Another tire question, sorry.
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Race Director
Joined: Aug 2000
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Another tire question, sorry.
I tried a search and had no luck. I am running a 255/60/15 tire. I am going to a 17 inch tire. In order to maintain a correct speedo reading, I should run a 255/60/17, yes? Someone posted a while back concerning this same topic, but I couldn't find it with a search. Thanks for repeating the info. :D
Race Director
Joined: Aug 1999
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From: Toronto
Re: Another tire question, sorry. (sd pacecar)
I tried a search and had no luck. I am running a 255/60/15 tire. I am going to a 17 inch tire. In order to maintain a correct speedo reading, I should run a 255/60/17, yes? Someone posted a while back concerning this same topic, but I couldn't find it with a search. Thanks for repeating the info. :D
A 60 aspect ratio for the 17 inch wheel won't do it as it is the same size as the 15 inch tire (both 60% of 255 milimeters or 153 millimeters). Roughly, your 15 inch tire has a diameter of 29 inches (15" + 153mm +153mm) and your 17 inch tire has a diameter of 31 inches. [NOTE: these numbers are actually around 2" shorter when inflated tire is on/under car].
Using that math, you want sidewalls on the 17" to be 2" (or 50.8mm or 25.4mm times 2) shorter. To achieve a 127.4mm sidewall with a 255 tire, your aspect ratio should be 50.
So try 255/50/17 for the similar ride-height/diameter.
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Joined: Feb 2001
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From: All in!
Cruise-In IV Veteran
St. Jude Donor '03-'10
Re: Another tire question, sorry. (SuperFast80)
I tried a search and had no luck. I am running a 255/60/15 tire. I am going to a 17 inch tire. In order to maintain a correct speedo reading, I should run a 255/60/17, yes? Someone posted a while back concerning this same topic, but I couldn't find it with a search. Thanks for repeating the info. :D
My understanding is that you need to keep the diameter of the tire the same so as not to require recalibration of the speedo.
A 60 aspect ratio for the 17 inch wheel won't do it as it is the same size as the 15 inch tire (both 60% of 255 milimeters or 153 millimeters). Roughly, your 15 inch tire has a diameter of 29 inches (15" + 153mm +153mm) and your 17 inch tire has a diameter of 31 inches. [NOTE: these numbers are actually around 2" shorter when inflated tire is on/under car].
Using that math, you want sidewalls on the 17" to be 2" (or 50.8mm or 25.4mm times 2) shorter. To achieve a 127.4mm sidewall with a 255 tire, your aspect ratio should be 50.
So try 255/50/17 for the similar ride-height/diameter.
My understanding is that you need to keep the diameter of the tire the same so as not to require recalibration of the speedo.
A 60 aspect ratio for the 17 inch wheel won't do it as it is the same size as the 15 inch tire (both 60% of 255 milimeters or 153 millimeters). Roughly, your 15 inch tire has a diameter of 29 inches (15" + 153mm +153mm) and your 17 inch tire has a diameter of 31 inches. [NOTE: these numbers are actually around 2" shorter when inflated tire is on/under car].
Using that math, you want sidewalls on the 17" to be 2" (or 50.8mm or 25.4mm times 2) shorter. To achieve a 127.4mm sidewall with a 255 tire, your aspect ratio should be 50.
So try 255/50/17 for the similar ride-height/diameter.
