[Zoomad75]

Here's my experience with gearing on my Blazer. Note that I havent changed the gearing at all, just tire sizes.

Starting out, 3.73's and 31" tires. Accelerates quite well, but at 70 mph it the poor 350 was buzzing at 2800 rpm.

Next up, same gears but 33" tires to fill the opening better and larger stance. Now 70 mph tach's out a 2600 rpm, but off the line power dips a little. Not much, but you could feel it.

Now I'm running 35" tires with the same 3.73's. RPM's at 70 mph dropped another 100 rpm to 2500. Off the line acceleration is way down and climbing moutain passes on the highway is seriously affected. Sometimes requiring running in second gear just to keep the engine pulling.

My 350 isn't the strongest out there, but I've realized keeping it tuned up helps. After doing plugs/cap/rotor and valve stem seals at Dirtylarrys place this weekend, I realize part of my hill pulling problem was the fact that I had a couple fouled out plugs. A couple of banzi runs in Larry's nieghborhood proved that little 350 still has some power left in it.

Point being, if you are staying with 33" tires, 3.73's is a good balance point. You still have decent off the line acceleration and not winding the engine like crazy at highway speeds. Bigger tires require more leverage to get rolling which is why you need lower gearing (higher numerically) to get them spinning because the larger tire travels further in one revolution than a smaller tire.

I can gain back the acceleration I had before with the 3.73's and 31" tires by running 4.10's with my 35" tires. Highway rpm at 70 would be 50 rpm less than it was with the 31's and 3.73's.