On average how many MPG did you loose going from the stock tire to 315's. I have 315's on the pickup now and have had them on since just about new. I'm sick of only getting 15.5-16.5 mpg and am wondering if this will make a significant differance. If I'm only going to gain 1mpg I wont do it. But, if it gets me to that 19-20 range I'm all for it. I suppose I should mention the tires are 315 BFG MT's.

 

I lost anywhere from 3.5-to 4 mpg when I went to the Toyo 35" MT. Needless to say that setup was gone in under 800 miles.

It has been my experience that many people will claim to get better mileage with big tires, but I seriously doubt that based on what I have experienced. I think a lot of that stems from not getting the speedo recalibrated.
FWIW I went down to 33's and my mileage is pretty close to stock. I have mud tires so I'm sure the rolling resistance doesn't help mileage but it's a fair trade off IMO. My truck would get stuck in wet grass w/ both the stock tire and Nitto Terra Graplers. At least with mud tires my truck will now perform slighty better than a Honda civic offroad.

 

On my 03 I lost about 1 mpg city and highway mileage stayed about the same....

 

On mine, like above, when I went from the stock 265s to BFG 315s I lost 1-1.5mpg city driving and my highway mpg stayed about the same.

 

Are you going by actual calculations or by the overhead console? If it's the console you are likely getting better mileage than you think since the computer is not calibrated to your size tires.

I had 315s but had vibration issues we couldn't resolve so I went down to 285s. I'm much happier with the overall look with the stock wheels and my mileage from a recent 700 mile roundtrip was 20.2 mpg.

 

Mine was always hand calculated and I did have the pinion factor reset. Mileage also stayed the same when I went back to 285s.......

 

Never checked in town, but highway mileage went from 17 to 19 when I went UP to the 315s. Depends how fast you drive though. At 75mph I am still under 2k rpms, with stock tires that was well over 2k rpms and that is what kills the highway mpg.

The MT is hurting at least as much as the size.

 

The wider the tire is the more rolling resistance it has. The type of tread has a lot to do with rolling resistance. Deep and open tread will hurt fuel economy. I lost about 1 mpg going from stock to 33" pro comp a/ts.

 

Without resetting the pinion factor how did you hand calculate? The pinion factor affects the odometer too.

I lost about 1.5 MPG when I went to the 315s from the stock 265s. Then I went to 285s and got most of that back. For me the 285s are a good compromise.


John

 

I really did not see that much of a change, maybe a loss of 1 mpg. I have the BFG 315 AT KO's, not the wider 35" BFG's. That kept the tire width closer to stock and dropped the rpm's, best of both worlds. I also changed the pinion factor, so both my hand calculations and the overhead now agree. I got about 17-18 mpg stock and am still getting the same. When I had my Quad STD box set on #2 I did gain about 2 mpg and saw 19-20 mpg, but I have removed it and sold it, so now I am back to the stock mileage.

CD

 

Your theory is 180 out. If they did recalibrate the speedo, they would show better mileage. If you do not, you are not getting the benefit of the longer distance traveled per revolution of the axle.

 

I have hand calculated my mpg on every tank since new. Always have had pinion factor set to correct tire size when changed.

My overhead is currently around 5.3mpg off actual.

 

I'm now running 285s and they seem to have less rolling resistance than the 33s and are about 1/4" taller.

 

Thanks guys. I'm thinking of ditching the 315's and going to a 285/75 toyo AT. I figure it about an inch shorter, inch narrower, and a tighter tread pattern. All those should equal better fuel economy. Also taking the 2" leveling kit out should help. I'm at a loss because I realy like the way the pickup looks, but I put on about about 3K a month and need the economy more then the looks.

 

I went from my stock 265s to the 285/75 Toyo Open Country ATs which are 33.9" in diameter. My highway mileage went up! I could never travel at 65 mph to keep my revs below 2k, so w/ the stock tires I was always around 2100-2200 or so. Now I am only turning 1900-2000 at the same speeds and my highway mileage went from 17.5 to 18-18.5. That is hand calculated with a corrected speedometer. I was expecting to lose 1-2 mpg due to the added rotating mass, but our motors really burn fuel above 2k RPM.