bump steer

[smcferran]

Carrol Smiths book seems to imply that a little toe in with bump (wheel up)
and thus a little toe out in droop is an ideal situation.

can anyone confirm this?
as for god only knows how long ive set my car the other way around with 0.5mm to 1mm toe out at 100mm bump (up travel).

Because somewhere in the distant past i was told this was how it should be.

have i had my leg lifted??

Stephen

[kintryin]

As far as I am concerned I dont want any of either. But sometimes we have to compromise. Unless you are in a newbuild or rejig situation then the pickup points and component/linkage lengths will be pre set . If you are fortunate to have the prior setup info for the vehicle then use it cos knowledge and experience costs £££ . Most vehicles will have an optimum setup to use what is there. So try and research that vehicle and its characteristics.
Toe in toe out, front or rear ?

[SteveSlowboy]

For the front you want no bump steer. I think the "little bit" refers to the rear axle?

Steve

[PumaWestie]

I would imagine that toe in on bump is related to improving stability under braking. In addition, toe out under droop and toe in under bump will aide ackerman when cornering

[Rob Stevens]

I have a fair bit of experience of bump stear from my OMS SC
on the rear I had some bump out and this was very bad, as the car rolled in a corner it would toe out and make for a wild style. I changed this to 0 bump and droop and the car was much nicer. at the front I got rid off it all but didn't make much difference.
On the force I have 0 both ends.
On my Road Lotus it has loads of front bump steer, the front bumps out and droops out a large amount perhaps 5mm max
The rear bumps in and droops in around 0.5 mm max, this is to counteract bush compliance during heavy cornering. This car drives like a dream all though the steering wheel may writhe in you hands at speed over bumps.

[windy]

Anyone who says that bump steer is bad should study a lotuses geometry. I have and was very very suprised at what I found. Since then I have changed my opinions about bump steer.

[Rob Stevens]

Windy, did your measurements come out like my Elise? There are revised steering racks to remove the front bump steer but people say it takes the feel away. Lotus does have a reputation for fine handling cars and I fully support that.

[Craig Powers]

The ideal should be no bump steer at all.
On the rear if you cannot get rid of it then adjust it so that it is toe-in for wheel up. Toe-out is bad as others have suggested because it promotes oversteer.
As I understand it.....

[windy]

Yes for the front, but there was a lot more toe change on the rear, up to 6mm on full bump I recall.
I don't have the measurements to hand it was something i did a few years ago now.
The thing that becomes a black art is understanding how the tyre, in particular the sidewall, responds to these toe changes and how that translates to feel. The Lotus guys spend a massive amount of seat time in the cars to perfect this which is obviously how they achieve fine handling machines.

[Lolat492]

Due to my ineptitude at suspension setting on the Lola i had 10mm toe out on bump at the rear. It literally threw me off at the kink up Cedar straight on compression...

Had the car fixed by McClurg Motorsport with zero front and rear, and the difference is stunning.
Car has slight toe-in static at the front, zero at the rear.

I certainly learnt it all must be dead accurate.