For those of you who have turned your ITR into a track-only car with track-only suspension, what kind of spring rates are you running? (Preferrably in kg/mm) And how does your spring rates help your driving style? I'm thinking about 20K front and 16K rear.

Thanks in advance!

 

You may get more responses if you post in the competition forum, or post a link to this thread

 

Thanks for your suggestion. I posted a link to this thread in the competition forum. Hope I would get more responses.

 

i think it depends initailly on what setup you are running now and plan on running.... I have heard a couple of R owners running 1000lbs front and rear, but that is with race valved shocks

 

Talk to Big Phat R.

 

I am running 400lbs (front) 500lbs int he rear. I wish I had gone a little stiffer in the rear. I have Bilsteins with eibach springs, and ground control sleeves. TrueChoice makes a very nice set for about $1250 I think.

Bryan

 

Wai: it depends on the track. On Sebring, most ITS GS-R guys run in the 800-1000lb front range and 1200-1600lbs in the back. That's for the 12 hour course anyways.. since my car has to be semi-streetable I'm running 450lb in the front and 600lb in the back.

 

For track only I would start with 600 lb/in (10.7 kg/mm) front and 900 lb/in (16 kg/mm) springs (7") with appropriately valved dampers. Start with the Mugen 26 mm rear bar too. With R compound tires - the car should still be fairly neutral. Up the rear spring rate if you want more rotation/looseness.

20 kg/mm up front (1120 lb/in) is pretty aggressive and you would probably HAVE to run 225 Hoosiers with mondo camber so you don't understeer like crazy. Why do you want such a high rate to start with? Running alot of camber up front will greatly increase your cost of operation from a tire standpoint.

 

Thanks everyone for the input. My initial thought of 20K front 16K rear came from those "Sunday racers" in the Japanese magazines. Honestly I don't know where to start, so I can only gather my information from the magazines and internet until I get a chance to experience it myself. Looks like 20K is too aggressive. I need to do more research on that.

One thing I don't understand tho, why you guys are running stiffer rear than the front? I understand that stiffer rear springs would induce more oversteer. But from the weight distribution stand point, the front springs should be stiffer right?

Here is my understanding:
The weight distribution of our car is approximately 60/40.
If I want neutral behavior, I should keep the front and rear spring difference at a 3:2 ratio (ie. 15K/10K or 900lb/600lb).
If I want oversteer, I can increase the rear ratio, but not necessarily having a physically higher rear rate. (ie. 15K/12K or 900lb/720lb).
This is only a general idea. I understand that sway bars and damper settings would greatly affect the outcome too.

From the King's website, the Mugen springs are available with the following rates to go with the N Series suspension:
Front -- 16, 18, 20, 22 kg/mm
Rear -- 6, 8, 10, 12, 14 kg/mm

That makes me further believe that my understanding is right. But please correct me if you found anything that doesn't sound right.

Again, thanks everyone for your input!


[Modified by Wai, 11:55 PM 12/17/2001]

 

FWD cars due to their weight distribution and drivetrain layout tend to understeer... d'uh.... however increasing the stiffness of the rear suspension can help to dial out some of that and will make the car oversteer (and/or spin) when you do something stoopid - such as braking or lift-throttle mid corner. But the car will handle better due to the stiffer rear end. That will make it more neutral.... why the king/mugen setup is not like this? i dont know... maybe they assume you are buying the 26mm rear bar, which will also 'add spring' to the rear as well.

-ryan

 

If you actually talk to Scott Zellner @ King, he'll have you run more spring in back too.

2:3 front:rear is a good ratio, not 3:2 f:r. If you run more spring up front, you will have to do lots of heroics to get the car to handle the way it should. If you run something more neutral like 2:3 then all you need to remember is gas, gas, gas. It's very predictable and controlled.

Warren

 

you guys should talk to Dave Hsu over at Skunk2 Racing. As you know they do Roger Foo's engine work...mostly the cylinder heads. Awhile back Skunk2 used to sell this humungus 26 mm front swaybar (which I have). When I purchased it, I thought this was a drag racing only setup.

Much to my chagrin, Dave straightened me out on why they had these in their product inventory. Apparently, some Asian-Pacific road racers had contracted them to make these . This is totally *** backwards to the way we do it. The way they make the car rotate is based on differential tire hardness (like F1) and playing with offset, camber and toe. Dave tells me the approach of running more oversteer with stiffer rear springs and bigger rear swaybars is a North American phenomenon.

So when you see a stiffer front layout in the Japanese magazines, pay attention to the offset, toe, camber and tire selection in that package. Please do NOT automatically extrapolate to our own North American conventions and rules.

That's the beauty of being North American I guess: we adapt many different approaches to have a broader repertoire than the "old home countries".

We like to skin the cat in as many ways as we can learn.

cheers




[Modified by Michael Delaney, 6:42 AM 12/18/2001]

 

like mike (ips) mentioned before and i have brought up as well, is that they change size of rims/tires for the rear for each track vs spring rates. look at spoon, they don't sell sway bars but there track cars run smaller wheels/tires in the rear. in the states we run the same tires front and rear, but increase the spring rate and rear sway bar to get oversteer. mugen offers the rear sway bar but not smaller rim size (for the itr). now is the reason we do this in the states because of rules?? how wants to be the test person and try running the smaller wheel/tire with softer rear spring rates??