Stock 245/75R16 vs 265/75R16 - Montana Owners Club

MacDR50 · 12-01-2008, 07:49 AM

I just purchased a new 2008 Chev 2500HD and want to upgrade the 245's to 265's to get the extra load capacity (3415 vs 3042). I know the 265's are about 1 inch higher and will throw the truck's computer off by about 3.7 %. Has anyone made this change and did you get your computer reprogrammed for the larger tire size?

For those who may be interested, the 2500HD is identical to the 3500 SRW except that it has a two stage spring package instead of three,(I installed Timbrens in the rear) and has a 6.5 inch rim with the 245 tire instead ofa 7 incj rim for the 265. The 3500 SRW has approximately 350# more payload capacity. After the springs the only difference is the tires/wheels.

exav8tr · 12-01-2008, 11:07 AM

Roger, when I had my '05 2500, I put the 265's on but didn't bother with the computer difference. Just compensated for the difference in speed when I drove. BTW: I also had an extra spring added and had air bags also. Traded it in this year for the 3500.

SlickWillie · 12-01-2008, 11:38 AM

I made the change a couple months ago. No problem except the engine fan was a lot more active in hot weather. The 04 LLY Duramax engines are prone to overheat anyway.

I haven't checked my speedometer, but, from reading on Diesel Place, many were more accurate than before. My son's 04 has the LT265 tires now, and his speedometer is about 3 mph slow at 70.

OntMont · 12-01-2008, 11:53 AM

I made that switch when we had our '01 2500HD. At that time, I was able to get the dealer to reprogram the computer to compensate. I think I heard since that they will no longer do that.

ARJ · 12-01-2008, 11:41 PM

I did this years ago and have not had any problems. Speedometer is only about 2 mph slow at 65 and will vary with tire wear anyway.

Also have air bags AND a rear stabilizer bar which improved handling IMO!

OntMont · 12-02-2008, 02:32 AM

BTW, if you have a GPS, it will give you an accurate speed reading regardless of tires or anything else.

Emmel · 12-02-2008, 03:09 PM

Roger, don't forget the spare also. If you have a flat on the rear, the difference in size could do damage to the rear end if driven very far. Same way on the front of a 4x4. Don't run two different sizes on the same axle.

MacDR50 · 12-02-2008, 04:03 PM

Dealer will trade all out at once including spare. They are just checking procedure to adjust computer before we do the switch.

mtheo · 12-02-2008, 06:38 PM

I changed mine out about two years ago. Didn't recalcuate the computer. The speedo runs about 2 to 3 mph low at 65. Other than that no problems, I like the extra capacity. I also added air bags.

mail2us · 12-03-2008, 01:41 AM

Roger,

In all the discussion here on the tires, I forgot to congratulate you on your new truck. We have enjoyed our 2007.5 and hope you and yours have safe journeys. Dennis

dsprik · 12-03-2008, 12:26 PM

Mac, I bought my 2002 2500HD with 265's on it. I switched back to 245's after a lot of debate on this forum. Put Michelin LTX M/S tires on. Pricey, but I have been very happy with the performance of them.

I checked with GM (through my dealership) on reprogramming the computer for the 265's. I was told "GM does not provide, nor do they intend to provide, a reprogram for any tire size other than the 245." They were quite insistent that ONLY 245's be run on that truck. This was in the summer of 2006. With that said, I personally know several RVers and many MOCers that run the 265's and swear by them.

I might be cautious if the truck is still under warranty and it wouldn't hurt to check GM's official position on this at this time. This was strictly my experience.

John, did your mechanic reprogram before 2006? Maybe GM changed their position on this before I asked? All I know is I really hit a wall with GM when I brought up the subject. My dealership checked with GM for me and that was the reply they got.

*On Edit~ Also, Mac, I might add that when my 2002 GMC 2500HD is level with the Airlift air bags and the 245 Michelins, the nose of my 2007 3400RL is already slightly elevated going down the road. I'm not sure I would want more height on my suspension.

MacDR50 · 12-04-2008, 08:14 AM

Well I took the plunge and got the Dunlop Rover RVxt tires 265's. The dealer will reprogram the computer and says no problem with either my new vehicle warranty or road hazard warranty on the tires. I believe, but won't be sure that, even with the Timbrens, I will have enough squat to level the box when towing. I now am embarking on the hitch search adventure. One of the best prices I have found was an 18k Reese double pivot on a square tube slider with under box mounts. For the next few years I will only be towing occasionally so didn't feel the need to go with an auto-slider. The DW is still digesting the price of the TV and I don't want to press my luck.

Clyde n Deb · 12-05-2008, 02:43 AM

Anyone that has a Tech2 scanner can reprogram this as well. It's the scan tool setup by GM to work on these vehicles. Has computer flash upgrades in it as well if the owner is keeping it updated.

mtheo · 12-05-2008, 04:20 AM

Roger
You didn't state if your TV is 2x4 or 4x4. Mine is 2x4, I went to Chevy and bought 2" lowering shackles for the rear. Easy install and the truck runs level when empty, with no lost in load carrying capacity. I did install air bags to level the TV and Monty after hooking up.
They also had 1" lowering shackles, only 4 bolts to change them.
Good Luck
Mark

MacDR50 · 12-05-2008, 03:16 PM

4X4 but I am not sure I can lower with the Timbrens installed.

berridge · 12-11-2008, 07:19 AM

A good source for checking tire specs and prices is tirerack.com. For example I was able to find that replacing the 235/85 tires on my 04 Ford with 265/75 tires would not be a problem as the specs showed almost the exact same revs per mile for both sizes. I bought Firestone Transforce tires (265/75) to take advantage of the 3415 lb rating. The original 235 size tires have a load rating of just over 3000 lbs.

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