Bigger Tire Question...

littleblazer

Original poster
Member
Jul 6, 2014
9,265
So I know that 30.5 is the largest we can go stock, so that equates to 265 70r16, most have no issues with this size if I can recall. Now my question is, besides the speed and odometer being off, what else can happen? I tried to ask the dealer how much it would be to get the truck re-calibrated for the slightly larger tires, and they just said no, they won't do it, there will be all sorts of problems. But since it's a 2004 all it needs is to be set up with the tech 2, now my question is, why won't they? Liability I assume? Sheer laziness/stubbornness? But if there is no associated problems once it's calibrated by the tech 2, why shouldn't I? Guess you can just call me curious. :undecided: I want the bigger tires. :rotfl:
 

Purefection

Member
Oct 23, 2014
119
Laziness. You can buy a programmer and do this yourself. Your truck will have a harder time turning bigger tires obviously, and will reduce gas mileage etc. But nothing major. Everyone puts bigger tires on their vehicles. The dealership may just be retarded
 
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Sparky

Member
Dec 4, 2011
12,927
Actually you can't change tire size in the computer on the 2002-2005 trucks anyway. It just isn't possible. They're actually right, if you do attempt to change anything related to it people have had all kinds of problems until it was set back. Even the aftermarket can't get it to tune right.

I have 32s on my 2002 and just live with the speedometer being about 10% slow (actually slightly less than that but 10% is an easy number to adjust for on the fly). Yeah, the odometer is also now 10% off, but at 203k miles I really don't care.

2006-2009 can be tuned for tire changes, but the dealer won't do it either more than likely. Liability reasons. Heck they can't even change your computer if you change rear axle ratios anymore. Last time I tried I took my old car to the dealer as I had swapped in the optional axle designed for that car and the service guy said yeah we can do that, do it fairly often, no problem. A few minutes later he came to me with a perplexed look on his face saying that GM said no. He even argued with them that it is a factory option axle in the car now but they said they won't allow those changes anymore due to liability. Go figure. He was really apologetic and I think was more annoyed than I was lol. So I went to a local speed shop and they had me tuned in just a few minutes.
 
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littleblazer

Original poster
Member
Jul 6, 2014
9,265
Got it. So basically the truck can only be programmed for the two factory tires, and anything outside of that set parameter causes issues. Okay. No other issues besides speed and mileage though? I think I can live with things being a little off for an improved stance. :undecided:
 

Sparky

Member
Dec 4, 2011
12,927
No other issues, nope. Even with a 10% change the shift points really aren't far enough off to be a problem. If you're just going up by 5% it will be even less of a concern.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Vehicle speed is also used in the calculations for the TCCM clutch preload in A4WD mode, but anybody who's been reading my posts for 5-6 years knows - if you use A4WD mode outside of a couple of very rare and specific traction conditions, you're reducing the life of your transfer case.
 
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HARDTRAILZ

Moderator
Nov 18, 2011
49,665
littleblazer said:
But since it's a 2004 all it needs is to be set up with the tech 2, now my question is, why won't they? But if there is no associated problems once it's calibrated by the tech 2, why shouldn't I? Guess you can just call me curious. :undecided: I want the bigger tires. :rotfl:
It can not be done with a Tech 2. If you read that here, let us know so we can remove the wrongful post please.

Purefection said:
Laziness. You can buy a programmer and do this yourself.
Really... How come no one has been able to do this all the years of people adding bigger tires to this platform in the pre-06 variety? What programmer can do this, please enlighten us?

Sparky said:
A... Actually you can't change tire size in the computer on the 2002-2005 trucks anyway. It just isn't possible. They're actually right, if you do attempt to change anything related to it people have had all kinds of problems until it was set back. Even the aftermarket can't get it to tune right.

B... I have 32s on my 2002 and just live with the speedometer being about 10% slow (actually slightly less than that but 10% is an easy number to adjust for on the fly). Yeah, the odometer is also now 10% off, but at 203k miles I really don't care.
A... Bingo. Can't be done correctly.

B... You know it is not a straight 10 percent across the board right? It will be a curve not a straight line. Not enough to worry about and with other vehicles I just found my common mph needs on GPS(40, 55, 70) and mentally noted what the vehicle read at those so I knew my speeds. I am sure you got it handled though, knowing you.

littleblazer said:
Got it. So basically the truck can only be programmed for the two factory tires, and anything outside of that set parameter causes issues. Okay. No other issues besides speed and mileage though? I think I can live with things being a little off for an improved stance. :undecided:
Increased rolling resistance can cause extra wear on bearings. Extra tire weight can cause extra wear on suspension. Neither are a real concern, but they are basic facts. Many go much larger on tires with little to no issues so you will likely be fine. Do keep in mind that any deferred maintenance of those items may appear with your tire change, but are not necessarily attributable to the size change directly.
 

Sparky

Member
Dec 4, 2011
12,927
HARDTRAILZ said:
B... You know it is not a straight 10 percent across the board right? It will be a curve not a straight line. Not enough to worry about and with other vehicles I just found my common mph needs on GPS(40, 55, 70) and mentally noted what the vehicle read at those so I knew my speeds. I am sure you got it handled though, knowing you.
Actually the percentage is a curve. A straight MPH amount would be the straight line. At 20MPH it would be 2 MPH slow, 40 MPH it is 4 MPH slow, 60 MPH is 6 MPH slow. There's the curve.

I've tested that with my GPS. Like I said with my tire size it is a tad under 10% actually but 10% is safe and easy to work with.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
I still did not think it was a straight %. Its miniscule difference but thought it was varied % in graphs and charts I have read.


EDIT-- More like half a bell curve than a straight curve from %
 

littleblazer

Original poster
Member
Jul 6, 2014
9,265
Being a percent, it will be less for a smaller number. According to the converter I found, speed will be 20.75 wjen it says 20 vs 67.xx when it reads 65. Its a curve but it increases per the percent. Not too bad if you ask me. 3700 miles off over 100000 isn't too bad.
 

littleblazer

Original poster
Member
Jul 6, 2014
9,265
So essentially extra wear is minimal especially being the majority of the components on my suspension are brand new, as well as bearings. I just hate my current tires, if the truck downshifts in the rain they break loose. Bringing it to 2500 off a light just spins them. The previous owner used elchepo china tires... they do work though, just not great, as good as the forteras on the envoy that are just about toast, but these still have excellent tread, no grip is all.
 

littleblazer

Original poster
Member
Jul 6, 2014
9,265
HARDTRAILZ said:
It can not be done with a Tech 2. If you read that here, let us know so we can remove the wrongful post please.

Really... How come no one has been able to do this all the years of people adding bigger tires to this platform in the pre-06 variety? What programmer can do this, please enlighten us?

A... Bingo. Can't be done correctly.

B... You know it is not a straight 10 percent across the board right? It will be a curve not a straight line. Not enough to worry about and with other vehicles I just found my common mph needs on GPS(40, 55, 70) and mentally noted what the vehicle read at those so I knew my speeds. I am sure you got it handled though, knowing you.

Increased rolling resistance can cause extra wear on bearings. Extra tire weight can cause extra wear on suspension. Neither are a real concern, but they are basic facts. Many go much larger on tires with little to no issues so you will likely be fine. Do keep in mind that any deferred maintenance of those items may appear with your tire change, but are not necessarily attributable to the size change directly.
I don't recall if it was here or not, but I do recall someone saying that they used to be able to do it with a tech 2. That's all I remember, don't shoot! :hopeless: :rotfl:
 

Grimor

Member
Mar 28, 2013
954
HARDTRAILZ said:
I still did not think it was a straight %. Its miniscule difference but thought it was varied % in graphs and charts I have read.


EDIT-- More like half a bell curve than a straight curve from %
As speedometer speed approaches infinity, the actual speed is infinitely more infinite....
 
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littleblazer

Original poster
Member
Jul 6, 2014
9,265
The_Roadie said:
Probably somebody guessing back on trailvoy. After we all left, all the refuseniks can do is guess, or parrot something back that one of us wrote. No original thought remains there.
It's bad there, I avoid at all costs! Well except when I want to laugh at the ignorance of some of the responses to questions on the new threads. Then I enjoy. :crackup: It's funny, I found out about here from there, I never joined though, saw the g m t n a t i o n . c o m statements and followed. place seemed like a ghost town, didn't want to be a part of that, but here, this is something else, best forum I've ever joined!
 

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