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Old 04-03-2009, 12:17 PM   #7 (permalink)
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According to Tire Guides a 1997 Isuzu Rodeo came with 2 tire sizes - P225/75R16 and P245/70R16 on either a 6" or a 7" rim.

The minimum rim width for a P245/70R16 is 6", so I think Tire Guides has an error and that ALL P245/70R16's came on 7" rims.

The allowable rim width for a P225/75R16 is 6" to 7".

Also, the overall diameter making the switch would drop the effective gear ratio by 3/4% - not a lot, but I don't think the improvment in areo would be greater then the drop in gear ratio.

Plus - everything else being equal - larger tires are slightly more efficient in RR - meaning for the same load and inflation pressure, the RR is lower.

And on top of all of this: The particular tire you put on is going to have WAY more effect than anything discussed above. RR values vary greatly.

And on a last note: If you are in Southern California - DO NOT buy used tires. This is one of the hottest areas of the US. Rubber deteriorates over time and is largely driven by temperature. There are some efforts underway to require California tire retailers - both new and used - to disclose how old the tires are at the time of purchase - AND to outlaw sale of tires older than 6 years.
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