BCP43002

Is it true that you have to buy 4 tires not just 2, when say one is not repairable with AWD? My nephew has a Pilot with AWD and one tire was flat and not repairable. He was told he must replace all 4 because of the AWD. I could see 2 but 4?

CBG

I don't know but to me it sounds like a tire store or car dealer is trying to suck alot of extra money out of your nephew saying he has to replace all tires because of one going flat. That sounds like BS to me. Most tire punctures can even be repaired if it was just a nail through the tread, unless the sidewall of the was cut or punctured or if he drive a ways on the flat tire. I would tell your nephew to go somewhere else.
Just my opinion.

mitsuguy

iTrader: (2)

I hate to say it, but if you don't know for sure, don't put an opinion of this sorts on here. That opinion could cost his nephew $3000 or more for a destroyed transfer case / viscous coupling...

On an AWD vehicle, the rolling diameter of the tires must be within 4/32" for most vehicles. If a tire is to be replaced on an AWD vehicle, the replacement tire must be the exact same tire, manufacturer, model and size. Also, the tires that are on the vehicle should have less than 2/32" of wear for this to work as well. Any differences greater than this, and you may be doing the transfer case and viscous coupling unit damage - that unit is designed to lock up when it sees slippage (one or more tires spinning at a different rate than another) - if you have tires of varying diameter, the unit will be in a constant state of being slightly locked and will overheat and fail... Some get away with it for a while, some last long enough til the new owner gets the car...

Some end up selling their car to me for real cheap because they don't know whats wrong with it... <true story I bought an AWD Talon cheap cause the kid had mismatched tires and destroyed the viscous coupling... I pulled the trans and replaced it myself for not a lot of money, but for someone that doesn't work on cars all day every day, it's a very costly repair...

To sum it all up, if the tires are very new on the vehicle and you can find a matching tire, then you only need to replace one, however, if not matching or the existing aren't very new, then yes, all 4 will need to be replaced...

stvincent

iTrader: (5)

^
thx for the info..

BCP43002

Thanks for the replys. I would guess that this is not widely known.

steviej

iTrader: (1)

just before I bought my GS AWD from my aunt she had to replace a nonrepairable runflat tire. The other three tires had 30,000 miles on them and the dealership replaced just the one tire. Mind you it was the same exact tire but now there were three with 30,000 miles (~5/32" thread) and one brand new one. I don't know if I would have done that but the dealership didn't seem to have a problem doing it. I have since dumped the runfarts for a dedicated set of winter tires.

check out www.tirerack.com and see if you can find you answer there.
here is a specific link I found for you.
Matching Tires on Four-Wheel Drive and All-Wheel Drive Vehicles

steviej

mitsuguy

iTrader: (2)

The reason that happened was that someone was too lazy or scared to sell her what she really should have purchased. By installing a new tire on that vehicle, it could have ended in failure of a driveline component, if it was driven that way for some time. I see it all the time - there are sales advisors at my company that are scared or do not fully understand the implications of mismatching, and they just do the easiest, cheapest thing, thinking they are taking care of the customer. Long story short, it's the exact opposite - if a customer has a problem with a AWD driveline after a mismatched tire was installed, it will default to the person or company that installed it, and that place will be liable for it... If it was not the company's fault, (carry out tire, etc), then the repair cost would fall to the consumer.

Being that I train sales advisors on tire technology, I attempt to instill this in them, but it doesn't always work...

BCP43002

I assume that the dealer did not shave the tire down as is suggested in the second tire rack link?

How long do you think using a like new spare against 3 say half worn tires would create a problem? 50, 500 or 1,000 miles or longer?

19psi

completely agree.


come train my advisor! i keep trying to tell him that we're causing future problems with the awd x types when he sells one or 2 new tires but he doesnt' listen/doesn't care/is scared.

mitsuguy

iTrader: (2)

here's the deal... some are lucky and can get away with it forever and not have any problems... some aren't so lucky and blow up a transfer case or transmission doing so... the uncertain part is how long you can get away with it... I would venture to say that you can get away with it for at least 50 miles and up to 50 miles per hour, as this is the time allotted for spare tire usage, which some AWD vehicles come with... however, when something fails, I didn't say crap!

S2racer

Let me play the devil's advocate:

There are at least three systems that are affected by mis-matched tires. Stability or traction control systems (1) and ABS (2) need closely matched tires sizes to work correctly, as they constantly compare wheel rpm as a datapoint. When the systems intervene, a warning light and/or alarm usually comes on, so you get immediate feedback if you install a tire so badly mismatched that the system is fooled.

The other issue is transfer case or differential action. I have a friend that fried his diff when he "got busy" and left a grossly mis-matched (visually, perhaps more than an inch in height) spare tire on his drive axle, and it took many weeks of abuse before it failed. So it does happen, & I acknowledge that. But let's look at the facts: a well worn tire versus a new tire is going to be about 1/4" shorter. Your tire size will enter in to this, but ballpark, that means the used tire is probably going to rotate somewhere around 6 additional revolutions per mile. At freeway speeds and in a straight line, 8 extra revs per mile means the differential section is going to go through an otherwise un-needed rotation about every 8 seconds. If that is enough to cause the diff or transfer case to blow, simply driving too many miles on a twisty road would also put your diff at risk.

Also keep in mind that most of the voices telling us to replace all 4 tires are from companies in the business of selling tires.

As for the transfer case that was blown immediately after installing a used tire? I'd wager a week's pay that the story is either an urban legend or very skillful fraud on the part of the owner of the car. Or maybe they left the tire dealership and immediately made a couple of passes on the salt flats at Bonneville...

Personally, I wouldn't willingly mix well-worn and new tires on the same axle, but I wouldn't hesitate to run a small mismatch front to rear.

CP_Ree

iTrader: (1)

Meh, front and rear tires on awd cars wear unevenly anyways. Just get two if the other two are fine. I've owned 4 AWD cars and have not had a problem ever with uneven worn tires because they will wear unevenly anyways unless I rotate them religiously.

GS4_Fiend

iTrader: (22)

By law, you have to replace all 4 tires for safety reasons. But when you approach them, don't tell them you have an AWD car. But you should replace 2 tires so it could be even. GL!

mitsuguy

iTrader: (2)

There is no law, and there is little chance that there is a safety reason as well.

Now, keep in mind, I do have an old friend who's center differential locked up going down the road in his 3000GT VR4, but that was due to insufficient lubrication - basically, it had a leak, leaked the fluid out and eventually the bearings in it just locked up... going down the road, I'm sure it was scary - all 4 wheels at highway speed just locked up...

however, when a diff fails because of improper tire selection, it is a relatively slow death... a differential will start being noisy when in reverse, then it will have resistance even in forwards, long story short, you will know there is something wrong and the car will be mostly undrivable long before any chance of it locking up...

so, if anyone tells you its a law, they are incorrect... if anyone tells you its their companies policy, well, that company is covering their ***... I know Discount Tire was sued a few years back over this same thing, IIRC, they didn't even fight it, they just paid for the repair/replacement.

oh, one more thing... tire places are (generally) not idiots... - just because you don't tell them it's all wheel drive doesn't mean they don't know... when I worked for tire places, we would send out lists of awd cars on an almost monthly basis, updating it as manufacturers released them...

mr3gs300

so the best bet is just get the same size tires all around like 245/30/20 now does offset mess anything up?