Tires & ECM reflash ?

[Toddster]

As you guys probably know I installed 33 inch BFG's (Whats left of them) My question is, is there any power advantage to a tire size reflash of the ECM or do you guys do it Just to correct the speedo ? Thanx.

[gun runner]

You don't have to reflash-
I went from a 215 / 85 to a 235 / 85 ; which is about 1 1/2" larger in diameter. The dealer hooked up a Tech 2 and changed the calibration for the speedometer. I believe the Tech 2 lists the actual tire size designation. Your size may not be on the list ?

[Kennedy]

Doug,

All your dealer did was change the ABS programming for tire size. There are no speedo calibrations available as there are currently no rear axle ratio or tire size options.

NOW, with the 4500 and such trucks having potential tire size matches...

[HotShot]

gun runner,

I did same swap 215 to 235. The dealer can only program for the ABS, as John said. Your speedo is about 5% low, so if you think you are doing 75 in a 70 zone you are doing almost 80.

[gun runner]

Hotshot - When I switched tires ,my speedo was 8 mph off. we input the 235/85 size and corrected the speedo by 4 mph. We used the 7.50 x 16 tire diameter , instead of the 235/85 size; My speedo is only off 1 mph.
Maybe my dealer knows something .