What is steering Ackermann?

Originally posted by dragnblazer



basically its showing the relationship between suspension travel and camber/caster angles. a control arm front suspension has unequal length control arms, so it changes the camber angle throughout the travel. in doing so it also changes the angles on you tierods which causing toe angle changes. also, it is why when you turn your wheels to full lock, you notice the wheel that is ont he side you are turning to is actually turned farther than the one on the other side. but they both come back straight in the center

What you are talking about is "static" bump-steer. A poorly designed suspension will toe in and out as you run through the travel, but that has mothing to do with ackerman. The inner wheel turning further than the outter wheel in a turn is ackerman, but the worst suspension design in the world can still do that, even with more "static" bump-steer than imaginable.

im 100% sure that that stuff is extremely helpful, but it just made my head explode!! might as well be speaking Japanese to me! thanks though, maybe if i read it enough ill figure it out but i doubt it.

Edited: 6/17/2007 3:46:19 PM by HarryBalls

well at least i was making sense of something, although its a completely different subject lol. thanks for clearing that up

cool deal, but can you define the points to make the diagram easier to understand? from what little ive heard it has something to do with the rear end, setup to help the vehicle roll easier when the wheels are turned.....

R- is the center of a line drawn through the middle of the rear axle.

A & B- are (for simplistic sake) the bottom balljoints.

e & f- are outter front-steer tie-rod mounting points

c & d- are outter rear-steer tie-rod mounting points

w & y- are inner front-steer tie-rod mounting points

x & z- are inner rear-steer tie-rod mounting points

The lesson here is: DON'T MESS WITH IT IF YOU DON'T UNDERSTAND IT.

I hope this helps

Taken from Wiki

When a vehicle is steered, it follows a path which is part of the circumference of its turning circle, which will have a centre point somewhere along a line extending from the axis of the fixed axle. The steered wheels must be angled so that they are both at 90 degrees to a line drawn from the circle centre through the centre of the wheel. Since the wheel on the outside of the turn will trace a larger circle than the wheel on the inside, the wheels need to be set at different angles.

The Ackermann steering geometry arranges this automatically by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle. The steering pivot points are joined by a rigid bar, the tie rod, which can also be part of the, for example, rack and pinion steering mechanism. This arrangement ensures that at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point.

Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low speed manoeuvres.

damn.

Edited: 6/17/2007 7:42:39 PM by bdroppeddak

thanks max! now, im not understanding how you achieve the angle to find out where you place the inner pivots.....