Speedometer Correction?

larryf · October 3, 2007

On my 05 1500 Z-71 4X4 I'm changing the tires from 265/70/17 to 285/70/17 and going from a 3.42 to a 4.10 gear ratio. I talked to the local service department today and was told that they could change the computer for the gear change but not the tire change. I really don't want to buy a tuner box just for that. Any suggestions?

Zembonez · October 3, 2007

On my 05 1500 Z-71 4X4 I'm changing the tires from 265/70/17 to 285/70/17 and going from a 3.42 to a 4.10 gear ratio. I talked to the local service department today and was told that they could change the computer for the gear change but not the tire change. I really don't want to buy a tuner box just for that. Any suggestions?

Reprogram for 4.10 gears would at least get you close. Tires are only 3.5% larger. Gear change is much more dramatic... If programmed for the 4.10 gears your speedo would read 60 when you were actually doing 62.1. Not too bad.

Right now you are doing something like 50mph at an indicated 60... and racking up miles on the odometer that you never travelled!

larryf · October 3, 2007

Reprogram for 4.10 gears would at least get you close. Tires are only 3.5% larger. Gear change is much more dramatic... If programmed for the 4.10 gears your speedo would read 60 when you were actually doing 62.1. Not too bad.

Right now you are doing something like 50mph at an indicated 60... and racking up miles on the odometer that you never travelled!

On a tire calculator it shows that after the tire change and gear change to 4.10 the new ratio will be 3.96. That is pretty close. Thanks.

Zembonez · October 3, 2007

It would be great if they could program it for a mythical 3.96 gear. I'm not sure what their limitations are when it comes to reprogramming. They may only have the option of a gear that was actually available...

larryf · October 4, 2007

Now the local dealer is telling me that they can't reprogram for the gear or tire change??? Has anyone had this done by a dealer?

KB06YUKONXL · October 24, 2007

I had my 2002 Suburban reprogrammed by the Dealer for tire size change. But there are only certain selections available that are pre-programmed in the ECM and they select the factory setting. I was going from the factory wheels to Z-71 wheels. Cost: $75 for the programming change. If you are not using a factory stock tire size you are SOL.

chakis24 · October 24, 2007

i upgraded to the same sizes as you are, i didnt think to regear the rearend. but they did fix the speedometer for me. they told me that they didnt have the exact tire size i had, but they had something that was its equivalent.

has anyone had a rear end regeared at the dealer, id definitely be interested. is there anything higher than a 4.10 that could be done? maybe this way if you program say a 4.30 on the stock tires, youd actually be in the 4.20's with the bigger ones?