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MG MGB Technical - Rear Axle Offset

I recently bought a set of rostyles of Ebay to replace the knackered chrome ones on my recently purchased GT. Having looked at the archives for the general concensus on tyre size I went for 185-70's. Having come to fit the wheels I have found the rear axle to be offset to the left which means the wider tyre on this wheel is going to foul the wheelarch. The rear springs are quite worn and are due for replacement. My question is:- Will the replacement springs have any effect on the axle alignment (ie worn bushes etc allowing it to move across) or is there any other method for shifting it over. As so many people appear to have fitted this size tyre I find it hard to believe that it can't be done. Having used the archives and from my experiences on the midget board I wait in anticipation of good news. Failing that does anyone want to buy four new tyres?

Many thanks,

Dave
Dave

Dave, there is plenty to think about when you find that your wheels foul the arches.

First, a common misconception is that the axle is off centre. It isn't! The spring hangers (unless they've been bodged by a PO) are symmetrical side to side. The off-centre look is due to the wings and rear part of the bodywork being off centre, and this is what was so variable from the factory.

Another problem is that rostyle wheels have been found to have a whole mish-mash of different offsets... it could be that one of yours is set more outwards than the other.

Re-bushing etc. will help keep the axle in place when cornering hard, but even with new bushes it will move around. If you really are running out of space then a panhard rod may be neccesary.

Hope this helps!
--
Olly
Oliver Stephenson

Oliver is correct about the variable positioning of the rear bodyshell and yours must be quite a bad example if your wheelarch is fouling a 185 on a standard wheel. I even saw an MGB which was offset to the other side, once! But usually the offset is to the left.
Check that it is not caused by a poor repair to some early damage - I had that problem and it didn't show until it was investigated very closely. Having the repair re-repaired mainly solved the problem and I was able to fit quite wide wheels with no real difficulty.
I didn't know about varying offsets on the Rostyles, but of course this would be characteristic and is what makes our cars so endearing. Isn't it?
Marc

Thanks for the suggestions about the bodywork. It doesn't look as if it is out of line, but then if it had I wouldn't have bought it! I'll try and get a comparison side to side to see if there's that much difference. If there is then the original question stands, is there any way of shifting the axle over? I have seen a suggestion in the archives of loosening the U bolts and knocking the axle over to gain 1/2 an inch or so. Has anyone tried this? It's got to be easier than fettling the bodywork and cheaper than replacing the tyres again. With an education in Agricultural Engineering I have quite a knack with a big hammer!

Cheers,
Dave
Dave

Dave, the axle is located to the springs by the bolt that holes the leaves together... it goes into a hole in the pad where the spring and axle meet, so you can't shuffle the axle to and fro in this manner.

Try swapping your wheels around to see if their offset is wierd; if they're all the same then place one on its back on the ground and measure the height from the centre down to the ground. I'll measure the spare in our roadster for reference if needs be.

Last option is turning the flange up on the inside of the wheelarch. No need for flaring which would be obvious to the casual observer, and you can get 1/2" of extra space to play with.

Good luck,
--
Olly
Oliver Stephenson

I shifted the axle sufficiently to centre it and fit 195x15 tyres, you may have to extend the 'u'bolt seats on the axle so one bolton ech side is 'inside' and one'outside the bracket,if it's more than 1/2" out of line.....nobody has ever satisfactorily explained why the offset....it isn't even always the same way, and my Heritage shell suffers the same problem......so clearly it's not cured.

Mike
Michael barnfather

I have 185s on my V8 which leaves plenty of clearance, and the POs 195s didn't foul either. Part of that is due to the higher ride height but a vertical projection still shows clearance. Is it fouling on the LH outer lip or the RH inner arch? If the latter then maybe it has a wire/wheel axle converted to bolt-ons which can cause this. Both my cars have the offset, but I have had the front to rear alignment checked and it is good, so 'centreing' the axle to the body is actually offsetting the rear track from the front. I can't recall anyone claiming to have a car with a RH offset axle, but even if there are a few the LH offset is far more common. I think it highly unlikely that the chassis rails or front hangers are out of alignment by 1/2" if all four or by a massive 1" each if only two of the four, but when you consider just how many panels and joins there are between the chassis rails and the outer arch lip a cumulative number of small dimensional differences on one side becomes much more likely.
Paul Hunt

I would be intersted to know the year of Dave's car, as it seems to me that the offset problem is worse on cars made in the early seventies. My '71 has a difference of about an inch in tyre/wing clearance, but 185 tyres still fit without rubbing.
Mike
Mike Howlett

Again, thanks for the comments/suggestions. I fitted new rear springs yesterday which may or may not have ipmroved the situation. It definately seems that the wheel is slightly further over, and the increased ride height gives more clearance. Taking a straight edge across the tyre up to the LH wheel arch indicates a foul of approx 5mm. Having seen the clearence in the axle 'locating holes' I think there is the potential to shift over by this much - I'll wait till it's settled down then try it.

Mike H - As far as I know the car was built in 1974. It originally went to Belgium (apparantly) and was re-imported in 1980. The Registration documents give a 'first used' date of 1974 but I'm waiting for a heritage certificate for more precise details.

Thanks again,

Dave.
Dave

Paul H has made the comment about front and rear wheel alignment which is interesting in the light of adding a Panhard rod to reduce offset, obviously beneficial re possible tyre rub.

On the assumption that Jigs etc created this problem from say 70 onwards then the New Heritage shells using same jigs will also have problem?

Paul
Paul

Paul,
My Heritage shell certainly had.....I would say it was worse than the Ex USA 1977 roadster shell it replaced, but not as bad as a friends 1979 roadster.

I still don't understand how it is caused, it can't be constant road camber, or the fact that they are generally driven 'one up' that has offset the springs, and I measured the Heritage shell before I fitted anything, and both sides seemed identical. I have established that it is possible to 'load' the axle sideways before tightening the 'u' bolts which centres it somewhat, if it wasn't for the fact that I have fitted 195 tyres, I wouldn't be bothered, but I needed every mm I could get.

Mike
Michael barnfather

I also have a '69 GT which has never been restored (that's my next project). The axle is dead centre in relation to the outer bodywork. I must try to keep the situation like that once all the welding is done.
Mike
Mike Howlett

One of the 'features' of the Heritage shells is that they are made using the original jigs and presses i.e. warts 'n all. Road camber would tend to shift the body to the left of the axle in the UK i.e. opposite to the way most seem to be both here and North America, although it could add to the problem in LHD countries.
Paul Hunt

Dave,

I had this problem and I found that by measuring the rostyle carefully there was a 4.3mm difference in offset. This made the difference between fouling and not fouling.

I wrote it up with pics at http://www.btinternet.com/~richard.thompson/mg/tools/rostyle_wheel_offset.htm

One comment I have is that with the Moss 1" lowered springs, which have now sagged a little, I will be going back to standard springs as the 185s do foul on hard cornering.

Hope this is useful.

Cheers

Richard
Richard Thompson

This thread was discussed between 19/10/2003 and 23/10/2003

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