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MG MGA - Tyre behaviour

First of all --> Excuse my ignorance on this.

I was wondering if it is normal that the tyre woble so much laterally. I have read Barneys pages on the tyre pressure and adjusted mine to something around 27psi.

The tires that came with the car are radials and have 'tubless' written on the side, but I suspect they have a tube inside given that they are mounted on some pretty old wire wheels.

I generally like tyres to be firm, but I guess this may not be achievable, or at least to the extent of that modern cars have them with lower profile tyres.
What is you experience and suggestions? increase the pressure? is there any adverse effect?

I really don't like the the car to 'move around' laterally when on the road. However I am prepared to accept that as a 'feature' if that is the way that these kind of tyres behave.
G Ramos

It does not sound like a tyre problem.
There are several things that you should check, the steering rack free play, wheel bearing free play, the wheel alignment, the wheel balance, and whether the wire wheels run true.
It is not a normal MGA problem to have wheel wobble.
You can tell if the tyres have tubes in them from looking at the valve. Tubeless tyre valves have a sealing bulge where the valve comes through the wheel rim. Tubes have the valve just passing straight through the wheel rim.

Mick
M F Anderson

Gonzalo -
I use 32psi as a baseline, maybe up or down 2 from there for fine tuning handling balance. Disadvantage is a slightly rougher ride - how could you tell! I like precision, and an MGA should feel like a scalpel. If the tires are too wide they get jellylike. 155 or 165 is the usual width, should be fine.

If you feel a pronounced side to side wobble on slowing to a stop on a smooth road, you have one or more with bad belts, an impending catastrophe.

Check date codes on the sidewalls, will be "DOTwwyy", if more than ten years old will be DOTwwy. w = week, y = year. End June 2005 will be DOT2605, end June 1995 will be DOT265. Ten years is the absolute limit, 5 is recommended.

Check for loose spokes by tapping on them, they should "ping". If they "clonk", they are loose and it's a wheel problem. If you see rust stains around the spoke ends they are loose and moving in the hubs.

FRM
Fletcher R Millmore

MGA roadholding is legendary. I always ensure 30 lbs/inch to give the best results.
Barry Bahnisch

I am with Fletcher on this one. Check the tyre dates and ensure the tyres are not as old as the wheels.
If there is a wobble there are various reasons including bent wheels, worn bushings on the suspension, worn steering componants (all the way to the steering wheel) etc.
The rear axle fixing also is important. Ensure that this is secure as it will also cause a loose feeling.
Having just driven my MGA out to lunch in the sun (okay it's only 4 degrees but the roof is down) I can say that there is no loose feel to the steering.

Neil
Neil Purves

Gonzalo, it seems your driving the car and saying that there's a tyre wobble. This would normally be felt as a vibration through the steering wheel and through the body of the car. But you say that the car is moving laterally. This is normally due to a problem with the steering/suspension set up and perhaps not due to tyre 'wobble' You may have two problems here and I would eliminate the tyre issue by getting them well balanced. Try swopping the front wheels around and see if the wobble changes. Also spin the wheels off the ground and check there's no gross out of true in both wheel and tyre. If you solve the 'wobble' you may be still be left with the lateral movement - if this is akin to the car wandering off the straight line then its a common problem and to do with the steering/suspension.
J H Cole

As J H Cole says, check the wheels to see if they are "out of true" by spinning them with the car jacked up, I'm not sure how much is permissable, but if it looks bad it probably is! I notice your wheels are the standard 48 spoke jobs, I had these fitted to my car to start with, and although the spokes seemed to pass the "ping" test, they did give the car a stodgy feel when cornering, they were also a little out of true, so I upgraded to 60 spoke wheels and the difference was amazing, it now feels really secure. You could check the balance of the front wheels by again, spinning them with the car jacked up (you may have to back off the brake adjusters while you do this test) and see if they always stop in the same place. If they do, you could add weight to the side of the wheel uppermost until they will stop anywhere. This may be wrong, but I did it to my front wheels and eliminated all the vibration I was getting through the steering wheel, so a suggestion. Last but not least by any means, check your shock absorbers, particularly the front ones. When I first got my car, it had a very disconcerting lateral shake when on an uneven surface, this was due to one of the front shockers having practically no damping at all. A replacement shock absorber cured it.
Regards, Lindsay.
Lindsay Sampford

I am going to check the tolerances in the suspension joints, etc anyway as I can hear some rattle sometimes when I brake.
I will also check tyre age.

However what I was referring to was not 'real wobble' where the wheel is not running true. I can feel the suspension is moving solidly with the wheel but but it is more the tyre movement in the direction of the wheel axis. Like what you would get if the tyre was severely deflated.

I think I am going to try to inflate them to 32psi nominal as Fletcher suggests and see how that goes, then I can see if there are other things that need doing.
G Ramos

What also gives a similar sensation is when the U bolts holding the rear axle in place are loose, normally because the rubbers have perished or the saddle plates have started to bend. Check all the 8 nuts and make sure they are tight. While you are there check the rubber bushings at the rear of the rear springs - they are often perished too, and don't help the handling if they are not in good order.
dominic clancy

Gonzalo, that's what I meant when I spoke of a "stodgy" feeling when cornering. I think your 48 spoke wheels could be flexing. Lindsay.
Lindsay Sampford

I found out that running 48 spoke rims with radial tires can be a problem in itself. After I had a 48 spoke rim shear its spokes while running at 55 mph I switched to the stronger 60 spoke rims which seem to handle the side loading of radials better. I find that The switch has improved the handling and ride. I second the motion on checking the tire's age. I just had to replace a set of tires with almost no tread wear but the rubber had turned hard and the side walls were showing cracks. They were approaching ten years old. If you have wire wheels you have tubes. You cannot run tubeless with wire wheels. They will not hold air without tubes and rim bands to protect the tubes.
Keith Lowman

I am going to check about this wheel 'flex'. Probably that could be correct.
I guess that in the future I may need to upgrade to 60 spoke chromes...

Dominic, you are right anyhow; last time I had a look at the leaf spring bushings they were completely perished.
Is it a big job to change them? Of can I do it with a jack in my garage without taking off the axle...?
G Ramos

You do not need to remove the axle to change the rubbers, but you do need to support the car properly when you do the job. Buy a set of stands, never work under a car supported only by a jack, even a trolley jack. Getting the rear shackles off can be a bit of a job, getting them back on is also tricky, but I suspect that Barney has some tricks on his site.

When doing the rear bushes, replace the pads where the axle bolts to the springs. Jack the car up and place the stands under the chassis so that the springs are completely hanging (so not under any compression) and then support the weight of the axle gently with your jack. Undo the U bolts and then just lift the axle slightly with the jack to remove the old pads and put the new ones in.

For the rear shackles, memory is a bit fuzzy here, but I'll be doing the MGB in about six weeks time.

Off to the beach for four weeks tonight, so that's the lot for now !
dominic clancy

Ok, thanks for the advice! Enjoy the beach.
G Ramos

Lift car, place stands under the frame, and let the rear suspension drop. Lift rear axle slightly and disconnect the rebound straps, then let the axle drop to lowest position. Place jack near center of leaf spring (not under the bracket or U-bolts). Lift slightly to assure unloading of the shock link. At this point you can R&R the U-bolts to replace rubber pads. When the shock link is disconnected, let the spring drop to lowest position. At that point you can R&R the Rear shackles to replace rubber bushings. Replacing the silentblok bushing in front end of leaf spring requires complete removal of the spring. The front bolt will be last piece out and first piece to go back in.
Barney Gaylord

thanks Barney.
I will order the replacement parts and proceed as per your instructions.
I will report on the outcome.
G Ramos

Just because I don't think it's been mentioned, not all tires are created equal. I've mounted tires that were so weak that they were dangerous on the road. I literally had to fight to keep my MGB in the lane once, regardless of pressure. I returned the tires and put on a model with much stiffer sidewalls and the car was returned to its normal precise tracking.
Steve S

Gonzalo,
This was briefly mentioned, but you may have missed it. Check the tires for separated belts and for bubbles in the sidewall. They will cause a car to change lanes while the wheel is straight. Voice of experience.
Mike Parker

Steve can you recommend a set of tyres that have a stiff sidewall got get a more firm feel?
Should a I get them from any local store as long as they are the right size?
G Ramos

This thread was discussed between 09/03/2010 and 11/03/2010

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