Moderator: volvite
I've been pretty vocal on the forum whenever this topic comes up in a thread. Yes, the on board cpu is basing all calculations on a 265/75/16 (for those with 16" wheels) tire. So, if you run a smaller size, everything will be off in the positive direction, meaning that mpg numbers will look better than they are in reality. However, I can attest the winter crap blend of gas has been killing my mpg this winter. I don't know if they use this special blend country wide, or if only select states.shv2sail wrote:There was some discussion on here regarding the spedo reading "high" by a few mph with stock tires on the truck. I noticed this too as confirmed by my GPS unit. As far as mileage (per the trip computer) I was getting about 20 on the highway on the stock tires. Now, since I've replaced the stock tires with larger 265/75's ATs, I noticed a significant mileage drop (some was to be expected) per the onboard computer.
Yes & yes. I've asked various technicians more than once if the CPU can be reprogrammed for another tire size (in case I go larger), but the answer has always been a resounding "no."So my question is: was the original fuel mileage being calculated by the truck incorrect from the factory since the spedo was incorrect as well? Is the spedo/trip calc/etc setup for larger tires than the stock size, creating an incorrect reading on stock tires??
Mine has 47k. We've been in the 19s on road trips, but no lower. City mileage is 15. Like Steve says, it may be the winter and the different blends of gas. Out here, our temps vary very little.shv2sail wrote:Spedo to GPS on the stock 245's was consistently about 3 mph off at highway speeds (70 on spedo was 67 on GPS)...now is dead on with the 265's. Mileage went from 20-21 to 15-16 on the onboard computer.
Sheesh...08Datusn...20mpg highway on the 265's - I'm lucky if I get 16 since the tire change! It looks like we have the exact same truck...how many miles on your 08? I'm at about 86k...