drnick

guys, how much difference does centring the rack make to things?

mark kibort

that was my original question, but i imagine that it starts to follow the bumpsteer curve as one tie rod gets longer and the other shorter.

MK

FlyingDog

The guy who did my alignment said he sets each side at the wheel for 1mm toe out front and 1mm toe in rear. The cars he set up did well at the Daytona 24, so I'd trust his judgment.

mark kibort

The statemement begs, " 1mm measured from what point?".

Considering lack of 928s finishing in the top 10 at Daytona, i dont really know if he is qualified to be an expert in 928 racing alignment. Street alignment might best be judged by who has tires that have lasted the longest

2mm toe out in front (total) if using the wheel diameter as reference points, would be futher than 1/16" toed out, and i was in the 1/8" toed out before. I can't think of a reason to be that toe'd out, especially for all situations. ride hight has a lot to do with the degree of bump steer that occurs as the ride hight is lower. I would suspect that the lower the car, the more toward 0 toe or even some positive toe in you would want. currently, mine set at near 1/16" toed in, is working pretty well, pushing the car on some hard mountain roads. However the acid test will be how it performs at one of the "turney-ist" tracks in the country - Sears Point Infinion Raceway.
On the rear, i have to imagine that 1-4 mm of toe in is fine. however, the more the toe in, (with the weisach not pinned as it is not on my race car) the harder its going to be to rotate the car in slow to medium speed turns. (ask me how i know this)

mk



QUOTE=FlyingDog;5199401]The guy who did my alignment said he sets each side at the wheel for 1mm toe out front and 1mm toe in rear. The cars he set up did well at the Daytona 24, so I'd trust his judgment.[/QUOTE]

dr bob

On 928's with wheel centers that sit out further (less than original negative offset) there's a good chance that setting toe-in at 0 or maybe even very slightly toe'd out will improve initial turn-in feel. This is a perceived benefit, since you normally depending on smooth weight transfer off the inside wheel, and you feel a less gradual transfer and think you are doing better because of it. Is it a real benefit? Hard to say.

FlyingDog

I figured saying "at the wheel" would be clear. 1mm difference front to rear on the wheel itself. That would be 1mm total since toe is relative to the the wheel centers. Mine was set up for track use while being tolerable on the street. It works very well.

mark kibort

so, .11 degrees toed out at 1mm toe out, vs what where i was at .36 degrees toed out to where i am now, .18 degrees toed in.

Sure it works well, even toed out where i was, but i was burning up the inside edge. It also worked well being near 0 a year or two earlier, before the car was lowered even further, and went through natural settleling as well. Ill see if being toed in slightly, makes a difference. Hey, 1mm is just a hair, while 1/16" is 1.5mm. still very slight.

all i can say is that on the track, there is so many other things going on with the suspension, that i dont think it has to be that perfect. if you are driving hard, that inside tire is along for the ride anyway!

mk

Bill Ball

Maybe soemone knows if the effect of unequal length tie rods on bump steer is noticeable. I've always aligned with the rack and steering wheel centered.

mark kibort

IN thinking about it, it shouldnt make any difference. The only difference i could see would be the range of motion of the steering in both directions. since the distance between the rack and tie rod will be the same for your car going straight, the only thing that will happen is that the rack will have more travel one way. on the race track, im lucky if i ever turn the wheel more than 180 degrees. (ie turn 11 at laguna or sears)

mk

Bill Ball

In theory at least, if one tie rod is shorter, it makes a different arc as the car is turned or the suspension moves up and down and the toe changes are unequal.

mark kibort

I think it would have to be a gross difference in length to make any noticible difference.
If the tie rod is 18" and you have 4" of droop, then the angle at the tie rod is 12 degrees. say one side was 1" longer than the other. the longer side would make the angle less by .5 degrees and the shorter side would make the angle greater, but the angle changes are so subtle, that i doubt that would make any diff. And, thats at 1" difference between tie rods!

Now, the changes we are talking about here are a thread or two or so on the tie rod .

I dont think that would matter much if at all.

Mk

Bill Ball

It is relatively simple to do the alignment with the rack centered. This avoids the whole issue.

I'll reiterate.

- First verify that when the steering wheel is centered, so is the rack. After that, since it can be hard to view the rack center point when the car is on the ground or if the bellypans are on, just set the steering wheel centered and you know the rack is centered.
- Then do the toe adjustment. I just do total toe in the front, as the setup is simpler.
- After setting total toe, drive the car straight down a level street. If the steering wheel is not centered, shift the toe adjustment to correct this until the the steering wheel is centered.

mark kibort

if you have the car on a rack. If not, moving one side might be easier as i have done. Im not saying not to do it the right way ( and Bill's way) im just saying for a quick , fairly accurate fix, its much easier to adjust one side and see where things end up. (less variables )

I did my BMW this way, and ended up with a litte more toe on both sides, even number of turns (1/2), but the steering wheel ended up a hair off center. It too was killing the inside edge of the tire. hopefully now, that will stop.

mk