I know this topic has been discussed in lengths in the past but here is the latest as of May/2014, at least from my prospective, and knowledge.
I finally replaced my 245/75R16’s with 265/70R-17’s, which through off my shifting times with the Allison transmission, and the spedo no surprise there.
I read post after post after post about having the dealer re-flash the ECM/Computer on the truck and it will recalibrate things to match the 17’s. I heard everything from its not necessary, the dealer won’t do it, the re-flash only resets the Speedo and DIC (drivers information center) and not the transmission shifting points.
Fast forward too today, my dealer had to call GM to verify that my size tires were in their data base for my truck before they would send the program to have the truck re-flashed. It turns out GM recognized my size tires in their data and sent the program to the dealer/technician, which was downloaded to my truck.
If my new tire size wasn’t in their data base, then the dealer wouldn’t have been able to update my truck.
It turns out that the re-flashing does in fact re-set the transmission shifting points back to the speeds that it use to shift. It also re-sets the DIC to match the new tire size, and in addition, the re-flash of the ECM also will update any updates that GM has generated over the years, so now that’s up to date with all the latest updates.
And MikeL, thanks for all of your imput with your pm's:thumb:, I decided to have the truck re-flashed, really just for a piece of mind!
I finally replaced my 245/75R16’s with 265/70R-17’s, which through off my shifting times with the Allison transmission, and the spedo no surprise there.
I read post after post after post about having the dealer re-flash the ECM/Computer on the truck and it will recalibrate things to match the 17’s. I heard everything from its not necessary, the dealer won’t do it, the re-flash only resets the Speedo and DIC (drivers information center) and not the transmission shifting points.
Fast forward too today, my dealer had to call GM to verify that my size tires were in their data base for my truck before they would send the program to have the truck re-flashed. It turns out GM recognized my size tires in their data and sent the program to the dealer/technician, which was downloaded to my truck.
If my new tire size wasn’t in their data base, then the dealer wouldn’t have been able to update my truck.
It turns out that the re-flashing does in fact re-set the transmission shifting points back to the speeds that it use to shift. It also re-sets the DIC to match the new tire size, and in addition, the re-flash of the ECM also will update any updates that GM has generated over the years, so now that’s up to date with all the latest updates.
And MikeL, thanks for all of your imput with your pm's:thumb:, I decided to have the truck re-flashed, really just for a piece of mind!
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