Wheel and tyre size question

Technical MGB discussion
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SteveH1960
Posts: 14
Joined: Thu Jul 01, 2021 4:23 pm
Forename: Steve
Surname: Hankins

Wheel and tyre size question

Post by SteveH1960 »

Hi,

I am new to MGB ownership, very new, so apologies for what could be idiot questions. I have tried searching the forum but without success and I am sure this subject has been done to death but I can't locate it.

I have a 72 Roadster with 14 inch minilites, they are a little shabby and the tyres are Goodyear NCT 185/70R14 and they look a bit balloon like.

I'd like to change to 15 inch minilites, something like the ones on MGBHive, 5.5 x 15 inch, what would be the correct size tyre?

Or do I have to stick with 14's?

Thanks in advance

Steve
Ian Fozzard
Posts: 611
Joined: Fri Mar 27, 2015 8:18 am
Forename: Ian
Surname: Fozzard

Re: Wheel and tyre size question

Post by Ian Fozzard »

Steve, take a look at a tyre size calculator such as this one:

https://tiresize.com/tyre-size-calculator/

This should tell you what will fit your chosen wheels.

You need to know the "standard" wheel/tyre circumference and ideally should stay close to that - important for speedometer accuracy.

The other factor is fit under the wheel arches. The MGB often has some asymmetry of the back axle - one tyre often being closer to the wheel arch than the other side. Depends what your car is like!

Hope this helps

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear
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Bumpa
Posts: 53
Joined: Sun Dec 13, 2020 9:58 am
Forename: Mike
Surname: Howlett

Re: Wheel and tyre size question

Post by Bumpa »

On the MGB Hive website they also offer the 15" x 5.5" wheel with tyres fitted and they are using 185/65 x 15. That size should give you the same speedo readings as the standard 165/80 x 14 fitted at the factory.

Ian is right about arch clearance being assymetric side to side. Most MGBs I have seen have less clearance on the left side. Also you need to consider that the axle can actually move sideways slightly during heavy cornering.
Mike
1969 MGB GTV8 3.9 Conversion, 1977 Triumph Dolomite 1850HL, 1971 MGB roadster undergoing restoration.
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