NorthernWoodsman

How's your mpg's and highway top end running the 4.88's and 33's? Where are your rpm's at when your cruising at say 65mph?

I'm about to switch to 33's and I'm trying to decide between 4.56's and 4.88's.

Thanks.

4Crawler

iTrader: (3)

Usually around 18 @65-70, used go get 20+ with the same tires and 5.29 gears. Will go as fast as I care to take the truck, gets a little unstable above 75.

Around 2800-2900 as I recall.

NorthernWoodsman

Cool, thanks for the info.

Any idea why you're getting 18mpg now instead of the 20 you got before?

4Crawler

iTrader: (3)

Those 22REs like to spin fast for best MPG. When I ran those same tires w/ 5.29 gears, the engine was turning like 3100-3200@65. It is more comfortable driving long distances w/ the 4.88s, engine is a lot quieter/smoother vs. it winding out with the 5.29s. That and the higher drive shaft speed with the 5.29s makes any imbalance/vibration a lot worse.

NorthernWoodsman

I'm confused....You used to get better mileage with the 5.29's? That seems counter-intuitive to me. You're saying that running the 4.88's and 33's are netting you less mpg than running the 5.29's and 33's?

4Crawler

iTrader: (3)

Yep. As mentioned, the little 4-cyl engines like to wind up for best economy. W/ 4.88s and 33s, you are running right about at the peak torque RPM @ 65, but hit any sort of grade or head wind and you fall off the bottom of the torque curve, so you end up down shifting a lot. With 5.29s, you have a few hundred RPM to play with at highway speeds.

Granted with a V6 or V8 engine, you are better off running at a lower RPM for better MPG, but with a little 4-banger, they seem to like to run faster RPMs and less throttle opening, vs, lower RPMs and more throttle opening.

NorthernWoodsman

hmmm, interesting. One more question for you. If I want to switch up to 33's and maintain good mpg's and power would I be better off with 4.88's or 4.56's?

Also, if I decide to stay with 31's, should I stay with 4.10's or switch up to 4.56's or 4.88's?

Thanks.

4Crawler

iTrader: (3)

Seems to be best to shoot for a little over stock gearing for best MPG. Just use (new_size/28) x 4.10 to get the approx. stock-like gearing for the new_size tire then round up to the next available ratios. For example (31/28)x4.1 = 4.54, so 4.56 is closest to stock gearing, 4.88 would be a good MPG setup, especially if you might want to some day go to 32" or 33" tires.

NorthernWoodsman

Awesome! I was wondering what the math behind figuring out gearing was. That helps me understand things so much better now. Thanks for all of your help and sorry to hijack the thread. Now, back to our original broadcast.....

Zpd426

I have a 96 t100 4x4 v6 3.4 No lift just raised from tightening the torsion bars. and I also do alot of stuff with the truck loaded up pretty heavy. I used to have 32x10.5x15 on the stock rims i think 8 inch. they fit and didnt rub at all I think that size is really good for street and offroad. i recently went to 33x12.5x15 on 9 inch rims with 3.75 backspacing and i had to hammer in my wheel wells a bit and remove the plastic from wheel well and got rid of the mudflap. After i went to the 33s i noticed a decrease in handling. I have 4.88 gears in my truck and running 32s i was over geared but for towing they were better than my 33s. i noticed a increase in gas mileage after i went to the 33s. the 33s and the 488 gears are a good set up i get about 15 highway i think. towing and fully loaded with a camper(really heavy! over 50lbs in the air bags) i get about 10 or 11 highway. Anyways i would go with the 10.5 over the 9.5.