Dedicated AutoX/Track Spring Rates

03threefiftyz

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.

GSS138

370 oem rear is somewhere around .55, if you switch to true type it is closer to .65, our front oem are around .65/.68. I think this measurement is also affected by your tire width as well because the tire is "extending the lever" a bit. Not 100% sure the correct way to calculate where to measure to, but common sense sort of tells you that if you put a wider tire on it is going to make this number a tad lower, hence needing a stiffer spring.

I still daily my car but have finally settled on 12k/10k full stiff stillen front and I ended up pulling the rear bar completely. I think 12k/ 8 or 9K with a rear OEM bar would probably be nearly equivalent. For autoX nice smooth surface you could definitely go higher, but I think I am at or near the limit of what you would want to DD.

That's a little soft by some standards, but our tracks in socal are not very smooth for the most part, have a lot of elevation changes, and I still need to get over those damn bumps in my office's parking lot.

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