Just bought an inTune for my 1999 GMC Sierra (first year of the new style with the 5.3). Updated fine and seems to work good. My question is on the tire size - does that ONLY adjust the speedometer to correct speed or does putting in a different tire size also adjust the tune itself? If it adjusts the tune itself for things like shift points or something I'll just reset the speed manually again, if changing the tire size only compensates the speedometer I'll reset it to the stock tire size.
Reasoning - obviously I'm running a non stock tire size. On my truck I upgraded the instrument cluster to one from an Escalade. Couple of reasons - primary is that adds the transmission temp gauge which is nice since I tow things a good bit, secondary is it looks a lot better and the top speed is increased to 120 from 100. That being said I'm running 285 all terrain tires. I had previously manually calibrated the speedo by running down the interstate with the cluster opened up and the speedometer needle removed - then using a GPS on a nice flat empty bit of interstate put the needle back on while running dead on 55mph according to the GPS. This actually works perfect and the speedometer is pretty much dead on.
However - now that I put my tire size in the tune that of course has now made my speedometer wrong again.....
So I need to decide if I should manually reset the needle again or set the tire size back to stock in the tune. If the changed tire size affects the tune and optimizes things based on the input tire size I'll manually reset the needle but if the changed tire size in the tune only changes the indicated speed on the speedo I'll just change the tire size back to stock.Hope this makes sense.... anyways love the inTune so far. Cannot tell much of a difference using the 87 tune so far but I have not had a chance to really drive it much yet. Only other semi performance mods to the truck are Borla cat back duals, and a K&N air filter.
My only other question for now is - I changed the tire size on the 87 tune. if I restore the stock backup tune then put the 87 tune back on, will the 87 tune remember that I had previously changed the tire size? Actually now that I think about it, I think the tuner may have somehow picked up on the fact that my Sierra has an Escalade instrument cluster. When I changed the tire size - it thought I had 20" rims (at least that is what I had to change it from) which was never a stock rim size on a Sierra pickup back in the 1999-2003 years. That was a rim size on a Cadillac Escalade though.... not really sure though but I do remember having to change it from 20" down to 16" for the rim size.
