Can tires DESTROy gas mileage? - Ford Powerstroke Diesel Forum
 
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post #1 of 6 Old 06-13-2011, 08:36 AM Thread Starter
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Can tires DESTROy gas mileage?

I recently swapped from the stock 265/75/16s to 305/70/16s with a much more off road tread design. It appears my mileage has dropped from 14 to below 10. Can a simple tire swap effect mileage this much?
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post #2 of 6 Old 06-13-2011, 08:50 AM
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You went fatter and taller. Your odometer is not calibrated for those new tires, so that coupled with the different tire design, will yield mileage reports you're not expecting. Are the tire pressures the same? Are the load ratings the same for the old and new tires?


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post #3 of 6 Old 06-13-2011, 08:56 AM Thread Starter
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Understood on the size difference... The 265's were mounted on a 16x10 rim which actually makes them rotate 6% faster than the speedo is calibrated for, as the ballooning of the side walls pulls the tire closer to the wheel. Moving up to the new tires put me back at exact calibration (verified with GPS). Its possible that the previous owner modified the calibration

I know that the pressure and ratings are also different with the new tires, but i didnt expect such a substantial impact to mileage. I'll check the pressure this afternoon.
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post #4 of 6 Old 06-13-2011, 09:06 AM
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Thr off road tread will add along with the taller/wider tire will add rolling resistance. Your mileage will suffer some, but I don't think 4 mpg worth. I would think trucks speedo is out of calibration also

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post #5 of 6 Old 06-13-2011, 09:10 AM
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Check you pressure, and your load rating. Seams you are on speedometer.

Broader, taller, more aggressive tires will kill fuel economy. However, if the previous owner did recalibrate the speedo and slap stock tires back on and sell the truck, the 14mpg you were seeing was slightly inflated.

As to a matter of revs per mile you went from the 265's which have a 637rpm, to the 305's which have about 615rpm. This causes a bit of a loss in mileage, both for the added weight of the tires, their wind resistance, and the compression of the sidewall during rotation. Seeing that kinda mileage decrease is not uncommon with the broader tires (since your speedo was off while on stock tires).
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post #6 of 6 Old 06-13-2011, 09:12 AM
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