Just for the sake of discussion......
I ran 49" tall tires on my old 95 F350 PSD. The truck had 4.10:1 gearing in the differential. I could NOT drive the truck 75 MPH in overdrive (5th gear) because the engine simply could not keep momentum. I went from 15 MPG highway with the stock tires (265/75-16) to roughly 5 MPG highway with the 49" tires even though gearing remained the same.
Mathematically speaking, I went from a tire that made 637 rev/mile to a tire that made 413 rev/mile. This is a nearly 35% difference. As far as MPG goes, the difference is nearly the same (33%). The truck would barely get out of it's own way, turned 1200 RPM at 75 MPH in 5th gear, but the mileage decreased significantly.
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Tuning, PCM flashing, and burning chips for 7.3s since 2008. Repairing all aspects of 7.3L Powerstrokes for 25 years.
Eight 7.3L PSDs in the driveway including a 1994 Crown Vic and 1973 F100/2002 F350. Looking for the next victim.
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Thu, May 20th, 2010, 11:35 AM
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