The S *is* a great track car in stock form, all model years included. However, when you change tires, and in particular when you slap on R-compounds, the design compromises in the suspension become evident. To wit:
- there is a relatively large stagger in contact patch front-to-rear (greater than the rated tread widths would imply)
- the rear has an unually large bumpsteer tendency under the high g-loadings of R-comp tires
- 1st-5th gearing is still a bit tall for road course work
- the torsen LSD performance is hampered by the relatively large rear swaybar under the high g-loadings of R-comps

The first three have been addressed over the years, to the point where the AP2 chassis ('04+) is really quite good. But a "real" (clutch-pack) diff is still needed for heavily modified (high-hp and/or light weight) cars. Race regs generally limit diff choice, so racers are usually forced to stick with the torsen and work around its limitations.

 

I understand slip angles, but always wondered why the rear behaved differently from the front (sorry if this is a stupid question, please entertain my stupidity). More front toe out reduces understeer, seemingly by reducing the slip angle of the front tires at the limit. However, rear toe out makes the rear break out earlier/more easily (my experience is also with FF cars, dunno how much diff that makes). I would assume more toe out in the rear would also reduce slip angles and more toe in would increase slip angles. Can someone enlighten me?...thanks.

 

Sorry if my previous post was misleading. I truly believe a stock S2000 with stock tires should be a pretty good platform for track. This is the main reason I got my S. The problem I encountered (at least most of it) was due to my mistakenly setting the front toe to an enormous number. When you run incorrectly massive front toe, both front tires are slipping on the straights. When you turn, more weight is shifted to the outside front tire which pulls the car even further into the corner. Therefore, once the body lean sets in, I had to countersteer. With the front toe-in fixed now, I don't see this behavior any more. The rear bumpsteer seems to be way much smaller of a problem compared to my massive front toe-in. Once I get some "real" tires, I'm sure I'll be happy with my S on the track.

I think I'd better change the topic title. Thanks for the comments.

 

[QUOTE=JSR_AP2,May 24 2005, 09:41 AM] I understand slip angles, but always wondered why the rear behaved differently from the front (sorry if this is a stupid question, please entertain my stupidity).

 

Also, if you run, say, rear toe-out instead of rear toe-in, the rears still HAVE TO run some slip angles in a turn. The static toe-out on the outside rear (the most loaded rear tire) now adding together the slip angle will direct the back-end of the car even more towards the outside of the turn. The bigger the radius the back-end needs to run through a turn, the more lateral load the rear tires will be asserted. Or think of it this way, since both the front and back ends of the car are going at the same speed through a given corner, guess which end asserts the most lateral force? The one running a smaller radius of the one running a bigger radius?

 

Wow, I'm utterly confused, but thanks for the info. Perhaps someday I can understand this. I tried drawing a pic, but it didn't work. When you say having rear toe-out adds to the slip angle to pull the rear outward, why does that not hold true for the front? I always thought toe-out reduced the slip angles since the tires would be already facing a bit in that direction. Oh well...I guess I'll just continue to work w/ the effects (end result) rather than the concepts behind. Maybe I'll see some of you guys at the track sometime and youz can learnz me sumfin. Thanks again for the info.

 

Take a piece of paper and let's say North is up. Draw a car with 4 tires on the middle right side on the sheet, front of car facing North. Mark an X as the centre of the turn about 2 car widths to the exact left of the left rear tire. Draw a straight line from the X to the centre of each tire representing the axis of rotation of that tire. This is the ideal situation with ideal rotational direction of each tire when no slip angle involves. Notice one straight line goes thru' both rear tires to the X, right? Notice the lines for the fronts don't coincide, right? This shows that the inside front tire needs a bigger steering angle than the outside front tire and that's what Ackerman is.

Going back to the rear tires in this "ideal situation", it's clear that we don't need any turning angle on them. However, in the real world each of the 4 tires has to run some slip angle in order to make the car turn. The slip angle is always in the direction opposite to the turn. In our case, that means we'll get some "dynamic" toe-change to the right on each tire. Because of this, all the straight lines we drew towards the X now needs to be rotated clockwise for this slip angle. Forget about the fronts for now as we can always use more steering wheel angle to compensate the slip angle. Since the tires stay the same position relative to the car, you can see that the new rotated lines from the rear tires don't meet at the same X position now and should be somewhat towards north. If we run the same, say, 5 degrees of slip angle on both rear tires, we project the 2 lines from the 2 rear tires 5 degrees clockwise towards X and you'll see that the 2 parallel lines never meet. Since we want to make the same centre of rotation for each tire, we'll have to rotate the line for the inside rear tire a bit more and rotate the line for the outside rear tire a bit less in order to have the 2 lines meet at around the original X location instead of infinity. That is exactly what rear toe-in gives you.

In some cases it does, but you probably won't notice it when you steer more into the corner to compensate that. But more importantly, it's because front toe-out gives you better "tracking" into the corner where the inside front wheel is not opposing the turn as much as in zero-toe or front toe-in.
You're right on that one. It does on the inside front tire just as I mentioned above. One simplified explanation of why the rear behaves differently to toe-out could be that the steering angle on the rear tires behavies the opposite to that of the fronts. If you make the rear tires turn right, the car will turn left. Think of it this way... If you treat the front of the car as the back and vice versa and you're driving backwards now, doesn't the rear toe-in now becomes front toe-out?

 

Thanks for the great explanation! I drew the pic and it helped a lot (tho, it may be somewhat off). There's still a few things I'm a bit fuzzy on, but that just shows how much I have to learn. Thanks again!

 

Thanks for the explinations, Race! I've tried several times over the years to get an explanation for why toe in/out here and this is the first detailed one ive seen.

- Michael

 

With good tires and alignment if the car is not behaving well - it's not the car's fault but the driver's. I think stock S2000 is one of the best handling cars out there which is evident by the laptimes it's capable of. Car rewards good drivers and doesn't tolerate ham fisted ones, which is not a bad thing unless u suck .