another suspension question......beating the topic into the ground...
 

Hi folks,
Curious what the ITS cars are using for spring rates. My setup is Koni shocks, hoosier 225's and the car weights 2555lbs. I am thinking 500lbs in front and 400lbs in the rear, Ground Control says the Konis are good up to 600lbs. Mazdaspeed sells their setup with 400/275lbs springs.

I am a bit of a knob when it comes to suspension componants. What is the benifits and drawbacks of higher rate springs....I have seen some Porsches that run 600lbs springs but they are dead slow in the rain....any corrolation between the two.


Thanks.....

FC? we started out with 320/225 springs, and eventually went to 450/350. drivers prefered the stiffer setup, although it didnt really affect the laptimes.

i think its more of a drivers preferece thing.

oh yeah, 88 FC, sorry.

My setup is Koni's, Toyo 225's, 2510lbs dry (add me at 175lbs and I just break the 2680lb requirement). The car is fully prepped, no shortcuts (except the Toyo's on there right now). It's got 500lbs on front and 300lbs on the rear. This was at the recommendation of Flatout Motorsports. I've got a pair of 400lbs but I haven't used them. The setup works for me, but I'm a noob as well :)

Good question you asked, "What is the benifits and drawbacks of higher rate springs" ....anyone?

I started typing a long post, but only have 2 hours of sleep and am working again after a 22 hour workday. SO i will try to keep it short. SOrry if its incoherent LOL.

Stiffer rate springs in ITS will force the tires to take up the irregularities in the road surface. The stiffer springs will prevent the suspension from doing its job of moving over these. They will have a tendency to keep the car's suspension from moving. This will cause the tires to loose adhesion over irregularities.

At Sebring, this is bad, because the track is rough, and has a lot of transitions in surfaces. You want a softer spring and shock rate there to keep the car on the pavement.

Datytona on the other hand has a lot of dips and irregularities in the high banking that causes the car to porpoise a bit on the banking. Also you are having the suspension compressed as you go around. The track surface is pretty good and smooth. So smooth track surface, plus the high banking is a good reason to have the stiffer springs and shock rates.

In a perfect world, if we could race on a glass smooth surface, we could run no shocks, and lower the ground clearance to a paper width off the track. THen larger diameter rims with 1/4 inch of firm rubber belting around them for traction.

As the road surface gets worse, the shocks need to get softer, and the spring rate lowered. Picture in the extreme a offroad truck with lots of travel. That would be the worst extreme.. so for us road racers we are splitting hairs.. but still... a slightly softer rate on rougher tracks would be a good methodology.

Also keep in mind. As you increase the rate of springs, and shocks, the car is going to become more and more responsive to a point. So your driving style will have to change as you increase these rates. Just yanking the wheel to turn with less compliance in the suspension will cause the car to over or understeer depending on your personal setup. It will become progressively less forgiving of driving mistakes, and suspension setup inconsistancies.

Hope that didnt cause more confusion. Im half awake lol.

gee whiz....nice work. That is big help and really makes good sense. Thanks guys!!!

A Slightly Different Opinion
 

I agree totally with what has been posted above, but let me just add a bit from my experience.

I started like almost everyone else with 400 fronts and 275 rears. I race mostly at Mosport which is very fast with my average lap speed at around 88 mph and pulling through most corners at over 100 mph. Most of the corners are loooong, blind, sweeping corners over the brows of hills. Our rules are also a fair bit different in that we can run WC aero, as well we run on spec Toyo RA1's (I run 225x50x15). What I found was that I was bottoming out the suspension a ton (over 5" of rear shock movement and 4" in front) with the 400/275 setup. If you watch the in car video from guys following me you can see the car porpoising a ton under accel and braking. I kept increasing the spring rates to prevent bottoming out and ended up at 600/400 and did okay.

At this point I was getting a ton of wheel patter and tire spin out of the slower corners, but the platform was stable and I could run close to the big dogs. To stay with them in the arms race known as motorsport, I ended up having to work with the bars, shocks and diff a lot to get the patter and spin under control and to maximize the grip available from the tires. I also had the luxury of being able to dial in as much downforce as was needed to keep it stuck in the high speed stuff.

So where am I know? At Mosport I run an AWR E/Prod nose with full belly pan back to the engine. An APC rear wing at about 12 degrees, race valved Koni's, Suspension Techniques front bar and stock rear bar or no rear bar at all. The rates are super high 700 in front and 550 rear. The car works great (pulls steady 1.3g's with surges to 1.7g's) and runs 2/3rd pack WC Touring type times and as fast as mid pack Grand Am ST times on 1/4 the budget and operating cost.

Needless to say at Shannonville, a much tighter bumpier track, I have to run the car an inch higher and reduce the rates to 375 front and 225 rear with a much bigger bar on the front and a Racing Beat rear bar. I add a 1" splitter to the front of my nose and crank the rear wing to almost 30 degrees. Add rain at either track and if I have time and enough crew, the bars are disconnected, the shocks are converted to Bilsteins and my rates are dropped to 300/200.

All I am trying to say is that you can use these rates as starting points, but suspension setup is still very conditional on spring rates, shocks, bushings, bars, brake pads used, F/R weight bias, side to side bias, track, weather and driver. I know guys that are run assymetrical spring rate setups with preloaded bars that go very fast indeed. I just don't have the time, crew and money to determine the exact best setup for each track we race at.

Ultimately, you have to test a fair bit to determine the right set-up for you as the driver and for the car and track. Experience will help a ton. Start with a well known and used setup and spend your time maximizing your driving skills with your car at 1 setup. Then start to spend your money where it will do the most benefit, or where you see you and your car need help.

Eric

(on track since 1982, needs to get a life)

Thanks Eric, great insight.

For cars with strut type suspensions this is often desirable. With a strut's unfavorable camber gain (none!) maintaining small chassis roll angles is often more important than suspension compliance. Keeping roll to a slight amount maximizes the tires' contact patch size. Check out the (what at first glance appear to be stupidly high) wheel rates fast fwd cars run for example.

High spring rates may indeed make the tires patter and bounce over bumps, but the time may be made up by increased grip everywhere else. YMMV.

As a rule of thumb faster tracks will allow higher wheel rates than slower tracks.