Thread: Handling, Suspension and Brakes Thread - What is your chassis telling you?

I've never experienced bump steer on any of my MacPherson cars until I flipped the tie rod upside down "to help fix bumpsteer". Simply put, if you don't overlower the car you will not have bump steer. I'm less then 1.5" lower then stock on my B15 and it has no noticeable bump steer, it just stays straight on any roads I've put it through.

P10/P11 is different story, unequal A arm suspensions keep your toe constant weather the front rises or compresses. Because of this you will have 0 bump steer.

@Vadim, unfortunately, I have experienced bumpsteer often in both B13 and B14 chassis'.

B13, not so much since it is all stock but I have felt it during extreme load/cornering while running over a dip or lift in the road.

B14, leagues of it since I utilized lowering springs that brought it down one inch over stock while using stock length dampers. That is a recipe for disaster.

Your B15 is lowered 1.5" and using a shortened damper, correct?

Your roads are probably much worse then most of mine, but the road to my house is horrific, full of bumps and pot holes, thus a perfect way for me to see if there is bump steer. When I had my B14 on RM's and AGX's I don't remember it being too bad either.

B15 is now on BC's, which are yes shorter, before it was on Tein Basic's, which again are shorter, but bump steer is not caused through the shock. Bump steer happens when your suspension rises and causes the wheels to toe out. A good way to see if your going to be bump steer prone is to check your alignment while full weight is on the car, then rise both of the wheels up (weather is two front or two rear), and check alignment again, if it toed out you got bump steer.

When I flipped my tie rods upside down (I have heim tie rods), I zeroed out the front toe, then when I raised the front up, I saw toe out. Drove the car and it was horribly unstable and wanted to follow ever crevice in the road.

As a fun test I might check at what height my B15 starts toeing out as the suspension rises. I bet it starts happening around 2" below stock.

Bumpsteer is caused by two main things on strut cars (and yes, wishbone cars suffer from the same issue as every car has it engineered into the stock geometry for safety as when the car toes in/out, depending on suspension setup, it exhibits understeer)

1) The difference in the arc travel of Tie Rod compared to the LCA (perfect example is the fact that the total tie rod length and its mounting location is not fully parallel with the LCA. Measure each from its mounting location to where it mounts to the hub. Once this is done, place the car on jack stands and compress the suspension through its range of motion and take note of both individual arcs).

2) In addition, the centerline of the tie rod must intersect with the instant center created by lower control arm (LCA) in order to have minimal bumpsteer (See diagram below).




Vadim is correct in the fact that a shorter damper has zero effect on bumpsteer

Thanks for the updates guys! No one ever said that a shortened damper had anything to do with bump steer but everyone will surely know by now it has nothing to do with it!

Next up will be roll steer!