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MG MGB Technical - New tyres - will they fit in the boot?

I am just about to buy some new tyres and plan going a bit larger to 185/70.

Might be a dim question as they seem to be a popular size but as I am also replacing the spare will it fit in the boot?

Mike Dixon

Roadster or GT? Wires or Stud?

Wider can be a struggle to fasten the cover in a GT.

Wires may need a longer clamp but stud can go in upside down. V8s were like that anyway but Rostyles will also fit like that.
paulh4

I would use a smaller tyre for the boot. Just like many modern cars do, consider it a "space saver" spare.
I have 185x70 tyres on Dayton 12" x 5" chrome wire wheels on my MGB, but I retained an original Dunlop 14" x 4.5" non-chrome wire wheel with a 165 x 14" tyre as my spare.
Otherwise you're slightly restricting your boot space, and hauling around the extra weight of a larger spare that you might not use for years, if at all.
T Aczel

It's a GT and the wheels are 14 inch alloy Minator, which I put in face down anyway to fill it up with stuff.

I am afraid a smaller spare tyre is not really an option - I am taking the opportunity of worn tyres to fit Veredstein Quatracs as we are doing a 3 day rally in the Scottish borders in late Oct/Nov. Winter rated tyres are a good compromise as I do not want to fit M&S or even Gravel tyres, not least because we do not trailer the car and we are not in that league yet!

The chances of a puncture are higher than normal especially on the gravel and I need to keep the handling correct - there are also some tests on tarmac in addition to a 200 mile drive home. So ideally I need a like for like spare.

The overall diameter will be give or take be the same so its a question of the, I assume, the extra 10mm width (currently on 175/70 ) stopping the board coming down?
Mike Dixon

Apologies for any confusion possibly caused my typo that I just noticed.
I of course don't have 12" diameter wheels on my MGB, they are 14"x 5".

The width as you say is different, and noticeable.
With 175/70 tyres, I never had rubbing issues on the rear wheel arch inner lips.
With 185/70 tyres I very occasionally will notice a slight rub with a full load and vigorous cornering.
With the 195/70 tyres I ran for a short time, rubbing would occur with minimal sideways cornering loads, especially with a passenger.

Apart from the rubbing issue, I actually disliked the really obviously increased mass of the 195 tyres. They "felt heavy" and didn't suit the car at all. Surprisingly, traction (Michelin) was also unimpressive.

Just my opinion, but I actually think an MGB feels nicest with 165/80 tyres. They also happen to be closer in size and mass to what was originally fitted to the car.

I understand your reasoning re handling in a rally. I too would not want a different spare in such circumstances. But, if I may add, after considerable exposure over many years to gravel and coarse road surfaces (in remote areas of Australia) both with cars and motorcycles, I have never noticed an increased propensity to flat tyres with such rough roads. But also, while I have covered 250,000 miles in my MGB in the 55 years I have owned it, I never drove it "in anger" on such surfaces for any length of time. I hated seeing the occasional appearance of daylight between the windscreen and the quarter vent frame when I tried!! (We have some truly awful roads out here). The greater rigidity of a GT such as you have would suit those conditions much better.
T Aczel

Rubbing is an odd thing. It's unlikely to happen on rubber bumper cars unless the rear suspension has been lowered. The offset of both wire wheels and Rostyles changed to make the track 14mm wider for 1977 and later models. V8 alloys are within a couple of mm of the earlier Rostyle, I don't know about later factory alloys.

I fitted wire wheels with conversion hubs to the stud wheel axle on my 73 and rubbing was really bad. I changed the axle to a pukka wire-wheel type with standard hubs which improved things significantly but they can still rub with 175s when touring fully laden, so I'm going to 165s as each pair needs replacing. It was then I discovered I had the later wire wheels with the wider track. Really I need the conversion hubs on this wire wheel axle and wheels which will bring things back to how a chrome-bumper car would have been initially.
paulh4

I had this issue with my MGA and deflated the tire somewhat (not to the point of breaking the seal of course) so that the oversized tire would fit better. I would always carry a small tire inflator in each car in case of low pressure on any tire anyway.
Just a thought.
L Frisch

Aspect ratio is another factor. Unless you reduce that as the width increases the overall diameter of the tyre increases as well as the tread width which can impact storage, and the speedo can under-read.
paulh4

I think the diameter is about the same 175/80 currently fitted (not 70 as previously stated) to 185/70 ?

We are not too bothered about the speedo as we run off a BRANTZ most of the time which is calibrated to 1/100 th of a mile - we have to change the calibration when we put more air in the tyres sometimes!

Bottom line is will a 185/70 r14 spare fit in a GT boot?
Mike Dixon

Put something of various thicknesses on top of the existing wheel and tyre and see when you can no longer fasten the turn-buckles. Even then the board can stick up a certain amount without fouling the tailgate. Or just remove the board. Or unscrew the hinges so it lies flat.

At the end of the day the LE used 185/70 as standard!
paulh4

185/70 14" tyres on V8 wheels fit in the GT.

No problem turning the DZUS 1/4 turn fasteners.
J N Gibson

Thanks 185/70 it is . In passing I found this

https://tiresize.com/comparison/


Great fun as you can easily visualise changes and compare! ( I need to get out more.....)
Mike Dixon

I fitted the 185 /70 R14 and they do go in the boot, just, you have to push down the lid a bit in the GT. Minor niggle is that you can no longer get the spare central due to the profile so a minor faff is needed to get it bolted down.

As an aside the Veredstein Quatrac all season were excellent. It turned out they are M&S and have the snow symbol. My limited ability found them really good on the mud, gravel and tarmac. Pity we missed the snow! I will keep them on and see what the wear is like.
Mike Dixon

This thread was discussed between 08/10/2024 and 19/11/2024

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