Dedicated AutoX/Track Spring Rates
 

I've read a ton of posts regarding "spring rates"....unfortunately, I didn't find anything that focused on dedicated race cars. No street driving compromise!

So if your insightful-of, or affiliated-with a dedicated race program, please REPLY!

Specifically, I'm looking for the following information:
1) F/R spring linear spring rates for dedicated race car (track or AutoX)
2) opinions on the ideal F/R split
3) advise if the rear is true Coil-over or OEM configured.

NOTE....just to keep this thread on point. There's plenty of data on all the "off the shelf" options.......I'm looking for those who have custom-configured their setup.

FYI....Once I can select the correct rates, I will order a set of DA Penske. Mid to late season, I will post some reviews for all to see.

Thanks!

My opinion (BSP car),

For silky smooth concrete you can run a pretty high natural frequency (close to 3hz on a dedicated SP or higher Z car). If you run on asphalt (less grip) or several sites with bumps, you will need to compromise. Even Lincoln would be too bumpy for that level of spring. As far as split, you will have to look at your existing corner weights. In street prepared we can get much more weight off the back of the car than the front. My car is a no compromise, full prep car and has a W/D of 56/44. I don't have the motion ratios for a 370z, but if they are anything like the 350z you will need to run a fair amount of spring. You really have to decide a few things....surface conditions you plan to run, tire size, what size bars (if any...particularly in the rear), whether you plan to have aero, and car weight.

Given the the current W/D and now that the car has aero...I tend to run about even frequencies on the front and rear. Less hz means better mechanical grip (to a point) and better on bumps....just to generalize. More hz means more transition friendly. The 03 350z comes from the factory with ~1.25hz on the front and ~1.3 rear. On the polar opposite, formula cars run in the 4-5hz range.

If you plan to run in street prepared, you must retain the OEM layout in the rear as going to coilover changes geometry and motion ratio (this part significantly).

As it sits, my 2920lb BSP car runs at 2.34hz front and 2.31hz rear on 900/750 springs and OTS Motons up front and custom rear. I run the front hotchkis bar at 3/4 stiffness (surface/grip dependent) and don't use a rear bar. Those frequencies may have to be raised depending on how the car shakes down in testing after the aero and wider wheels....particularly on concrete.

Calculating the frequency is pretty easy... it is 3.13*sqrt(wheel rate/sprung weight).

Debated on posting this in the general thread, but it may help...

Again these are highly generalized....using a STOCK 370Z nismo and 350z motion ratios. Taking ~75lb off the rear of the car for light exhaust, no spare/tools, and a minus a few gallons of gas (OP's set-up). This would likely shift the WD from 53/47 (stock) to a bout 55/45 or so...

Front frequencies using 350z MR (OEM LAYOUT), 3240lb with 55/45 WD and equal L/R weights (not going to happen), and taking 65lbs per corner off for unsprung weight...

900lb spring: 2.25hz
1000lb spring: 2.37hz
1100lb spring: 2.48hz
1200lb spring: 2.60hz
1300lb spring: 2.70hz

Rear with same stuff as above...

800lb spring: 2.23hz
850lb spring: 2.29hz
900lb spring: 2.36hz
950lb spring: 2.43hz
1000lb spring: 2.49hz
1100lb spring: 2.61hz

Also in case those are wanting to do the math on their own. Wheel rate = spring rate * motion ratio^2. Sprung weight = corner weight - unsprung weight.

350z motion ratio is .688 front and .649 rear.

We are 245 front tire and 275 rear Conti's.
Ginormous front bar (and I would really like to try larger front bar) and our rear bar is about equal to that of the OEM rear bar.
We run coilover setup in the rear and our split varies ..but we have settled to about 450-500lbs split.

I run 1000 front and 450 lb rear with JRZ pros Coilovers. stock Nismo rear bar and 35 mm progress front bar.

Track setup is 295 Hoosier r6 rear 285 front.

Setup is differnt if you use stock spring locations. Rear spring rate has to go up and front has to go down a little.

are you guys running the 245/275 stagger because it's ideal or because of the rules for the series?

Pretty sure it's the rules from the way BJ was talking in Daytona.

yeah i was pretty sure its because of rules and they are tuning aroud the setup, rather then 245/275 stagger is the fastest sizes for the Z34 chassis, but id still like their input

It's per the rules.
After the dyno pulls in Daytona Grand Am has asked us to list some items that could benefit us...more weight out of the car etc.
One of the things we talked about was that we are the only car with the most weight on the 245 tire.
The Porsche is the same 245/275 but they carry their weight on the rear.
Everything else in the series is 275 F/R
That being said...the car is very well balanced and it's not like we are wearing out the front tires..but it would help under braking.
I'd rather they give us a weight break.
Tires are tires...the only 4 things that touch the road so they are a pretty big deal...
For tracking...get what you can afford...because you will use them.

gotcha, thanks for the input. 275 square on your guys car would be pretty good, but then the bigger/heavier cars would prolly complain LOL

Great information. Does anyone else want to share?

I'm moving to 315 front 335 rear later this month. But then I don't have rules to follow.

I might give the 335 in back a try also. Also plan to give the R1S a shot if and when they release the 315/30.

It might be good....but it may make less of a difference than overall weight reduction.
It's one of those things that we would need to test back to back.
Our car is one of the best in class on tire life and consistency.
There are other areas we have continued to develop...we just have to see how It goes.

Update...I got all my measurements and calculated rates/ratios. Hats off to 03threefiftyz and everyone else who chimed-in. :tiphat: I'm now torn between Penske 7500 DA and Ohlins TTX....any objective reasoning to a preferred brand/builder is welcomed.

Also, the math says I could go between 1000-1200 lbs up front, and I would likely ratio that to the rear based on the factory split as a percentage (I like my current balance). I wonder if this is TOO stiff. Any thoughts as to where the limit is? I run 295/315 Hoosier A6's

Hope to have something on order within a week or so.....