Stuck on mpg

[Southpole560]

I have gone down in tire size from 35 inch tires to now a 265/70R17 on third gen steelie rims. Even though my final ratio is closer now it seems like I still can't break over 19mpg tank average. My average overall with 35 inch tires was around 18-18.5 and now it seems like my average has gone up just a little to 18.7-18.9. I've been playing around with the timing still on the quad but no matter what timing I'm at it seems like it really doesn't make a difference. I'm at 1870 rpms @ 65mph and that's the speed I drive at most of the time. The only thing I can think of is my rotating mass. The 35's were on 17 inch alluminum rims and these other tires are on the steel ones. I think overall I've only shaved off about 20-30 lbs of rotating mass. Only other thing I can think of is going with the 3rd gen alluminum rims if I can get a good price on them but I still feel like I should be somewhere in the mid 19mpg range with my final ratio. What could I potentially gain with going to a 245/70R17 tire? Any thoughts?

Edited April 6, 2020 by Southpole560

[Mopar1973Man]

I run 2,000 at 66 MPH, 2,500 RPM at 80 MPH. Still pulling good 21 MPG empty.

 

245/75 R16 tires which are 30.5 inch tires and produce final ratio of 3.69:1 to the ground with 3.55 gears. Still even on my camping trip I laid into the power a bit too much and the rear tires came to life with more blue smoke (tire spun loose). Then I'm heading for Lake Fork Idaho tomorrow and moving my best friend from Lake Fork to Donnelly Idaho. This combo has be a towing dream and quick for power, I can get to highway speeds really easy with out a huge amount of EGT's. Yeah I could stomp it to the floor and run the pyrometer up as high as I want but I don't need WOT to get a 8,000 pound RV rolling and 8,000 pound truck moving too.