doesn't adjusting your rear rebound/bump help with the wiggly back end?

 

The problem is that when the car is lowered and you unload the back end you get toe out, which makes the back unstable. It's not a traction issue, so messing with shocks won't fix it.

 

The factory spec for rear toe is 0.12"±0.07 toe in. I'm currently running 0 toe. Since the rear tires toe out under braking, I wonder if that's the back end instability under braking. How much rear toe do most people run?

 

I have seen a few folks mention a little rear toe in on their alignments but don't recall the exact numbers. I would assume in part for the reasons listed above.

I know I had a one time odd issue on the back straight at Mid Ohio where under very heavy braking the car got very "jittery" and felt as if it were on roller skates. Thank goodness I had pulled a pretty good lead on the few folks close to me as the car drifted maybe 5-6 feet to the right which pretty well ruined my line to the turn but I was not about to try and overdrive the car and choose to just let it settle itself in on it's own terms.

At the time I figured I had just over worked the tires as it was late in a rather competitive session but it was acting very much like what is inferred above.

 

For autocross most people run zero toe or a little toe out. You want the back end a little unstable there. The biggest challenge on an autocross course is getting the car to rotate so you want that instability in the rear.

On a track I would definitely run a little toe in and use swaybar and shocks to tune the car's balance. The bump steer kit (now that I understand how it actually works) should fix much of the toe issue under braking. If it moves the pivot point enough to get it above the ball joint you'll actually get toe in under braking instead of toe out. If you want to check it, jack the back of the car by however much you think it'll lift under hard braking and check the toe then. If you're seeing a bunch of toe out at that point you may have some issues.

 

I run 0 toe all around.

l8r)

 

Hmmm...I think someone with a trailered Evo should install a set upside down and see if it helps rotate the car on corner entry.

 

mmmmh.... youd have significant toe in, if that's what you want.

 

Nah, you don't install it and leave the toe setting with toe in. You install it and set your toe to 0. Under compression it'll toe out MORE and make the car rotate more at turn in. It'd be interesting to see what it would do for an autocross car but I'd NEVER drive it on the street like that.

 

I do have it installed on my car. I can't make a direct comparison b/c I installed this with Ohlins before I turned a single track day in the RS. However, compared to my '03 with stock suspension (only a rear sway), the RS is more stable in braking until lock-up.

 

bump steer can be used either way, to make the car rotate, or settle the car the car down..

it affects the car while the corner is under compression...

bump steer isnt something you really want in a car, unless its a last resort for rotation.

cb

we are installing EVERYTHING whiteline makes for the evo, including the new camber plates etc.

ill post pics

 

For those of you with the whiteline parts installed.... what did the shop charge to press the old ones out and the new ones in?

I can yank the control arms myself but I do not have a press (yet).

 

I always thought of it as autoX'ers would install offset hole up for increased bump steer , and roadcourse drivers hole down for reduced bump steer (rotation vs stability).
There are plenty of roadcourse drivers who live by "Loose is fast" and may prefer it hole down however.

 

I was asking because I work with many race cars with intentional bump toe out (or in). Not only evo/sti type of cars, but GT cars, prototypes and formula as well.

If you know where you want it when, its a great tool. The EVO has a whole lot of front weight, and I see a lot of cars with the same front/rear tires running tons of horsepower. Achieving the right bump steer can help you make better sense of your spring/bar/shock/ride ht. package to great effect.

I highly suggest testing (on track) your bump steer amounts. There is a whole lot of wiggle room between hole up and hole down.

-Bryan

 

Bump for any information.
I'm installing mine in a month or so and my goal for autox next year is better turn in and less understeer on exit. I'm using toe out in the front and the roll center kit to improve turn in and corner exit.
I'm just wondering if the bump steer kit might work against me on corner exit when the back corners are compressed.