Tires and Mileage variance

[RSlater]

I recently put a fresh set of tires (same size/make as before - BFG A/T315/70/17s) on to prepare for the oncoming snowfall. Just before, on Sept 29th, I recorded 20. 1 mpg hand calculated (vs. 25. 3 according to the habitually lying overhead) while completing my normal commute. But after installing the new tires, it seems that they've adversely dropped my mileage - I'm now seeing about 17. I'm not sure when the "winter blends" of fuel start having an impact, but it seems coincidental with the fresh tires. Anyone else experience something similiar? 3 MPG loss seems a bit high, and I've been consistently added Stanadyne to my tanks after a recent injector "clogging". Could it just be the newness of the treads?

 

[BDaugherty]

Check the air pressure in your new tires and make sure that you are comparing an average and not just a single fillup.

 

[MChrist]

A couple of things... first is that the new, thicker tread will throw off your odometer/speedometer a little. You will actually travel farther than your odometer says you are. And the thicker tread will "give" more, which increases rolling resistance, thereby lowering mpg.

 

[AH64ID]

New tires always get worse mileage than old tires. The tire is heavier, less resistant to air, etc. .

Then the "winter blend" effect is more than just winter blend. . Its cold tires, oil, gear lube, transmissions, cold dense air has more resistance than warm air, idling to warm up. . All of those effects get lumped as "winter blend", where the winter fuel itself is probably the least noticed effect on winter mileage.

 

[RSlater]

I check my air pressures pretty consistently, rotate every 5-6K, and I run 'em @ 50psi. I also check my speedo calibration with any tire change using my GPS, and of course I can tweak the speedo with the Smarty. I read somewhere that rolling resistance does increase with new tires (as mentioned above), but a 3 mpg loss is higher than the 5 - 6% loss I was expecting. I guess the symptoms aren't striking anyone as unusual, so perhaps I should let it go. It's not like I bought the truck to get great mileage - but man, I just achieved 20 mpg! I'm sure others get better, but the way mine is configured, I was happy. Oh well. Thanks for the input guys.

 

[AH64ID]

I check my air pressures pretty consistently, rotate every 5-6K, and I run 'em @ 50psi. I also check my speedo calibration with any tire change using my GPS, and of course I can tweak the speedo with the Smarty. I read somewhere that rolling resistance does increase with new tires (as mentioned above), but a 3 mpg loss is higher than the 5 - 6% loss I was expecting. I guess the symptoms aren't striking anyone as unusual, so perhaps I should let it go. It's not like I bought the truck to get great mileage - but man, I just achieved 20 mpg! I'm sure others get better, but the way mine is configured, I was happy. Oh well. Thanks for the input guys.

I just noticed where you live. . My mileage has been down a point or two lately. . So hard to track with the winter we are having!

 

[RSlater]

My commute is mostly highway, so my results are easy to track (no stoplights for 20 miles!), but there's a significant amount of hills on the way to Wilderness Ranch. With my old tires, I could literally coast all the way from Hilltop to Lucky Peak Dam (about 5 miles). Now, some pedal is needed, so I suspected increased rolling resistance from the new tires. If you're seeing a 1-2 mpg drop (and I did notice you're in the valley), then my circumstances seem normal enough. I love my Mega, but sometimes I miss my 2nd Gen (which got over 20 mpg all the time!)

 

[AH64ID]

I also just noticed that BFG has two different 315/70/17's, On is 64lbs and rolls at 601 rev/mile and the other is 66lbs and rolls at 606 rev/mile. Maybe you had the other one last time. .

I would say that between the rolling resistance, winter, and possibly heavier tire that its not too bad.

 

[Grumpy John 4x4]

milage

Winter fuel is to blame! Always!

 

[cerberusiam]

I check my air pressures pretty consistently, rotate every 5-6K, and I run 'em @ 50psi.

Thats probbaly part of the problem, not enough air. You need at least 70 psi in the fronts to keep the tire rolling decently with the weight, 60 psi in the rear keeps the ride bearable. If the tire is not a 10 ply then the pressure is even more important or they flex too much. Add to that the cool weather and it is what it is.

 

[MChrist]

I had the exact same tire size and brand on my '06, and as I recall the max psi is 50, because it was a load range C I think... When I switched to the 285/70/17 Nitto Dura Grapplers, I could coast forever...

 

[AH64ID]

Thats probbaly part of the problem, not enough air. You need at least 70 psi in the fronts to keep the tire rolling decently with the weight, 60 psi in the rear keeps the ride bearable. If the tire is not a 10 ply then the pressure is even more important or they flex too much. Add to that the cool weather and it is what it is.

I had the exact same tire size and brand on my '06, and as I recall the max psi is 50, because it was a load range C I think... When I switched to the 285/70/17 Nitto Dura Grapplers, I could coast forever...

They are a LRD, but max psi is 50 (usually LRD is 65 and LRC is 50).

 

[cerberusiam]

They are a LRD, but max psi is 50 (usually LRD is 65 and LRC is 50).

That would be even more of a problem on a diesel, 50 psi on a 7-8k truck is unrealistic for optimum rolling resistance. Would be better off with an M/T and 70 psi.