Tire Size Computer Flash?

[Lt .59]

Just like a lot of others, I've went from 245s to 265s and my mileage sucks. Does anyone know if there is a computer flash available to compensate for this change? The dealers can only make the change for the ABS or at least that's the way it was some time ago. Now that they're coming out with a SRW 3500 am hoping that my computer can be flashed for the tire change. Any ideas would be appreciated.
- DW

[afp]

Changing to 265s should not make your mileage suck. With 265s and 90 HP Juice, I got a best of 21.6 mpg on the freeway, and would routinely get over 20. In town was 14.5.

Blaine

[JimWilson]

Unless you compensate for the difference in your odometer reading between indicated and actual miles you're not making the correct calculation. With larger tires you should be adding about 3%-4% to your total miles before trying to determine your mileage.

Westers can custom tune a new PCM that will take care of your tire size issues. It can also give you better mileage and performance, on regular gas even. Check them out at Westers (http://www.ecmprogrammer.com)

[DinoMax]

Lt .59, another thing to consider is getting a programmer, such as the Predator, to calibrate for tire/wheel size changes. Not only will it correct your speedo/odo, it offers a load of other features
(HP/Torque gains, scan tool, engine data monitoring, etc.), and you can return to stock settings w/ ease. Good Luck, DinoMax :D :D

[airtime]

LT,
ANY gm dealer can re-calibrate your truck for that tire size! Most will do it for free, if you talk nice and act cool. I had mine done. Don't let them tell you they can't, They should be able to program them (computers) at least to a 31" tire. Hope this helps,
AT

[chrisinkanata]

Noticed the same thing with the loss of mileage. Really sucks, but the truck looks WAY better so I'll live with it.

Interesting point though about the speedo. I have access to Laser speed testing equipment and checked my speedo after the change from 245 to 265. Speedo is dead on now, with the 265's and no change to the programming that reads them as the stock 245's. Never did check it with the 245's but obviously it is incorrect.

Chris

[DinoMax]

airtime, the only thing the dealer can do with a computer reflash is recalculate for the ABS. It allows the ABS to function normally with the new tire size, but does NOTHING for your speedo or odo calibration. DinoMax

[airtime]

Dinomax,
I took mine to a dealer 2 miles from where I got the 6" lift and 315's put on and he said "No problem, pull it in the door." It took him about 10 minutes, but however, he said he couldn't go all the way to 35's, 31 inch tires were the highest he could go. I do believe that he changed the speedo, because I had my wife chase me and at 60mph in a good car, she said I was doing 66. Now, going from 245's to 315's will decrease your mph by more than 1/10th of a mph. I know I changed my stock 31's on my 84 4x4 to 33's after a 2" lift and it was off by 1/10 of a mph. I may be wrong, but I also noticed the shift pattern changed. That may also be because of the increased load on the truck. They liked the look of the truck so much that they didn't charge me. Now that you mention it, what does flashing the abs do? Someone pulled out in front of me 2 days after putting the lift and tires on and when I swerved to stop from killing him, the tires barked like they locked up, but I got no feedback in the pedal from the abs, they also left some rubber in the street, but I thought that that was just because they were still new. Let me know, I may need to take it back to GM.
later,
AT-

[DinoMax]

airtime, I also have a 6" lift & 315's. I was told by a GM dealer, and have heard the same many times here on TDP, that when a GM dealer reflashes your computer for tire size changes, it only affects the ABS calculations. When you hit the brakes, the computer takes into affect many variables, including your tire size, vehicle speed, etc., before adjusting brake pressure to each wheel. If you are running a different size than what the computer recognizes, your ABS cannot function properly. It is basing the calculations on the data that is has. If your actual tire revolutions per minute, actual vehicle speed, etc., are off somewhat, the computer makes an incorrect calculation for the ABS system, and you experience one or more wheels locking up. The only way that I know to reflash the computer w/ ALL the correct data, is w/ a programmer such as the Predator. I think the reason the dealer can't (or won't) reflash for the speedo/odo is simply liability. They do not want a lawsuit from someone in a truck that has been modified that far from stock. Check w/ your dealer again, and ask specifically if the reflash he performed on your truck included speedo/odo correction. I am anxious to see what he says, because I have heard different so far. Thanks, DinoMax :D :D