Cool youtube channel you have.Hi guys,
i will race my dc5 on rally-events next season so i try to dig deep in the suspension geo thingy.
Im aware of the Scrubradius. I think thats my first issue. Im running 8,5J with ET-35. I swapped Topmounts for Caster and i grinded the topmount holes more the the inner back. Im at -2,2° Camber at the moment, so with the increased camber i should be changing the SAI as well. Im unsure of how much Scrubradius i have left. I tried to measure it but its close to impossible with a cord and an McPherson Strut. I might just change to a rim with less offset and see how it drives.
Now to the Bumpsteer.
I also was in the believe that manufactors know what they are doing, and fitted Hardrace shperical inverted track rod ends. So I heard alot of negativety about this stuff and i am sure that ive done nothing good with that mod. BUT, i just dont understand why. If the tie rods are at an angle and move on the arc (=circle), the more they are on an angle, the more they move inwards (view from infront)! Hence changing toe, hence producing bumpsteer. If they are flat - or better, slightly leaned down, and the coil compresses, the movement ist mostly traveling up and down, and not inwards, without changing the toe that much.
I asked that in the facebook group but nobody could explain me exactly why it is. As i said. I am certain that its not good from what you heard from very clever people, but i cant get my head around it whys that.
So any help would be appreciated!
As Sam said with you need to concern with Instant Center. Instant Center is where the Upper control arm intersects the lower control arm. On the DC5 the upper control arm would be the top nut of the strut tower. When you lower our car you will notice that the lower control arm starts to change its angle. But the upper angle doesn't change because its not like a wishbone that has a upper control arm. So now you have an ARC of travel based on where these arms intersect(if you were to extend them with imaginary lines). Typically you have the steering rack mounted low down where the lower control arms. So with a low rack mount tie rods can be flat like the lower control arm(when you lower your car). But for the DC5 the steering rack is mounted up high on the strut. So if you were to lay that Tie Rod flat it would NEVER intercept the Instant center. Thus its traveling on a different axis/arc the control arms are not. So you must give it an angle so it can intersect the lower control arms imaginary line with its imaginary line coming from the tie rod. And you want this intersection to be as close as possible to instant center(having a little bump steer is not bad). If you take a look at the stock RSX you'll notice that the tie rod still has a slight angle to it.