[dthomson]

HI guys,

I need your expert help in figuring out what adjustment I need to make to the MPH and MPG readings since I switched from the 245 tires my new LBZ came with to some new 265 Michellins I switch from the old Dodge. The new truck has almost 700 miles on it and will get introduced to towing the 5th wheel on Monday. I'm excited to see how it does. My understanding is that some of the programmers can make the necessary changes to account for the tire size change. Is this true? I will probably wait for a while before doing anything like adding a programmer. Thanks all for the expert help.

 

[chp777]

i would say go with the predator it has the tire settings and other setting you will want. i know you didn't go up to many sizes in tire but it will still mess with the computer calibration by confusing the computer so if you can get a programer soon i would
just my 2 cents
rob

 

[66flh]

You're local dealer can do it for tire sizes up to 285/75r16.Should be free when you remind them you bought a $$$50K truck...

 

[dthomson]

Thanks for the advice. I would still like to know what adjustments I need to make mathmatically to the readings as it might be quite a while unitl I get the programmer.

 

[SixPak]

Thanks for the advice. I would still like to know what adjustments I need to make mathmatically to the readings as it might be quite a while unitl I get the programmer.

With 265's, you'll be travelling 3.86624% farther than you would on 245's.

Just calc your mileage normally and then multiply the result X 1.0386624. That'll give you your corrected mileage. Of course, this is assuming your speedo/odo were accurate before the tire change.

Here's an online tire size calculator that you can compare many tire sizes:

http://www.miata.net/garage/tirecalc.html

 

[dthomson]

Thanks SixPack

 

[RichLockyer]

You're local dealer can do it for tire sizes up to 285/75r16.Should be free when you remind them you bought a $$$50K truck...

They can't adjust the speedo/odo.
They can recalibrate the ABS computer up to 285, but not the speedo.

 

[66flh]

They can't adjust the speedo/odo.
They can recalibrate the ABS computer up to 285, but not the speedo.

Are you sure?The service tech told me the speedo,tranny,brakes were all recalibrated by the reflash.I have no info except for what he told me/showed me.I could swear he showed me about 10 different tire sizes and asked me if I was sure I wanted the 285 size(I had 255's on) because it would throw the speedo off. I explained that they were about the same size...

 

[RichLockyer]

Are you sure?

99% sure, based on other posts here.

 

[SixPak]

They can't adjust the speedo/odo.
They can recalibrate the ABS computer up to 285, but not the speedo.

Seems strange the dealer can't calibrate the speedo for tire size changes, but I can do it with my Predator (up to a certain point, I'm sure). What's up with that?

On my truck, the speedo was reading about 1.5 mph faster than what my GPS indicates (at 70mph GPS). I used my Predator and told it I had 240's instead of 245's and now my speedo matches the GPS within a couple of tenths.

 

[RichLockyer]

If the Tech-2 could adjust the speedo, then anyone who owns one (they are not limited to GM techs) could intentionally program a smaller tire size and give themselves an extended warranty. The Tech-2 is a GM-sourced product.

The Predator, Bullydog, and other programmers are not GM products.
Likewise, they do not allow adjusting of the ABS computer... probably for liability reasons. EFI Live will let you tweak anything (but not on LBZ).

 

[r1_hauler]

They can't adjust the speedo/odo.
They can recalibrate the ABS computer up to 285, but not the speedo.

TechII's can adjust for tire size its just a pain. The deal has to call GM and get them to unlock the section of techII's.