[Shiny]

Originally Posted by Sirrotica

... I suspect it will continue as long as people steer their cars to go around corners. Putting the problem onto very minor tire circumference mismatch is a cop out by the manufacturers for bad engineering from the get go....

If I understood the systems and issues better I'd probably agree. Designing a clutch and/or differential for "limited-duration" use rather than continuous accommodation of mismatch over a reasonable life seems a compromise between cost and reliability that will leave a large proportion of customers with an early and expensive failure. A previous Jeep GC we owned had Quadra-trac and the transfer case (or whatever it was) failed... was a frustrating and expensive experience.

[Sirrotica]

Originally Posted by Mike Davis

I am a Jeep Fan.
I had a 2010 Jeep Commander Hemi AWD (same platform as the GC). I had a tire get cut down on a forestry road. Tires had approx 15K miles on them. Changed 1 tire on the rear and it tripped the service 4wd light and at times the Anti lock brake light. Purchased another to match the other side of the rear and reset light. About 2 weeks later the service 4wd light came back on. The actuator went out. Coincidence? Maybe. I bought 2 more tires and no problems after that.
The Jeep AWD system is very sensitive. They use electronic limited slip diffs and have a brake lock differential. It does not care how fast the tires turn just they are turning the same speed. This is tied into the electronic stability control as well.

My newer Rubicon is very picky with tire size and rotations.

Here is a good article on the ESC, BLD and ELSD system.
https://blog.fcanorthamerica.com/200...rol-explained/

So how do you keep the tires at the same speed while turning corners? I doubt you're driving in a straight line constantly. As I said with any AWD vehicle the axles are not going to be turning the same speed while turning, the front steer axle will always be covering more real estate than the rear axle, it's just physics, reduced arc on the rear wheels.

Still goes back to wheel sensors detecting different wheel speeds. A 4l80e has an input sensor and an output sensor to detect slippage internally in the transmission, too much differential between the two will set a code in the PCM, same principle in a AWD vehicle sensing front and rear driveshaft differentials, above a predetermined value it sets a code (PROM Programmable Read Only Memory) is where the values are stored.

As I said, 1/3 of 1%, or .3%, is minuscule when compared to 25% while turning a corner. I imagine that the PROM parameters are over a sustained period of time, or distance that sets the 4X4 code.

Jeep engineers, FCA, should have a better engineered package so that their owners aren't constantly buying new tires, or shaving them to keep the 4X4 warning light off.

Older used GCs without AWD are much more desirable in the used car market, there's a good reason why the older AWD Jeeps are less desirable.

The article tells me what I already knew, that the ABS is being used to make an open differential act like a positraction unit in the axles, and the transfer case while being used off road. It doesn't tell anything about minute differences in tire circumference setting a code in the PCM while being driven on the street.

A poorly engineered system is going to cost the owners of Jeeps money they shouldn't have to pay out. Since I have owned half a dozen jeeps I was considering buying a new one or a late model used, but poor engineering in the electrical system, and minor problems such as the PCM setting a code for a tire 1/4 of an inch larger in circumference than another, is exactly why I haven't purchased any of their vehicles.

When AMC, Kaiser, and Willys owned Jeep, they at least had a reason for poor engineering. No development money, and they were buying parts that the big 3 had engineered for their cars and marrying them all together in one vehicle to save on development costs.

Since Chrysler bought Jeep they aren't buying parts from GM and Ford and trying to build a vehicle with parts originally engineered by some other company, for another application. They have their own engineers, aren't strapped for cash and can afford to build, or have another vendor build anything they want, or need. For the money they get for a Jeep, it should have better engineering and component quality than they currently do. It seems as the price on Jeeps goes up, the quality and engineering goes down.

I guess if you're okay with trying to keep all 4 tires within 1/4 inch of circumference, and buying new tires, and then shaving them to match the other tires on the vehicle, then a Jeep is just fine. I'm just not willing to accept those engineering parameters.

The Mahindra ROXOR is closer to what I'd be willing to spend my money on. Brand new, very basic and simple as far as engineering goes, and very reasonably priced.



A safety issue and liability may be a good path for you to try with the insurance company, they don't want to hear that their repair may have a safety liability tied to it, at least in my dealing with insurance companies. You'll probably need some type of documentation to back up your argument though.

[Chief of the 60's]

Originally Posted by Radman

Probably wasn't the engineers idea. More likely a front office bean counter.

I suppose it was the "bean counters" that designed the trunk floor with 1/2 of a spare tire well too.

I really liked that car but it was an engineering nightmare.

[John V.]

If the damaged tires were “almost” worn out such that they wouldn’t make it thru the winter, I’m surprised the insurance company didn’t depreciate them. In 1982 (I know, a long time ago), I had all 4 tires and the cast aluminum snowflake wheels stolen off my ‘80 Phoenix. Zero deductible on my State Farm comprehensive coverage. They paid for new wheels but depreciated the tires 50% because the car had 20,000 miles on it. I was bummed cause I felt if I was prepared for new tires I would have been price shopping. But felt I got hosed on the price of the tires so that in reality my share was more than 50%.

I would ask the tire seller for a written letter stating why 4 were needed, preferably stating that they would not install just 2 because they didn’t want the liability for consequential damage. The insurance company might cave because if they disagreed and something did fail, their denial would be a huge smoking gun. And imagine if the failure resulted in an accident with injuries.

Of course, you already realize, if the insurance company paid 50% of the cost of 4 tires, that is better than if they had depreciated worn out tires 70% and only paid 30% of the cost of all 4.

My sister who spent most of her career in auto insurance would advise NOT to even make a claim in this case. I’m assuming new set of tires was around $600. Insurance companies see a small claim as a red flag. Especially for new customers. They will quickly cancel a customer that statistics show will likely abuse them. And finding a new insurer after being cancelled could be expensive, negating any small claim reimbursement you got.

I’ve been with State Farm now for over 40 years. My policies are non-cancellable. And it’s not like I’ve never had a claim. My then 18 yo son totaled an $8000 car, I’ve had 2 roofs replaced for hail damage, 2 cars repaired for same hail damage events (all told, over $20k in hail damage repairs), and a few windshields replaced, etc. I’ve had a few things I could have claimed but didn’t. They’ve treated me right and I’ve not abused them. And now I have the peace of mind that I’m a customer for life.

["QUICK-SILVER"]

John V got this right. From insurance liability stand point, LKQ (like kind and quality) was all they were liable for. The two new could have been shaved down to LKQ and matched the worn out.

The diameter of the all terrain tires on my pathfinder would change 1.5" to 2" between new and worn out. That would be a lot more than 1/4" circumfrence.

Clay

[Shiny]

John V., Quick-Silver,

Thanks for the feedback.. my son ended up summarizing his perspective in a note to the adjuster. He pointed to all the on-line big-chain tire store recommendations to replace or shave, referring to them as reputable tire experts. He pointed to online anecdotes of Jeep dealers recommending replacement.

He then finished with this:

"I guess my question to you as to why your initial choice not to agree with replacing all 4-tires as if it was an “elective” decision by myself, is that if I had only replaced the 2 tires that Company is offering to provide coverage on, would you warrant that my 4-wheel drive system would not get damaged by only replacing 2? Would Company be willing to take the liability if I got into an accident because my tire depths were different and caused inconsistent rotation in my tires thereby damaging my 4-wheel driving system while driving my car? If your answer is no to this question, then I am confused why that would be your recommendation.

I am grateful to have coverage but I certainly pay for it every month. I acknowledge that my tires were not brand new and that this vandalism made me replace brand new tires full value. I can say that my tires were somewhat worn for sure, but they did not need to be replaced at this time. So I am open to partial coverage of the value of the other two tires if that is agreeable to you."

As to a company dropping a customer for filing a small legitimate claim and calling it abuse, that's just wrong. May be the way they act but doesn't make it right.

[SR-71]

My brother in law had the transfer case go out in his Traverse twice because he wouldn't buy all four tires when they wore out two of them. You would think he would learn by his being cheap took out two transfer cases but when the one on his BMW went out he was finally convinced.

[The Champ]

Originally Posted by SR-71

My brother in law had the transfer case go out in his Traverse twice because he wouldn't buy all four tires when they wore out two of them. You would think he would learn by his being cheap took out two transfer cases but when the one on his BMW went out he was finally convinced.

He probably blamed GM for the first two. Now he knows that it was him, not the manufacturer...

[Chris65LeMans]

Originally Posted by SR-71

My brother in law had the transfer case go out in his Traverse twice because he wouldn't buy all four tires when they wore out two of them. You would think he would learn by his being cheap took out two transfer cases but when the one on his BMW went out he was finally convinced.

I know someone who paid $3,000 for a new BMW wiring harness after a rat chewed through it. Can't imagine what BMW nicked him for on a transfer case...

[John V.]

Shiny, just to clarify, your son may have a legit claim. But insurance companies use actuarial science to make decisions.

I wasn't suggesting your son didn't have a legit claim or that this particular claim would be viewed as abuse.

What I stated was that customers, especially new customers, that make a small claim, are statistically more likely to abuse them, ie., make many less than legit claims in the future. Actuarial science shows them this.

To guard against this, the insurer is more likely to simply drop a new customer before they get burned.

They will pay the claim without a fight but they do have recourse, refuse to offer renewal.

From my vantage point, I want my insurer to cancel these customers. That helps to keep my rates low. Purely selfish? Yes, of course.

Your son may have a legit claim. It sounds like he is presenting his case in a very reasonable way.

My sister would also say that every claim is negotiable. So no harm in your son asking for a more favorable settlement. I was able to do this when my son totaled my car. After some back and forth, they gave me about $1000 more than the initial offer and I was happy.

Just wanted to caution your son about the possible outcome of having made this claim especially if he has only been with them a year or so.

[The Champ]

Originally Posted by Shiny

My son had two tires punctured by vandals. Tire store told him he needed to replace all 4 to avoid damage to AWD (2010 Jeep GC), presumably caused by significantly mismatched radius. So he bought 4, being told the wear on the two "good" tires was significant enough they would not make it safely through the winter..

After all the postings, I went back and read this again.

If the insurance company paid for 2 new tires without depreciating them, your son was treated fairly.

They could have allowed 4 new tires, but depreciated all 4 tires by 50% (or more) from the sounds of the two remaining tires needing to be replaced before the snow flies.

[mgarblik]

Your son did the right thing and has 4 fresh new tires on his Jeep. I can add a few comments and shop policy and what we teach at the college as well as what we teach the Chrysler dealer techs. The Jeep AWD system has a weak link in the system, and it's the viscous fluid coupling in the AWD transfer case. When all 4 tires are the exact same size, the many plates in the coupling turn as a solid unit except on turns. When straight driving on the highway, especially in the summer with ANY variation in tire diameter, the viscous coupler is "working", generating lots of heat. The more tire variation, the more heat. That's the piece that will fail first in an AWD. The differentials are open design and it would take much longer to kill them, front or rear. Rule of thumb at dealers in this zone is All tires to be the same brand and tread style. Tires on a common axle should not vary in tread depth by more than 2/32". Tires front to rear should not vary in tread depth more than 4/32" absolute maximum. If customer refuses 4 new tires for a variety of reasons, shaving tread to fit the above ranges is strongly recommended. Replacing the viscous coupler in a modern transfer case is a $2000,00-2500.00 repair at a dealer. So they are happy to do that out of warranty as well.

[Shiny]

Thanks again to all.

He knows 4 tires were needed and feels good that he made that choice.

I don't know exactly what they offered him but he clearly now understands his loss was 4 used tires and I suspect he'll align with compensation for 2 new tires or 4 used tires being about the same.

I know he was more upset about the principal than the money. Being told something by the adjuster that conflicted with the tire store upset him. After learning more about the risk to his Jeep and seeing all the online recommendations, I think he was even more motivated to challenge the adjuster's justification for the initial offer. Regardless of the outcome financially, I think he will feel better having asserted his position.

[Sirrotica]

Originally Posted by mgarblik

Your son did the right thing and has 4 fresh new tires on his Jeep. I can add a few comments and shop policy and what we teach at the college as well as what we teach the Chrysler dealer techs. The Jeep AWD system has a weak link in the system, and it's the viscous fluid coupling in the AWD transfer case. When all 4 tires are the exact same size, the many plates in the coupling turn as a solid unit except on turns. When straight driving on the highway, especially in the summer with ANY variation in tire diameter, the viscous coupler is "working", generating lots of heat. The more tire variation, the more heat. That's the piece that will fail first in an AWD. The differentials are open design and it would take much longer to kill them, front or rear. Rule of thumb at dealers in this zone is All tires to be the same brand and tread style. Tires on a common axle should not vary in tread depth by more than 2/32". Tires front to rear should not vary in tread depth more than 4/32" absolute maximum. If customer refuses 4 new tires for a variety of reasons, shaving tread to fit the above ranges is strongly recommended. Replacing the viscous coupler in a modern transfer case is a $2000,00-2500.00 repair at a dealer. So they are happy to do that out of warranty as well.

Mike, I notice that your saying FCA recommends maximum 1/8 inch radius, or 1/4 inch in diameter variance, where the original poster said 1/4 inch in circumference.

That is apples to oranges in comparison. If your figures are correct, (and I'm sure they are, since you teach this, and are in touch with the manufacturers) that equates to roughly 13/16 inches in circumference, or 3.14 times the originally stated "1/4 inch circumference".

That is much more believable, and palatable than the original post. I assume the OP was told the incorrect info initially by the person selling the tires. I would go berserk if I had such a slight mismatch, that could even be attributed to a low tire that caused the transfer case to self destruct.

Thanks for the clarification of diameter, versus circumference mismatch, causing transfer case damage. That sheds a completely different light on the conversation. Words make a difference.

[Shiny]

I don't think it was me that introduced Subaru's 1/4" circumference limit but a search online has multiple repetitions of this claim. May be folklore but is the legend nevertheless. I agree this difference feels like noise but I don't know the truth.

Here's an example:

https://www.subaruoutback.org/forums...tread%20depth.

[chevymad]

Subaru TSB TIPS 1210-04 December 2010 "Binding on Turns a reminder" Specifically says 1/4" in circumference. Just yesterday had an outback in with the center diff burned out. 90 year old lady had been driving the car with 2 low tires. Subaru has a test location marked FWD in the underhood fuse box. Inserting a fuse in this location causes the car to go into FWD mode only. This stopped the binding.

[Sirrotica]

Originally Posted by Shiny

I don't think it was me that introduced Subaru's 1/4" circumference limit but a search online has multiple repetitions of this claim. May be folklore but is the legend nevertheless. I agree this difference feels like noise but I don't know the truth.

Here's an example:

https://www.subaruoutback.org/forums...tread%20depth.

As I previously said, .3 % is not a realistic engineering goal to achieve (1/4 inch in circumference variation) is not enough to be concerned about. I've seen brand new tires same make, same size vary 3/4 of an inch in circumference after mounted and inflated. Now someone assumes that because they're made in the same mold by the same manufacturer, and the same size, that they're identical, many times they're not. Tires aren't all that uniform.

Race tires are all measured when new to see how much variance there is from side to side on oval track cars. The taller larger circumference tire is mounted on the right side and the shorter smaller circumference tire is mounted on the left side (stagger). Now if no one measured those tires and the taller one was mounted on the left side the car, the would push through the corner (not turn into the corner), and handle terribly.

With a locked rear axle, the short tire helps turn in on a left handed turn by traveling less distance per revolution. Circumference is much easier to measure accurately than diameter is, so circumference is the standard to check variance in 2 tires, not diameter. I've measured many tires to check how much they vary, and never did we use diameter to check variance, always circumference. 1/4 inch in circumference is negligible, but 1/4 inch in diameter is is roughly 13/16/.785 inch in circumference, or 3.14 times, also known as Pi.

Mike's explanation clarified how much FCA (chrysler/Jeep) allows in variance front to rear as well as side to side, his explanation has much more clarity than the subaru link you referred to. I know Mike fairly well, and he teaches for the local automotive technical school in my area. I have more faith in his specifications for AWD vehicles than someone posting on a subaru forum.

I read your link, and I believe, from what Mike has said about tolerances from Jeep, that someone has interchanged circumference, and diameter measurements on that subaru forum. They're apples and oranges. Using the wrong term makes a big difference in the actual tolerance that the manufacturer allows.

[Sirrotica]

Originally Posted by chevymad

Subaru TSB TIPS 1210-04 December 2010 "Binding on Turns a reminder" Specifically says 1/4" in circumference. Just yesterday had an outback in with the center diff burned out. 90 year old lady had been driving the car with 2 low tires. Subaru has a test location marked FWD in the underhood fuse box. Inserting a fuse in this location causes the car to go into FWD mode only. This stopped the binding.

Did you measure the difference? I cannot believe 1/4 inch in circumference is going to make the differential bind up. That's only .080 of an inch in diameter difference, or .040 tread depth, or radius. That's the width of a spark plug gap. If that screws up the differential WTF happens when you turn a corner throwing a 25% difference in wheel revolutions front to rear?

I believe that differential could be junk, just plain worn out, and dropping out the rear drive is going to fix that symptom. I find it hard to believe equalizing the tires fixes it, does it? What year, and how much mileage?

When Jeep had Quadra Trac, the center differentials would wear out and bind, nothing would fix it but replacing the differential. They didn't blame it on a .080 diameter tire variance. It was a faulty design, plain and simple. After 5 years they dropped Quadra Trac because of the problems with it.

I've been around the car repair business for 50 years and have seen from the dealership standpoint how they try to wiggle out of warranty claims every which way they think they can, pushing the blame onto the customer.

When I bought my 2005 GTO new I had front end problems with it linked to shipping the cars by boat from Holden in Australia with the suspension locked on the boat. The rough trip with the suspension locked ruined all the strut mounts and bearings. Pontiac tried to weasel out of the responsibility of fixing the car, but my background in dealerships allowed me to get a hold of the people that finally fixed the car and the extended the warranty on the front end for an extra 30,000 miles no charge. Many people just paid to have the problems fixed because they didn't know what caused the ruined front suspension.

Maybe subaru should be re thinking their designs if its been 10 years since the bulletin, and they're trying to blame owners for not measuring their tire diameter every month. For them to put out a bulletin, they've definitely had a bunch of owner complaints and probably a bunch of warranty claims they don't want to pay. It's pretty easy to blame the owner for having a low tire rather than fix the car. It's pretty ambiguous for subaru to deny claims having such a small tolerance for tire wear.

Subaru has a faulty design if .080 tire diameter (.040 tread depth) variance blows the differential out.

I've never liked subarus engineering when I had to work on their cars, and screwups like this is why I never liked their engineering. I'd never, ever consider buying one.

[chevymad]

Screen capture of the TSB

[Elarson]

I rebuilt the transfer case on a '99 Jeep Grand Cherokee. New Process 241 IIRC. Full time 4wd was truly an open differential and would be a lot more tolerant of mismatched tires.

The newer AWD transfer cases that have any sort of clutches or viscous couplings will be way less tolerant of mismatches.

If in doubt, go with the plan that is less financial risk. Replacing tires is cheaper than a damaged transfer case.

FWIW:
Eric