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MG MGB Technical - Tyre size for MGBGT with WW

I need to replace the tyres on my 1968 MGBGT which has W Wheels.
165/70 R14's are readily available but 165/80's are not. Can I fit 165/70's, or should I consider another size such as 185/70?
Thanks for your help.
Mike Christie

155/70 reduces tyre diameter by 1.3inches which will effectively lower the gearing and the car. At 30mph your speedo will under read by 1.2mph and at 60mph will under read by 3.2mph. Consumption will rise a bit and acceleration improve a bit. It might also handle a bit better because of the lower aspect ratio but may become slightly less supple, but whether you would notice or not is a moot point.
Allan Reeling

Thanks Alan, but the tyre size is 165 not 155. I need to know if there is any reason not to fit the 165/70 or even the 185/70? The difference between the 70 & 80 is 17.5mm
Mike
Mike Christie

Are the wire wheels narrower than the Rostyles? Something in the back of my mind says that they are. I fitted 185/70 x 14 on my old B Roadster without trouble, but I think they would be too wide for a narrower wheel. Using this calculator http://www.tyresave.co.uk/tyresize.html there is less than 1% difference in the diameter of the two sizes. The 165/70 is over 5% smaller than standard size, affecting your gearing and speedo.

I found several 165/80 x 14 tyres on this web page http://www.mytyres.co.uk/rshop/Summer-tyres/165-80-R14-T

I have used Barum Brilliantis on an MG midget, and they were very good. A good all-round tyre.
Mike Howlett

165 gives the information as printed, 155 was a typo on my part.
Allan Reeling

Mike,

I am running 185/70x14 on my 77 wire wheel B and they do not look oversize to my eye. I don't know if you can tell much from this low res photo, but maybe you can get some idea. I think the cars are geared too low as it is, so I would avoid short tires.

Charley


C R Huff

I've been running 175/70 tires, for several years now, with no problems whatsoever. RAY
rjm RAY

I just bought 185/70R14's for my Rostyle wheels 79 B. These replaced 185/75R14's . I notice the ride height has increased and I think the speedo is more correct. I will compare it when I see a radar speed sign.

The 185/75's always looked a bit small within the fender well. Placing one of the 185/75's next to a 185/70, the 185/70 is larger in circumference.

Noticed also a smoother ride and handling.

cheers

Gary
79 MGB
gary hansen

"Placing one of the 185/75's next to a 185/70, the 185/70 is larger in circumference"

? The '70' and '75' specify the height of the sidewall as a percentage of the tread width. Therefore a 75 should have a greater diameter than a 70 for a given tread width.

I've got 175/70s on my (pukka) CB wire wheel axle and they occasionally rub on the arches when cornering, 180s would be significantly worse. Next time I'm going back to 165s, 70s if I can't get 80s.

Taking 155/80s as a reference, 165/80s have 2.7% higher dynamic rolling radius, and 165/70s 2.7% less.

Roadster disc wheels are 4J, GT disc 5J, wires are 4.5J, and Rostyle are 5J.

Black Circles are a good source of a wide range of tyres makes and sizes. They have arrangements with many tyre fitting places, you choose one that is local to you when ordering.
Paul Hunt

Paul, et al: I stand corrected. Went to the garage and discovered the tires I replaced are 185/65R14 NOT 75's. The new 70's are indeed larger than the old 65's which explains why my ground clearance is higher.

Cheers

Gary
79 MGB
gary hansen

Hi Mike,

I might be a little late to this, but I have just had a set of 165/80/R14 tyres. They're Falken, I ordered them through my local garage. I run a Mk1 GT on 14'' wires and am delighted with the tyres. They even manage to look a little more period than some out there.

Piers
Piers Colver

MWS also supply 165-80x14
Paul Walbran

This thread was discussed between 15/04/2016 and 06/05/2016

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