I am looking at new tires and have another thread going on what type seems to perform best for other people. My question is, what sort of MPG losses woudl I end up with if I went from 245-75-16 to 285-75-16 or 265-75-16? My daily commute is <4miles each way so I already get horible mileage from that due to the fact the truck never warms up. On weekends I often go out to the desert which is 100 to 225 miles away depending on where I go. Also, I have read some threads about large tire sizes and re-calibrating the speedo for shift point reasons. Unless I am off base here, shift points are determined by torque input of the engine vs torque 'load' on the drive axle, not speed, could some one clairify?

Thanks,

 

My odometer/speedometer registered a flat 10% low error when I went from 245's to 285's. I checked everything with GPS after the install. I have a 97' F150 3 door with a cap on the back, 4.6 liter engine, automatic, K&N, and a Flowmaster single 40 series with dual outlet 2.5" pipes.

I get 13.5 MPG(corrected, looks like 12.25 if you use the odometer number)static over the last 7000 miles. What you really need to remember is 70 MPH is really 77 MPH.

Hope that helps. Oh yeah if I remove the cap it drops to 11 MPG(corrected)

 

Well there are some things that can make a difference. For instance, which engine are you running? If you have a V6 I would expect your mileage to decrease by a greater amount than if you had one of the v8s.

You're moving up by quite a bit in one step, so I would say you will notice quite a bit of difference in how much power you "lose"

For instance, my truck had 265's on it when I bought it, and I put on these BFGs a few months later. My next set of tires will probably be 285's, so I doubt I will notice much difference since its only a 1" taller tire.