Question about LLY Duramax Calibration for Tire Size

[Grabs]

Any GM techs out there? Or anyone with some experience trying to reprogram a new LLY Duramax for a tire swap from 245's to Revo 265's?

Working with my saleman, and after two tries the speedo and odometer are still off by 3.9%, exactly the difference in tire height between the stock tires and my new ones. I would like to get this right, but I guess if it can't be done then it can't be done. The thing that gets me is that having an inaccurate speedometer & odometer is illegal and I don't understand how GM can prevent this change from being made to the vehicle?

[Gus]

There is a forum that is something like GM-Trucks dot com or somthing close. Do a search and go there. They will know.

[LMITOUT]

I've always been told that no calibration can be done to correct the speedo error with larger tires, but 265's can be corrected for since that size tires is offered on 1/2 tons.

There are also bulletins out that advise the dealer not to perform service on trucks with the Allison transmission if they come in with non-OEM size tires and complain of tranny problems. I'm surprised your tech is even trying to help. I also have 265's on my Duramax but use a programmer to correct for the error. Adds a little power too.

[Moose-Hunter]

Hey Grabs...

I'm almost certain they (the dealer's techs) can do the re-calibration for you. If memory serves, they need to "manually" program the brain (ECM) to a new "tire revolutions per mile" setting. And with the tire swap you're talking about, it's not that much of a change. Like you said 3.9%....

Have you checked your speedo with GPS? After my tire swap (265's to 285's) my speedo was right one the money. I guess my gauge was off (typical for the powerstokes) before the swap and the added tire height brought it back in...

Just a thought....

------------------
M-H (aka: Dan)

[Grabs]

Thanks for the help guys,...this seems to be a recent change of events for GM. I found a TSB from GM that states:
*******************************************
Info - Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns #01-03-10-010C - (04/20/2004)

Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns

2001-2004 Chevrolet Silverado Pickup Models

2001-2004 GMC Sierra Pickup Models

with Allison® Automatic Transmission

This bulletin is being revised to add the 2004 model year and additional vehicle/tire sizes. Please discard Corporate Bulletin Number 01-03-10-010B (Section 03 - Suspension).

Proper diagnosis of engine, transmission, speedometer and cruise control concerns must begin with an inspection of tire/wheel size.
• The 2500 series trucks have LT245/75R16E tires as standard equipment.
• The 3500 series trucks with dual rear wheels have LT215/85R16D tires as standard equipment.
• The 3500 series trucks with single rear wheels have LT265/75R16E tires as standard equipment.

A truck that has different tires and wheels will have engine power/performance concerns, transmission shift concerns, speedometer registered speed concerns and cruise control concerns.

Before any diagnosis is performed for these types of concerns, inspect the tires/wheels for the proper tire and wheel combinations.

If a truck is found to have other than the above listed tire sizes, no further diagnosis should be undertaken until the original size tires and wheels are reinstalled on the truck.

The Engine Control Unit (ECM) and Transmission Control Module (TCM) use (RPM) and (VSS) inputs as operational parameters for engine torque, transmission shifting, cruise control operation and speedometer indicated vehicle speed.

Calibrations for different tire/wheel combinations are not available.

Therefore, changing of tire and/or wheel size should not be undertaken by dealerships or truck owners

Reinstalling the proper wheels and tires on the vehicle, prior to performing any type of diagnosis of the truck, would be considered truck owner responsibility and not a warranty repair.
*******************************************
Pretty ****ty if you ask me!

Dingelhoof, your off 1 mph at what speed? Its should off by a certain percentage across the range. I am off ~1 mph at 30 mph and nearly 3 mph at 70. Bascially 3.9% across the curve.

At this rate I get an extra 1400 miles in my warranty period, but that doesn't matter because I drive so many miles (25-30K) in a year any how.

[LMITOUT]

Yep, that's the TSB I was referring too. Sad isn't it?

[Whoaru99]

Grabs,

Yeah, it kind of sucks, but I work for a very large company (not GM) and we have much the same guidelines for troubleshooting performance complaints.

You would not belive the amount of money we have paid out in warranty claims trying to fix something that, in the end, we find out was a customer-induced situation because of changing gears, tire sizes, hydraulic settings, etc.

You have to understand that all specs are written according to the factory configurations so when those are altered, a lot of troubleshooting goes right out the window.

I'm honestly not trying to rain on your parade, but when you figure an hour or two or more (plus parts sometimes) on all the vehicles, it really adds up. You and I know that companies do not just absorb that added cost. They pass it on to you and I.

[hawkeye43]

Grabs send me your email and i will give you a very good HSOforum for your duramax kmader"at"frontiernetdotnet

[This message has been edited by hawkeye43 (edited 06-01-2004).]

[Guest]

I have 285's on my 2002 Chev 2500 HD with the gas 6-liter! Looks really sharp! Kinda tight getting them under the front end, I had to put three cranks on the torsion bar! But thats ok because I carry a plow! They could only calibrate mine tow 265's they claimed they didnt have a code for the 285's! My speedo is off about 1-mph! According to gps!

[Gissert]

Grabs -

That is a bummer.

Sadly, I have had to walk into to dealers with copies of TSB's they were not aware of.

It really chaps the hide after you cough up that kind of $$ for a truck, and then have to help them with continuing education.

I hope you can get this straightened out.

[Grabs]

Hawkeye43, tried your e-mail but didn't work, spelling? try e-mailing me graberc@msoe.edu

I understand the arguements made here, but here is problem with the situation.

#1 The tire swap was done by the dealership prior to taking delivery, heck I didn't even see the truck until I picked it up.

#2 The salesman volunteered to update the ECM for me for the speedo/odometer settings.

#3 This same tire size is stock on 3500 trucks with the same engine and transmission, why can't I put them on a 2500HD?

#4 There was no mention of this TSB until now, heck I found the TSB before the dealership even knew about it! I should have been told about this prior to making the tire change and then been allowed to make the decision for myself based upon the consequences of it.