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Steering alignment
https://www.ausmini.com/forums/viewtopic.php?f=2&t=94227		 Page 1 of 1
Author:  Bill B [ Tue Nov 15, 2016 5:21 pm ]
Post subject:  Steering alignment
Reassembling my mini - when last running it had a bump steer effect as the suspension travel changed from bump to rebound over different surfaces. If it went over a jump, the car would land wanting to steer left and when the weight of the car loaded the suspension it quickly wanted to steer right.
The shell is still on a trolley and off the ground so I've used a laser to plot toe in/out for front hubs when I jack them up through their suspension travel.
Results are similar both sides: from standard ride height to bump (wheel going up into wheel arch), steering remains straight.
Rebound (when the wheels hang down as in going over a jump) the wheels toe in a fair bit.
Is this normal?
Subframe is square, rack is original/reco'd, steering arms are original/correct numbers.
Author:  peterb [ Tue Nov 15, 2016 8:25 pm ]
Post subject:  Re: Steering alignment
Wrong steering arms?
Author:  Lillee [ Tue Nov 15, 2016 8:31 pm ]
Post subject:  Re: Steering alignment
Not to answer your question but when I had 0 castor or even negative castor my car would bump steer and generally be unpredictable. With 3 or 4 degrees of castor dialed in all of that is gone and she is very stable at speed and over bumps. Requires adjustable bottom arms and castor bars.

(!) check castor bar length and bushes are on correctly?
Author:  Bill B [ Tue Nov 15, 2016 8:40 pm ]
Post subject:  Re: Steering alignment
peterb wrote:
Wrong steering arms?


They have casting nos AYA4116 and AYA4117 on them which I believe are correct for Aust made rack assemblies.
Author:  Bill B [ Tue Nov 15, 2016 9:00 pm ]
Post subject:  Re: Steering alignment
Lillee wrote:
Not to answer your question but when I had 0 castor or even negative castor my car would bump steer and generally be unpredictable. With 3 or 4 degrees of castor dialed in all of that is gone and she is very stable at speed and over bumps. Requires adjustable bottom arms and castor bars.

(!) check castor bar length and bushes are on correctly?


Thanks for the reply.
I once had a steering shop heat and bend the upper control arms to give more positive castor, which I think only disguises the problem by giving more shopping trolley self-centering.
When you say "Check castor bar length" do you mean the tie bar?
I have thought that adjustable arms might be a final fix but I'd like to understand what is happening first.
Author:  Lillee [ Tue Nov 15, 2016 9:17 pm ]
Post subject:  Re: Steering alignment
Quote:
When you say "Check castor bar length" do you mean the tie bar?


Yes. If the tie rod bar is too long or incorrectly installed it can push out your castor (ask me how I know this). Shorter in theory is OK but that could also pull camber inwards undesirably. Castor and Camber on minis are related, shorten or lengthen one and the other will move. So if you get adjustable tie rods, you will want to look into adjustable bottom arms.

Best to just get the suspension measured to figure out what castor, camber (and toe) currently is and figure out from there. I recommend Jim Hunters Suspension in Blacktown.

Bump steer can be exacerbated with a loose/worn steering rack

Is the bottom or top arm bent? Are these heat bent steering arms still on the car??
Author:  1071 S [ Tue Nov 15, 2016 9:41 pm ]
Post subject:  Re: Steering alignment
Bump steer is caused when the upper arm moves through a different arc from the steering tie rod as the suspension moves up and down. You fix it by moving the junction of the steering arm and tie rod upwards using spacers.

Cheers, Ian
Author:  Bill B [ Tue Nov 15, 2016 10:11 pm ]
Post subject:  Re: Steering alignment
1071 S wrote:
Bump steer is caused when the upper arm moves through a different arc from the steering tie rod as the suspension moves up and down. You fix it by moving the junction of the steering arm and tie rod upwards using spacers.

Cheers, Ian

Thanks for the reply.
Is the spacer meant to lengthen the steering arm?
How does the spacer fit between the steering arm and tie rod end joint and what does it look like?
Is it shown in Binky?
Bill
Author:  Tim I [ Tue Nov 15, 2016 11:17 pm ]
Post subject:  Re: Steering alignment
While eliminating all bumpsteer for the full range of suspension travel is a good thing to aim for, what you have now is not an entirely bad thing.
You mentioned that you only have toe gain in droop... is it progressive from normal ride height or only really in the lower half or third of droop travel?

If the toe gain is only appearing in the mid to lower droop travel, and the toe is virtually unchanged for the first part of droop travel from the ride height position, then I would not be too bothered by it.
Bumpsteer is more of an issue if it is in the bump part of the travel, or if there is a lot of change for travel close to the normal ride height setting i.e. when the tyre is loaded.

When the wheel is moving into more than say 1/3 to 1/2 of the droop travel the tyre will be quite lightly loaded and therefore have little effect. And if you are worried about bumpsteer at the extremes of droop travel, you are probably forgetting that the contact patch between the tyre and road is now too small and lightly loaded to be effective... and ignoring far bigger potential issues stemming from the fact you are airborne.

There is a point where the effort required to eliminate bumpsteer for the entire range of suspension movement simply isn't warranted for the benefit gained, unless you are setting the car up from scratch and have the ability to relocate suspension pick-up points and/or the steering rack.
Author:  1071 S [ Wed Nov 16, 2016 4:53 pm ]
Post subject:  Re: Steering alignment
All this is true..

However to correct bump steer you need to make sure the steering tie rod is parallel to the upper suspension arm with the car sitting on the wheels. You do this by adding a perpendicular link that attaches to the steering arm and raises the outer end of the tie rod.
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