big differences in roll centre...

[carbonae86]

and what did the reading say ? what was it at 2'

[fantapants]

ruff numbers but 2mm toe out from memory... basically something that wasnt a huge deal considering the gains, plus the mount changes ackerman and a few other things slightly so i figured it would be different anyway, so plan on redoing it when i get the knuckles sorted

[munki]

2mm toe out where? at what point of bump/droop did they measure?

2mm is alot.

any change in toe straight ahead will be compounded as the ackerman is a dynamic change in toe.

Adding RCA as slyder said will change both piviot points and (gasp) will only change the roll center, which is a good thing if you havent changed the rear.

(hope this makes sense i dont have paint on the mac)
As for the lowering thing, imagine a tangent line 10cm long attached to a circle with 4 times diameter. the point where line touches the circle is the static ride height. The top of the line is 100% bump and the bottom of the line is 100% droop. This would be they typical plot for a standard car with mcpherson strut. Assuming the car is setup like a ke70 bump would have a small amount of toe out getting worse as the travel was taken up. Conversly as the suspension moved into droop the toe would come back inwards and have a small amount of toe in.

now look at around 50% bump, this would be a lowered car around 2-3 inches. See how you would start in the place where the angle gets more pronounced and the change in toe is greater. Thats why you get bigger change in toe in a lower car. Fitting a rca to a stock car will place the angles at the original position acting like 'bump steer correcters' as they are sometimes known as.

Now because you have changed your steering knuckles, total strut height lca length etc etc youre in a world of time money and pain to get it all corrected.

the easiest solution i would think is to check out a s13. check the distance to the strut tops, the position of the rack and lower control arm mounts on both axis. Compare it with what you have and draw up diagrams.

You may be able to get away with simply changing the height of either the tie rod end or the lca. I would assume that there is a difference in rack positioning that causes all the problems in the conversion. noone can tell you exactly what to do unless they have the same setup as you and have done the research themselves.

[carbonae86]

Does a s13 have a wider rack and track & wheelbase ?

[fantapants]

toe out was at the top of the storke - 100% compression.

i know the toe will be there... more curios about the theoretical effects because the nissan guys dont seem so keen on rca. However, they all seem to think that lowering the tie rod end will result in a correction of bump steer issues. But i dont see how as there is a 2 inch difference in the static position of the ball joints, and im sure this would be exzaserbated , ie an increase in toe changes as the arcs run through their different strokes. I think they are talking about the dead spot a lot of nissan guys have in their s13's at lock. i think eddie was dealing with this when he moved his rack. I dont think it has much to do with toe changes as such, more to do with the binding of the tierods. or i could be smoking the crack again

[Konakid]

Head to toymods, there is a good roll centre discussion thread atm.

[fantapants]

heheh i keep forgetting to join lol

[Jonny Rochester]

Roll center discussion, on Toymods... so many reputation points... I am shaking in my boots. I dare not even look. I'm sure it goes for many pages.