help with argument over 4:10 gears!?

[ammo troop]

My gas miliage actually increased when I switched to 33"s from 31"s, have 3.73 LS..doesn't make sense to me either!

 

[unclemeat]

There are a couple of points that people are not grasping about tire size. First point a larger diameter tire increases the moment of inertia, the weight of the tread is farther out from the center of the wheel. It requires a greater force (torque) to rotate the tire.

Second point, for maximum highway gas mileage you want the most horsepower to be generated for the least fuel to be used. Our Explorer engines generate the most fuel efficient horsepower around 2,500 RPM. The most gas efficient gearing will produce a highway speed of about 60 mph with engine rpm of about 2,500.
Gearing creating higher or lower rpms requires requires more fuel to do the same amount of work.

 

[rfuree11]

but on the highway with that same inertia, youre not accelerating, so its working to your advantage and keeping you from slowing down.

 

[Alec]

But the fact that you're running at a less efficient RPM negates any benefits from the tire inertia. No matter the tire inertia and other factors, the motor is forced to run at "X" RPM and is thus forced to use "Y" amount of fuel.

 

[Alec]

BTW, you also pointed out another problem going with larger wheels and tires: brakes!

 

[Robert]

The best mileage my Explorer ever got under the following conditions:

1) 32" with 4.10 (stock axle) = 20.8 MPG
2) 30" (stock tires) with 4.10 (stock axle) = 20.2 MPG
3) 33" with 4.56 = 18.5 MPG
4) 33" with 4.10 (stock axle) = 17 MPG

 

[Alec]

Hey Robert!

See his results with 33s and 4.10 vs 4.56?