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I have MT ATZ 245/70/17 on my vehicle, and at a jeep event on the weekend here in Australia I damaged the side wall and could not get a new tyre (this is not a common size over here). I had the option of getting an original 245/65/17 but someone said if you have different tyres on with QD II you will stuff the diffs in no time at all, so much so that you have to have similar tread wear on both sides. If it is that sensitive it would mean you have to buy 2 tyres if you damage one that is over half worn. Does anyone know if this correct?
 

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I'm not sure about the difference in circumference, but I wouldn't run just one. I would recommend getting at least two and keeping them on the same axle, but I'm sure others will have more insight.
 

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I don't think it will make damage in short time as the difference is not that big.. but if I were you I wont put a different size tire permanently !

Other option is possible to put 265/65/17 which very very close to 245/70/17 in circumference (only 0.19" difference) and the difference in height is negligible too (only 0.3") .. but its wider !
 

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I had a nail in my side wall. I knew not to change just one tire. I wasn't sure about only putting on two. So I got 4 new ones. I was going to need all four tires with in 12 months anyway.
 

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is the spare the same size? if not then it shouldnt be a problem.
 

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I have MT ATZ 245/70/17 on my vehicle, and at a jeep event on the weekend here in Australia I damaged the side wall and could not get a new tyre (this is not a common size over here). I had the option of getting an original 245/65/17 but someone said if you have different tyres on with QD II you will stuff the diffs in no time at all, so much so that you have to have similar tread wear on both sides. If it is that sensitive it would mean you have to buy 2 tyres if you damage one that is over half worn. Does anyone know if this correct?
From the Owner's Manual (note: QDII uses the QTII transfer case):

Quadra-Trac II Operating
Instructions/Precautions — If Equipped
The Quadra-Trac II transfer case is fully automatic in the
normal driving 4 HI mode. The Quadra-Trac II transfer
case provides three mode positions — four wheel drive
high range, neutral, and four wheel drive low range.

This transfer case is fully automatic in the 4 HI mode.
This transfer case divides engine torque almost evenly
with 48 percent of engine torque to the front axle and 52
percent of engine torque to the rear axle. When speed
differences are increased between the front and rear drive
shafts, the transfer case can transmit up to 100 percent of
available engine torque to the front or rear drive shafts.

When additional traction is required, the 4 LOW position
can be used to lock the front and rear driveshafts together
and force the front and rear wheels to rotate at the same
speed. The 4 LOW position is intended for loose, slippery
road surfaces only. Driving in the 4 LOW position on dry
hard surfaced roads may cause increased tire wear and
damage to driveline components.

When operating your vehicle in 4 LOW, the engine speed
is approximately three times that of the 4 HI position at a
given road speed. Take care not to overspeed the engine
and do not exceed 25 mph (40 km/h).

Proper operation of four wheel drive vehicles depends on
tires of equal size, type, and circumference on each
wheel. Any difference will adversely affect shifting and
cause damage to the transfer case.

Because four wheel drive provides improved traction,
there is a tendency to exceed safe turning and stopping
speeds. Do not go faster than road conditions permit.
 

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How do you get that info 5253? Are you typeing all that from the manual?
I assume he did a copy and past out of the PDF version of the manual. There is a link to it somewhere and I guarantee he will find it for you!!!!
 

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Discussion Starter #9
Thanks for that 5253. It would be interesting to know how much leeway there is in the circumference requirement, at what point of tread wear do you need to buy more than one tyre due to ruining one. ie. after 10% wear, 30%, 50%?
 

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I'm not the most knowledgeable on this, but in the QDII there are clutches in the transfer case and both axles that drag all the time. That is why we need those additives in the fluid to prevent the strange noises and premature wear. I doubt there will be a published spec, but the less the difference in tire size, the less difference rotational speed of the drive train, the longer everything will last.
 

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Thanks for that 5253. It would be interesting to know how much leeway there is in the circumference requirement, at what point of tread wear do you need to buy more than one tyre due to ruining one. ie. after 10% wear, 30%, 50%?
For the this type of full time transfer case tyres MUST be of the exact same size and brand ... different brands even in the same size will have a different rolling circumference.

Even with the same brand and size you have to be very carefull mixing with different tread wear. European all wheel drive vehicles normaly recomend no more than 3/32" (2.4mm) difference in tread depth (some actualy say 2/32" or 1.6mm ) ... on the big tires on the Jeep that's what about 20% to 25%

Even though the Commander is a Jeep ... I'd tend stay very close to these recomendations, rather than risk transfer case failure.
 

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I'm thinking about the spare. On mine, the spare is a different wheel, (and I think no TPM but not sure). So it never got rotated in.

Regardless, I still have the original spare with full tread but it is the stock 245/65R17 and I'm running 4 255/75R17's. I had been planning on selling the 'new' spare and getting a used 255/75R17 to have only for emergency to limp in to get a flat fixed but now I'm not sure what to do. Plus, the larger spare won't fit underneath.

So, my cheap lift is turning into a major expense...need another chrome clad wheel, new spare tire, add it to the rotation, and buy a spare tire carrier. Sheesh.
 

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I don't think that the difference between a 255/75 w/new tread and a 255/75 w/almost no tread would be enough of a difference to hurt anything. I think that there is a certain amount of give to the system but not enough to run a 2" smaller tire. My 4 tires on the jeep now are about 3/4 worn and my spare is still new but I would not worry about putting it on if I had a flat.
 

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Yes there's no way you can run that smaller spare ... in low range off road it might OK .. but even at 40 MPH on the hiway it would be causing damage

I never looked underneath there might be a way of increasing space under there for a full size spare?
 

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Yes, the 2.5 inch tire difference will not work for a spare...I've just been rolling the dice for not needing a spare since I put the larger tires on. I think I'll look for hitch mounted spare tire carrier. I know GetLost has them but I can't spend that kind of money right now. I see universal hitch mount spare carriers for about $100. I might do that ...then mount a used 255/75/17 on the current spare wheel and not include it in the rotation.
 

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I can promise that you will have transfer case issues if you do not have tires that are within 1/4" over all circumference(Diameterx3.14). Having tires with the same size, but different brand is an issue. Every tire mfg has different tread wear ratings, carcass rigidity and tread height, even though it is the same size printed on the side of the tire. If you experience engagement issues, etc....Jack up your rig, run a string around your tire, center tread, and then measure that length....x4 make sure they are all within 1/4" you can play with tire pressure to get them closer.

It used to not be such a big deal with the NP231J, manual engagement, nuetral shifts while rolling, etc. Now, with the computer controlled NV245, NV236, NV246, among others, we are seeing 2x the technical calls on these issues. Having non-matching tires will also affect other on-board computer controlled components such as ESP, ABS, etc.

Even though my status here is a newbie, I will be happy to answer any transfer case related questions.
 

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I can promise that you will have transfer case issues if you do not have tires that are within 1/4" over all circumference ...
Thanks for the input! ... I agree fully.
 

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Hey MountainGarage, welcome to the forum.

On another fresh thread, I posted accident photos from a couple days ago. We have an 07 Overland. The right front took all the damage. Broke a steering rod and I think a suspension linkage and the axel is broken. http://www.jeepcommander.com/forums/showthread.php?t=8841

If you wanna take a quick look.

She was slid on/off a flat bed twice before getting to JEEP collision for 3-4 weeks of R&R. In your experience, do you think there could be damage to the rest of the drive train? I asked the collision guys about that but they said they won't know till it's put back together and driven.
 

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Hey MountainGarage, welcome to the forum.

On another fresh thread, I posted accident photos from a couple days ago. We have an 07 Overland. The right front took all the damage. Broke a steering rod and I think a suspension linkage and the axel is broken. http://www.jeepcommander.com/forums/showthread.php?t=8841

If you wanna take a quick look.

She was slid on/off a flat bed twice before getting to JEEP collision for 3-4 weeks of R&R. In your experience, do you think there could be damage to the rest of the drive train? I asked the collision guys about that but they said they won't know till it's put back together and driven.
Oh, you are ok. These are issues that happen over a few days or months of driving with different size tires. limping it off of the trail on 3 wheels wouldn't hurt it either....or in your case, on and off a flat bed would be nothing to worry about.

2 different speeds of axle rotation causing Binding, and Heat causing transfer case chain stretch are the enemies we are fighting with tire pressure/size. So my final answer is No.

As for the accident: There are 2 joints on the front drive shaft to absorb any movement from a lateral axle shift. Transfer case is fine. The fixed front diff, probably absorbed a hit if the FR CV axle collapsed all the way. make sure the front axle mounts are not torn/crushed.


btw- I hate dealing with insurance companies. :icon_redface:
 

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thanks for the heads up...I'll ask the guys about the axle mounts. I'm betting they'll do a pretty thorough job. All these guys have done lately are hail damage cars in the lot from some recent storms. They were fairly 'excited' to do some real work.
 
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