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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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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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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.

Sent from my Moto X using Tapatalk
 

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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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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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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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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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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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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.
 

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Ingenious solution!

I went into the well, removed the excessively large heat shield and cut it in about half. Then I got the grinder going and cut off the excess receiver hitch that protruded into the spare well. Deflated, a full size spare with full tread fits in, albeit tight.

There is a tiny bit of rubbing against the track bar, but not even enough to remove the paint.
 

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I'm NOT a Lawyer, I don't know all the idiosynchronicities of the law, but usually Federal Law only applies to the sale of new vehicles, State Law applies to ownership of vehicles. i.e. Fed Gov can pass laws telling manufacturers what to include in a car and what standards they have to meet, BEFORE THEY ARE SOLD (and then only if the vehicles are to be sold over state lines, which every car is), once sold, the treatment of the vehicle is a State Matter (I know there are exceptions, right or wrong, lets avoid that debate).

Regardless, there may be laws that keep a tire shop from disabling TPMS systems, also, its simple liability, if I owned a tire shop I would refuse to disable federally mandated safety equipment, simple because I know if that vehicle is ever involved in an accident, regardless if its related to tire pressure or NOT, some greedy lawyer will be dragging me into court to make me liable for what the owner did, simply because I have deeper pockets than the owner.

Simply blocking the signal from/to the antenna? Common sense tells me that would produce the same result as the sensor NOT being there. And disabling the system or part of the system, is going to light the TPMS light.

They do sell aftermarket pre-programmed to your vehicle, TPMS sensors for as little as $25 online. Any tire shop should be able to pop the bead on one side and depress the tire enough to pull the old valve stem and pop in the new TPMS sensor. For about $33 you can get the newer, smaller/lighter with rubber stem TPMS sensors, they retro-fit just fine. But since they are smaller and lighter, but still heavier than a plain valve stem, the wheel will need to be rebalanced.

Again, the biggest factor in the whole discussion is different tire diameters on 4WD vehicles, you just can't do it. It will wear out / damage the differential in the XFR Case. So if your spare doesn't match your oversized tires, you have a problem, again if you use it, drive very slowly only a very short distance. I'd even stop and let the XFR case cool down half-way as well.

The Ford Explorer/Firestone Tire Fiasco is the entire reason why we have mandated TPMS for all cars now. The problem was a tri-fecta of causes, the poor design of the Ford Explorer suspension and Ford trying to cover that up by recommended a tire pressure that was absolute lowest safe pressure possible, then selecting a tire from Firestone, that Firestone was well aware they had a poor tread compound, that wasn't holding up to heat, combined with poor quality control, then owners purchasing a car without learning about it, then failing to read the owner's manual and NOT ever check the air pressure on their tires. All combined to a few accidents caused by the car/tire/and owner overloading their vehicle and driving it on hot southern roads with tire pressure way below safe pressure limit; which resulted in a tire blowout, which shouldn't cause a bad accident, but remember the owner's part in this, and the fact they had a high CG vehicle overloaded, so no shock, many of them over reacted and made the situation even worse resulting in roll-overs, which I'm sure they and their passengers weren't wearing their seat belts either.

Then the media and Government went into a frenzy, and you know there was NO hope of getting down to the truth of the matter after that.

I suppose we should be thankful the federal government didn't mandate a load sensing system to keep people from overloading their vehicles as well as TPMS.
 

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The people failing to find out about the car before purchasing it? If people were aware of the Ford Explorer's Gross Weight, Distribution of Weight Limits before purchase, they would never purchase them. In that model Explorer, if you put passengers in all 5 seats, you could NOT carry any cargo, even with empty seats the cargo limit was something ridiculous like 2 suite cases. Meanwhile, people were buying them, never reading the owners manual and taking long vacation trips with all seats occupied, rear deck loaded with luggage and luggage on the roof rack. Then the vehicle came new with 28PSI in the tires, and the owner that never checked the tire pressure since they bought it 2 years earlier was NOT away they were driving on only 19PSI tire pressure.

Yea, Ford had a hand in this, BUT, if the owners were doing the absolute minimum an owner/driver should do, they would have avoided this.
 

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I read up on the TPMS system again, refreshed my memory.

http://www.wkjeeps.com/wk_tpms.htm

Very interesting...basically there is one wireless unit for the entire vehicle, and it controls not only TPMS but wireless remote also. Does not specifically say if it receives everything itself or deploys antennas to the wheel wells.

Anyhow, so far my light is staying off with the pressure vessel spoof method, so next time it lights up it will probably be dead batteries in 10 year old sensors and I can shop for new ones like Mongo described.

Now to replace my track bar with a slightly narrower one.....RRO adjustable version I guess/hope. The deflated sticker 265/70/17 and the cutting I did left me about 1/16 to 1/8 inch shy of clearing the track bar. Really not an issue but being a perfectionist and all......
 

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....Very interesting...basically there is one wireless unit for the entire vehicle, and it controls not only TPMS but wireless remote also. Does not specifically say if it receives everything itself or deploys antennas to the wheel wells......
What I have read is NOT clear, I have seen references that there is some sort of TPMS device in some of the wheel wells.

It "could" be that central TPMS system receives the signals and information from each TPMS sensor, then there is just several additional and simpler devices in the wheel wells just to identify which sensor is at which location, and again, you would only need one less than the total number of sensors, because it could easily logically conclude the position of the last sensor after its located rest.
 
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