Is your bar softer than my Miata bar? U can haz

 

I had the same issue with my TT4 car. On Hoosiers it would light an inside tire up in any medium to lower speed corner. That was on the Ohlins 12k 10k setup with a Moddiction front bar on the middle hole and stock rear 03 bar.

Went to a OS Giken rear end and never a problem since. Just recently changed to custom 16k, 14k Ohlins and still no issues.

Expensive solution I know so try to tinker with it. I will say I never had tire spin running my old setup on RC1s at any of the tracks in the Southeast. So it may just be in your setup. Good luck!

Davo

 

Measure your droop travel before the spring decouples. If the spring becomes loose before at least 30mm, add assist springs (150lbs or higher) to get that full extension. Most diff's die because of lack of appropriate droop no matter the brand.

 

The sway bar weight is usually the limiting factor here when one wheel is still weighted. Even if the shock has more extension, no typical helper spring will counteract the sway bar weight to force the inside wheel back down. The better option is to remove sway bar weight and increase spring weight.

 

You misunderstood my statement. Swaybar stiffness high or low or none, if the spring decouples he will have the same issue. And yes, proper assist springs can have enough force to overcome swaybar stiffness. Droop is very important and often overlooked even by the highest levels of motorsport. He can solve his inside wheelspin issue with a clutch type diff;yes, but if he has a droop issue then he will burn up the new diff in no time.

At the same time, if his primary issue is a droop issue then he can fix it and not have to invest in buying an aftermarket differential for now. Cheap fix!

 

Oh I understood what you are saying about the spring (IF unseated is an issue) but what I was saying is that's moot because he is running a rear sway bar, which I can say with almost certainly is going to be a factor before dealing with an unseated spring in his driving scenario. The spring could very well be unseated with both rear wheels in the air, but with the sway influence (even with total inside wheel lift) the sway would keep the spring seated unless he is running a thick helper spring and super weak sway that counteracts, and just a hunch i'm going to say he isn't because a typical 50lb helper spring to keep the main spring seated isn't going to counteract a typical sway bar weight. Also a helper spring that would isn't really a helper spring at that point but more of a progressive dual spring set up, and to my knowledge that isn't a typical use on the s2000 with a limited 1-2" of upstroke available. Agreed on the diff.

The cheaper and possible effective option to play with would be to just remove the rear sway bar all together and run a stiffer main damper spring to give the same effective total rear spring weight that was had with the old sway, retain his traction bias he is happy with and get the rear end working totally independent.

 

^Agreed, helper springs are irrelevant here.

The S2000 has a "rear bar problem". Given all the other constraints in designing the car, it's clear that Uehara-san & co. ended up boxed in to a situation where, in order to make ride comfort remotely tolerable, they had to use unusually stiff sway bars. I estimate that for '00-'01, the front bar contributes over 50% of the total front spring rate, and about 70% (!!) of the total front roll stiffness. At the rear, it's a little better, but not much: the bar contributes about 40% of the vertical spring rate, and 55% of the rear roll rate. Overall, the '00-'01 car gets about 63% (nearly two-thirds!) of its total roll stiffness from sway bars. Things got much better for '02, and then improved again for the AP2, settling in at a ratio of around 45/55 for overall coil-spring roll rate vs sway bar roll rate. (The CR, with its ultra-stiff coil springs, further improved to about 47/53.)

But the point is clear: the rear bar (even on the AP2) is so big that it's impossible to soften it enough to allow full droop without drastically changing the car's handling, and drastically increasing overall roll. Consequently, once you've done it, you need drastically stiffer coil springs to control the body roll and restore the handling balance. (You could control roll with a huge front bar, but that only exacerbates the handling issue.) And super-stiff rear springs, in turn, bring their own set of issues -- like, will you ever want to drive on the street again lol.

P.S. In fairness to Uehara-san, none of this is a problem with the original tires and tire stagger, which resulted in a max sustained grip of around 0.9 lateral g. In fact it's really only around 1.1 or 1.2g that you start unloading the torsen diff enough to lose inside-rear traction, and that's a pretty fair bit of "design margin". Unfortunately that's also right where R-compound tires put you.

 

OP describing issues with aftermarket setup, but let's talk about what OE does

Lugod brings a good point of droop, should be looked at for sure and spring length/adding assist springs might be a relevant fix too.

As usual suspension setup goes whoosh for most.

 

Put it in another way, you are saying the rear shock must have 30mm of rebound travel available from static position. In order not to burn up the diff.
May i ask how to determine this droop amount? Is it just a rule of thumb or is there a way to calculate it? It seems complicated to calculate with the sway bar in the picture.

also what happens when a shock is setup with say 30mm of rebound travel from static position, but the spring becomes loose at 20mm of rebound travel?
does the shock then never get to use the remaining 10mm of rebound because the spring loses contact with the seat?

 

For what it is worth, the spring never ends up just loose in back. At full rear droop the spring is basically full extended and able to rotate on the Torrington bearing but can't be lifted to create a gap between the perch (Torrington) and spring bottom.

I put a used OSG in it last month and promptly blew it up this past weekend at its first event, so as massiah helpfully pointed out in another thread, there are likely multiple issues with my setup.
Question becomes what is step one? I'm open to input.