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Old 05-09-2007, 08:15 AM   #1
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Tire question.. no laughing..

Ok.. so I was using the Tire, Wheel and Suspension package builder on 4wd.com and came across something that confused me. I selected 30" tires and it came back with two responses. 30x9.5 R-15 and 245X75 R-16.. now I know the R-15 and R-16 are the rim size. However, I was under the impression that
"245" meant it was a 24" tire. So does that also mean that "75" and "9.5" are the same thing, just on a different measurement scale?? Oh man.. I really am a new guy! I used to own a stratus and there was no real problem with tires, it was only one size and there was no changing it! lol

A little help w/o making me feel dumb would be great! haha

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Old 05-09-2007, 08:27 AM   #2
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nope you are reading it wrong.. the 245 is the the thread width of the tire while the 75 is the hight of the sidewall.. the 245 is in milimeters.. metric while the 75 is a %

add..
245mm=9.645"
75%= so 9.645 x .75 = sidewall height

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Old 05-09-2007, 08:28 AM   #3
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245 is metric vs the 30" thing.. both are very close in size to each other.. depends on what type of tire, who makes etc. etc.
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Old 05-09-2007, 08:32 AM   #4
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245 is metric vs the 30" thing.. both are very close in size to each other.. depends on what type of tire, who makes etc. etc.
ok.. so in that sense.. a "255" tire would be like a 31"?? Or close to it at least.
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Old 05-09-2007, 08:34 AM   #5
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ok.. so in that sense.. a "255" tire would be like a 31"?? Or close to it at least.
sort of...
one of many out there....
http://www.s-series.org/htm/calc/tiresizeconv.htm
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Old 05-09-2007, 08:39 AM   #6
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Ok.. so currently I have 235x75 R-15's on the jeep.. thats what was on when I bought it.. so those are about 29's according to that site. Alrighty.. I think I'm getting the hang of this! lol
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Old 05-09-2007, 08:53 AM   #7
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a 255mm x 75 would be a 31" but it would be wider also.. (not worrying about the manifacturers smaller tires)

The sidewall height is a combinatio of both not just one number so keep that in mind. let say you have 200mm x 90 vs 300 x 20.. the first one altough its smaller mm its taller tire.. if both are on a same size rims

255mm is tire width 10"
255 x .75 = 191mm or 7.5" per radius so 15" + rim size is the height of the tire
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Old 05-09-2007, 11:10 AM   #8
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ok.. so in that sense.. a "255" tire would be like a 31"?? Or close to it at least.
That depends on the aspect ratio there are different series. A 255 is the tread width and then the other number is the aspect ratio. So if it was only a 50 series on a 16 inch rim it would only be about 26 inches tall. It all depends on rim size, aspect ratio and tread width.
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Old 05-09-2007, 11:15 PM   #9
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...A little help w/o making me feel dumb would be great! haha
That's ok Fondo. It confuses me too! That's the real reason why I stay with a 15" rim, just so I don't have to do the math, not just cause the tires are cheaper.

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