Tire Size Guru and MPG

[Ken1]

My F350 CC 4X4 W/4:10’s came from factory with 245/75R/17/E tires. Could I change to a 265/75R/17/E and improve fuel mileage. With the tire size change what would be my adjusted gear ratio? With this small ratio change I would expect some improvement in MPG. I also understand I would need to have speedometer adjusted to new tire size.

 

[Maxtor]

My F350 CC 4X4 W/4:10’s came from factory with 245/75R/17/E tires. Could I change to a 265/75R/17/E and improve fuel mileage. With the tire size change what would be my adjusted gear ratio? With this small ratio change I would expect some improvement in MPG. I also understand I would need to have speedometer adjusted to new tire size.

245/75r17 tire is 31.46 inches diameter
265/75r17 tire is 32.64 inches diameter
You would have to have 36 inch tires to get the same rpm as a stock truck with 3.73 gears.
The heavier tire would lose some of the mpg gain.

stock 2006 psd 18 inch tire is 275/70r18 equals 33.15 inches diameter.

If your goal is to increase fuel mileage, you might consider going to a 3.73 differential.



fyi

5 spd auto over drive ratio with 4.10 gears is 2.911
5 spd auto over drive ratio with 3.73 gears is 2.64
manual over drive ratio with 3.73 is 2.68

 

[Ken1]

My goad is to improve MPG but at the same time not to limit towing. I was only think in another 18 months I will need to replace tires so with a tire change due could I pick up some MPG. The gear change would limit towing but also would be costly. If diesel stay above $4.00 we all could be looking for 3:08 ~ 3:73's

Thanks

 

[MBRPCrazyford]

no worries here, got 3.55s already