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

[strat61caster]

Originally Posted by Ro_Ja

So I'm playing around with Hyperco's spring rate calculator and I found a lot of information here and here, but what I can't seem to find are dimension A and dimension B for the rear. According to the research I've done, 98/100 is the approximate ratio for a McPherson strut, so I'm able to get a rough estimate for the front, but the rear is unknown to me. Does anyone know the two dimensions for the rear, so I can get a clearer picture of what rates I might prefer?

Also, what sort of suspension frequency would I be looking at for an aggressive street/light track vehicle? I'm currently hovering around 2.1 Hz front and 2 Hz rear per general information I've gathered. Does this sound correct?

Look here again:
http://www.ft86club.com/forums/showthread.php?t=26661
Motion Ratios:
F: ~0.95
R: ~0.76
Different terminology, same numbers.

Decent starting point if we did our math the same way, no replacement for experiencing the stuff yourself, different people can make radically different setups work.

[Ro_Ja]

Originally Posted by strat61caster

http://www.ft86club.com/forums/showthread.php?t=26661
Motion Ratios:
F: ~0.95
R: ~0.76

Right.. Ugh. I'm not very good at the numbers thing and apparently reading as well..haha

So, I got ~362 lb/in front and ~403 lb/in rear (man, that seems stiff). Based on Kost's testing, I suppose I'll be looking at a 6in spring with helpers up front. How about the rear? 6in springs (and helpers) too?

Decent starting point if we did our math the same way, no replacement for experiencing the stuff yourself, different people can make radically different setups work.

Yeah, that's exactly why I'm pulling my hair out over this. Also, since I don't really have experience with different setups and such, there's no real way for me to validate my spring choice. I could end up with something horrible and not know it or not really know how to fix it.

[Shankenstein]

Originally Posted by Ro_Ja

Also, what sort of suspension frequency would I be looking at for an aggressive street/light track vehicle?

I remember hearing Shaikh from Fat Cat Motorsports talking about his standard "aggressive street + light track" setup is 1.8-1.9 Hz in front and 1.9-2.0 Hz in rear.

As the CSG guys can attest, a good damper can be tuned for much higher rates (3.0-3.5 Hz)... but the only reason you'd want to go that far is when you've dropped the car low or there is a super-low splitter on the front.

The theory of flat ride is that your front tires will hit the bump first, and depending on the speed, the rear tires will hit it shortly after. The front and rear need to settle simultaneously (per the theory). At autocross speeds (50-70 mph), I've calculated a 10-15% bias to the rear is best. For track only situations, you'll be driving faster, so a bias of 10% is probably better.

BTW, you're welcome to use my suspension calculator spreadsheet. One of our forum members got it from the Miata guys, and I've done some fiddling with it.
LINK to Google Drive

[strat61caster]

Originally Posted by Ro_Ja

6in springs (and helpers) too?

imo anything over 300# is going to want a helper spring on this car.

[Ro_Ja]

Originally Posted by Shankenstein

I remember hearing Shaikh from Fat Cat Motorsports talking about his standard "aggressive street + light track" setup is 1.8-1.9 Hz in front and 1.9-2.0 Hz in rear.

As the CSG guys can attest, a good damper can be tuned for much higher rates (3.0-3.5 Hz)... but the only reason you'd want to go that far is when you've dropped the car low or there is a super-low splitter on the front.

The theory of flat ride is that your front tires will hit the bump first, and depending on the speed, the rear tires will hit it shortly after. The front and rear need to settle simultaneously (per the theory). At autocross speeds (50-70 mph), I've calculated a 10-15% bias to the rear is best. For track only situations, you'll be driving faster, so a bias of 10% is probably better.

BTW, you're welcome to use my suspension calculator spreadsheet. One of our forum members got it from the Miata guys, and I've done some fiddling with it.
LINK to Google Drive

Awesome! Thanks for sharing that calculator.

While I've noticed that while the rear motion ratios of 0.77 is agreed upon by a lot of people who have done their own calculations, I have noticed that the front seems to vary between 0.95 and 1. Why is this?

I also see there are a lot of variables that seem to play into all this. How do you (or rate calculators) factor such things such as aero (or lack of it), tire width and compound, etc.?

It's a little difficult for me to understand the math here (let alone check it), but I found this:

Another setup – the RCE T2s that come in 400/400 result in NFs of 2.27 Hz Front and 2.16 Hz rear.

Isn't that opposite of the theory above? How does RCE do it (and get away with it too?). I understand RCE favors a square setup, which not everyone prefers, but it seems like they make it work and people are generally happy with their way of doing things.

Originally Posted by strat61caster

imo anything over 300# is going to want a helper spring on this car.

Yeah, I had no intention of running without helpers. I'm just unsure of spring length and not being able to get the car at the desired height.

[ajc209]

Problem with looking at only wheel frequency is that is doesnt consider roll stiffness contribution from the roll bars.

I suspect RCE selected their spring rates to give the balance they wanted to work with the stock roll bars.

Starting from scratch you pick spring rates with frequencies 10-20% higher at the back then sort out the roll bars to balance the front to back roll stiffness to give handling characteristics you are looking for.

[stockysnail]

I had AR Auto Service give me a corner balance and alignment since I needed it after I installed my RCE Tarmac 2 coilovers. I'm using the oem top hats with the washer/spacer and also have the Whiteline front camber bolts and the Whiteline upper inner bushing (camber correction) KCA326.

Here are the stats of the alignment:
Height front: 375mm rear: 372mm (about 1.5-1.7 inches lower is my guess) It feels low very as well.
Corner weight: LF: 865 RF: 807 LR: 704 RR: 675 LF+RR=1510 RF+LR=1511
Caster front before: Left: 6.11 Right: 6.43
Caster front after: Left 6.39 Right: 6.07
Camber front before: Left: -2.64 Right: -1.67
Camber front after: Left: -2.73 Right: -2.78
Toe front before: Left: .06 Right: .08
Toe front after: Left: .01 Right: .01
Camber rear before: Left: -2.9 Right: -2.79
Camber rear after: Left: -3.1 Right: -2.91
Toe rear before: Left: .16 Right: .10
Toe rear after: Left: .05 Right: .06

I was thinking getting new coilovers would be a minor upgrade and I'd only notice it a little bit. I was also worried that it wouldn't be worth all the $$. I'm very impressed with how amazing the car is handling on the street. I can't wait to push the car in autox and on the track to see how crazy this thing handles. Fall in love with your car again and do what I did!

[Calais]

going to buy coilovers and am debating on whether or not i should do the swap out myself, i am not mecanically ignorant but have not done anything like this before is it easy for a first timer to do or would you recommend i pay to have a professional do it?

[ScionOfHorus]

Doing it myself, the first corner took 2 hrs. The other 3 took like 45 minutes combined.

Sent from my MotoE2(4G-LTE) using Tapatalk

[Racecomp Engineering]

Originally Posted by Ro_Ja

Isn't that opposite of the theory above? How does RCE do it (and get away with it too?). I understand RCE favors a square setup, which not everyone prefers, but it seems like they make it work and people are generally happy with their way of doing things.

The theory that many subscribe to that the rear natural frequency has to be ~0.3 Hz more than the front was NOT a theory that was developed to make the car faster around a track. It was NOT developed to produce a "correct" handling balance. It does NOT incorporate swaybars, alignment, tire compounds, differentials, aerodynamics, dynamic suspension geometry changes, drive wheels, etc.

This theory was developed by Maurice Olley in the 1930's. That's a long time ago. It's a guideline that was developed for passenger cars so that the front and rear of the chassis react sort of "in phase" togehter for the initial period after hitting a bump at a specific vehicle speed. This does help the car feel more comfortable. It was a very important step forward and chassis/suspension design...Olley was a very smart and interesting guy.

But passenger cars (perhaps more so on passenger cars 85 years ago) run very low damping ratios...meaning yes, the cycles per unit time (natural frequency) of the suspension may be something you easily feel. Think old school big ass Cadillac bouncing down the road after hitting a bump. It's not something that's felt quite so much on a car with firmer shocks. You hit a bump on a car with proper shocks with damping ratios around the often cited 65% of critically damped ratio and the car settles very quickly because of the shocks. It's not all spring, bouncing and bouncing down the road.

We've felt that rear spring rate and damping ratio has been hugely influential on ride quality and the ability to put power to the ground. When we want to control front roll and limit front dynamic geometry changes as well improve transient response with a certain front spring rate, the flat ride theory would require us to run rear spring rates that are just too high for comfort and rear traction. There are compromises and tradeoffs. We generally don't run spring rates as high as some others.

Every motorsports level suspension engineer has told me the same thing about flat ride. It's a starting point at best. But they don't care too much. The "correct" spring rate balance is the one that makes the car go around the track the fastest.

- Andrew

[Racecomp Engineering]

FWIW we don't always run even spring rates...we do go with slightly stiffer rear rates occasionally depending on the car, tire, and driver preference.

Bottom line, with good shocks and a set up that's well thought out and complete, even spring rates will get you a car that's fast and fun. Yes, it can still dance. Slightly rear biased rates can work well, too.

- Andrew

[Calum]

Here's a silly question, if the damping is especially stiff, could increasing spring rate actually make the car more comfortable?

[n0thing]

Vehicle is a DD and has about 5 track days per year.

Mods on vehicle:
- Nankang NS2R 215/45/17 120TW on stock rims
- Hawk HP+ F/R
- SS brake lines F/R
- RBF600

Plans:
- Tein Type Flex (7k/7k)
- SPC LCA
- lower by 30mm F/R
- camber -2deg F/-1.75deg R, toe 0deg F/R

Any comments are appreciated.

[Bach415]

Question: I'm planning to change up my suspension setup. I was thinking of Bilstein B14 coilovers with Raceseng CASCAM plates and swift sports swings.

Correct me if I'm wrong but for the B14, the bottom spring perch is 60mm while the top is 90mm right? So I would just only need a 60mm top spring perch for my cascam plates in order to run custom spring sports springs (ID of 60mm).

Also which swift sports swings would you recommend for comfort yet aggressive driving.