Bump steer

[jonners]

Originally Posted by GORDON STREETER

In a straight line agreed, but in roll steer the suspension pick up points are starting at a different hight on a corner. The inside will always be higher than the outside.

I'm confused by this - can anyone explain??

How does Ackermann fit in to the overall picture?

Please feel free - if you haven't already - to assume that I know nothing and am slightly pedestrian on the technical front.

[GORDON STREETER]

http://tentenths.com/forum/showthread.php?t=104623
There's not a lot of sense in going all through this again. (above)
The suspension pick up points when cornering will be at a different height from the track simply because of body roll. I shouldn't have confused this with rear roll steer, where the wheelbase alters when the suspension lifts.
At the end of the day most race cars have very limited suspension movement anyway what with stronger springs and ARBs.

[Tim the Grey]

So, Gordon?
If I understand you right, the wheels move independently of the chassis?
How do you achieve this?

[GORDON STREETER]

Originally Posted by Tim the Grey

So, Gordon?
If I understand you right, the wheels move independently of the chassis?
How do you achieve this?

I keep the chassis in England and the wheels in Spain

[JohnD]

Originally Posted by ian_w

In my experience, what you want to aim for is slight toe-out in bump.

Resurrecting this thread, because we are building the steering now. How much toe out is "slight"? Staniforth quotes +/- 5 thou at the wheel, that I take to be less than 0.05 of a degree.

And how important is deflection in droop? If the tyre is unweighted by roll in a corner, does it matter if there is bumpsteer then?

John

[GORDON STREETER]

Ideally you don't want any bump steer. But if there is it should err on towing out.
If it tows in it will tend to make the car oversteer. This is assuming that the car is designed and set up correctly. An oversteering car is more difficult to drive on the limit and good mechanical grip with wide tyres excentuate this.
How can you get bumpsteer if the wheel is in droop ?

[St Eval]

The same way as you get it in bump, If you have bumpsteer in bump you will have it in droop. A whole thread and no one has mentioned bumpsteer at the rear, (solid axles need not reply)

[GORDON STREETER]

http://www.flickr.com/photos/16345037@N03/1766974993/
Could you explain how the unloaded wheel can change the direction of the car please !

[St Eval]

I didn't say that the unloaded wheel would change or steer the car, just that you can have bumpsteer in droop, because if you have it in bump you will have it in droop. Anyway the unloaded wheel has got to come back to earth at some point, so if the wheel is waggling around it will have some effect at that point.

[PTRACER]

Sorry to bump an old thread again, but can I confirm which is correct?



I get the impression a) and c) are correct, but b) is not? Or is b) right and c) wrong?

[JohnD]

The rule is that the ratio of the distances between steering arm and suspension joints on the upright should be the same as that between the steering rack knuckle end and the suspension brackets on the chassis.
SoA and possibly C, but not B.

John