prosiaq

Does anyone have an idea how does our rear multilink suspension behave when put under load (lowered) ? does it toe in or out?

M.

mayhem

iTrader: (9)

In. Look up bump steer.

Dustin@Vishnu

iTrader: (1)

At the optimal ride height it will actually toe out under bump transition. Check it with a tape, some plates, and a few fat dudes.

trinydex

iTrader: (12)

where can i find some fat dudes?

Silk

iTrader: (4)

McDonalds

mayhem

iTrader: (9)

So you're saying that during compression it toes out, (bump steer), and this promotes understeer? I disagree.

https://www.evolutionm.net/forums/sh...ght=bump+steer

Djazair

iTrader: (1)

I've measured bumpsteer on PG's lowered Evo (with and with out Whiteline bushing) and a stock MR, as well as measured all the pivot points and entered them in my suspension analysis program. All methods say toe-out under squat and roll, but at varying amounts. I worked with Dustin over the phone for a setup change once, and he saw the same numbers on an alignment rack that I was telling him.

I'm confused where the toe-in belief is coming from

boostedwrx

iTrader: (27)

I believe you would want it to toe-in more. However I believe by default it is set up to toe-out.

mayhem

iTrader: (9)

You very well could be correct as I have no hard data to back up what I'm saying. I'm just referring back to the bump steer scenarios. BS being something evo owners are trying to reduce to help combat understeer during cornering. It just makes sense (to me) that if the loaded outside rear wheel toes out during cornering/compression then oversteer would occur, not understeer.

boostedwrx

iTrader: (27)

I just ordered a set of bump steer bushings... I only purchased them to aid agains the bump steer I have been reading about. From what I have read, the bump steer is caused by too much toe-out as the suspension is compressed. Am I wrong and are people trying to fix the rear toe-out for other reasons?

Noob4life

Bumpsteer will not automatically cause understeer or oversteer - by definition, it is simply the wheels "steering" themselves with no direct input from the steering wheel. It depends on the suspension geometry of the car. Bumpsteer toe-out would aid in turn-in, and could potentially be designed into a setup for just that reason.

The way I understand it, if the outside rear tire becomes heavily loaded in a corner (such as corner exit), the slip angle of the tire will increase as well, and will toe-out more. So it would seem that toe is more of a function of tire load, with more tire load producing greater grip (to a point). On paper, it would seem beneficial to have toe-out under compression for the outside, with some (but less) toe-out on the inside tire as well.

edit: It sounds like you, Joe and Dustin are saying the same thing?