SakeBomb Garage

No worries! We want to make sure the community is well informed so anything we can do to help we will. As everyone wraps there head around this new method we expected there to be some confusion.

SakeBomb Garage

Possible to get this stickied by a mod? We've had a number of people PM us looking for the link and name who were having a hard time finding the thread

DennisRen

Nice work SBG!

I'm still having trouble understanding that, why did you exclude shock angle from the wheel rate equation? I think we only care about forces in z direction.

Cheers,
Han

DennisRen

Ohhhhhh get it. Great info!

SakeBomb Garage

Lol I'm glad we could help! It's a lot to wrap your head around and many people spend many many years studying vehicle dynamics before it clicks. It is a very challenging but rewarding field. Let us know if you have any more questions!

ckowalc

I was going back to look at my rear suspension settings spreadsheet and I cant match the amount of spring compression by using the corner weight and these motion ratios. See calculation below:

What I actually measure on the car is 46mm of spring compression at rest (B_Serious measured 41mm compression in this thread). There are only 3 variable used in this calculation. Is one of them wrong? Am I neglecting another variable?

I read that there is a 50 lb of initial force from the nitrogen pressure. Subtracting that from the corner weight still results in 61.8mm of spring compression in this calculation.

DavidNJ

What were your other 3 spring compression distances? How did you determine unsprung weights? You might have some wedge in the car from the spring perches or anti-roll bar reload. How did you determine the unsprung weight? Was that with or without the driver? 4x 680lb is 2720 lb. The wheels and tires alone are over 160lb.

ckowalc

I only measured both rear springs and they were both 46mm give or take 1mm. Unsprung weight was just a guess but you're right it should be closer to 640-650 lb. The point is the calculation is not even close. The unsprung corner weight would have to be 520 lb for the calculation to work out assuming a 50 lb gas charge in the damper.

If you put in the 0.67 rear motion ratio that was commonly used before Sakebomb's post (I think it came from Gernby?), it results in a 590 lb unsprung corner weight w/ gas charge included.

DavidNJ

Someone here has probably measured the unsprung weight, but numbers closer to 600 lb sound about right. If the shaft has about 50lb on it from the compressed nitrogen, and you have a .67 force ratio your calc is within 2% or so, which probably within the combined errors of the unsprung mass, spring rate, motion ratio, and your measurements. With a set of scales, you can get the weights accurately. Similarly, you can test the spring rates with spring rate tester (once a common race shop too, when metallurgy wasn't as good and springs sagged and lost stiffness over time. The scales are necessary to set corner weights.

This is probably not something you need to worry about from a calculation standpoint. Any S2000 lowered with changing the spindles and/or mounting points is going to have a compromised geometry anyway.

There are kits that have the corrected spindles. There are shocks you can order in the correct length for an application. Springs can be ordered in 1kg/mm or 2kg/mm increments from 6kg/mm to over 20kg/mm. Anti-roll bars can be ordered, front and rear, that use 1.25" spines and can be ordered in a wide range of wall thicknesses. Quaife has a sequential gearbox specifically for the S2k. The F20/F22 or similar K20/K24 can be pushed over 300hp and with forced induction over 1000hp. People have swapped Chevy LS and Toyota 2JZ engines; with FI and the right fuel, over 1000hp. About the only thing not readily available is a positive displacement supercharger, although there is a thread around here about a Chevy LS9 with its twin-screw supercharger being swapped in.

In the end, the S2000 has joined the Miata and Supra TT that preceded it as iconic sports cars.

ckowalc

Haha, well that got off topic quickly.

I guess my point is that when you use the 0.578 rear motion ratio from Sakebomb the calculations are not close. It seems like they legitimately measured these values so I'm wondering why the calculation does not work out.