i recommend just getting the tool, because then you won't have to pay the dealer when changing tire sizes and gearing ratios and that stuff. and if you later upgrade to 33's or 35's the dealer cannot change the tire size more than a 32" tire, is what the told me. when they were done they also said that my speedo would only be off about 2mph, turns out at highway speeds i'm off about 5-6mph. so if my speedo says 65 it's 70, so i just follow the speed limits now it's not so bad.. but it still throws off your mileage and such

 

I would run a few tanks through it. I am gettin 16.5-17 with a 4-door on 35's and 6" of lift. I have not recalibrated my speedo yet either

 

I have been rolling around on a 2" and 33s for a while and just threw 35s under it. 4" coming this week. My mileage is always 12.8-14.5. I had the dealer set the speedo for 32s, Even if I add in like 6% on my odometer reading I am still under 14mpg usually. I think the larger rotating mass, and the larger gap in the fender wells makes a big difference. BTW I have 4.10s until tomorrow.

 

I recalibrated mine again when I got 35"s with the hypertech. I just filled up this morning and did a long math calculation and I got 18MPG mixed hwy/ city but mostly hwy for my last tank....

recalibrating might keep you out of a ticket too. Most people I know run 5-8 over the speed limit and are usually fine. If you don't recalibrate and you are off with your guestimate of what you are really going you could easily be doing 12mph over on the highway and not know it which in a lot of places will get you a ticket for sure.

 

im in the same ball park bro, i drove home(500miles) yesterday on the highway, i just divded the miles driving(according to the trip meter) by the amount of gas used and was 11.4-13.4 mphdriving highway speeds from 65-72(havent reset spedo since lift/tire change) i didnt buy it for fuel economy but damn

 

Wow, glad to know I am not alone on this. I am trying to be a "better driver" and see how much that helps.

 

Do you have a stick or auto trans? I've been reading this board for a while now it seems as though the auto trans is much more sensitive gas mileage wise to lift, tire and gearing changes. Seems like everyone getting upwards of 18-20 mpg's has a stick and those getting in the lower to mid teens has an auto. I have an auto x unltd bone stock with 3:21's (highway gears), I NEVER go above the speed limit, drive 55mph on the freeway, coast in neutral whenever I can, turn the engine off at red lights, accelerate slowly, etc., and I get about 19 mpg. I can go 440 miles on the 22.5 gallon tank. When I drove "normally" I got 16mpg. Driving like a typical driver would probably give me 14. Driving like a typical driver plus larger tires would probably give me 12.