TheHaflinger.com

I have been looking to upgrade to 13” wheels, probably with 155/80 tyres. The rim width has thrown up an interesting question. I can get new 4.5 rims but with a B profile, not J. But the tyres I want are a J profile. I have seen one post on Google that says mixing J and B is illegal, so I cannot put J tyres on B rims. I could go to 5.0 J but the offset on those rims is 35 which should be ok, but would that be a good combination? Anybody got any more info on the bead issue?

I found this which just shows how different beads are categorised.
https://www.tyresizecalculator.com/whee ... m-profiles

This might also be useful:-
https://www.tyresizecalculator.com/tyre ... calculator


But I think it is going to be something that there is no real hard and fast rule - I will see if I can find a government web site / MOT regulation which states what can and can't be used.

John
P.S. I found this which lists rim size and bead shape letters on page 1 under RIMS FOR ’80’ AND ’75’ SERIES – METRIC DESIGNATION
https://btmauk.com/wp-content/uploads/2 ... d-Rims.pdf
According to it, you can get these sizes:
155/80 R 12 4.00B 4.50B 5.00B
R 13, 14 4.00B 4J 4.50B 4 ½ J 5.00B 5J

So the R indicates the tyre size either 12 inch or 13 inch. This document does not show the offset of these rims.

John, that’s all very interesting but not definitive regarding using J tyres on a B rim. However, your last link does indicate, in the notes at the foot of the charts that it may be ok to use J tyres on a B rim if less than 5.5. And the tyres I was considering are Malatesta KobraTracs made by an Italian company. The UK importer won’t commit yeah or nay.. it would be nice to know that it wasn’t illegal in the uk to mix up J and B.

And R is Radial, B is for belted ie cross ply.