Quote:
Originally Posted by JRMichler
The 235/75R15 tires are 2% oversize, so about 1800 RPM at 55 MPH. My truck has the 3:73 rear end.
I did an informal coasting test after installing the current tires. After increasing the pressure from 33 or 35 PSI to max sidewall of 47 PSI, it coasted much better. They have been at 47 to 52 PSI ever since.
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Interesting, the 2005 Z71 came standard with 265/75R15 which is ~ 6% oversize (diameter) from where you are now and with the same 3:73 ratio. My 265/65R17 tires are just a slight bit smaller than stock for the Z71 and I'm turning about 1825 RPM @ 65 MPH. I'm wondering how my oversize tires really impact MPGs. It seems as though the Colorados & Canyons with the best mileage tend to have the smaller diameter tires, even though this creates a need for higher RPMs at a given speed. Perhaps the increased torque puts the engine at a more efficient load rating?
I was planning on replacing with 245/70R17 once these are done. The tires I'm looking at would reduce my tread width from 9.75" to 8" and would reduce weight by 4 lbs. Diameter change would be negligible. Perhaps a bit of testing is in order.