Texasplayboy

The other week i put some bigger tires on my truck (275/70/18) so now my speedo and odometer are off. This is causing the readout on my MPG to be lower than it actually is. My question is should i take my truck to the dealership and have them recalibrate my computer for the larger tire size? Can they even do that? I normaly can deal with stuff like this but when im going 55 and reset my MPG it struggles to stay around 16 and i know there is no way that is accurate. it would be around 20ish before and i know one inch bigger tires would not cause that much of a drop in MPG

any input or opinions would be appreciated

RES4CUE

What kind of tires? Mud tires create a heck of a lot of drag compared to the stock street tires. Also did you go wider, wider footprint also means more drag. They could be heavier, there are so many variables that effect it.

skyhawk1

I went through this with my 08 Super Duty. I put 20" wheels & tires on (had 17's from the factory) and it threw my speedo off by about 5 MPH up around 60 MPH and up. I used my GPS to determine this. My fuel mileage dropped also. The bigger tires also threw off the odometer. I took the truck in for a recalibration and they said they would do it but the speedo was still off the same, so I took it back for a re-recalibration and they said there was nothing that they could do for me. I just learned to live with it. Good luck with getting your dealer to re-calibrate your speedo.

09dreamer

I dont think the dealer can do a recalibration. From my understading, the only way to recal is to buy a programmer, which is nice, but will void your warranty.

with 35s, my speedo is only off by 2 to 3 mph compared to my Garmin GPS. I would do a manual calculation of MPG to find out what it really is. I think the computer is off anyway so I wouldnt stress about it, however it is nice to know your range. Mine appears to have already learned, going from about 628 miles per tank to 579 or so. Good luck and let us know what you find.

GATORB8

Give the dealer a call and ask them, they should be able to recalibrate since you can buy the trucks with different size tires on them from the factory and it's a basic OBDII calibration.

The change in speed is proportional to your change in tire diameter, so you can factor it that way. I.E. going from a 30" diameter tire to a 33" is a 10% increase, so you will be going 10% faster than your speedo shows and 10% farther than your odometer shows.

firstfordguy

All you need to do is buy a programmer and calibrate the speedo yourself. Very simple to do. Just need to measure height of tires and enter info into programmer. Done. Although programmer will cost you about $300.00.

GATORB8

Procomp and Hypertech sell speedo calibrators that aren't tuners, but they'll run you $200.

Texasplayboy

Well im waiting for the edge ct to come out. IMO they make the best product on the market. My new tires are only one inch taller but they are the same width as stock. Goodyear Duratracs. Love these tires so far. I will go to the dealer sometime this week and see what they say. Any info and i will post it

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Wow, even stock mine never said 579+ until empty...Best I got was 520,
Now with my 35's it only says 450 until empty after the last fill up.
I always thought my truck was getting lower mileage than what others posted up here though..best I ever got stock on a 300 mile highway drive was 15.9 mpg on the dash computer.....now with the 35's its 11.9.

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I did call a local dealer that said they would reprogram my truck, but they weren't sure if they could program a 35. If they can't, they said they would go as big as they could.
$98 bucks for an hour of labor.
I'm wondering if I should give this a shot or just wait and put the money towards a programmer.