Axle Ratio, tire size, and final drive ratio ?s


#1

I have a very large Dodge one ton truck that I sometimes have to drive to work. The truck has a 4.10 rear gear ratio, which pulls great, is not gas friendly. I was wondering how tire size might affect the final drive ratio, say if I went with taller tires, or shorter…not sure which will do what. Any ideas? Thanks


#2

Taller tires (greater diameter) will effectively lower your numerical final drive ratio. However, there are other factors involved in fuel economy, so you won’t see a proportional increase. You might even see a decrease.


#3

As a matter of fact, too often the axle ratio “number” is mistakenly looked at seperate from the wheel/tire number. The old Ford 4.11 rear ends made stump pullers of the cars they were in but they had 7.00x15 tires which look miniscule compared to the tires on a late model truck. Engine RPM/road speed is the important ratio.


#4

The small differences that a tire diameter would make (and still fit in the fenderwell) are not worth mentioning. Don’t forget, the speedometer accuracy would also be affected.