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Old 10-23-2006, 12:44 PM   #1
doberman_52
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tire size - 8-17.5LT?

I am working on a 58 GMC Model 150, I need the tire size so I can figure out what size of ring and pinion gears i need, the tires say 8-17.5LT, does that mean sidewall is 8 in, rim size is 17.5 meaning diameter is 31.5?
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Old 10-24-2006, 06:21 AM   #2
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Re: tire size - 8-17.5LT?

An 8R17.5 is 31.8" in diameter. Don't forget to deduce 3% to account for the difference between the physical diameter and the rolling diameter.
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Old 10-24-2006, 08:03 AM   #3
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Re: tire size - 8-17.5LT?

what i the physical diameter and the roling diameter? nut i would take that off of 31.8?
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Old 10-27-2006, 05:53 AM   #4
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Re: tire size - 8-17.5LT?

The physical diameter is what you can actually measure. In this case 31.8".

The rolling diameter is the diameter the tire appears to be rolling, which can't be measured directly - only by counting revolutions over a given distance. In this case we can estimate the rolling diameter = 31.8*0.97 = 30.85"
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Old 10-27-2006, 08:01 AM   #5
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Re: tire size - 8-17.5LT?

I dont think it will mater too much, i tried 30 in and 31 in and 31.8 in in the equation and they were all so close it wont matter
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