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FD race suspension discussion

Old 03-10-08, 12:41 PM
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FD race suspension discussion

Here is something that has been bothering me for a while and especially due to the fact that im on the verge of buying some coilovers.

When it comes to coil overs there seems to be 2 schools of thought, I will use examples.

School #1: Even rates or even greater rear rates
As we all know RE Amemiya makes some bad cars, their winning touge car for example. That car is using 15k front and 18k rear
http://www.dailymotion.com/video/x3l...reamemiya_auto
they also sell a 16k/18k coil over kit http://www.re-amemiya.co.jp/commodit...2a2e3&scd=7934

School#2: 10k/8k rates
These higher front, lower rear rates have been used with good effect by such people as Damian. I believe he is running JIC-FLA2's though which are 12k/9k
https://www.rx7club.com/race-car-tech-103/2-new-track-videos-659471/


So Id like to hear some discussion about it, hopefully someone has tested both types and can offer some insight.

Jason


Edit: Id like to add that we will be talking ONLY about track use, keep pot holes and speed bumps out of it
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Old 03-10-08, 01:43 PM
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Don't know bout the spring rates but penske offers a setup for the fd now. As you know they are one of the best suspension makers in the world and are US made so tech support is great.
you can get them form www.twinsturbo.com
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Old 03-10-08, 02:04 PM
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Old 03-10-08, 03:49 PM
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yup howard would be lumped into school 2, he is very knowledgeable and a great resource for suspension tech. I have learned a lot from his posts.

Originally Posted by howard coleman View Post
I run 432 front and 378 rear. Expressed metrically 8 KG and 6 KG. I am delighted with this rate. If my springs vaporized I would repurchase this rate. It works on the track. It works on the street.

That said, Frank runs 566/422 or 10Kg/8Kg. I consider this rate the outer limit.

Remember, both rates transfer the same lateral load. The higher the rate the harder it is to drive at the limit.
That is school 2 it works great for some people


Also on the other side Tsuchiya can drive a rx-7 very fast with 15/18 spring rates
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Old 03-10-08, 04:00 PM
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Does the RE Amemiya car retain the stock motion ratio front and rear? If not, comparing spring choices to your street car is kind of apples and oranges.
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Old 03-10-08, 04:10 PM
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I assume you mean stock suspension arms mounted to stock places, yes they do.
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Old 03-10-08, 05:13 PM
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Originally Posted by JTurtonRX_7 View Post
Also on the other side Tsuchiya can drive a rx-7 very fast with 15/18 spring rates
Ok, but are you Tsuchiya? Spring rates alone aren't going to dictate the performance. We have no idea what damper adjustments they are using.

Howard is a very experienced "real" racer who is here, on this forum, providing a lot of good knowledge. A lot of knowledge that most of us will never be able to test/accumulate on our own (whether due to money/ time restrictions as true racing can be damn expensive).
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Old 03-10-08, 06:13 PM
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yeah i understand, Im just trying to play devils advocate to try to flesh out the performance differences between these two very different ways of setting up the suspension in our cars.

Not knocking Howard at all, frankly I think hes awesome.
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Old 03-10-08, 07:08 PM
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One very important thing you left out is sway bars. If they're using a sewer pipe for a swaybar in front and nothing in the back then they can give it the same overall balance as school 2 using school 1 spring rates. The road surface has an impact too, as most North American roads and tracks arer rougher AFAIK.
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Old 03-10-08, 10:21 PM
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we've done some testing and our results say that going from full stiff to full soft (disconnecting sway bars) had, no real effrect on lap times (0.02 of a second at thunderhill), but one of our drivers liked it full stiff, and the other doesnt.

so by our data, the spring rate; to a point, only matters for drivers preference.

also they dont have bumps in japan
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Old 03-10-08, 10:47 PM
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from what ive seen (from watchin videos) it really seems that cornering in 15/18 setup really depends on throttle input, how you can jab the throttle and get the car to rotate easily through a turn. While in a 12/9 setup you can floor it and it just grips and goes. Thats the main difference I can see. I made this thread to see if i can get any real world examples from people who have tried it.

because its time to move from stock springs and struts
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Old 03-10-08, 11:06 PM
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I suppose there's a key difference right there. As a car goes faster factors come together to make it more prone to oversteer, so a setup that's easy to rotate at low speeds will become extremely tail happy and downright unstable at high speeds, which is bad. So for things like autocross, where the speeds are low, being able to adjust the car's attitude with the throttle can be very helpful, whereas at higher speeds on the race track it's often better to be able to just floor it and go without worrying about having the back end come around on you.
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Old 03-10-08, 11:22 PM
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yeah, thats exactly where i think the difference is. The touge is one lap of slower speed corners when compared to the normal tracks that I will see in America. (lots of 90-100+ turns when compared to the touge when he dips down to 2nd gear quite often)
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Old 03-11-08, 12:47 AM
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Fritz Flynn also had some input on spring rates in some thread. If he doesn't chime in, try searching for it.
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Old 03-11-08, 07:18 AM
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Originally Posted by JTurtonRX_7 View Post
from what ive seen (from watchin videos) it really seems that cornering in 15/18 setup really depends on throttle input, how you can jab the throttle and get the car to rotate easily through a turn. While in a 12/9 setup you can floor it and it just grips and goes. Thats the main difference I can see. I made this thread to see if i can get any real world examples from people who have tried it.
Well, I think that you have summarized it pretty well there. From a quick Google of "Tsuchiya RX-7" we see some video of various drifting and time attack events. Now I will admit that the boy is very quick. But watching the footwork as he goes through a corner, we see him go "stab-stab-stab-stab" on the throttle - he likes to steer with the back end of the car, so he has the car set up so that rear will dance around very easily. This can work well in short/tight courses where you are constantly in a turn (think: auto-x). But you have to be very, very quick to pull it off correctly.

Compare and contrast this with what you will find at most US (and European for that matter) roads courses - higher speed turns and more straights. Best lap times are not determined by your speed through the corner, but rather your speed exiting the corner out onto the straight. And to maximize that exit speed you need the rear end to grip under throttle. So a softer rear end is more appropriate here.

If you get a chance (and are familiar with the show) go find the Top Gear episode where Jackie Stewart is giving some track-day instruction to one of the hosts. He makes some great observations about getting on, and staying on, the throttle coming out of turns.

So the bottom line here is that for ideas on suspension setup for road courses you are probably better off listening to Howard and Fritz and Damian.

-bill
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Old 03-11-08, 08:01 AM
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since this thread is track only i will leave it to you guys but i would just like to mention that, perhaps, AERO is the key as to the spring rates being used.

i haven't looked at the car being mentioned but i do see lots of aero on many of the Japaneses circuit cars. Aero is often greatly underappreciated as to the downforce it is capable of generating.

most race cars that use aero are set up entirely differently. the spring's main function is to offset aero downforce to maintain a constant rideheight.

longitudinal trim is set by changing front and rear aero rather than the usual springs, bars and air pressure.

aero trumps everything.

if you aren't running big aero you won't need big springs

hc
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Old 03-11-08, 09:34 AM
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Good point. For instance if you have a setup that naturally tends to oversteer at low speeds and have a highly rear biased aero setup with a huge wing you might just be able to tame the rear end at high speeds. That said, Damian has a fairly big rear wing AND wider rear tires, so...
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Old 03-11-08, 09:56 AM
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I read on some European car forums a while ago and they like bigger rear springs so they can get rid of the swaybar. They get the same overall stiffness and the springs dont pick up the inside rear like a swaybar would so they get more traction for the exit. Also, I found a setup guide that says a faster rear frequency makes a car handle bumps better because the rear always hits a bump after the front and this allows the rear to "catch up" and doesn't let the bump affect weight transfer as much

http://www.optimumg.com/techtips_techtips.htm This is where I found the setup guide, Keep in mind it might be for porsches...
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Old 03-11-08, 10:04 AM
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Lets not complicate this.

The car is basically a 50 50 car that's extremely neutral.

Whatever you add or take away form one end or the other will either cause the car to push or oversteer. If you go from 225 street tires to 285 slicks you had better make some drastic susp and brake changes.

I primary drive my car at VIR which is a hilly fast road course with competition rated 275 to 285 tires and without heavy springs the car will eat fenders, get nose heavy under threshold braking and make like rocking horse in and out of corners.

I've run 1000 front and 700 rear with upgraded sways but the car pushed a bit too much for me. However it was a very driver friendly combo unless it was raining That said if you're driving in the rain you will need to make a spring change pronto to have decent lap times.

Currently running 1000 1000 and like it. Even on fast road courses you usually slow down to 60 or so for the sharper corners and if you can't get the car to turn you can't get back into the gas. The guy that hits the go pedal first and the slow pedal last wins the race

That said springs don't tell the whole story you need a good spring shock, sway, tire, brake, aero combo I repeat there is no perfect spring rate it all depends on tire size, driving style, aero, power, weather, how many cups of coffee you had etc...

Finally the one thing I do know from personal experience is 550 ff and 450 rr springs at VIR w/ 285 hoosiers on the car means I have to set the ride height at almost stock levels, the car takes too long to take a set, is unstable under heavy braking and the combo of these factors means my lap times suck. I could take the same car with stock tires and brakes drop in down an inch and run almost the same lap times because the coilovers aren't letting me take advantage of the bigger wheels and tires.
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Old 03-11-08, 10:22 AM
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^^^^

I'll chime in here as someone who runs 500/400 springs at 25" ride height w/ 285 Hoosiers at VIR, AND also logged a fair amount of miles riding along w/ Fritz in his 1000/1000 set up on the same weekend for the hell of it.

A. My springs are too light.
I'm into the fender liners a bit on most tracks, and the car isn't particularly stable under braking. I'm running 2:12's, vs. 2:08's for Fritz, and the difference is at least in part time made under braking, and transitions. The same for Watkins Glen. I know there's more time in the car, in the same places. I've gotta go at at least 600/500 I think.

B. Fritz knows VIR like the back of his hand, and drives with a LOT of slip, so that's partially his style... I don't think that I could suddenly adopt it because I bought the same coilovers.... but the difference in his car under braking vs. mine, and it's entry to the climbing esses and hog pen were dramatically different, even from the passenger seat.

C. Both of the cars he refers to DO have aero in the form of an air foil wing at the rear, whereas mine is wingless.

Last edited by ptrhahn; 03-11-08 at 10:51 AM.
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Old 03-11-08, 12:07 PM
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Pete,
I think the perfect setup for your car would be some koni double adj or Advanced Designs with 750 550 and get a nice wing and I'm not talking about the 99 spec wing because it won't give you enough down force. A wing is huge when driving up the esses, down the back straight along with the bend in the front straight. It also probably helps when coming out of t2 into t3. Basically if you're going over 70 it starts to make a pretty significant difference so think how much it would help at Watkins.

The GTC wing I have bolts on and off fairly easily so you don't have to drive around town with it

Try to make it to the THSCC event April 5th and 6th at VIR on the N course. They run a very cool TT session as well

Originally Posted by ptrhahn View Post
^^^^

I'll chime in here as someone who runs 500/400 springs at 25" ride height w/ 285 Hoosiers at VIR, AND also logged a fair amount of miles riding along w/ Fritz in his 1000/1000 set up on the same weekend for the hell of it.

A. My springs are too light.
I'm into the fender liners a bit on most tracks, and the car isn't particularly stable under braking. I'm running 2:12's, vs. 2:08's for Fritz, and the difference is at least in part time made under braking, and transitions. The same for Watkins Glen. I know there's more time in the car, in the same places. I've gotta go at at least 600/500 I think.

B. Fritz knows VIR like the back of his hand, and drives with a LOT of slip, so that's partially his style... I don't think that I could suddenly adopt it because I bought the same coilovers.... but the difference in his car under braking vs. mine, and it's entry to the climbing esses and hog pen were dramatically different, even from the passenger seat.

C. Both of the cars he refers to DO have aero in the form of an air foil wing at the rear, whereas mine is wingless.
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Old 03-11-08, 02:10 PM
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Hey Bud,
I'm finished w/ my last semester of grad school mid April, so I'll prolly miss that one.... but, the Porsche First Settlers will be there in late May. THAT sounds like me.
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Old 03-11-08, 05:16 PM
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Originally Posted by Fritz Flynn View Post
Lets not complicate this.
Ha! Bench racing is about the only thing I can afford to do these days.

-bill "still in the job hunt" rankin
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Old 03-12-08, 02:37 PM
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i run 14/12 kg springs on my car with a wing (re amemiya gt II) and i want to go with 16/16 or 16/18kg springs.

on the issue of tsuchiya and amemiya's cars. tsuchiya isnt always the time attack driver for amemiya, and also amemiya's cars have held time attack records on almost every circuit in japan. so his spring rates are not just for the low speed touge segments on hot version video. amemiya used to run 16/16 but now runs 16/18 on most of his cars.

in the end i think a lot of it has to do with driving style, either school of thought can be fast around the track. the main thing is that you are comfortable with it.
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Old 03-17-08, 04:51 AM
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The fastest cars now are R-Magic and Panspeed when it comes to timeattacks.
R-Magic runs F16 R10 on their car....

And I agree with it not always being Tsuchiya-San driving on the touge.
Do remember that on the timeattacks the cars are not very standard in any way. :P
I have almost all the info on the cars at home regarding springrates and stuff. Will try to remember posting later.
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