Stock sized spare w/ 265/70's - Jeep Commander Forums: Jeep Commander Forum
Wheels / Tires This section contains discussion about wheels and tires for your Jeep Commander.

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post #1 of 15 (permalink) Old 02-18-2016, 09:33 PM Thread Starter
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Stock sized spare w/ 265/70's

So I'm prepping for installing my RC lift w/265/70-17 Nitto Terra Grapper G2. My concern is keeping the 245/65 (stock size) spare. If I had to put the spare into service, would my Quadra Trac 2 sense the smaller diameter tire's wheel speed as being greater than the 265's & attempt to apply the brake to that wheel with the 245 because it thinks it's slipping (spinning too fast)
Maybe I'm looking too far into it, but I think I know how this 4wd system works.
Thanks in advance for your comments.
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post #2 of 15 (permalink) Old 02-18-2016, 10:21 PM
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I believe that all tires are to be within 2/32 of each other. Someone correct me if I am wrong, cause it is late and I am not going out to get the OM
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post #3 of 15 (permalink) Old 03-19-2016, 10:00 PM
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You need a full size spare. I just shoved one up there flat to make it fit and I disabled tpms so it wouldn't complain.

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post #4 of 15 (permalink) Old 03-20-2016, 07:34 AM Thread Starter
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Can you explain how you disabled the TPMS? (Was it for just the spare?)
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post #5 of 15 (permalink) Old 03-23-2016, 11:29 AM
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I too would like to know exactly how TMPS on the spare was "disabled."

I have the simple TPMS system, that does not identify the location.

I ran the flat spare but would get TMPS low pressure light, so i removed the TPMS sensor. Then every so often (unpredictably) I would get the flashing TPMS light, apparently indicating it was unhappy with the missing TPMS sender. This is the flashing light for 1 minute every hour, or something to that effect, not a constantly lit low pressure warning.

Eventually just made the TPMS "pipe bo_b" to fake it out.
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post #6 of 15 (permalink) Old 03-24-2016, 07:50 AM
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You increased Tire width and cross-section height, while keeping the same rim diameter, there is no way they are the same diameter.
P245/65/R-17=29.54"
P265/70/R-17=31.61"
You increased overall tire diameter by 2.07" or 7%.
Keep in mind these are calculation of the nominal tire size listing, the actual overall tire diameter will vary and should be listed in the detailed specs by the manufacturer. Its safe to say though, there is enough difference between these two tire sizes, there is no way the typical manufacturer variance is going to make them close to equal. The most valuable information is the Number of Rotations per Mile, that is an actual tested figure to tell how much different the rotation speed of the tire will be compared to another.

If you have 4WD, you have to have all 4 tires spin at the same speed when driving straight. If the tires spin at different speeds, the differentials will have to rotate internally to make up the speed differences, just like when you make a turn. Keep in mind, with the intended configuration of all 4 tires at the exact same diameter, the differential may rotate internally 10% of the time, with one tire a different diameter, the differential will rotate internally 100% of the time. You will wear out XFR case first and then axle differentials.

Why do you think the O.M. recommends rotating tires every Oil Change? To keep the tire wear even enough that it doesn't create stress on the differentials, especially the XFR Case Differential. On another forum, I had a former Jeep Engineer say that simply driving on 4 of the same tires, but the half the tires at the tread bars and the other half brand new tread depth, front/rear, is enough difference to wear out the XFR Case differential.

Yes, if you use the smaller spare with 3 larger tires, the ABS/Traction Control/SCS/BAS/etc is going to recognize the difference in tire rpm, it likely will react unpredictably and undesirably. But the stress on the differentials is worse IMO. Once you get the tire fixed and go back to the same diameter for all 4, the ABS/Traction Control/SCS/BAS/etc will go back to normal no damage. Meanwhile, depending on how long and how fast you drove with one tire significantly different in diameter from the others, you may have significant wear, significant reduction in the life of your transfer case.

If you don't get a spare the same diameter as the other tires, and you have to use it, I would only drive very slowly a few miles, to get the tire repaired, otherwise you're risking the XFR case.

TPMS, yes Commanders have 2 different systems, Premium that displays the pressures of the 4 tires in their relative positions, and Base that will only light a warning light if something is wrong with the system or one or more tires is below acceptable pressure.

I have the Base TPMS system, my spare has NO TPMS sensor, that has never caused any problem at all in my 2010 Commander. (I bought my Commander used and missing a spare, that was replaced by ordering the cheapest steel wheel that fit using an OEM tire in stock, so I have no idea if the Base TPMS system spare came with a TPMS sensor or NOT).

I've seen posts from people with the Premium TPMS system talking about the Spare Tire and its sensing the presence and condition of the spare, as well as having problems because of TPMS sensors in the spare.

I was assuming the Premium TPMS includes monitoring the spare and the Base TPMS does NOT monitor the spare. On this thread we have posts from folks that say they have the Base system and get puzzling reaction to do with the spare. So, I'm at a loss, NOT sure how the spare plays into the Base system, perhaps they changed it over the model years. I have a 2010, from all my TPMS interactions, it appears the 2010 Base TPMS system does NOT monitor the spare tire.


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Last edited by Mongo; 03-24-2016 at 08:40 AM.
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post #7 of 15 (permalink) Old 03-24-2016, 11:36 AM
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Mine is 2007. It did indicate low pressure from the spare. It apparently did not like having the spare TPMS removed. It could be throwing a fit for some other reason though? After I run the pipe bo_b for a while I will be able to tell if that solved it. For whatever that is worth.

If anyone could tell me where to look for the TPMS receivers, especially the one that would cover the spare, I'd love to have that information.
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post #8 of 15 (permalink) Old 03-24-2016, 12:39 PM
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Quote:
Originally Posted by danb View Post
After I run the pipe bo_b for a while I will be able to tell if that solved it.
What's a pipe bo_b?

I "know" that the TPMS for the Commander is part of the Wireless Receiver Module that also does remote door lock and start, etc. That each TPMS sensor has a unique identifier, serial number, that is transmitted to identify it and gets registered in the TPMS control module as one of the TPMS that it should read. It is possible for the TPMS to pick up sensors from other cars parked nearby, that is why there are several weird rules about handling the sensors, like having to drive at least several miles, with the system consistently reading only the number of sensors it should, when you install a new sensor, to prevent it from accidentally registering a sensor from a nearby car.

I "think" the TPMS will have one less wheel receiver (I think its has a different term) than the total number of TPMS sensors that are being monitored. Its usually in the wheel well, often behind any plastic liner inner fender. The idea is, the closest transceiver will be able to identify which actual sensor is in that position. Once its identifies the positions of all but one sensor, that last sensor must be in the last location without an antenna.

My 2010 with base TPMS system, has never had a TPMS sensor in the spare and it has never lit a warning for a missing TPMS in the spare. The system works as advertised, lighting the warning light for low pressure in one tire that had a leak with a nail in it, and it lit the warning light for a sensor that went bad and needed to be replaced. When replacing the bad sensor, the warning light remained lit until I drove 1.3 miles all by myself on a deserted road, then it chimed and went out and never turned on again. (i.e. it registered the new sensor and turned out the TPMS light because all was good again after driving 1.3 miles).

I'll have to look up what it says in the O.M. about the TPMS system. For my 2010 Base TPMS system, there has never been any warning or reaction for a TPMS sensor missing in the spare.


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Last edited by Mongo; 03-24-2016 at 12:43 PM.
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post #9 of 15 (permalink) Old 03-25-2016, 11:37 AM
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Thanks for the detail! I understand it basically the same as you have written. I wondered if there were little antenna in the wheel wells? I heard mention of it being behind the plastic, but have never seen one in captivity.

I wondered if i could find the TPMS receiving antenna for the spare well and wrap it in lead tape, and keep it from receiving low pressure signal? That would probably be the same as removing the sensor however.

The pipe bo(m)b (NSA redaction) is a homemade pressure vessel that you mount the spare TPMS sensor in, and inflate to 35 PSI to spoof the system into thinking the spare is pressurized properly. Generally made of PVC pipe. It is a redneck solution, but it works.

As I understand it from my friend who runs a Discount Tire, alterations to the TPMS system are not allowed by Federal law, after the Ford Explorer Mexican tire debacle that killed folks. Frankly I am surprised that the Superchips programmer allows alteration of the warning pressures. Wish there were just a spare disable option.

Back when my Commander was new I got the low pressure light, aired up all the tires and still had the warning. Sure enough, it turned out to be a low spare. So when I went to carry a flat oversized spare, I knew this would affect me. I pulled the sensor and started getting the flashing TPMS error light as I figured would happen.
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post #10 of 15 (permalink) Old 03-29-2016, 07:07 PM
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I cheated a bit on the full size spare... I work at a shop that does a fair amount of tires, and we put our tires in a special spot for the tire recycling truck to pick up.

Long story short, I managed to get a free 265/70/17 that was still at about 6/32" tread depth across the face. Not an ideal spare for extended use, but far better than the stock size. One major plus is that this worn size actually fits into the factory spare location fully inflated. It may be an inch or so lower than before, but it works for me.

One thing worth noting is that I've got an aftermarket hitch which does sit lower than an oem unit.

2007 Commander 4.7
265/70/17 Falken AT2, 17x9" Level 8 - Strike 5
RC Lift, Bilstein Struts, JBA 6.7s, Monroe LL's
AEM Intake, SuperChips Flashpaq
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