fuel mileage and tire size

[Execut1ve]

I'm in the fantasy stage of putting bigger tires on my truck. I'm considering the interaction between tire size and fuel mileage. Currently on the truck the tires are about 29" and I would be stepping up to 31's or 33's if I went bigger.

Pros: lower RPM at cruising speed

Cons: tires weigh more and have greater moment of inertia

Not sure: larger tires act like taller gears, so I would probably experience reduced power and acceleration from a stop. unsure how that would influence fuel econ

Anyone else want to weigh in? Any thoughts on what the overall effect on fuel econ would be? Thanks!

[d0sitmatr]

Ive gone through this several times, the larger diameter helps lower RPM, that is true, but you have to temper it with something that isnt going to make your truck work harder to get, and maintain, speed.

my ranger actually gets better mpg now with the slightly smaller tires I put on recently due to the previous tires size making the truck work much harder just to maintain speeds, and I could really feel the truck working a lot harder to get up to speed.
the biggest thing I noticed is going over highway overpasses.
with the previous tires, my truck would down shift 1, sometimes 2 gears. now it doesnt downshift at all.

[Jim-Bob]

You also have to look at the rolling resistance of the tread pattern of your new tires versus the old ones. Are we talking about off road 4x4 tires? If so then you aren't likely to ever get decent fuel mileage out of them. if you are talking about a road tire then you might have a chance at finding a decent FE tire for your truck.

[Execut1ve]

not a full MT tire, but I would like to keep decent AT's on there

[Frank Lee]

I tried bigger tires on my PU and they didn't help. But they were wider and heavier too.

[cfg83]

Execut1ve -

I *wanted* to try the two-size-up from OEM on my SW2. However, whenever I researched the tires, the one-size-up was usually 1 lb more, but the two-size-up was always 3 or 4 more lbs. One-size-up nets me a 2% gain, but two-size-up would have netted me a 4% gain.

It still nags the back of my mind that I haven't done the two-size-up, but the problem with tires (for me) is that you just can't swap 'em out on a whim. Once they're on for me, they're on for 50K+ miles.

CarloSW2

[Execut1ve]

yeah that's exactly my dilemma... that and larger tires aren't cheap Frank can you tell me about your F150? 4wd? reg cab? longbed?

[Frank Lee]

It's there in my garage: '94 F150 5.0 a/t 4x4 x-cab shortbox with a couple minor mods.

[Execut1ve]

having trouble deciphering the slang... a/t = ?
is xcab the one with the full second seat or just the mini seat?
shortbox is 6 1/2 foot bed?

[Frank Lee]