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GT V8 original tyre size
Posted: Mon Apr 10, 2023 9:27 am
by 1340fxd
My MGB GT V8 original handbook states the tyre size to be 175HR x 14 - no mention of an aspect ratio to determine tyre diameter. The car has 185/70R 14 fitted. Does anyone know the original tyre aspect ratio or diameter / circumference please so I can work out of the tyres fitted have the same gearing and speedometer reading please?
Re: GT V8 original tyre size
Posted: Mon Apr 10, 2023 10:23 am
by Paul Scott
Re: GT V8 original tyre size
Posted: Tue Apr 11, 2023 9:41 am
by Bumpa
The original size tyres, 175 x 14, will be full profile, which means they have the tallest side walls at about 82% of the width. So they would be classed as 175/82 (or 80 is close enough) x 14. There are dozens of tyre comparison sites out there, eg,
https://tiresize.com/tyre-size-calculator/. Using that comparator shows that your 185/70 x 14 tyres are slightly smaller in circumference than the originals and will cause your speedo to over-read by about 4%. Whether you can actually buy the original size now I don't know.
Re: GT V8 original tyre size
Posted: Thu Apr 13, 2023 11:07 am
by Gareth
Bumpa wrote: Tue Apr 11, 2023 9:41 am
The original size tyres, 175 x 14, will be full profile, which means they have the tallest side walls at about 82% of the width. So they would be classed as 175/82 (or 80 is close enough) x 14. There are dozens of tyre comparison sites out there, eg,
https://tiresize.com/tyre-size-calculator/. Using that comparator shows that your 185/70 x 14 tyres are slightly smaller in circumference than the originals and will cause your speedo to over-read by about 4%. Whether you can actually buy the original size now I don't know.
Even Halfords are saying this is an available size (175/80 R14), so any tyre specialist should have a better choice
Re: GT V8 original tyre size
Posted: Thu Apr 13, 2023 2:22 pm
by Bumpa
That's good that those tyres are still available. I said I didn't know because I don't need that size. My car runs on 195/65 x 15.