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ok
i have a 79 f150
300 i6
9'' rear
dana 44 front
np435
3.50 gears
right now it runs at high rpms at 70mph.i want a a good highway and all around friendly truck.''good on gas''.
my question is i want to put 33/10.50/15 tires on it and what gearing would be what i'm looking for.
thank you,for any info.
33s with a direct trans and 3.50s will have you running 28 mph per 1000 rpm, or 2316 rpm at 65 mph.
The 33s, being heavier and thus harder to get moving (and harder to stop) along with the increase in tread width and (I assume) an MT tread, will take back any MPG gain you could hope for from the change in overall gear "ratio" due to their larger diameter.
A gear change would be pretty expensive. You could change to an OD trans, but those aren't free either.