Had new 285/70-17 tires on 17x 9 rims talked to the local dealer about having the speedometer set for my new tire size and he told me I could lose up to 3 miles a gallon on my truck. Said he changed his 04 screw from size 17's to 18's and when he made the computer change he lost miles has this happened to anyone?

 

We need some more info than that to help you. Are you replacing the rims with stock ones, chrome ones, alloy, ect. Most any time you add weight to the rims and tire set-up mpg will suffer but not too bad.

 

The Rims I had put on are 17 x 9 chrome with 285/70-17 tires . I know I will Lose some mpg with the new size but he told me if I recalabrate the computer for the tire size I could lose alot more mpg's

 

Ok, first, you not going to notice a difference in Mileage. My truck comes with 275-60-18 tires, so your tires are not enough bigger to decrease your mileage. My dad went from stock tires on his diesel to 38's with a 6 and a half lift, he lost only around 20 miles to a tank. Also, if you don't recalibrate your odometer for the bigger tires, your odometer will read less miles than you actually drove so the guy at Ford doesn't know what he is talking about.

 

I would say find a new dealer that knows what he is talking about. If you are wanting to recalibrate then buy one of the programmers like the Edge or Xcal2.

 

I strongly agree with above, find a dealer thats not blowing smoke up your a$$. He's obviously full of crap, and your probably much better off getting a tuner (XCal II or Edge will both let you change tire sizes), especially since you'll probably have to pay the dealership some kind of programming fee to get things recalibrated anyway.

 

The larger diameter tire and wheel combo will always reduce you mpg. Especially around town and towing. What you are doing is changing your final drive ratio. How much torque and mpg you loose will depend on you gear ratio, and stock tire size.

You can also install new gears to off set the larger tires. That way you have the bigger tires and get to keep your off the line throttle response as well as towing capacity.

Get a tuner and do it yourself. You'll like the better throttle response and acceleration with a tuner anyway. And if you can keep your foot out of it, you can even increase your mpg with a good tuner.

Good luck.

 

ya i just got the 2.5 as and put 33s on 20" chrome and barely notice a difference. The guy who put on my wheels and leveling kit said it would mess up the spedometer a little at the higher speeds, but around town it would be fine. I would not worry about lonsing massive amounts of mpgs

 

Besides, the dealer can't reprogram the instrument cluster for a tire size that wasn't offered as an option from the factory. They might be able to get you close depending on how tall that tire is compared to an available factory offering.

 

I think the dealer doesn't know what he is talking about. That size is only about 1/2" taller than the stock 275/65-18's that are on my truck. A significantly taller tire will hurt overall power but, if not much heavier than stock, should increase your mileage on the hi-way. It's like over-drive. I doubt you will see much difference in anything with that size tire.