I got in my car (1998 Land Rover Discovery) this morning, and after a mile or so, I noticed that it was handling oddly. I pulled over to a safe spot and changed the flat tire for the spare. I bought four new Michelin tires for the Land Rover at CostCo back in 2005 and so I decided to drop the flat off with them on the way to work. The guy told me that the flat would be fixed under warranty and I could pick it up on the way home. He also informed me that the tires were worn by 60%. I got a call from CostCo when I got to work and the mechanic said the sidewalls were damaged and they would have to replace the tire. He then went on to say that since it?s a four-wheel-drive vehicle and in order to satisfy manufacturer?s recommendations, the other three tires would also have to be replaced ? at $160 a piece! Sensing a racket, I asked him to simply replace the damaged tire. He said that CostCo would not be allowed to put the tire on the car, since it would violate ?manufacturer?s recommendations? so I said I would do it myself. What gives? Is CostCo really that scared of being sued in the remote possibility that one slightly larger tire would damage something? This rule is awfully convenient for them!
What, if anything, does your owner’s manual say about the matter? Or you could try to confirm this by calling a Land Rover Dealer.
If your vehicle were Subaru the case would be true. Most AWD vehicles(your is mainly) cannot tolerate significant differences in the rolling circumference of the tire without wrecking the AWD system.
Also, sidewall damage is not repairable; the damaged tire must be replaced. I’ve heard some places will shave a new tire to match the tread wear of the other 3 tires; seems kind of a waste to shave 60% off of a new tire, though.
I completely agree with the following post from VDCdriver.
As has already been stated, most AWD vehicles are very sensitive to differences in tire circumference, and the result is expensive (or in the case of Land Rovers, VERY expensive) replacement of the center differential, and–if so equipped–a limited slip differential. Also, sidewall damage to a tire makes it too weak to sustain high speed driving without a blowout. The net result of all of this is that placing that damaged tire on your vehicle would likely result in an accident and replacing just one tire may result in very expensive repairs to the center differential and (possibly) a limited slip differential.
The ultimate way of determining if your vehicle is one of the AWD vehicles that is sensitive to differences in tire circumference is to consult your Owner’s Manual. You might try asking the service people at the Rover dealership, but many service dept personnel are woefully ignorant of the vehicles that they service, so I would use the manual as the best authority on the subject.
So, I suspect that Costco is being honest with you, but you can confirm this by reading the information on tires in your Owner’s Manual (which I suspect that you have never done!). If it turns out that your vehicle is not subject to differences in tire circumference, then you can replace just that one tire, but it will probably have to be at a tire store other than Costco. And, under no circumstances should you drive on a tire with sidewall damage!
After reading all the posts I hope you realize that the CostCo guy probably saved you from major drivetrain damage.
MB–Maybe the OP will realize that, or maybe not!
Haven’t you noticed that more and more people nowadays become very angry when someone gives information contrary to what the person already decided to be true? (or, in other words–Why do people ask for opinions if they have already decided that they are absolutely, infallibly correct?)
But, with any luck, the OP will realize that Costco’s employee(s) were not merely being arbitrary in their policy.
Actually a lot of them just cruise on through asking questions and never coming back. I think the crowd here is getting very young and inexperienced.
Yup VDC, Ive noticed that.
And on November third we’re all going to the polls to vote!
It’s human nature.
Thanks to everyone (who wasn’t getting catty) for taking the time to reply to my post. When I made my post, I was hoping that someone had already thought this through and come up with a complete answer, either validating or refuting my hunch. I am an engineer, and I admit to being somewhat jaded by the many companies who sell into people?s ignorance and/or fear. By the way, if I didn?t make it clear, I am now driving with one new tire and three tires that are 60% worn. I do not advocate driving with sidewall damage.
I looked in the owner?s manual (you were right, VDCdriver, I hadn?t done this) and I could find no mention of an intolerance to differing tire sizes. My 1998 Land Rover Discovery does not feature any limited-slip differentials (there are three differentials, and the center one can be locked for off-road operation). Differentials exist to take up differences in wheel sizes and also, to allow the wheels to turn at different rates when the vehicle is being turned around a corner ? on any car, all of the wheels follow very different paths while the car is being turned. So here?s the work that I was hoping someone else had done:
I have two questions:
Since I now have a tire that is slightly larger than the other three, how much stress am I putting on things?
Is CostCo justified in demanding that I replace all four tires?
To answer question #1, I took a tape measure to the new tire and one of the other tires. The new tire measures 96.5 inches in circumference and the worn tire (other tire of same axle) measures 96 inches. This is about half a percent difference. Admittedly, my precision in doing this is not high, so let?s call it one percent just for convenience. The wheels measure 59 inches apart center-to-center, so a bit of grade-school math reveals that a 1% difference in tire circumference is the equivalent of driving in a circle with a radius of about 460ft with tires of the same size. Further calculations show that at 60 MPH, driving on a straight road, the differential is experiencing a difference in wheel speed of about 6.6 RPM. My guess is that it can easily handle that. It seems unlikely to me that a Subaru or any other car would notice either, with or without an LSD. So, to those who say “AWD vehicles are very sensitive to differences in tire circumference” do you have a reference?
As for question #2, I?d say they are not justified ? mostly. OK, if I did a lot of off-roading (I don?t) and locked the center differential, I would get more than average drive-train wind-up due to the greater difference in axle rotation rates. This is a stretch however, since this happens every time I turn the steering wheel.
I smell a rat, folks. Does anyone out there have a 4WD that actually says in its owner?s manual that one new tire is ?not recommended??
Thanks for your time!
"And on November third we’re all going to the polls to vote!
I’m going on November 4!
Volvo, for example, issued a Technical Service Bulletin on the subject, so you might want to check for one from Rover. In the case of Volvo, it’s the viscous coupling in the center differential that fails.
The problem for Costco - and other tire shops - is to have a simple, easy to remember rule that - at worst - doesn’t cause any harm, but completely prevents a problem from occurring. So while a Rover might not need to have tires that are very close in diameter, a Subaru (for example) is well known and the rule would save the tire shop a lot of money and headaches.
Where I lived for many years, the unofficial slogan on election day was, “Vote early and vote often”. Of course, they were famously corrupt in that county.
If a new tire is 96.5 in. around and used is 96 in., then side to side rotational difference is 3.4 wheel revs per mile. With one new tire the difference between front and rear tire sets would be half of that and the center differential would see a difference of that times the final drive gear ratio. If the final drive ratio is 3.4:1, for example, the rotational difference would be 5.78 revs per mile for the center differential. Sounds harmless to me but what do I know?
It’s my understanding that tires wear faster when tread is deeper and then wear slows so the difference should diminish over miles.
Differentials are designed for slippage when turning more extreme not continuously.
You design differentials for a living, yes?
Now you guys really have me confused. If having 4 equally worn tires on the vehiclel is so critical, why would the manufacturer include a spare tire on the car? Surely, that spare will likely be “new” the first time it is needed, probably when the other tires are worn to some degree.
If you say the spare is only to get you to a service garage so that you can replace the other three, this seems to me to be a pretty lame design.
Am I totally off?
Subarus with automatic transmission and the standard AWD system are definitely very sensitive to differences in tire circumference. In fact, the Subaru Owner’s Manual directs owners of these vehicles to insert a fuse (included) into a special receptacle just behind one of the strut towers in order to temporarily convert the AWD system to FWD while the temporary spare tire is installed. Additionally, the manual contains verbiage on the differences in individual tire circumferences that the drive system can tolerate, as well as a statement about not using tires of varying circumferences.
Subarus with the more sophisticated Variable Torque Distribution (VTD) AWD system are not subject to this problem, and as a result, the special fuse receptacle for the drive system does not exist on those models. The manual for these vehicles simply states that all 4 tires should be replaced at the same time “in the interest of safety”, but it does not warn of mechanical damage if varying tire circumferences are used.
While my current Subaru has the VTD system, my previous one had the standard AWD system, I am very familiar with the advisory/warning in the Owner’s Manual of that model, and I did follow this advice when I had a couple of flat tires. And, it should be noted that my old Subaru is still going strong at well over 160k, with no repairs ever having been made to either the drive system or the transmission. Would the drive system have been damaged by failing to follow the advisory in the Owner’s Manual? I don’t know the answer to that question, but I am also not one to ignore advisories or warnings.
If you rotate your tires and include your spare in the rotation pattern, then you would have no worries, right?
I wouldn’t think of running one new tire and three at 40% remaining tread. Way too much difference IMO even for an open differential. I would buy at least TWO new tires and put them on the same axle. Pennywise and pound foolish…