After installation of the 285-75-16 on my stock rims I noticed that my mpg has dropped significantly. At 70 mph I was getting 22mpg on the dash readout with the stock tires. Now at the same speed I am at 15mpg. Someone told me something about getting the truck recalibrated to the new tire size. Anyone here know anything about this recalibration or what it might be? http://www.dieselplace.com/forum/smileys/smiley5.gif

You can purchase a programmer that will reprogram your tire size so that you will have a more calculated read out. I would not trust the DIC for your calculations and instead do them by hand. It is close but can still be off sometimes.

Your dash readout is now giving incorrect readings because of the tire size change. Calculate it by hand a few time. I don't have the in-dash computer. I assume my speedo is 8% off and by hand I am getting around 21 mpg with the cruise set at 80 (Attitude corrected) on the interstate. The best way to do it by hand would be to use a GPS to get the exact mileage you have driven between fillups, instead of assuming a percentage.


I took mine to the dealer to get the computer reflashed for the 285's. They made a big deal about not knowing if the tire size was in there and having to charge me whether it was there or not. It was not, and I got charged for a scan. They can do 265's but not 285's. There are programmers that will do it, or I think Superlift makes a little module for just that purpose.Edited by: WYO_DMAX

Your stock wheels are only 6.5 inches wide and I believe 8 inches is the narrowest wheel recommended for 285-75's. Think I would be careful on high speed cornors.

Larger tires will drop mileage even if you adjust the speedometer to read correctly. There is physics behind that that I won't try to explain. I lost about .5 mgp when I went from 245 to 265 and this is all corrected numbers.

Exactly what was posted above - get something to reprogram for tire size and your speedo will be corrected, and the DIC will be somewhat close to accurate but not dead on - to find out for sure though just to the hand calc's. I always find that my DIC will be off -1 to +1 depending on driving conditions

Hey Chuntag95,


I ran 255x85-16 from day one so I do not have any experience with the 245s. I lost about .5 mpg when I went from the 255s to the 315x70-17s. I now have a 15% error which will give me a little more warranty!!! http://www.dieselplace.com/forum/smileys/smiley2.gif


So Chris, why did you loose so much MPG with such a small diameter change??? Must be the Allison!!! http://www.dieselplace.com/forum/smileys/smiley9.gif


MaxRock

With a bigger tire....wouldn't you see less milage put on truck? Bigger tire makes less revolutions.....

With a bigger tire....wouldn't you see less milage put on truck? Bigger tire makes less revolutions.....


correct - i think thats what was mentioned above in reference to more warranty with bigger tires = less mileage on truck if you dont run a programmer to adjust for tire size