Which is better for mileage, tall or short tire?

[MrGoodpliers]

I recently pulled the 18s off my 72 suburban in favor of rallys for ride quality, towing a camper, etc. The tires I have on 8 inch rallys right now are 245/60 front and 255/70 rear. We just took a trip to the Smokies and with the burb loaded down with coolers, firewood, camping gear and the family, towing a pop-up we got over 16 mpg. I was pleasantly surprised. Now my question- I recently had some 9 inch rallys made for the rear and I was wondering if a taller tire would give me better mileage. I could use the 245/60s on the front and a 265/60 or 275/60 onthe rear--- or use the 255/70s on the front and a 275/70 or 285/70 on the rear. What do ya'll think?

[Dingfodgy]

There are alot of factors that can affect MPG, but generally speaking a taller tire will yield better mileage due to the fact that the engine is turning fewer RPM's to maintain the same speed. Of course their are limits to this.....get too tall of a tire and the engine has to work harder to keep the mass moving, which means you start hurting your MPG.

[chevy72blu]

Basically, you can use tire height to compensate for your gear ratio. A little.

Tire height is a very important factor in your overall drive gear, because of how rotational motion works. A tall tire has to rotate at a lower rate than a small tire to maintain the same speed (think of those big roundabouts that you spun on as a kid - the outside most part of it would be haulin arse' when the inside would be rotating visibly much slower). This translates into lower RPMs for a taller tire vs a shorter tire, but there are some trade offs.

If already have a low-rpm rear-end gear ratio, you may have to push the vehicle a lot harder to get it up to speed (using more gas), as well as maintaining speed. I have seen vehicles get better city gas mileage with 4.11's than 3.07's, because they were just bursting from stop-light to stoplight.

What rear end gears and transmission are you running?

[MrGoodpliers]

That is basically the idea that I had, taller tire might be better as long as I didn't put 44s on it. It has about 18k on a rebuilt 350, mild cam, dart s/r heads, edelbrock intake/carb, hei, stock exhaust manifolds. 350th, 3.08 open rear.

[ERASER5]

I like a taller tire myself. I am running 31X10.5X15 on my GMC. I also have the 3.08 gears. I want to go 33s, but I think my engine will struggle at take off. My reasoning was derived from some experience and running dozens of gear/ tire size combos through this handy calculator. Have fun.

http://www.richmondgear.com/streetcalculators.html

[special-K]

If it`s a 4wd then 3.08s is plenty tall of a gear.There`s a point that tall tires will hurt you if you have to keep pushing it to keep it rolling.I have 35s with 4.10s and 4spd.That seems ideal.Figure that`s right about 3.73 at the road.I had a 4spd Blazer w/3.08s and 33s.That seemed ideal,too.So,I guess 3.73s w/35s would be good.This is for traveling light,not hauling.

[Longhorn Man]

in reality, it's normally a moot point becouse very few ppl recalibrate there speedo after a tire swap, they just hold the gas till the speedo says 70 (or what ever) and hold it there. With taller tires you'll be doin 75, shorter, 65 (granted, that's a large difference in tire diameters there)