Larger tires

[railbuff]

I am trading in my 2000 Silverado Z71 with 5.3 L engine. for a new 2003 Silverado 2500HD Duramax/Allison. This comes with the stock LT245/75R16E off road tires. My Z71 has the larger LT 265/75R16 which look much better that the 245's. If I change to the Michelin LTX M/S 265/75R16 tire. the rolling radius will increase by a calculated 3.8% which will reduce the engine RPM for a given speed and will also reduce the tractive effort by 3.8%.
There seems to be some difference of opinion as to whether the various computer modules on the truck can be reprogrammed to accept the new tire size. From you experiences:
a) Which modules need to be reprogammed?
b) Will there be an infringement of the GM warranty?
c) What are the advantages and disadvantages of changing tire sizes?
d) Any other comments

Pete Davenport

[DinoMax]

Railbuff, the dealer is capable of reflashing your computer for the 265's, and it will not affect you warranty. If you go any larger, you need an aftermarket programmer like the Predator. I am currently running 315/75/16's on my '02 C/C 4X4, and have re-calibrated with the Predator. Speedo/odo is now spot on :D Any aftermarket upgrades should not affect your warranty, unless the dealer feels the upgrades actually caused the problem. This is a little bit of a gray area, and just depends on your dealer/service writers attitude. Go ahead with the larger tires, the truck will ride/handle a lot better than with the stock 245's. Good luck w/ the new ride, and welcome the Duramax gang :D

[JimWilson]

Originally posted by DinoMax:
Any aftermarket upgrades should not affect your warranty, unless the dealer feels the upgrades actually caused the problem.Actually, they have to be able to prove the modifications caused a problem, otherwise warranty coverage can't be denied.

[afp]

The dealer can ply hardball. Yes, you will eventually win, but it will be a hassle. Many have already been there and done that.

I have 265s on my truck. All the reflash did was correct for the anti-skid. I didn't know it was 3.8% difference in loaded roll-out, but thanks for posting--I won't have to ge measure mine now.

Blaine

[TBC]

There are many posts on this site regarding this issue and the bottom line is this. The dealer cannot reflash for the tire size change. Changing to 265's don't affect anything that I have found on my truck except the speedo error. When calculating fuel mileage I use the 3.8%. The speedo will show less miles that is on the truck which doesn't amount to a lot in the long run. I like the 265's. I have the same tires Raibuff is wanting to install.

Tom

[letsgo]

GM service bullitin, any drive line problems CHECK TIRE SIZE, so you will be up the creek and totally pi$$ed because without the original size tire how can the service dept. road test your truck to original spec. no can do, keep the 245s until your out of warranty.

good luck

[afp]

As has been posted here many times, and as I have personally experienced, there is indeed a reflash for 265s at the dealer. However, it does not correct for speedo error, it only changes the inputs to the anti-skid so it operate properly.

Blaine

[Riverholic]

Just as letsgo said the dealer put out a bulletin on changing tire sizes. My friend is the service manager at my local dealer and he warned me about it. I kept the stock tires in the garage and will save until the warranty runs out. I did upgrade my wheels and tires to 17's and 37's. Good Luck

[Bullseye54]

When I picked my truck up at dealer fri after warranty work I asked the service manager about changing tire sizes.He said no problem but they could only reflash to 265,s.He said it would cost $68 & take about 15 min.This is a small dealership & they are pretty laid back.

[HD-Nate]

Originally posted by letsgo:
GM service bullitin, any drive line problems CHECK TIRE SIZE, so you will be up the creek and totally pi$$ed because without the original size tire how can the service dept. road test your truck to original spec. no can do, keep the 245s until your out of warranty.

good luck After reading about the tire size issues here, I drove out to my dealership which is strictly a GMC Truck dealer. I specifically asked about some of the issues that was being discussed here. I told him that I wanted to go to the 285/75R Bridgestone REVO

[thechevyhdman]

Their is no possible way to adjust speedo, shift points etc, with a TII. The only thing GM can adjust for bigger tires is ABS brakes and that is it. GM wants to cover their own butt. A dealership can call up... I guess it is dealerworld, or VCI, GM can only change your TII inputs if that tire size was originally offered on your truck. Basically all we can change on our truck is to the tire size 215-85-16, that is the only tire size change program GM has for our trucks(dually tire size) Nevermind the fact it should be free because it takes 2 minutes with the T2 I saw it done firsthand. The 65 bucks would be much more worth being put towards a Predator. My own thoughts Bill