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 Author Topic:   GR70X15 equals WHAT? Davewilunregistered posted April 25, 2001 02:50 PM            I am looking for replacement tires for my 1974 Trans Am with GR70X15 tires. What is the equivalent new tire size? 235R7015???If I want to go to a 60 Series tire what size would provide a tire of the same diameter?THANKS IP: Logged Ryanunregistered posted April 25, 2001 03:22 PM            I don't know what size GR70X15 is, but the calculator below should help once you can indeed determine that. http://www.ring-pinion.com/RPMCalculator.html IP: Logged GregZunregistered posted April 26, 2001 11:20 AM            I forget now, the older system of tire ratings for width /aspect ratio used some combination of letters and numbers, didn't they...?! I think yours is a 'G' width, 'R' simply for 'radial' 70 series aspect ratio and of course 15" rim.... I took a quick look at tirerack.com and for the '74 Pontiac 'Firebird' the OE tire is a P225-70R15 -no other Pontiacs listed. I'm sure they could help you with an equivalent to a 'G' series quote:Originally posted by Davewil:I am looking for replacement tires for my 1974 Trans Am with GR70X15 tires. What is the equivalent new tire size? 235R7015???If I want to go to a 60 Series tire what size would provide a tire of the same diameter?THANKS IP: Logged DaveBunregistered posted April 28, 2001 02:50 AM            If I remember correctly I think it is a P205/70r15. G's were 205, H's were 215 and L's were 235.IP: Logged Markunregistered posted May 01, 2001 02:39 PM            The equivalent size to the GR70-15 would be P225/70R15 - almost identical in O.D. but slightly wider O.W. than the 'G'(0.3"). The best match in 60 series would be the P265/60R15 - approx. 0.1" taller in O.D., but about 1.7" wider. You may want to check your wheels, though, the minimum width for the P265 is 7.5". The minimum for the P225 is 6.0". While you are at it, make sure the wheels are radial approved - some early cars with bias tires at OE are not.IP: Logged
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