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Changing the 11X20 tires to 12X24.5 tires increased my top speed more than 5 MPH in my 262 powered Crown.
We can now cruise easily at 70 MPH at 1900 RPM. It hasn't made an appreciable difference in the hill climbing ability of fuel mileage.
Your fuel mileage won't change very much regardless of what you do with the rear end ratios. It takes a certain amount of fuel to move the bulk and the weight down the highway and through the air.
What ever you do, install a pyrometer. With a 2-cycle DD you can get a pretty good idea of how hard it is working by the water temp and the oil pressure--high water and low oil means it is time to shift down. With a Cummins, by the time you start to notice those two changes you will most likely have melted down a piston. With a higher speed rear end, you will reach melt down temps much faster.
Good luck and happy trails.
Mark O. |
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