Help with understanding tire sizes--
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Melting Slicks
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From: TEXASTEXASTEXASTEXAS TEXASTEXASTEXASTEXAS
St. Jude Contributor
Help with understanding tire sizes--
I gotta admit I just don't get what all the numbers mean, exactly. I need a spare for my '78, and thought I'd pick up something cheap at the local used tire shop, but of course I don't expect to find a 255/60R15 to match the tires I have on my car. All I want is one that's the same height/profile so I don't screw up my differential if it's in the back or run into a tree if it's in the front. What tires should I be looking for?
JB
JB
Melting Slicks
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From: Casa Grande AZ
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 3,023
Likes: 2
From: TEXASTEXASTEXASTEXAS TEXASTEXASTEXASTEXAS
St. Jude Contributor
Re: Help with understanding tire sizes-- (lbell101)
Cool, thanks. Anyone know how much of a difference in overall diameter would be safe to run at moderate speed for a relatively short distance?
JB
JB
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From: Plano TX
Re: Help with understanding tire sizes-- (JB)
A 215/70-15 will have almost the same diameter as the 255/60-15 (26.85" vs 27.04). Close enough not to damage the diff.
Here's what the numbers mean:
255: width in millimeters
60: sidewall is 60% of width
15: Rim size in inches.
Here's how to get the diameter:
255*0.60 = 153. This is the height of the sidewall in millimeters.
Next multiply the sidewall by 2 (since there are 2 sidewalls in the diameter of the wheel) = 306 mm.
Convert to inches by dividing by 25.4: 306/25.4 = 12.04"
Add the rim diameter of 15" and you get 27.04".
Here's what the numbers mean:
255: width in millimeters
60: sidewall is 60% of width
15: Rim size in inches.
Here's how to get the diameter:
255*0.60 = 153. This is the height of the sidewall in millimeters.
Next multiply the sidewall by 2 (since there are 2 sidewalls in the diameter of the wheel) = 306 mm.
Convert to inches by dividing by 25.4: 306/25.4 = 12.04"
Add the rim diameter of 15" and you get 27.04".
