Gearing change question?

[topo4u20]

On my 94 Sierra 4x4 it has factory 3.73 gears. Does anyone hazard a guess as to what fuel mileage increase I could expect if I was to swap in 3.08 gears?

Thanks so much

 

[am92]

Depends on what kind of driving you do...If you do mostly city driving you'll actually lose mileage, but if you do mostly highway driving it willl keep the rpms down to help gas mileage

 

[Blue95]

Much worse in everyway, totally the wrong way to go when re gearing.

TO low of HWY cruise rpm and you will eat through the gas. 3.73's is great for stock size tires.

 

[outalne94z71]

Much worse in everyway, totally the wrong way to go when re gearing.

TO low of HWY cruise rpm and you will eat through the gas. 3.73's is great for stock size tires.

i agree, it would help if he had the right tire size to begin with, a z71 with 3:73 has the tow package and should have 265/75/16 not the 235/85/16 in his sig.

i would suspect his mileage is a little off now beacause chances are the drac was not modded for the tire change

 

[topo4u20]

Thanks for the replies. 235/85/16 are the same height as the 265/75/16 so no speedo change needed and likely are giving better mileage due to less rolling resistance as they are thinner. I was just thinking different gearing might improve mileage as I do not use truck for towing.

i agree, it would help if he had the right tire size to begin with, a z71 with 3:73 has the tow package and should have 265/75/16 not the 235/85/16 in his sig.

i would suspect his mileage is a little off now beacause chances are the drac was not modded for the tire change

 

[outalne94z71]

lowering the gears to 3:08 will cause more resistance and will make it jump in and out of o.d. constantly which will make the mileage worse, you can do little stuff like change to synthetic lubes in the motor,trans and axles and gain a little mileage, other than that theres not much you can do except make sure no brakes are hanging up and alignment is good, if the motor is high mileage then that can cause it to be eating some fuel too.

what kind of mileage are you getting?

 

[topo4u20]

I agree...forgot about the tranny issues. Alright will look at fluids etc. 14mpg highway

lowering the gears to 3:08 will cause more resistance and will make it jump in and out of o.d. constantly which will make the mileage worse, you can do little stuff like change to synthetic lubes in the motor,trans and axles and gain a little mileage, other than that theres not much you can do except make sure no brakes are hanging up and alignment is good, if the motor is high mileage then that can cause it to be eating some fuel too.

what kind of mileage are you getting?

 

[Blue95]

See these engines like to cruise at 2000-2300 RPM on the hwy at 70 so any lower will lug the engine. kick it out of OD alot and MPG will go in the crapper.


You have a 5.0 which is going to get a bit worse then a 5.7, but you could spend a few hundred on a TB spacer, new gasket kit and filters for the Injectors, synthetic fluids for the diffs and T case, do a good tune up and probably be looking at 16 MPG HWY.