Reduction In Mileage Tire Change 245 To 265

rat454 · October 19, 2011

I recently replaced my OEM tires general ameritrac 245/70/17. I hated how puny they looked so I wanted a little larger tire. I put some continental crosscontact lx 265/70/17 on it and since have seen my mileage go south. I made a 200 mile trip with the oems and the DIC showed 22 mpg. I made the same trip at the same speed with similar atmosperic conditions and barely got 18 mpg. I made no other changes to the truck beside the tires and run the same pressure ~45 psi. Has anyone else experienced a reduction in mileage when going from 245s to 265s?

txab · October 19, 2011

Have you recalibrated the speedo/odo for the size change?

Ryan00TJ · October 20, 2011

Sounds right. New tires are taller, wider and heavier. I am replacing my LT245/70/17's here soon with LT275/70/17's and I expect a 2-3mpg loss overall. I'm going to send Justin @ Blackbear my modules and have him adjust them for the larger tire size though so I can get an accurate comparison.

Wires · October 20, 2011

Keep in mind if they are stickier than OEM, you get more drag and less MPG as well.

What you are experiencing sounds normal....

October 27, 2011

its normal

any chage in tire size result reduction mileage

in this case u change the power transmission ratio

big tires need more power to starting up and acceleration

wavery · October 28, 2011

I'm glad that you posted this. I was just getting ready to do the same thing....... may re-think it....

Mckenzie · October 28, 2011

That's still good! Try going to a 285/75/16(a 33 inch tire) and well see how happy you are then

00Silverado4x4 · October 28, 2011

All right, total change of thought, but what kind of tire/truck set up do you have? I only ask but you state you are running ~45psi in your tires? I ask because in the standard half ton with standard tires (non LTs) your pressure should only be around 35psi. So if your running extra pressure on standard tires, that's not doing you any favors either. Of course if your running LT tires (wish I could have found some for a decent price) then my question is irrelevent & read above posts, reprogram for tire size change, & bigger/heavier tires, less MPG. I personally would gladly take the hit on MPG if I could have found a LT tire for my truck that wasn't astronomically priced in my area.

LURCH HD · October 28, 2011

The OP didn't reply about having the speed-o recalibrated. I bet he didn't!!!!!!!

elcamino · October 28, 2011

The problem with changing tire sizes is that the PCM does not know you changed tire size and it still operating with the assumption the OEM size are on the vehicle. This can throw off when the transmission up-shifts/downshifts, when over-drive kicks in, when the torque converter locks. This can cause the engine to work harder because it no longer is operating within the designed torque range that the PCM is programmed with.

Also, when you go bigger, the tires get wider causing more rolling resistance (pavement friction), drag (pushing air) and more un-sprung weight, all detrimental to fuel economy.

[email protected] · November 17, 2011

You will regain some of the perceived MPG loss when you reprogram your spedo. Right now your truck is going further with every tire rotation than it thinks it is. You'll still burn the same Gal. but your odometer will have bigger numbers.

wavery · November 20, 2011

You will regain some of the perceived MPG loss when you reprogram your spedo. Right now your truck is going further with every tire rotation than it thinks it is. You'll still burn the same Gal. but your odometer will have bigger numbers.

Actually, it's the other way round.....your odometer will have smaller numbers but your analysis is correct.

If you drove 300 miles (according to the odometer) and used 15 gal of gas, you think that you got exactly 20MPG...... but you actually went farther than 300 miles (although the odometer read less) so your MPG would be better than you thought.

frdfandc · November 21, 2011

I just installed 285/70/17's to replace the stock 265/70/17's. However I did not correct the speedo (yet). I did a few tests (distances) and found that my odometer is approx .08 (point zero eight) tenths of a mile off. So if I traveled 300 miles according to the odometer, my actual distance is 324 miles.

I got approx 19 mpg cruising 70 mph most of the way.

BTW, I got approx 12 mpg towing 6,000 lbs going down to Charlotte.

Not too shabby.

pm26 · November 22, 2011

When you go from a 245 to a 265 width tire, it is a good idea to go with a slightly smaller aspect ratio (e.g. 65 vs 70) to keep the tire diameter the same. This way you get a wider tire, but of the same height and no speedo correction is necessary. It also will not affect the vehicle gearing. If your new tire is 10% taller than the original tire, you will have effectively changed your gearing by 10%. Just like replacing say 3.42 gears with 3.23 (taller) gears).

The only effect will be slightly higher rolling resistance and heavier wheel/tire.