First of all, I'm not sure if this is the right place to post. Moderator please move this thread if necessary.

I just got some new stock-sized all-season tires and wheel alignment done (a little background info here on why all-seasons). Now that I rule out the bald Pep-Boys all-season tires and some unknown wheel alignment that came with the car, I still find that there's some funky cornering behavior that I would like to know if that's normal with an S2000. FYI, my preliminary alignment right now is 1.14/2.12-deg camber and 0.04/0.11-deg toe in. I've driven 2 different other S2000s at autocross and have never noticed it but then I don't notice the funky behavior with my S2000 at autocross either. This behavior could only be noticed on corner long enough for events to happen slowly. I would describe the behavior as follows:

1. When I approach a corner on braking (and perhaps downshifting as well depending on speed), the initial turn-in is sharp with minor understeer, which I like BTW, which makes for accurate turn-in.

2. When I transition from braking and coasting to minimal gas (just to remove the engine-braking), I can feel the understeer is gone.

3. Further into the corner, I apply more gas to weigh down the rear and now I find the understeer comes back, which is understandable as weight shifts to the rear but it feels like the understeer comes in before the weight shift.

4. After the apex, I continue to squeeze on the throttle to power-exit the corner. At this point even with constant steering wheel angle or even slowly unwinding, I can feel the added power starts rotating the backend out.

Before you say it, for point 4 I know what power-on oversteer is when the outside rear is running too-high slip angle but this is something different than an increased slip-angle on the rear tires. It feels like the outside rear is changing to less static toe-in or more toe-out on added power. The first few times it happened, I was scared and back-off a bit on whatever input to get into that stage. That hurts cornering speed quite a bit. When I tried it a few more times and get over the fear of the backend coming out, I found that this "backend rotation" actually helps power-exiting the corner because like I said the rear tires are NOT starting to run bigger slip angle. Instead, it seems that the outside rear tire is changing static toe-angle to help rotate the car more so that I can unwind the steering more and that means less likely to go power oversteer.

From the look of the rear toe-control link geometry, it looks like the toe curve against suspension compression is first toe-out (or less toe-in) and then toe-in. This is normal for a toe-controlled rear suspension in general. Toe-out on initial suspension compress helps turn-in . Toe-in on further suspension compress helps stabilize mid-corner behavior. But from what I described above it's like understeer ==> neutral ==> understeer ==> oversteer for a single corner. If it's just due to the toe-control link, I don't see how stage 4 comes in. You would've thought that when power-exiting a corner you'd get more rear toe-in and therefore less oversteer, wouldn't you? Has anybody noticed this behavior on long corners? What would be the cause? In any case, it doesn't seem something evil but something to get used to instead. Or have I seen it all?

 

Mine seemed to do this once after a bad alignment. There was a slight toe out on the rears instead of toe in. You may want to confirm your alignment specs.

 

I never seen specs. or measured the rear toe curve of the car, but I can't see a toe out then toe in on compression. Here are a few comments.

I've noticed a similar slight oversteer in autocross on "high speed" constant radius sweepers. With steady to very light increasing throttle the backend will slowly lose grip and slide out. Seems to happen only on heavy suspension cornering compression. It doesn't seem like power oversteer, but it probably is with the rear toe change.

The rear toe you're running is a lot less than the stock alignment on a stock suspension. Suspect this would make the rear a little lively on hard braking and cornering.

There is an anti-bumpsteer kit that GoFast and I think J's has that reduces the toe curve. This seems to make the rear suspension less variable and more controllable.

 

Thanks guys for the suggestion.

The reason I run about 1/16" rear toe-in is that I've never heard of any car manufacturer suggesting as much as 1/4" rear toe-in. My engineering self just pops out and is so curious about the stock suspension. Also, like I said this is just my priliminary alignment and I'm subject to change. What surprises me the most is the way toe changes throughout the corner. If I had more rear toe-in, it would probably have been

understeer ==> mild understeer ==> understeer ==> neutral

instead of

understeer ==> neutral ==> understeer ==> oversteer

There'd still be some funky toe-change throughout the corner.

I just had a look at my stock rear suspension. It would seem that at some point about 1" above stock ride height, the most toe-out (or least toe-in) would be achieved by the geometry. But Fongu is right that any height below that, it would be an increasing toe-in. I don't know if that fits my observation of point 1 to 3, but my observation of point 4 definitely doesn't fit here. In any case, point 4 of "backend coming out" feels like a result of a toe change instead of a bigger slip angle (i.e. the rear is not losing grip) so I don't regard it as an evil thing for now.

I've read about the rear anti-bumpsteer kit from GoFast, but like I said my engineering self is so curious about the stock suspension. Also, so far the funky stock suspension behavior doesn't seem something evil but something to get used to instead. I'll do some more testing before deciding on what to change next.

Thanks again for the suggestions.

 

You skipped a lot of basics and jumped to details.

What model year car? Original shocks? What tire brand and model. What tire sizes? Original springs and swaybars?

Are you talking about driving on the street or a track or autocross?

 

Your problem is the rear tire size. It looks like you've got 225/50-16s on the back when in fact you need 245/45-16 in anything except the oem S0-2 tire. The narrower rears are throwing off the balance, thus the oversteer.

I test drove a car with 225/50 non-so2s once. It handled like poo.

Read all about it here:

link

 

I'm aware of the width of the rear OEM S02s and the threads here talking about it. I know my tires under test are not up to par with the OEM S02 or its front/rear balance, but the cornering behavior I mention here is not related to tire slip angle. It happens even way below the tires' traction limit.

For some background info, although my newly acquired S came with tight and straight chassis and bone-stock suspension, the bald all-seasons tires at the back and unevenly worn all-season tires on the front plus unknown wheel alignment (oversteer on left and understeer on right turns) on the other hand needed work quick. I wanted to do some preliminary alignment before deciding on what to do with suspension and wheel/tire combo and it doesn't make much sense to do wheel alignment with bald and unevenly worn tires so I picked up some OK all-seasons (which I've had OK experience on other cars) for the stock wheels and will perhaps use them later as my winter tires if I decide to let go of my E36 half-daily driver.

When I mention about the funky handling behavior, it's not autocross-specific or track-specific. It's just cornering in general and is easier to observe on long corners since events happen slower. This behavior does not happen at or because of the traction limit of the tires (i.e. not because of change in slip angle). Otherwise, the "backend coming out" on power-exit would've been easily amplified by flooring out of a corner. Instead, the backend just stays the same tracking whether I'm at 3/4-throttle at 5000rpm or WOT at 7000rpm in the same gear power-exiting the same corner.

I have gotten use to my old miata for 9 years with its double-wishbone suspension all around and no rear toe-curve so I'm quite sensitive to any rear toe-curve in a different car. The E36 runs multi-link suspension on the rear and the toe-curve is mild and transparent. Below the traction limit, I don't feel any change in rear toe that would require my compensation on front steering angle. However, it would somehow magically keep the backend planted a little further when close to the traction limit compared to my miata at the limit.

The S is different in that BELOW the traction limit, I can feel the toe-curve being more aggressive than the BMW and even need compensation from front steering angle at times due to the rear toe-change. Varying the throttle in small amount smoothly at mid-corner is a good way to detect this rear toe-change. But when near the traction limit the backend seems to be able to hang on with its tracking better than say my miata (good!).

In any case I haven't seen the stock S suspension doing anything evil (knock on wood) and that's what I like about the stock S suspension so far. Looks like I just need to get use to the toe-change mid-corner.

Thanks guys for your suggestions.

 

This is a well known characteristic of the S2000 rear suspension. As you know, we've developed a kit to remedy this in pre '04 cars based on our shop's measurements of the toe change throughout the range of suspension travel.

 

Any link to the detailed info of the product?
Thanks

 

Yes, there are plenty of links to detailed, exhaustive discussions of the product. Try scanning the first page or two of the forum.