Wondering if anyone has installed this so they could actually get a correct MPG drop on running 37s...I understand the MPG calculator is not very accurate according to most people on these trucks.....My question is since the odometer has been corrected on the truck with the hypertech has anyone actually been able to correctly determine the MPG loss of running 37s?.....My trucks lifetime average is 17.4 only because I haven't reset the trip #1.....I hand calculate a lot of my fill ups and consistently get around 18 mpg. That is cruising around 75 and on a zero grade mostly and no towing. The truck has the 6.7L with 3.55s and 20 inch rims right now.....I'm leaning towards staying with 35s and just a level to try to keep the truck getting semi descent MPG but I love the look of 37s on these trucks with a small lift. Let me hear your opinions remember this is only my opinion also. Thanks

 

I have 37's and the hypertech correction. I drive an even mix of highway and craptastic city traffic. I have the 3.55 gears and I had the larger 34" stock tires on the 20" rim. I averaged according the dash about 17.2 mpg with the stock tires, and now on the 37's with 22" rims I average 14.1 mpg.

I know the MPH is correct but I haven't taken the time to verify MPG by hand. I'll do that to see what it comes up with over the next few fill ups.

 

 

I haven't noticed any strange rpm/shifting behavior when driving around town. But I'd have to say I don't know for sure if it's shifting at the correct point or not. Admittedly I don't know if it even uses mph to know when to shift or if it's RPM/Gear based. Something else I now want to find out.

 

I installed the Hypertech Speedo a few months ago. I have 37x13.5x20's on the truck. The Hypertech works as advertised. Gas (diesel) mileage is averaging around 14.8 mpg. No issues whatsoever.