Just in case no one has given it much consideration, the speedo/odo can be calibrated to be very close with the Star Scan tool when going to 35's or larger.

True, the largest tire that is offered on the tool is a 33 (285/70-17) but you can also play with the gearing to make adjustments.

I recently went from 31's (265/70) to 35's (315/70) and the speedo was way off on the low side. At an indicated 60 on the speedo, the actual speed was 71 via a Garmin GPS.

I did some calculations and had the dealer change the tire size and ratio within the computer to compensate for the 35's.

Again, the largest tire in the computer on 06+ models is a 285 so we set it at that and then looked over the gear ratio's available. The truck has 3.73's installed and I needed to speed up the readings so we told the computer that the truck had 4.10's. At an indicated 60 on the speedo, the actual speed was 62 via the Garmin GPS.

The gear ratios available on the Star Scan range from 3.23, 3.54, 3.73, 3.92, 4.10, 4.32, 4.56. All of these in combination with the tire sizes available will get the speedo adjusted to be fairly accurate.

Hope this helps!

 

thats a good idea, i could have used that a couple weeks ago.....but now i have a smarty

 

thats a great idea! did you try all of the different tire sizes/gear combination to see if there was more accurate combination, or is this the best? what tire sizes are you able to select with star scan?

 

265/70-17 and 285/70-17 are the largest tire sizes that can be selected with Star Scan.

I think it'd be real easy for DC to add larger sizes into the tool but doubt they do it. Bummer!

 

yea are there other tire sizes availble other then the 265 and 285. im wondering if there could be a more accurate combination with smaller tires/higher gear ratios.

I still cant understand why the idiots didnt program in larger tires being that lifing trucks is so popular....

 

i programmed my 06 with the star scan and used a 22 or 24 inch rim size and was only 2 mph off.