Reprogram?

[Bsbalser]

I have a 2014 Silverado. Back during the summer I put a 2.5" level and 1.5" rear and went with 275/70r18 grabber at2. Can my truck be reprogrammed to calibrate tire size and v8/v4 variant? My mpg has diminished horribly 12-12.5 now combined compared to 18-20 before modifications

[Jsdirt]

Any handheld tuner should have a tire size parameter in it. Not sure if that'll help the mileage, unless the trans is shifting strangely.

 

I recall setting that parameter by accident (was either that or rear gearing) and the truck went absolutely haywire. Ran like crap, shifted wrong, and threw a million lights on.

[Doug_Scott]

Looks like tire size change is about 5%. That will alter your odometer/speedometer about 5% as well. Your speedometer will be 5% slow, which means 60mph on the speedo will be about 63mph in real time. You may want to take one of your new wheel/tire combinations and compare the weight to the original wheel/tire combination to see how much heavier the larger setup is. It actually makes a huge difference in performance, much more than you would think.

 

The dealer can change the tire size setting in the ECM, provided the tire size you are using is available as a factory option. Aftermarket tuners can make the changes to match what you need. Your mileage numbers have dropped by 33%, that is not possible from just the tire size change. All else being equal, the change I would expect to see would be in the 5% range, and that would be corrected by fixing the speedo calibration. The change in weight is likely making a difference as well.

[tbarn]

All factory option tires are approx. same diameter on '14 and up. No calibrations are available.