Wheel Balance and Bump Steer

[david.g.chapman]

My +2 seems especially susceptable to front wheel inbalance - as little as 5 grams out and you can feel the steering wheel shake at motorway speeds.

This is a pain, because.... put one of my steel wheels on the balance machine at a tyre shop and fix the weights to give 000 000 (grams) on the balance display. Then take the wheel off , turn it and refit it to the machine. Check the balance and you get 005 010 typically! I have a feeling that all steel wheels are like this.

I has a special adaptor made up for the clamping cones used on the balancer to duplicate the way the wheel nut bears on the wheel, but this has not entirely fixed the problem.

My question is... if my rack bump steer setting was out, whould this increase the sensitivity to this inbalance (out of balance forces could be likened to a bump impulse)?

As an aside, I have found out that a there does not seem to be any difference in balance effects between a wheel that has no run out and one with 1-2mm run out.

Dave Chapman.

[mikealdren]

Dave,
A frustrating problem and there are other possible causes.

I would expect bump steer effects from the rack height being wrong but not balance problems. Front balance problems usually cause vibration through the steering at higher speeds. Sounds silly but I had wheel balance like symptoms from a propshaft imbalance.

Sounds like you've discounted run out (have you checked the tyre runnout?) and balancing can vary a little if you try it twice but modern equipment is very accurate.

Are all the wheels the same - have you tried switching front to back? If a wheel is damaged or out of balance, the problem will switch with the wheel and you can isolate it to an individual wheel. If you get the problem with all the wheels, it's probably something else.

It may not be the wheel balance itself but whether it the wheel is sitting true on the hub. Is it centre lock or bolt on? The pegs or bolt holes may not be true - are they worn?

Have you taken the hub apart - could it be disc runnout? Is the wheel bent or damaged in any way, older steel wheels are particularly vulnerable - have you tried switching front to back?

Good luck
Mike

[Foxie]

Agree with all the foregoing checks, but balancing the wheels on the hubs will bypass many of them. The difficulty in these modern times is to find a place which still has this equipment.

You will need to mark each hub and wheel with a dab of paint (on the inside !)to make sure the wheel goes back on the hub in the same position, in case you need to remove it.

Sean Murray

[david.g.chapman]

Thanks for your replies so far.

A bit more info - I have just replaced the front shocks with AVO adjustable types, set to one up from the softest setting. Trunnions and disks have both been renewed, and I have stripped the steering rack, reshimmed it and replaced the bush at the far end. Front wheel bearings have also been replaced and set to 4 thou end float. Bushes are OK.

I have tried swapping the wheels from front to rear already, and there is no difference. All +2's have centre hole fixing, by the way. I had measured the run out with the wheels on the car, so I suppose the hubs are OK. Anything below 2mm doesn't seems to make any difference anyway.

Tyre radial run out (out of roundness) is about 1mm, and can vary depending on how long the car has been standing. I feel that is something I can't do much about.

What is galling is that after I had Avon tyres fitted on the front two years ago (on the wheels with the worst run out) I had no balance problems for several months. It then just started up again - and a balance weight had not fallen off. This was before I restored the front end as well.

I could go for alloy wheels of course, but I do like the steel wheels - they go well with the car.

If any of you out there know of a place that still does on the car balancing in Essex, I would be grateful. The last place I know of in the area was in Wickford, but they have now dumped their machine.

It's my last problem after 6 years of effort - and this car is worth it!

Dave Chapman

[Sarah Ryan]

I had the same problem with my Alloys at highway speed you could feel a vibration. The only solution assuming all else is Ok is to find a tyre place with an on car balancing machine that can compensate for everying that spins. Usually tyre places do not have these anymore but I found that specialists who prepare race cars have them!

[david.g.chapman]

Thanks, Sarah.

Goodwin tyres in Green Lane, Ilford still have one

I used them in the seventies but had forgotten about them.

I will go there next weekend.

Dave.