taller tires lower rpms?

roadrash63 · Nov 6, 2009

hi
ive got a 85 f150 302 4x4 w/ t18 trans 3.75 rear diff
and its turning a lot of rpms going 65 ( base model no tach yet )
i have 28" tires on it now what kind of rpms am i turning now?
and how much of a drop in rpms can i expect with a 31 " tires
thanks!

Skandocious · Nov 6, 2009

Your final gear on the T18 is a 1:1 ratio, so you're turning 2909 rpms at 65mph. With 31" tires you'll turn 2628 rpms.

roadrash63 · Nov 6, 2009

thanks for the info !

thanks for the info !
i really did not want to get into the tranny swap plan
what the red line on a 302 ? 5000?
i just want to be able to cruise on the freeway
what would be the rpm drop with a 5 speed ?
seems to have a sweetspot at 50 now...

Skandocious · Nov 6, 2009

If you were to swap to a 5 speed? Well say you use an M5OD, the final gear ratio on that transmission is 0.8:1

So with 28" tires + the 5-speed M5OD transmission you'd turn 2328 @ 65mph.
....with 31" tires + the 5-speed M5OD transmission you'd turn 2102 @ 65mph.

With your current setup, 3k is a little high to be running for long periods of time but I don't think it'd really damage anything. You would definitely be better off if you had one more gear though.

roadrash63 · Nov 7, 2009

m50d thats the mazda trans?
the only trans that has a good rep around here is the zf but it sounds like overkill for an f150 daily driver/grocery getter..
does the m50d have a granny first ?
thanks

Skandocious · Nov 7, 2009

Yes that is the mazda trans that was offered in this trucks. Not as heavy duty as the ZF but for a regular daily driver that ain't gettin worked too hard, the M5OD should do just fine.

First gear is not quite as low as the ZF. 1st gear in the ZF = 5.72, while 1st in M5OD = 3.90.

5.0Flareside · Nov 7, 2009

yeah the M5OD will do fine if your not hauling big heavy loads or drag racing with it. its a good solid tranny.

roadrash63 · Nov 9, 2009

ty 4 info

thanks
now i got another project for next summer...
just got to find one ..........know what they go for?
can i reuse the flex plate? clutch disc?
flywheel ?

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