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hey guys, first post and first duramax. I have owned both powerstroke and cummins, so I am deffantly not new to the diesel stuff. I just traded the cummins in on an LBZ and I was discussing with the floor manager about going bigger tires. He said be careful becasue it could damage the allision. He mention 265's were probably ok, but was unsure on 285's.

I have browsed threw a few photos of some of the sweet trucks you guys own. I think I like the looks of the 285. It seems like there are several folks running them. Anyone have problems?
 

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There was a TSB essentially notifying tech's that if the complaint has to do with the transmission, etc to verify that the truck has 245's on it. If it doesn't, the techs are instructed to tell the customer to put 245's on before any further diagnostics are performed.

If I weren't so lazy, I'd look up the TSB in the old TSB forum. (It's there.)
 

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Commissioner Gordon
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Let get this strait, a slightly larger tire will kill an Allison trans., but a 10000# trailer won't.:cool:
 

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Let get this strait, a slightly larger tire will kill an Allison trans., but a 10000# trailer won't.:cool:
:lol: EXACTLY!!!!
 

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It will not kill an Allison. What a Maroon! The tragic part here is that he (thinks) he is in control being a floor manager, and if he flags your tranny then it could cause you problems down the road with waranty stuff...not that he would be right, but there would be arguing to do...that is for sure. Too bad there are plenty of morons like him out there. If you do upsize, then keep the 245's (I would keep them mounted on POS steel rims if you can get them) around for waranty work
 

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Kill is a little absurd for a description of what could happen.Changing the tires will change the final drive ratio.This will change affect shift points of the Allison TCM calibration.

It wont kill the Allison but it might kill any chances of the dealer service department addressing any driveability concerns unless stock rubber is in place.

Tough call getting a straight answer from the service department or anyone at your dealer unless you have a good relationship with them.

Some dealers are ok and often you will see some dealers selling vehicles used and new with bigger meats.

It's your call,but I would retain stock tires and wheels until you feel the service department out.Most likely you wont even have driveability issues but I would caution against jumping in feet first.
 

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It's kinda hard to believe that bigger tires will trash the allison. The hummer comes with 37" tires on it....I doubt it will hurt the allison. I kept my 245s just in case the dealer gave me a hard time about my tires, but so far they seem to be cool with it anyway. They even asked if I had them try to recalibrate my speedometer. It all depends on the dealer and what problems you might have with the truck down the road.
 

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The only way I could see it hurting it is by causing the trans to slip more. What I mean by this is that you are actually gearing the truck higher. So instead of a 3.73 with 245's, you might have a 3.08 with 285's. When pulling a heavy load, the truck has to work harder to move that weight, and that causes the trans to slip more than is would normally, or more than it was designed to slip. That will create more heat inside and wear clutches and things out faster.
I am not a dealer, nor do I work for one, but that has some logic to it. If you you put really big tires on the truck, you are asking it to do a job it was not designed to do. If you put lower gears back into it, you get that power back and therefore not slip as much.

Lasts month issue of 4 wheeler magazine had an article about putting larger tires on trucks and how, based on the tires overall diameter of the stock tires divided by the OD on the new tires times the gear ratio, you could come up with an affective ratio with the bigger tires. Was sort of interesting.
The example they had was with a 30 inch stock tire going to a 33 inch tire, with a 3.73 stock gear. You would need to drop to a 4.10 to get the same pulling power as the old stock setup.

What you can see by this, is that the larger tires definatly put you at a big disadvantage when it comes to pulling. That in turn makes the trans work harder and slip more trying to move that load a further distance for every revolution. Hope that makes sense.

I wish they would just put lower gears and bigger tires from the get go, and then we wouldn't have all these issues.
 

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I was talking to the owner of the dealership I bought my truck from. He said my truck looks good and I told him the only thing I didn't like about it was the tiny tires. He suggested why I don't get larger ones and I said would it affect the warranty and he said nope not at all.
 

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Discussion Starter #13
The floor manager never said it would void my waranty!!! In fact he is a d-max owner (running 265's and deffantly not stock power) and seems like a stand up guy. I mentioned and-on power mods and he says "no problem, in fact we sell them here!!!" 1 word... COOL! I have delt with SEVERAL dealership with my previouse ford and Dodges, and these guys seem to be way better to deal with!

Anyways I think he was trying to inform me that bigger tires could harm the tranny. As CStone mentioned (and I was unaware until now) that there is a TSB out about bigger tires and drive ability problems. I deffantly see that the Allison could have problems with oversize tires. It appears this tranny relies on feedback from the truck and it's currant conditions. Therefore I think it could effect shift points and in turn be hard on the clutches and bands. With that being said I would think that if you re-calibrate your speedo to the correct tire size, SHOULD eliminate that posibility.

I was just hoping for some feedback. Apparantly it appears bigger is ok! Thanks gents I look forward to all the help in the future.
 

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my dealer said it could affect warranty if a major failure happens, said gm will call your milage fraud due to the speedo being off. he said it happened in the past. gm's way of getting out of paying.
 

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The floor manager never said it would void my waranty!!! In fact he is a d-max owner (running 265's and deffantly not stock power) and seems like a stand up guy. I mentioned and-on power mods and he says "no problem, in fact we sell them here!!!" 1 word... COOL! I have delt with SEVERAL dealership with my previouse ford and Dodges, and these guys seem to be way better to deal with!

Anyways I think he was trying to inform me that bigger tires could harm the tranny. As CStone mentioned (and I was unaware until now) that there is a TSB out about bigger tires and drive ability problems. I deffantly see that the Allison could have problems with oversize tires. It appears this tranny relies on feedback from the truck and it's currant conditions. Therefore I think it could effect shift points and in turn be hard on the clutches and bands. With that being said I would think that if you re-calibrate your speedo to the correct tire size, SHOULD eliminate that posibility.

I was just hoping for some feedback. Apparantly it appears bigger is ok! Thanks gents I look forward to all the help in the future.
No bands in the Allison only gears and clutches.Clutches wont be effected and the TC wont be bothered either.It's all about driveability and shift timing and Od holding while towing.That is what the TSB represents,driveability issues.

Sure that tranny might work a little harder but I have yet to see anyone say crap the bigger tires ..... ;)

There's guys out there running lifts and big meats and stock Allison's.Most dealers wont have a problem with larger tires with in reason.

Just FYI be cautious about dealers selling aftermarket goodies and GM warranties.Just remember dealers are independently owned and operated.It isn't GM sanctioned.
 

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Tell the floor manager he is an idiot. Here in California I know of at least 4 Chevy dealers that install lift kits and larger tires and sell them that way from the dealer. They have no mention of different gears and I assuming if they did the dealer would have definately added that to the list of add ons. I am lucky when I drive to my dealer and see they are selling lifted trucks with bigger tires I know they won't give me a hard time.

Good luck with that dealer on anything you do to your truck. One of the dealers even listed a hypertech programmer on the list of add ons.
 

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I put over 40,000 mi. with 35 in.tall tires on a stock tranny.No tranny problems.Could 285's be harder on the tranny?:muahaha:
 

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The only way I could see it hurting it is by causing the trans to slip more. What I mean by this is that you are actually gearing the truck higher. So instead of a 3.73 with 245's, you might have a 3.08 with 285's. When pulling a heavy load, the truck has to work harder to move that weight, and that causes the trans to slip more than is would normally, or more than it was designed to slip. That will create more heat inside and wear clutches and things out faster.
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That's what T/H is for....to lock the TC so you don't slip the clutches. Yes, it could be a problem when towing near max weight...but I have yet to see a problem. I towed a 24' enclosed trailer with 3 sleds in it through the mountains with no problems without using T/H. I do see what you are saying though. I think it is when you go bigger than 33" tires that it really becomes a problem. Then it forces you to be going faster before the TC locks out on the highway. I'm not too worried about it though since I did keep the 245s for "just in case" the dealer decides they want to become difficult.
 

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I would assume that all dealers would have no problem doing the warranty work because they get paid by GM; however, they could be in some trouble if GM sent a tech. out to verify.

I kept my stock tires for this reason. The only problem is I would have to relax the torsion bars. I would love to put a lift or just a leveling kit on in order to prevent front end damage. The problem is that I would not be able to remove if a warranty issue came up - a catch 22. Anyone else have a plan to handle these issues.

I can't understand why GM did not put a little larger tire on.
 
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