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

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

Have you read Howard's thread?

https://www.rx7club.com/suspension-wheels-tires-brakes-20/howard-colemans-fd-chassis-setup-723617/

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.

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

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.

I assume you mean stock suspension arms mounted to stock places, yes they do.

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).

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.

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.

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

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

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.

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)

Fritz Flynn also had some input on spring rates in some thread. If he doesn't chime in, try searching for 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

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

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...

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...

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.

^^^^

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.

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 :icon_tup:

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.

Ha! Bench racing is about the only thing I can afford to do these days. :(

-bill "still in the job hunt" rankin

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.

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.

yes but the rmagic car aslo has the fuel tank in the passanger seat area. plus it has about 150hp more than the amemiya

pan speed runs (or ran, my mag is kinda old) 16/16 kg spring rates

the pan speed car just got beat by the top fuel s2000 on the tsukuba time attack. not really relevant to anything, but interesting

So the RX-7 no longer holds fastest RWD in Tsukuba anymore?

thats correct. its the fastest rwd car around tsukuba is now the top fuel s2000

if its the same top fuel s2000.. the thing has 871 hp.. and cf body panels, maybe all the panels?

Dont think so, panspeed hold the record with there new wide arch car dont they?

Pan Speed - Tsukuba 55.603
R Magic - Tsukuba 55.7
Top Fuel/Zero-1000 S2000 - Tsukuba 55:350

Maybe if the rx7 cars put some wider tires on the car rather than 255's? Or is there some regulation with tire sizing?

the top fuel runs 265's i believe, so they could go bigger

Slightly on a tangent, but I do find it fascinating that all the Japanese tuners use such small tires. Even on some of the highest hp racecars over there they use (by american standards) ridiculously narrow tires.

i've also found that interesting why 255 seems to be the largest tire used on the fd. i use 255 on my car, but then again i am still using the stock turbos

http://www.maxrev.net/index.php?location=revspeed.htm

thats a good article talking about the 07 tsukuba time attack (the one were pan speed set the previous record). it has some good info on some of the time attack cars and really good pics

Well there's more to grip than tire size, and there's more to speed than grip. As you go wider it's harder to keep the full tire in contact with the pavement (camber sensitivity) and those wide tires will be causing more drag, slowing them down on the straights, presuming they can get traction.

I was gonna get some 285 tires for my car after I do a widebody. So should I forget about that idea and just look at more suspension setups?

Can anyone give more incites on tire sizing?

Wider is better, even if a wider tire is more camber sensitive, a track record setting car on 255s probably has the tire flat as can be throughout its suspension travel anyway. More tire equals more grip at some cost to drag, weight, and slip angle. Lower slip angle at a certain g load is faster anyway because of the drag caused by high slip angles. These cars should have enough power to negate the drag, plus with the huge wings, the tires' drag is basically irrelevant. The only flaw, imo, is weight and the fact the whole suspension has to be adjusted to suit the new characteristics.

Btw, the fastest stock class autox rx8s use 285s

That'a not entirely true, I believe thenationals winning RX-8 was actually on some 245 V710's. I know that on Miatas, with stockish power 205's are generally faster than 225's on the track, so sometimes wider isn't better. The tradeoff is that you get more corner speed, but you loose some acceleration and top end speed on the straights. Depending on the track this can help or hinder.

Only testing will tell if one's faster than the other, and I'm sure they wouldn't be using 255's unless they were faster for them, but that's not to say that they'll be faster for you. Wider is usually more fun though, and unless it's a competition it doesn't really matter that much anyway.

sleepyhead: So you think that Panspeed say "oh no, we have to reallign the suspension now that we have wider tires so we better not do that" when they have done all the things to their car already. Don't forget how much driving they actually do and have done with the FD's in Japan.

Has anyone here actually gone back to skinnier tires?

I have a theory that mabe they limit rim size? Since i am sure there are restrictions, or we would see people bringing the supergt cars out...........

In autocross where wheel size is limited people put 285/30/18's on 18x8's, 225/45/15's on 15x6's and stuff like that. In Prod and GT racing with the SCCA where they limit rim size they run cantilever slicks that are over 10" wide on a 7" wheel.

That's probably not it, unless it's a rim and tire size limit.

I meant because they are limited by rim size, they have found the optimum to be what they are?

Since we are on the topic of race suspensions, I wanted to ask about people's experiences with sway bars and why they chose their sway bar setup.

My FD is running Koni sport adjustables, H&R street springs and an Eibach front sway bar with the stock rear 93 bar. Long story but I had to switch out my Eibach rear bar due to a problem with the bushing.

I was at Horse Thief Mile recently and while I was there I had the opportunity to screw around on their skid pad. I found that with this setup, my car understeered a lot. It was very difficult to get the rear out or even just keep the cornering attitude balanced.

I see a lot of people running the large Tripoint bar up front with the stock rear bar. Don't you guys see a lot of understeer with that setup?

Thanks.

That'll be entirely dependant on the spring rates being run. If you've got stiffer rears then you don't need as much bar to have the same balance. Also, as you go stiffer, the influence of the bar goes down (less roll = less deflection = less force).

werd up :) did you make any adjustments while on the skid pad to address the understeer? what tires? what air pressure front and back? what alignment settings? what shock settings front and rear? If you had understeer, you could have softened up the front shocks and you could have lowered the air in the front tires in an effort to get it to the style you want. Or leave it alone and live with the understeer because it is safe on road course.

For the last 2 seasons of AX/RR, I had progressive rate springs (approx 412 lbs front, 288 rear) and KYB/mazdaspeed shocks. It was very compliant and soft. Easy to drive. But lots of body roll with sticky tires (only 245's up front, 275 rear v710):
http://209.177.55.37/images/rx7/DSC_0248.jpg

Over winter, I got JRZ triple adjustables with 900 lbs front/ 650 rear springs (16kg front/12 rear is about what they convert to I think). The national winners in SCCA run slightly higher so I wasn't really concerned they were too stiff. Feels great on street.
Switched to bigger front tires (more grip) and ran 285/30 v710's all around on 18x9.5's +50mm.
Yesterday was first event of year for me. I got a real experienced friend to co-drive with me and after a few adjustments to low speed bump (set it to softest setting, 1 of 6) the car felt amazing. Supremely balanced when I did loose traction. Less body roll even though grip increased. No rubbing at all:
http://209.177.55.37/images/rx7/ax03302008/DSC_0065.jpg

The car reacts a lot quicker but even on a pretty cold 45 degree day, tire temps didn't go over 100 with 2 drivers, the stick was amazing. Still using suspension techniques 1.25 solid front sway bar. I will put tripoint bar on for tomorrows event and put it to the 2nd softest setting to start out with.

Tire pressures were 29 hot front, 25 rear. Rear grip was pretty good. I had thoughts of removing rear sway bar, but now I will leave it on because of how well it felt. I put new hawk HP+'s pads and new fluid and the braking was awesome.

My co-driver, set FTD with a 44.1 and I came in 3rd with a 44.5 (missing 2nd by .008 seconds from an EVO that made that up at the starting line only). 3rd out of 105 cars ain't bad for my first event of the year.
I did have axle hop at the start so I know I was leaving time on the table at the launch; 30 aspect ratio can't take a shock. Maybe in the warmer weather it'll hook up better. That issue was just at the starting line. On a warmer day, I will adjust the slow speed bump up from softest to up 1 or 2 clicks (out of 6).

My setup is not final as I'm waiting for a fix to my rear sway bar bushing but this is what I was running at HSM...

My Koni shocks were set full stiff front and half a turn from full stiff rear.
Air pressures were 31 Front and 29 Rear set cold.
Tires are Kumho MX 255/40/17 all around.
Front camber was around -1.5 front and about -1.2 rear.
Caster at 6 degrees.
Front toe maybe .04 or .06 toe in. Rear toe should be at 0.
I had just done rear diff bushings and a new gas tank and I think the alignment might have changed slightly.

I didn't get to the skid pad until late in the day and didn't do much in terms of adjusting through the day other than playing with shock stiffness. I was mostly out for fun and testing the various changes I made to the cooling system and brakes and making sure the car was reliable. It was. :)


Looking at the spring rates that some people run with the Tripoint bar, it doesn't seem like the rear spring rates people use are all that much higher from a percentage standpoint to balance the car against the size of the front bar. Hence my question.


Its not worth commenting on my setup right now as it will be changing shortly. I guess I'm more interested in understanding how much spring you need to balance the large TP bar or if people are indeed running the car with more understeer.