2nd Gen Non-Engine/Transmission RPM vs Tire Size

[roadbyte]

I have few questions regarding RPM vs Tire size and MPG.



First after reading the article in the TDR From The Shop Floor about tire size and going to the www.differentials.com site. I still do not fully understand what will happen to the MPG and RPM when I change from the stock tires size.





Tires on the truck: 245/75/16 Michelin LTX MS

Rear gears: 4. 10

Auto:

1998. 5 24 value



Doing the posted speed limit of 70 MPH my RPMs is 2300 the site (differential) computered it to 2220. close enough.



The questions are if I install 285 size tires will this put the truck at highway speeds in the sweet spot for the RPM and will this in theory increase the MPG based on the RPM’s being lower. Or will it lower the MPG based on more rubber that has to be pushed down the road.



Does any one have data on this subject matter.



The other part what type of tire life for the bigger tires compare to the stock ones?



Thank you all

 

[illflem]

Larger tires will give you better mpgs on the highway due to lower rpms but may lower your stop and go mpgs because larger tires take more power to get rolling.

 

[NVR FNSH]

I've had 315/75R16s on my truck since mile 16 so I have before and after mileage comparison. At 2000 RPM I'm going 66 mph according to my GPS - it's an indicated 60-61 mph on the speedometer. The taller (larger diameter) tire - 285 - will take fewer revolutions than the stock tire - 245 - to travel the same distance. For an actual 70mph your engine rpm will be lower with the 285s - probably on the high side of the sweet spot at ~2100 rpm. I'm with illflem on the increased hwy MPG but decreased city MPG.



Brian