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Great, AWD needs all four tires due to one bad one.
 

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

3/13/13 10:22 PM

Great, AWD needs all four tires due to one bad one.

The Michelins on the Equinox have about 1/2 the original thread on them @ 40k, with in 1-2mm. Impressive that they are wearing so well. But a curb bruise/cut in the sidewall apparently means finding a used one that matches closely, or buy four new ones.

Did not think about that when we got the car. Apparently 4mm difference makes a difference.

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ErikS
Joined: 19 May 2005
Posts: 8337
Location: Slowing boiling over in the steamy south, Global Warming is real

3/14/13 4:51 AM

Rotation differences lead to AWD engament that easily?

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Dave B
Joined: 10 Jan 2004
Posts: 4511
Location: Pittsburgh, PA

3/14/13 7:12 AM

Are you sure that small difference is critical?

"Part time" 4-wheel drive systems, like older Jeeps, pickup trucks, etc. with a solid connection between the front and rear axles are intollerant of rotational speed differences which is why you disconnect them in dry conditions.

Modern full time AWD (all wheel drive) systems use a fluid coupling between the front and rear drives and they allow plenty of slippage to keep the two from winding up the drivetrain due to small rotational difference. They aren't much different than a two wheel drive where the differential allows the wheels to spin at different speeds.

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Pat Clancy
Joined: 13 Jan 2004
Posts: 1353
Location: Manchester, CT

3/14/13 7:34 AM

AWD and tires

We drove Subarus for years - probably would be still if the local dealer wasn't a classic sexist jerk to my wife. On our first one we had an unrepairable puncture with maybe half the tread life gone, and everyone we talked to confirmed that all four tires would have to be replaced. Likewise with our AWD Honda CR-V, we recently had a bad puncture and the tire had to be replaced. The service rep mentioned that if the tires had a few more thousand miles on them, he would have strongly recommended replacing all of them - not for lack of remaining tread life but due to the AWD.

I think it has something to do with the fact that most, if not all, AWD vehicles, are not designed for continuous AWD engagement. Even under slippery conditions the wheels are operating at the same speed most of the time. With tires not well matched in diameter, the AWD is "on" all the time.

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Wheels
Joined: 11 Jan 2004
Posts: 1160
Location: Needham, MA

3/14/13 7:56 AM

You can get by with two.

That's horse poop that you need to replace all four. You only need to replace two. The damaged one and the one on the other side of the axle. As long as the diameters of the same axle tires are closely matched, your fine.

Four new tires of the same make/model installed don't wear the same during normal operation on AWD cars. Most modern day AWD systems are actually AWD at slow speeds and at highway speeds, RWD. Also on the more complex AWD systems, your actually RWD until the system experiences slip, then the AWD kicks in.

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

3/14/13 9:17 AM

I think it has to do with the 'Stabilitrak' in conjunction with the AWD. The <b>real question is legally can it cause a warranty fight</b> on a drive line claim? I can tell you the dealer is a rotation Nazi. Apparently the most even wear is important to keep the system from having issues.

I like Michelins due to the long wear. But they stay on a car so long it is likely you will loose one due to an issue like this.

I guess if I get new tires, I will get road hazard coverage on them. Les Scwabe, the biggest tire joint in these parts offers this, but does not sell Michelins.

I think I am going to put a curb feeler on the front right. I watched Elaine run the front right into the curb [again?] two days after seeing the cut and her saying adamantly she did not hit any curbs. We live on and inside radius lot, single wide drive. She just had come home and I waved her off to park in the street as I was working on the Del Sol and would be going for a test ride shortly.

Make me wonder what the system does when the spare is on ?


My neighbor in TN with an AWD Ford Exploder I recall had Walmart put a pair of 'close size' tire put on. Walmart wound up paying for an expensive repair AND put 4 new tires on for a huge discount.
It did cause a mechanical problem apparently.

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dfcas
Joined: 11 Jan 2004
Posts: 2815
Location: hillbilly heaven

3/14/13 9:23 AM

What happens to the roll out when you put 2 or 3 heavy people in the back seat?

I don't know how intolerant fluid couplings are or how much heat is created, but here are some thoughts. What if you inflate the new tire less than the old ones.? Does the rollout become more similar?

What if you buy 1 tire and have it shaved? It would be hard to see that rubber fall on the floor, but track people do it. I'd shave it to where its still -slightly- bigger than the other 3. There are shops that have tire shavers, even in West pennsylginia, so I'm sure you can find 1 there.

On my AWD Honda Element, they want 32 PSI front, 34 rear. Front wheel drive normally, the clutch pak/viscous coupling is at the rear differential. The right front sees the most wear.So going from empty to fully loaded,where all added weight goes in the rear, the rollout between the front and rear must change quite a bit.

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

3/14/13 9:28 AM

"As long as the diameters of the same axle tires are closely matched, your fine."

With AWD ?

"Four new tires of the same make/model installed don't wear the same during normal operation on AWD cars."

Maybe this is why the car came with Michelins. @ 40k the tires are all within 2-3 mm of wear.

BTW, not reported on the car more than once since posting about the purchase. We like the car more and more. Although we sometimes miss the room of the Town And Country Van's with the stow and go seats stowed and go-ed. ;) It was so big and a nice low floor with 3 big door to get at shit. It made trips from the storage unit to the rental, and moving from the rental to the house a breeze. And I had the E350, and used the T&C more due to loading ease. Lifting heavy shit like 13-14 higher and the climbing in on the big van... no much fun...

I traded it off and the beast E350 is gone. I will rent a u-haul if I need to load or tow anything substantial.

Our average fuel economy for two cars is almost double what it was.

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Wheels
Joined: 11 Jan 2004
Posts: 1160
Location: Needham, MA

3/14/13 11:19 AM

Doesn't make sense


quote:
Maybe this is why the car came with Michelins. @ 40k the tires are all within 2-3 mm of wear.


Tread height or wheel diameter? If tread height, that's a difference of 4-6 mm in diameter.


quote:
"As long as the diameters of the same axle tires are closely matched, your fine."

With AWD ?
Yes, with AWD.

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

3/14/13 11:31 AM

"Tread height or wheel diameter? If tread height, that's a difference of 4-6 mm in diameter."

Yes tread height, lets assume especially a premium tire like a Michelin diameters are consistent. As I stated in assumption previously, maybe why the car has premium tires to begin with? To open the window, else perhaps cheaper tires might cause problem a lot sooner. The treadwear number on the tires is 720, the highest of any tire I have had on a car by a bit. I wonder how they even grip. ;0

So it is about the distance traveled per rotation I am thinking. And the shit counting the revolutions making decisions based on this presumably. My car thinks.
Obviously I mean it is programed to engage or disengage components based on the count.

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Kramer
Joined: 12 Jan 2004
Posts: 121
Location: Richmond, VA

3/14/13 2:11 PM

Subaru's and Spares

I've done the lose a tire replace all four thing on one of our Subaru's.

As for spare tire use, there is a fuse you need to insert that changes the AWD to FWD during spare use. The fuse is in a dummy slot until you need it.

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KerryIrons
Joined: 12 Jan 2004
Posts: 3234
Location: Midland, MI

3/14/13 6:42 PM

4 for 1

We had the same experience with a gash in one tire on our Outback. Two different tire stores had two difference tolerance figures but both sang the same song. The tires had about half their life gone so it wasn't like we had to replace new tires with new tires but either way the thread of damage to the AWD was enough to convince me. I did some research on it after we replaced the tires (we were on a road trip) and everything I read was in support of needing all tires the same size.

As to having something heavy in the back squashing the tires down I would think that it is all about the circumfrence of the tire and that deflection of the sidewall would not change that. The circumfrence is fixed by the size of the casing and the thickness of the tread.

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