume Ohlins will include instructions on how to set the preload, no?

Do you guys have any thoughts on working/teaching about the concept of 'frequency' into more ordinary suspension discussions?

I understand it is something that you need to sort out for each car, but ballpark figures for average weight models with stock springs could be used as the baseline. (Stock Imprezaru F/R 5kg/5kg Relative Stiffness 60/70 CPM* vs Modded FRZ 4.5kg/6.3kg RS 106/111 CPM)

It would introduce the concept of 'relative stiffness' to readers so new-to-suspension people could start to develop a better/more accurate understanding than just quoting F/R spring rates, since it takes spring rate, mass and motion ratio into a single figure.



*Cycles Per Minute. Or Hertz could be used.

they do but I guess the question is why is adjustable if there's only one way to really do it?

They come with the adjustable threaded 'sock' for ride height adjustment, right? I'm sure you can raise or drop the preload a bit to suit your needs. Upping the preload will obviously increase the effective spring rate by a tad if you plan on carrying more equipment on the car (stereo system, fat girlfriend, etc) or lower the preload if you want to lighten the car. If your anal about it, I'm sure you can get spec sheet of the springs from Ohlins. 5mm of preload = xxx lbs/in, 15mm of preload = xxy lbs/in, etc. etc.

Just curious, does the instruction also tell you to measure the sag of the suspension and to adjust according to that. I suppose you can do that if you are, again, anal about your suspension. :) [/points to self]

Ohlins will work well for you.

I don't recommend playing with preload. Just get it snug...a few mm. It doesn't change things as much as people think unless you really go to town. It has zero effect on spring rate, which is a common misconception.

15mm drop front and 10mm drop rear would be fine.

Should settle within a day. Drive it carefully.

Damper settings front vs rear...don't think about it in those terms. The front and rear damper do not have the same valving for Ohlins so click 5 on the front is not click 5 on the rear. Same neighborhood maybe. You need to find a setting that is firm enough that the car isn't bouncy but soft enough so that it doesn't crash over bumps. Do your best to separate the front and rear of the car in your head.

Makes it easier to take apart for one, and if anyone ever uses different than standard springs.

- Andy

I would like to do an article on suspension frequencies. :)

Soon.

- Andy

The rear camber curve is much better than the front. You'll notice when people lower the car, the rear gains a ton and the front just a tiny bit. Ride height affects balance in many ways...changing where you are in the camber curve is just one of them (and it is notable). Yes too low and you might find yourself with a lot more understeer unless you change a few things.

Not very much bumpsteer on this chassis up front, little bit in the rear.

IMO the 20mm lowering number just plain depends on a lot of things. For springs, yes. For coilovers, much more going on and firmer springs can make certain problems less of a problem.

I'm a big fan of front control arm bushings. We have so many in the rear for our car I'm not sure where to begin. The subframe bushings are awesome. I like the camber bushings but they suck to install and adjust as everyone knows. The difference between our car with essentially everything replaced and a stock car is massive. So much more connected.

- Andy

How do you find the balance of lowering the car's center of gravity (lowering the car) and not destroying the factory suspension geometry? Is one more important than the other? For example, is keeping the factory suspension geometry (stock ride height) better than a lower center of gravity?

What exactly gets ruined when you lower the car too much? Can you provide some examples? Is it the fact that the front struts gain positive camber when you lower it too much?

Is there any weirdness with the wheels under compression? For example, do the rear tires toe out/in under compression?

Thanks!

I'm not in the market but just curious. Years ago, when I had Tein RAs on my Miata, I couldn't find anyone local (San Francisco Bay Area) to do rebuilds on them. Are there any shops in CA that rebuilds Teins now? I was very happy with the RAs but found local support to be limited from the race shops.

One reason why I went with Ohlins is because Performance Shock is nearby and they do rebuilds of them (along with Koni, Motons, Penske)...
http://performanceshock.com/index.php?main_page=product_info&cPath=1&products_ id=677

Thanks,

I'm looking foreward to understanding about 9 words in this entire thread.

The collaboration will be a formidable one, for sure

Your right, a spring's rate does not magically change when you compress them.

But, lets say we have 2 springs of equal and linear spring rates. One spring is compressed an inch the other left static. Wouldn't the compressed spring offer more effective rate then the static one at the next inch of compression?

Sorry, not here to argue. You are right, you should just go by whatever Ohlins recommends. Carry on. :)

Swaybars have an effect on roll damping, but it is essentially zero in ride (i.e. 2 wheel bump). When you use 4 dampers total like most cars you are making a compromise between ride and roll damping ratios.

Add another 4 dampers if you don't want to compromise at all. ;)

- Andy

When the springs are let go, they'll both compress an equal amount, proportional to their length.

The spring constant for both springs doesn't change, and unless there are unequal forces acting on them, they will both absorb energy (compress) proportionally.

Compressing a spring 2 in vs 1 in means you have to exert twice the energy. If you want to compress it 3 in, you have to exert triple the energy. This is, of course, assuming an ideal spring, and most quality springs are pretty close to ideal for all intents and purposes.

Tein USA is the shop to contact.

http://www.tein.com/service/price_list.html

Mmmm I have a lot of respect for PSI.

Spring rate on a linear spring is linear. :)

It would be providing more force but the rate doesn't change.

If you preload a 100 lbs/in spring a half inch, you have a force of 50 lbs upwards. It will still need another 50 lbs to go that next half inch.

Now drop 750 lbs of car on it and you'll understand why I don't bother messing with it. With a LOT of preload, you can change how much it takes for the spring to move, but it takes a lot.

- Andy

Can we talk *comfortable* coilovers for a second?

I've been on the search for a comfortable coilover package that is adequate for street tires with enough adjustability for the occassional trackday. The car will never be on anything stickier than RS3s and even then that'd be a rare occassion. I will mostlikely just drive it to the track in the same trim as how I'd drive it to work (year round, summer tires).

I rode in a prototype CSG Spec Tein SRC and the suspension was amazing but it may have also been Mike's inhuman driving skills. With that said, I still prefer something more compliant for the street. I've had the RCE Yellows on the stock damper. Spent a good amount of time on the KW V3s and now i'm on the RSR Sports-i setup. These are not what folks consider high end coilovers and I'd have bought "expensive" coilovers by now but I want my final decision to be final. I'm also not yet convinced I can find a good coilover for this car in a single adjustable format. I'm even considering just dropping down to a Koni insert or whatever Bilstein comes up with or going back to stock.

I am thoroughly convinced this car has either
A. very limited suspension design (mcpherson, multi-link rear vs. say double wishbone) (why is the rear shock travel so damn short???) OR
B. few have put in the R&D into a proper suspension package for this car

I've also noticed that the label on the coilover is not nearly as important as the amount of effort given to tune that coilover specifically for that car. In other words, i've been in cars where say.. a KW V3 was crap but on another car a KW V3 was pretty darn good. Both were adjusted by "professionals". I have to correlate that to the amount of tuning effort allocated for that platform. Am I incorrect?

Not sure how many folks here know of Tsuchiya's previous suspension company(s) (K-Office > DG5). His philosophy for tuning was not to sell race car level suspensions but instead to build a properly balanced sporty car that can be adjusted for a fun day at the track but also incredibly comfortable for daily driving. This resulted in a broad range of adjustment but via just one knob. Guys like me don't want to tinker anymore with adjustable this.. adjustable that. I'd rather have a company find the critical damping point for the car in an easily adjustable suspension. Which coilover system out there employs this philosophy?

Also to add to my previous point, it's my understanding the DG5 coilover is overrated - fine. I can see that happening on platforms were there wasn't enough R&D allocated to the car (say the S13). On the NSX the DG5 is absolutely amazing. I heard its pretty awesome on the original 86 also. On the NSX it rides like a sporty sedan on the street but can be dialed up to perform better than a Type R on the track all via a one-knob, easy to get to adustment. It also ships with stiff spring rates (11k/14k) so I know spring rate isn't the only factor to a comfortable ride. Tsuchiya himself uses this suspension on his NSX-R which can likely explain all the R&D attention this coilover has gotten. Do we need some cocky Japanese "Drift King" ex JGTC champion to design a coilover for our 86? I sure hope not!

I'm hardly a DG5 fanboy but on the NSX i've tried many coilovers including the KW V3s (not bad), Motons (too many adjustments), JRZ (R/R1s), Tein (mono, RAs), and Bilsteins. I prefer the DG5 and it's not even the most expensive of the bunch.

Maybe i'm asking for too much here and I should just go back to the stock suspension.

SIGH :iono:

Finding the balance is dependent on application.

At the most basic level, I tell people this: If you have trouble getting around, e.g. over speed bumps and into/out of driveways, you're too low.

For the enthusiast, I tell people to lower their car to their preferred height, and align based on wear, and to keep an eye on both the inner and outer shoulders.

For an enthusiast that wants to understand how it works:

The front camber curve goes negative as you drop, and then goes positive as you keep dropping. The rear camber curve stays and gets more negative as you drop. Imagine cornering with *positive* camber on your loaded tire. That outer edge is going to get shredded!

Additionally, dropping the car too low will drop your roll center, hurting response (at the basic level) at corner entry. Here's a picture shamelessly pilfered with a google search.

http://i88.photobucket.com/albums/k1...lustration.jpg

Here's an article that goes into depth re: roll center:

http://www.motoiq.com/MagazineArticl...ll-Center.aspx

The rear wheels do toe in slightly under compression (bump steer).

Regarding frequencies, for each corner, you can use:
fn = [sqrt(wheel rate/sprung mass)]/2pi
Easiest if you just use metric units: wheel rate in Newtons/meter, mass in kilograms

Wheel rate is the spring rate divided by the *square* of the motion ratio.

On my FD, one corner = ~3000lb/4 = 750 lb
Unsprung mass per corner ~50 lb.
sprung mass per corner ~750-50 = 700 lb, divide by 2.205 lb/kg = 317 kg
11kgf/mm springs, multiply by 9.81N/kgf = 108 N/mm = 108,000 N/m
motion ratio ~1.6 front, so wheel rate = 108,000 N/m / 1.6^2 = 42,188 N/m
motion ratio ~1.4 rear, wheel rate = 108,000 N/m / 1.4^2 = 55,102 N/m

fn front = sqrt(42,188N/m / 317kg)/2pi = 1.8 Hz
fn rear = sqrt(55,102N/m / 317kg)/2pi = 2.1 Hz

~2Hz is a pretty damn stiff street ride, pretty damn soft track ride, a decent-enough compromise...

The lesser drop should be just fine, IMO. You may need to get a LCA for the rear to get the proper camber for maximum cornering grip, but that may or may not be ideal for a dual duty car.

I'd try to drive it around town for a day or two; usually driving 50 miles will get all settling out of the system.

You should be okay without messing with preload. If there's no play, you'll be fine.

The damper settings are analogous between the front and rear. Based on my personal preference, given the default spring rates offered on the Ohlins R&T, I'd probably end up with slightly more damping in the rear to induce rotation via loss of grip. This would be better addressed with a rear sway and possibly tire pressures as well.

My biggest issue is that it is single adjustable. If it were double adjustable, then it would:

- Offer more flexibility with spring rates
- Offer more fine-tuneability for maximum comfort AND performance
- It's really friggin expensive for a single (although the JRZ RS1 is even more!)

I suppose I used the wrong term when I said "effective rate." I was thinking of it from a motorcycle suspension set up standpoint when I was talking about preload adjustment.

After the spring rates are selected, the preload is set by checking the suspensions sag, then adjusted accordingly on a motorcycle. The preload on a motorcycle greatly effects how it's suspension performs. When you set the front forks, for example, with less sag or more preload it makes the front suspension stiffer. This adjustment is often made when we switch to a softer compound, track oriented tire from a harder compound street tire. For the rear shock, sometimes people will use a hydraulic preload adjuster to jack up the preoad when taking on a passenger. I suppose on a car it would effect performance to a lesser extent, but shock absorbers are shock absorbers. They should have somewhat the same type of effect when done on a car. (preload adjustment, I mean)

lol Hmmm how can I mount some swaybar dampers... :laughabove:

It's just a matter of demand in the market, and an appreciation for a truly well designed coilover.

The problem with the market nowadays, is that there are just two many low end (i.e., imo, garbage) offerings, that are good for lowering the car, but do not really bode well in terms of both performance AND comfort.

Given the resources, I'm 100% confident that ANY company can dedicate the time and manpower necessary to create such a 1-way adjustable damper. All you'd need to do is choose a middleground spring rate (I'm thinking maybe 7.5k/9k or 6k/7.5k), and then determine a few differing pairings for a less damped street setting, and a more damped track setting. Once the pairings are made, it needs to be transferred into an internal construction in the damper; this is the more difficult part, as the single adjustment has to have purpose-designed crosstalk to simultaneously adjust both compression and rebound, and adjust both by specific amounts so that they're properly balanced.

Would the ROI be there for the suspension company and/or shop? Unfortunately, probably not. 10 years ago when we didn't have all of these cheap taiwanese/chinese brand setups, it was much more viable; selection was limited, and EVERY manufacturer was getting a larger share.

With the amount of R&D cost involved in designing the damper internals to get that exact curve, the end cost very well may end up higher in cost than a good double-adjustable damper.

For every damper setup CSG dials in, we always show the owner how to properly make the adjustments, and give them different settings for different scenarios.

If I had the resources, believe, I'd have already done exactly what you want. It would be so easy to adjust...


Have time to ride in the latest re-valve on the prototype CSG-Spec SRC? We're currently focusing on street comfort. I just put it in last night, so I need to dial it in tonight... ;)

I have whiteline rear upper control arm eccentric bushings for camber adjustment. My target alignment for street and track is -2.0 F and -1.6 R.
And that maybe too aggressive for street. Thoughts?

All I want to end up doing at the track is dropping in pads, adjusting pressures and damper clicks. No pre and post corner balance alignment and height change.

Thanks for thoughts on settling.

I agree about the price, believe me. In this case we are not testing price we are testing the product. But that will be apart of the conclusion of course.

Thanks for that, how many customers in the wild do you have with the Ohlins? What are the impressions thus far and do you have any advice etc?

That camber should be fine. It's aggressive for *just* street driving, and not aggressive enough for track driving, but between the two, it should result in somewhat even tire wear.

I prefer zero toe, front and rear, on this car, but you can dial that to your preference. Depending on how you are with bump steer, you may want a hint of toe-in in the rear (maybe 1/16" or 1/8" total toe-in).

Toe is what really eats up tires, so 0 toe will be nice for wear.