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Alright guys, this is a question about tires for a '91 f150/ 302 with 235/75/15" factory tires. Currently it has 31 x 10.5x15's, and getting approx 12 mpg. I'm looking at going back to factory size tires - all terrains since I use it on the ranch which is mostly sand and loose dirt/rock. I also pull a 3000 lb boat up slippery concrete ramps. How much will going from the 31's down to 235's increase mileage? Can anyone recommend a good tires for around $120 each that will suit my needs? I REALLY dont want to find out that my tires are spinning when I'm on a near verticle ramp on Lake Amistad with a 3k lb boat pulling me down. :help:

I wouldn't imagine they would save you a penny.

All it's effectively going to do is change your overall gear ratio - which might make your truck shift at different RPM points, and maybe make it a bit quicker to 60mph because of it - but if anything, the smaller wheels will make your engine run at higher RPM's at highway speeds, meaning worse gas mileage, not better.
(not to mention - with larger-than-stock tires, currently your speedometer is reading slightly lower than your actual speed - the plus side is your odometer is recording fewer miles than you are actually clocking Going back to stock size would restore this)

I could see skinnier tires possibly helping - decreasing rolling resistance - but that's a "theoretical improvement", in reality I would wonder if the difference would even be noticable. Would you be able to notice 1mpg or 2mpg improvement? You'd notice better improvement by changing your driving habits.

And skinnier tires probably wouldn't help you in the boat dragging you down the ramp scenario.

Realistically... the way to get better gas mileage? Drive a vehicle that gets better gas mileage. There's no way to turn a 5000 pound truck with a 10mpg V8 into a 2000 pound lightweight with a 30mpg 4 banger... or make it behave like one.

Like Geo said you're not going to see a big difference, but going to a skinnier tire will make more of a difference than the small height difference. The biggest difference that most see in mpg is when they go from really tall and wide back to stock or visa versa (like 36x11.50's plus). I went form the stock to a 32 x 10.5 on my old s-10 blazer and it only had a 2-3 mpg difference.

as for worrying about a boat. My Ascender has 245/70/R17's and it pulls my 3800lb boat up a ramp with no problem. Just get SUV tires and you will be fine. Check out tirerack.com and discounttire.com
both are excellent places to find fitment for your truck.

Well, I'm due for new tires anyways, so I think i'll go back with stock and pick up the gas mileage. every little bit helps. Thanks guys.

Just make sure you get something that is HD or Off Road rated (for sidewall strength), then that extra weight of the boat won't even phase the tires and they'll last ya a lil longer (saving you in the long run)

yep, just called about some pirelli scorpion atr's for $108 each. Think I'll go put 'em on tomorrow.

Those will do nicely :)

yeah Id say, and damn you americans(sarcasim) I wihs I could get tires cheap..

bah :)
My dad has a 94 F150 and I found some lug tread tires in stock size for 54 dollars each. Only benefit about working at a shop we get stuff from others at cost. There Aurora tires but heck he doesn't drive that much so they'll probally last untill they dry rot.