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RVAnderson

Tires on a 4-wheel-drive vehicle

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My elderly parents in law experienced a blowout while driving their Jeep Cherokee. The doughnut was flat. Since there was a chain tire store not too far away, Triple A towed them there. Once there, the counter guy declared that on a 4WD vehicle, it was "too unsafe" to replace a single tire and announced that he would only replace all 4. He readily admitted that the remaining tires were in fine condition with lots of tread but said it's "corporate policy" that all 4 tires must be replaced on any 4 wheel drive vehicle. So they used all their ready funds and got 4 new tires for almost a grand.

I have never heard of this "safety issue" before and wonder if it's true, or if my parents-in-law, who were over a barrel at the time, weren't being ripped off.

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Benefits of AACA Membership.

This is very common today (ABS is the other reason that's used). Frankly, I think it's a combination of liability lawyers run amok and marketing opportunism. The rationale is that if the tires are different diameters, the 4wd or ABS won't work properly. The different tire diameter causes one wheel to turn at a different speed than the others, causing a problem.

The trouble with this line of reasoning is that if it were true, cars with 4wd and/or ABS wouldn't be able to go around corners. When you turn a corner, the outboard tire travels a longer distance and thus turns faster than the inboard tire. This is why you have a differential in the drive axle. The tire rotational speed difference caused by a slightly worn tire is negligible compared to the speed difference caused by cornering. Frankly, running one tire slightly underinflated has a bigger effect than the new/old tire combo.

This is pure BS, but unfortunately all tire stores have taken this position. I'm sure it's a sales boom for them. I've actually had to remove the wheel from my vehicle in the parking lot myself and roll it into the tire store to get them to sell me only one tire. The rationale is that since they "don't know" what vehicle it was going on, it was not their responsibility.

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Well, as usual, it's a case of myself not keeping with the brave new litigous world. Now I read that a MS senator wants to keep me and my kind out of his state's restaurants.

Fine by me.

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I've driven 4X4 vehicles for 50 years and this is the first time I have heard of this sales scheme. I might see some rationale for changing two tires on the same axle depending on how worn the tires are. To be forced to change all four seems like a rip-off and another example of taking advantage of uninformed people.

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its happened to me but it was a fleet car and fleet admin seems to have some clout cause they changed 2 tires. My question is then if wear is not even then you should not rotate either

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RVAnderson</div><div class="ubbcode-body"> brave new litigous world </div></div>

You said a mouthful, RV.

I had a similar situation when I wanted to buy two snowtires recently for my front wheel drive 1992 Taurus from a "leading" (perhaps THE leading) online tire store. You would not believe the hassle I got from the salesperson (who called me back immediately after I completed my online snowtires purchase), who was very upset about my only purchasing two, and telling me "how dangerous it was to only buy two," etc. Finally I had to *lie* to them and tell them that I already had two identical snowtires already on the back of my Taurus, to let the transaction proceed.

RV and joe p.are right, though--it's litigation run amock--that's the root; and the tire vendors are just reacting now out of pure fear of lawsuits.

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I just had the same experience with my daughter's Taurus. My wife drove it home after a service job. It was wallowing all over the road. I had a front end alignment job on it. The toe in was out of specs. As I drove it home I noticed that there was still a shimmy in the steering wheel. Every tire on the car was a different brand. My daughter has bought one tire at a time all her life. She's a little "tight"! eek.gif

I had my local tire shop rotate the tires, even crossed (Xed)them (horrors, a real no-no...they say).

The car now drives and handles fine. Amazing what a little rotation will do for you. smile.gif

Wayne

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: stock_steve</div><div class="ubbcode-body">I had a similar situation when I wanted to buy two snowtires recently for my front wheel drive 1992 Taurus from a "leading" (perhaps THE leading) online tire store. You would not believe the hassle I got from the salesperson (who called me back immediately after I completed my online snowtires purchase), who was very upset about my only purchasing two, and telling me "how dangerous it was to only buy two," etc. Finally I had to *lie* to them and tell them that I already had two identical snowtires already on the back of my Taurus, to let the transaction proceed. </div></div>

Actually, with snow tires, this is very true. I attended a winter high-performance driving school a few years ago (wow it's actually been 11 years--where does the time go?). They told us that putting snows on just the driving wheels is a recipe for spinning your car, and gave us a vivid demonstration with a "skid car" they had on-site. They were going less than 25 MPH and tried to turn the car at a modest angle and it spun twice before coming to a stop facing the opposite direction. Granted, this was on a fairly slick surface, but that's what you encounter in the winter, right?

What happens is that the end with traction will allow you to go faster than the end without, and you'll tend to "over drive" the non-snow tires. And forget it in an emergency maneuver. You won't even notice the traction differential until it's too late and you back your Taurus into a snowbank at high speed.

After that demonstration, I wouldn't put my family in a car with just 2 snows on it.

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Matt, That is true with front wheel drive vehicles and that is why the "experts" recommend putting 4 snow tires on the car. I don't have the same experience with my rear drive ones and have been putting snow tires on the rear axle only for decades and have never had an accident while driving on winter roads (touch wood!).

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Matt Harwood</div><div class="ubbcode-body">

Actually, with snow tires, this is very true. I attended a winter high-performance driving school a few years ago (wow it's actually been 11 years--where does the time go?). They told us that putting snows on just the driving wheels is a recipe for spinning your car, and gave us a vivid demonstration with a "skid car" they had on-site. They were going less than 25 MPH and tried to turn the car at a modest angle and it spun twice before coming to a stop facing the opposite direction. Granted, this was on a fairly slick surface, but that's what you encounter in the winter, right?

What happens is that the end with traction will allow you to go faster than the end without, and you'll tend to "over drive" the non-snow tires. And forget it in an emergency maneuver. You won't even notice the traction differential until it's too late and you back your Taurus into a snowbank at high speed.

After that demonstration, I wouldn't put my family in a car with just 2 snows on it. </div></div>

I have no argument with your technical explanation.

But that's not the point.

The point is that a responsible adult made an online purchase of two tires and assumed the next thing that would happen would be the tires showing up at his doorstep a few days later--not having to play word games with an uppity salesperson on the phone after having "completed" my purchase.

It'd be like Wal-Mart refusing to sell me a bag of charcoal unless I also purchased a fire extinguisher!

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: stock_steve</div><div class="ubbcode-body">

RV and joe p.are right, though--it's litigation run amock--that's the root; and the tire vendors are just reacting now out of pure fear of lawsuits. </div></div>

Call me a cynic, but I think it's also the tire vendors reacting out of pure fear of not making enough profit... grin.gif

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Steve I agree with you, but I also understand that tire companies have gotten burned on civil liability. Remember the Ford Explorer/Firestone lawsuits? I investigated some of those crashes locally.

My understanding is that those same tires, when properly inflated, and used appropriately went many miles without problems. However, in this society, when you put them on a particular light weight SUV with a slightly higher center of gravity, overload the vehicle, underinflate the tires, and make a panic stop, it is called Defective Tires and lawsuits get filed.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RVAnderson</div><div class="ubbcode-body">Now I read that a MS senator wants to keep me and my kind out of his state's restaurants. Fine by me. </div></div>

I've met you and you sure look/seem okay to me. smile.gif Well with the exception of being an old car nut. wink.gif

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Matt Harwood</div><div class="ubbcode-body">After that demonstration, I wouldn't put my family in a car with just 2 snows on it. </div></div>

Back when I had each of my VW's (a 1967 and then a 1980) I put regular snow treads on the front and studded snow treads on the rear. Kept the gas tank in front full and had enough stuff in the trunk to equal out the weight of the engine in the back.

That sucker would go anywhere in any weather. I never missed work because of snow or ice.

And for extreme weather, I had a pair of V-Bar chains. grin.gif

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Susan, I have a better deal. I don't buy four-wheel drives, snow tires, or bags of salt! confused.gif

I stay home! I've never seen it get so bad here in Virginia where I couldn't survive a couple or so days at home with the kids. When they were kids. grin.gif

Before, I married my wife, she used to make them come and get her if they wanted her to work. She got a lot of free snow days that way. shocked.gifgrin.gif

Wayne

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: R W Burgess</div><div class="ubbcode-body">Susan, I have a better deal. I don't buy four-wheel drives, snow tires, or bags of salt! confused.gif</div></div>

We have all of those things. But now that we are retired we can choose to stay home if we want to. smile.gif

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Before, I married my wife, she used to make them come and get her if they wanted her to work. She got a lot of free snow days that way. shocked.gifgrin.gif

Wayne </div></div>

I wish!!!! frown.gif I worked for the telephone company and they expected us to be there. It was rare to get out early or get a snow day. It had to be REALLY bad for that to happen. Two years before I retired we had a horrible snow storm here. I made it into work for a half day. Everyone lived closer than I do. But I was the only one that made it in. Because I came in I got credit for being there grin.gif and the rest had to take a vacation day. cry.gif

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: stock_steve</div><div class="ubbcode-body">

I have no argument with your technical explanation.

But that's not the point.

The point is that a responsible adult made an online purchase of two tires and assumed the next thing that would happen would be the tires showing up at his doorstep a few days later--not having to play word games with an uppity salesperson on the phone after having "completed" my purchase.

It'd be like Wal-Mart refusing to sell me a bag of charcoal unless I also purchased a fire extinguisher! </div></div>

Roger that, Steve. I agree 100%. It is indeed a shame that we've been driven to such a nanny state by lawyers. I wonder if they enjoy the world they've created for themselves?

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Back when I had each of my VW's (a 1967 and then a 1980) I put regular snow treads on the front and studded snow treads on the rear. Kept the gas tank in front full and had enough stuff in the trunk to equal out the weight of the engine in the back.

That sucker would go anywhere in any weather. I never missed work because of snow or ice.

Susan, I have to agree with you that those old VW are great vehicles in snow or mud. With that flat floor pan and the tall skinny tires they would go just about anywhere a 4X4 could go. On badly rutted bush roads they were narrow enough that you could straddle the ruts and go where most big vehicle couldn't. A local paper company owned a fleet of VW as bush vehicle for their employees.

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Stupid me, i've been airing my tires down on snow for years in my Jeep Wrangler !

THATS GREAT ! now i can sue someone if i have a blowout!!!!! lol

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I read this when it first came out and also thought it was a rip off,but wanted to check it out befor comenting. I hate to say there is a little truth in the story. The problem is not so much a safty issue but may cause transmission problems in all wheel drive vech. such as subaru due to computer controled shifting. Thats the word I got from the nys service and repair shop org. of near 12000 dealers.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: windjamer</div><div class="ubbcode-body">I read this when it first came out and also thought it was a rip off,but wanted to check it out befor comenting. I hate to say there is a little truth in the story. The problem is not so much a safty issue but may cause transmission problems in all wheel drive vech. such as subaru due to computer controled shifting. Thats the word I got from the nys service and repair shop org. of near 12000 dealers. </div></div>

I'll ask the question again. If the minor difference in tire radius from worn to new, which causes a difference in wheel speed, will result in damage to the transmission, transfer case, or differential, then HOW does the car go around corners where the outside wheel travels faster than the inside wheel? Do differences in air pressure from side to side (which also cause rolling radius differences) also cause the trans to fail? I'm STILL waiting for an answer from any of the "experts" as to what EXACTLY causes this failure.

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I continue to believe this is pure, unadulterated BS. A bad alignment can cause wear more on one tire than the others and it happens all the time. Or as Joe points out above, what about going around corners and tire inflation variances? What about those dinky spares that are close, but never exactly the same size as the tires they replace? Automakers know this stuff happens more often than not. Would they really design a system that can't compensate for this and risk blowing up hardware/software that's under warranty? Would they expose themselves to the liability involved in failures related to these systems? Would they risk a car with an already hobbled system when using a space-saver spare having additional problems with the other systems? No freakin' way.

Any mechanical or limited-slip differential can physically accept these small differences without injury. It won't "wear out" anything. Heck, the crown in the road can cause slight differences. If anything, this might add a little heat, but most have more than enough fluid capacity to maintain the temps well within spec. It's not like it'll start wearing out clutch packs or breaking off teeth on the ring gear. I know for a fact that Jeep Grand Cherokees use viscous couplings for center differentials--there's no mechanical connection between the front and rear wheels at all! Such minute differences in wheel speed won't heat up that fluid sufficiently to cause any kind of lockup.

Transmissions use a myriad of factors to determine shift points, not just feedback from ABS sensors (which I doubt are accurate enough to measure such slight differences anyway--most use 1-tooth reluctor wheels, not really a lot of resolution there). I can't imagine a situation where the transmission would get confused by, what, a 1/16" difference in wheel diameter on a 28+ inch wheel? That's less than 0.3%. No car computer needs to be that accurate.

Since the primary factors a transmission uses are not really related to the relative speeds of the wheels, it shouldn't matter. It is more directly related to driveshaft speeds. If a Subaru transmission is vulnerable like this, it's poorly designed, which I don't think Subaru is famous for.

I also wonder how it can possibly be a computer thing. If something is wrong with the system, it'll throw a code. If readings are outside of normal operating parameters, it'll throw a code. No codes, the computer is cooperating with the differences and everything is functioning properly without concern for long-term damage. There's no way wheel speed differences can "break" the computer or other electronic traction/braking systems or render them non-functional. Heck, GM uses variances in wheel speeds to determine tire pressures for their low-cost on-board tire monitoring systems. It's <span style="font-style: italic">designed</span> to accommodate different rolling diameters.

Other than the problems with physical traction where the rubber meets the road, it won't affect braking, cornering or acceleration performance in any way.

I suspect this is, as mentioned above, a CYA situation all the way up and down the food chain and maybe even a plausible-sounding money making scam for the ignorant public just like the 3000-mile oil changes. Mechanics and shops buy into this because 1)they don't want to risk being wrong and accepting that liability, 2)there's money to be made by selling someone 3 tires they don't need, or 3)they don't know any better (many mechanics can do their jobs while still being mystified by the inner workings of computer controls). Nobody will ever be able to demonstrate a failure because of different tread depths on tires on the same car/axle.

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Matt Joe, Im to darn dumb to give you the ans. you want,I agree with everything you say,BUT I checked with our dealers assc. and they say there is truth in the practice..Our shop is connected to the Mitchel web site so I chose a 2004 Subaru outback at random and pulled up the tech, service bulatin. There are 4 differant tsbs that pertain to mismatched tires causeing trannt problems Go figure.

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Is that the kind of thing you could send me, Dick? I'd be very interested to read them. I'm always willing to admit that I don't know everything.

I thought I was wrong once, but I was mistaken. laugh.gif

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