Reflash for Bigger Tires? Fuel Mileage Impact...

[lawdog1]

I just put 285/75/R17 tires on the truck...3 inches of tire added and I know that has effected the speedo...by about 4 mph at highway speeds using the GPS. Can the dealer reflash the speedo for the new tire size? I have 4.10 gears and the new tires lets me cruise a little faster on the highway which is nice, but my mileage (hand calculated) has dropped, by about 1 MPG on highway and city. Is that mileage change typical from what others have seen with larger tires? Thanks for you thoughts.

 

[EDankievitch]

I had the dealer adjust the computer/ speedo for the 285's I put on my 2012 and now on my 2013. With the 285's the tire size is already in the computer the tec. just has to choose it. any other size they have to d pinion off set calc, figure how many rev's per mile. I found no change in the Mpg's with the 2012 and a slight loss about .25 mpg on the 2013. The 13 has the 3.42 gear set in the rear ends. The 12 had 3.73's But the truck looks so much better with the larger tire. almost worth the loss

 

[6speed]

I am sure you took into consideration that taller tire affected your odometer reading and that caused the mileage to be different. I would wait until you get it recalibrated for the taller tires and then do your fuel math.

 

[lawdog1]

...at first I did not, but then I got my bearings and realized I should be off 6-7% due to tire size, that minimizes the discrepancy but I still may be giving up a little MPG. We will see once I get the speedo and odo right. ...I didn't by this thing for great fuel mileage....but it does sometimes make my wallet whimper...but then I hear that turbo whine and the smiles begin.

 

[NIsaacs]

I just put 285/75/R17 tires on the truck...3 inches of tire added

Were your oem tires 265/70/R17? If so, isn't that more like 1 inch taller, 32" v/s 33"?

Nick

 

[lawdog1]

265/70/17 to 285/75/17, 31.6" v. 33.8" , 638 revolutions vs. 596 revolutions per mile, so a 6-7% change in tire revolutions per mile based on the data I have seen. ....so 2.2 inches not 3 inches of increased height. Respectfully, I am not trying to get into a super technical discussion of the exact tire dimensions, it be what it be, my question was focused on the availability of a reflash or speedo adjustment at the dealership for the new tire size and what others have seen in terms of a mileage penalty to see if what I have experienced with this new tire is normal. I appreciate people's thoughts.

 

[wyosteve]

Maybe I'm too simplistic, but when I went to 285's, rather than go through the time an effort to re-calibrate the speedo, I just mentally add 6% to my speed and miles traveled. After a few times it becomes pretty automatic, i.e. 70 on speedo is really about 75, 40 is about 43, and so on.