Steering, Suspension, & Brakes

What is the largest with of wheel that a stock MGB GT can have

Your stock rear axle probably isn't centered side-to-side. If you carefully center the axle, you should be able to fit 15x7 wheels with a -22mm offset and to use 225/50 tires. (That's the combination on Graham Creswick's roadster. I know no difference between roadster and GT when it comes to fitting wider wheels.) You'll almost certainly have to grind a bit on the lips of your fenders for tire clearance! Tire sidewall shape/size varies from manufacturer to manufacturer and from model to model, even within a nominal size (e.g. 225/50.) You may find that you need to install some sort of device to keep your axle centered, such as a Panhard rod or Watts link.

Your results may vary. Actually, mine did. I have 15x6 -22mm offset wheels and 205/50 tires on my GT yet I found that my front tires scrub on my Addco front anti-sway bar, both sides, which evidently reduces my turning radius. A different anti-sway bar would help.

Some people cut into (and rebuild) the bump stop mounting feature inside their rear wheel wells to provide tire clearance... but as far as I recall, Graham didn't have to do that.

ok i guess i will have to go with the 15 by 6 becase i dont have the tools to do it right with the 15 by 7 wheels

With more offset (~38mm) you can use 16X7" wheels. I run 205/55/16 on my 1980 MGB and 9 mm spacer on RHS and a 6 mm spacer on LHS. No rubbing on the inner fender/bulge but sometimes I get a slight rub on the outer fender lip. Ten minutes with a grinder and there would be no issue. Just worried I might slip and make a mess of my shinny new paint. Not sure if 15" rims would end up closer top the inner bulge from the bump stops however.

Lots more wheels to choose from in 7" vs 6" wide.

Is the rear axle not centered from the factory or is it something that happens over time?

J Man,

Yes the factory had a messed up jig and most are off by 1/4" I believe.