Pontiac Owners Club UK

Hi,
My rear tyres are 225/70R14 and measure approx 25" diameter (with wheel jacked off ground), yet the specs suggest these are 26.4" diameter. Where has the ~1.5 inches gone? The tyre is wearing in the middle on the rear tyre also. Am I missing something?
Thanks
Paul

tyres vary greatly in size from make to make

if its weaing in the middle then tyre presures are to high (assuming tyre size is correct for rim width)

Thanks, yes I'm conscious they may be over inflated (havent actually checked!) but seems odd the official diameter states 26.4" yet it measures 25"...

Could it be the tyre is / has been over inflated which has caused side wall to expand, and overall wheel diameter to reduce - could that explain the lower diameter than spec for this tyre? It's cooper cobra radial GT.

no, tyre structures are strong enough not to stretch
the official diameter you state, is that from coopers or general spec?

26.4" is the general spec you see listed for this tyre size. I see the actual Coopers tyre listed as 26.27 inch. That's still over 1" bigger than mine. Mine will have some tread missing, granted, but not 1.27" off the overall diameter surely. The front tyre is a 205/70R14 and the rims look same size, so suspect the rears are squeezed in which may be causing a bulge / wear in the middle. Just seems odd to me why my diameter is less, it's as if I'm missing something. Bottom line is I'll likely go for a 3.08 gear and change the wheels at some point for a fatter set, which may be slightly taller i.e, 26-27", so just want to be careful I dont make the performance underwhelming, but want to future proof it. From what people say, it doesnt appear that will be the case and in fact over driving will be far nicer, with still some serious power under the foot.

I have found with most tyre sizes the quoted dimensions are more of a guide than hard and fast rules