Tire Size/ Fuel Mileage

[383]

Can larger tires improve fuel mileage? I've got an 8.1 Allison with

4.10 gears and with the 245's it's turning about 2000 rpm's at 60 mph.

Would 265's or 285's gear it higher and improve the mileage? Does

anyone know how many rpm's it would turn at 60 mph with 285's?

[D10KEN]

285's behind my 8.1 did not improve mileage. It stayed the same, if not got a little worse. Either that or I'm into the loud pedal more than usual. As far as the RPM's, I've never paid attention.

[Zembonez]

Sadly, about the ONLY way to get better mileage out of an 8.1 with 4.10s is to park it! Driving habits can make a small difference if you go easy.

[davzog]

I put 265x70x17's on my 6.0 HD and mpg went down 1-2 mpg.....you are adding mass and unsprung wieght (the worst kind) and adding friction on the road with a wider tire....it looks great but costs mpg...

[01 HD]

I have the same 8.1 with 4.10 rear and Allison and I can tell you that with 285 75 16 running at 65 It turns 2000 RPM.

[Q101ATFD]

Here are some numbers to consider - note, however, that they are mechanical and include no consideration to friction loss, wind resistance, etc, and that tire revs vary with speed...

 

Gear RPM Speed (245) Speed (285)

1st Gear (3.1000) 2000 13.86400108 14.89177403

2nd Gear (1.8100) 2000 23.74497423 25.50524834

3rd Gear (1.4100) 2000 30.48113713 32.74077979

4th Gear (1.0000) 2000 42.97840335 46.1644995

5th Gear (0.7100) 2000 60.53296247 65.02042183

6th Gear (0.6100) 2000 70.45639894 75.67950738

Reverse (4.4900) 2000 9.572027473 10.28162572

[ws6_guy]

I heard bigger the tire worse the mpg, i'd like to upgrade my 265s to 285s but apparently i'll just drop down lower in the mpg range?

[Q101ATFD]

The only way that bigger tires would hurt mileage is with the wider profile. However, this is minimal compared to the difference in circumference. Imagine for example, if you were to run your truck on skate-board wheels compared to bigfoot tires. The engine will have to run at a higher RPM to get 65 MPH on skateboard wheels than with bigfoot tires. With 245's you'll be running around 2270 RPM at 65 MPH, where with 285's 2110 RPM gets you the same speed. The biggest sacrifice with bigger tires is a loss of torque at the wheel.

[tbyrne]

I run 305/45/22s on my NBS '07 Sierra. Mileage tends to be at least 2 gallons down from what others report. The package is quite a big heavier and the tires are 40mm wider. None of that helps MPG.

[TxTruckMan]

Q101ATFD isn't really correct.

 

First of all, 245 vs 265 vs 285 is the width of your tire's tread in mm, and does nothing to suggest a different tire height. You can have a 285 tire that is shorter or taller than your stock 245s. The second number (aspect ratio) describes the height of the tire with respect to the width.

 

A wider tire will probably have a slightly higher rolling resistance, but the main contributor to worsened mileage is rotational mass - the increased weight of the tire. It'll take more energy to start it rolling, and keep it rolling. It will also take more brake to stop it.

 

If you want taller tires but don't want to sacrifice fuel mileage, then try to stay with a narrower tire width. This will keep rotational mass and rolling resistance lower. Though it doesn't look as cool as the wider tires.

 

Good luck.