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Discussion Starter #1
I had been getting conflicting reports on whether the LLY computer could be programmed for larger tires...


My GMC dealer connected the Tech II, verified the VIN, and changed the tire setting from 245 to 265. I checked the speedo against my GPS, and the speedo was dead on. A 400 mile trip followed, with everything working perfectly. My RPM's are about 200 or so less with the larger tires. 70mph puts me at about 21-2200.
 

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What kind of tires did you go with and what was your mileage on your 400 mile trip? Better or worse with the larger tires?
Thanks in advance,
LarryEdited by: ldand
 

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Discussion Starter #3
I have Michelin LTX/Load E with "all season" tread as opposed to the AT. The truck came with Bridgstone AT's, which seemed like a decent tire, but I already had the Michelins with only 5000 miles from my previous truck. Just so happened I have a realtive that wanted the 245's.


Hard to say about the mileage since I am only on my 3rd tank of fuel. My first tank with the 245's and 50/50 mixed driving ended up at 15 mpg and 16 mpg on the DIC.
 

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Discussion Starter #5
I believe that the reprogram adjusted everything. My DIC odometer seemed to be consistant with the GPS. In addition, my DIC trip mileage was reading 1mpg better than actual with the stock 245 tires, and the reprogramed 265's.
 

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I am also a new duramax HD owner and had Michelin 265/75/16 LTX MS installed and my stealer told me that the allison transmission picked up the driveline rotations and therfore adjusted the speedometer to be correct. He also stated that since it had a duramax under the hood that "no" tire sizes could be changed. I disagree fully and have heard others talk about getting theirs changed. Any info would be appreciated
 

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Discussion Starter #7
I stood right next to the mechanic (who is a friend of mine) while he programmed the 265 with the Tech II. According to the Tech II, the truck is now programmed for a 256.


Is your speedometer correct? If it is, I would not worry too much about it, especially considering the 265 is not that much taller than the 245.
 

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Sammy, You're right, the speedometer isn't off that far going to the 265's but I don't have the gps to go by and would just as soon have everything as close to factory as possible when it comes to mpg and speed. What type of gps system are you running?
 

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Discussion Starter #9
just using a hand held GPS.
 

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It's like 3% error w/265's ...just forget it and drive it.
 
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