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Spare Tires on AWD cars

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Spare Tires on AWD cars

Postby XMULE » Mon May 06, 2013 9:48 am

Ran across this discussion on dealing with flat/spare tires on AWD cars. In effect, the advice is to disconnect the AWD before you drive anywhere on the "doughnut" spare tires. Curious what experience others have had . . .

http://www.meetup.com/pittsburghhikers/boards/view/viewthread?thread=34098542
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Re: Spare Tires on AWD cars

Postby TheOtherIndian » Mon May 06, 2013 9:56 am

It'd be nice if you could cut and paste the relevant discussion here. The group's content is only for members and I'm sure not many would want to join the group just for this discussion.
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Re: Spare Tires on AWD cars

Postby GregMiller » Mon May 06, 2013 10:01 am

I haven't heard that, I'd only heard that you want to put similar sized tires on the front wheels, since they're doing the steering and (in most situations) providing the majority of the power.
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Re: Spare Tires on AWD cars

Postby SchralpTheGnar » Mon May 06, 2013 10:04 am

I have a 98 subaru with AWD and I've driven many times over many miles the past 10 years with the donut tire on and AWD engaged and have had zero problems with the AWD system of my car. So there!!!

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Re: Spare Tires on AWD cars

Postby BenfromtheEast » Mon May 06, 2013 10:21 am

I have no experience driving an AWD car with a doughnut, but I'll assume since you're asking a car question on a mountain website that you're open to random opinions. :)

If you have equal sized tires and drive straight on a flat road, your wheels will all turn at the same rate. When you go around a curve, the outside wheels have to travel farther than the inside wheels. Your car is built to allow for this. But if you have the doughnut on, the doughnut wheel has to turn many more times to keep up with the wheel that has the full sized tire. This sounds like it can't be good for AWD, or 4WD either, or even 2WD on the drive axle.

How does one "disconnect" the AWD?

I bet your owner's manual will tell you what to do when you get a flat tire.

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Re: Spare Tires on AWD cars

Postby Vincopotamus » Mon May 06, 2013 10:24 am

I had a blowout that punched a hole in the rim on my Outback this winter, and considered just replacing the one tire when I was looking for a fix. I found an article that said that if there is as little as 2/32" difference in tread between the tires on an AWD vehicle, it could result in long term damage to the AWD system from continuously having to let that one wheel spin at a different speed than the others on dry ground. So if you are going to replace one tire on an AWD vehicle, you either need to replace all four so they are the same size, or find a new tire that is the same circumference as the others. The latter likely means getting a new tire's tread shaved down to match the other three.

Just another reason to try and limit the number of miles you put on your doughnut.

BenfromtheEast wrote:How does one "disconnect" the AWD?

Ditto
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Re: Spare Tires on AWD cars

Postby SchralpTheGnar » Mon May 06, 2013 10:56 am

To disable AWD in a subaru just pour gasoline over the car and throw a match on it, that disables AWD in a addition to several other annoying features of a subaru.

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Re: Spare Tires on AWD cars

Postby GregMiller » Mon May 06, 2013 11:19 am

I believe in Subaru's there's usually an empty fuse slot labelled 'FWD' that when you stick a fuse in it converts the car to FWD only. I haven't done this myself, and you should investigate this before finding out hard way on some dirt road in the middle of nowhere.

Personally, avoiding this sort of situation is why I purchased a full size spare. Yes I still rotate the tires so I have similar sized tires on the front when I get a flat, but it's nice to not be speed limited when you have 200 miles of highway driving to get back home after finding out you have a flat tire at the trailhead, not to mention if you're 10 miles up a 4wd road.

As always, take any automotive advice you get on the web with a <del>grain of</del> salt lick.

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Re: Spare Tires on AWD cars

Postby BillMiddlebrook » Mon May 06, 2013 11:30 am

SchralpTheGnar wrote:To disable AWD in a subaru just pour gasoline over the car and throw a match on it, that disables AWD in a addition to several other annoying features of a subaru.

Ha ...and then buy a real 4WD... :-"
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Re: Spare Tires on AWD cars

Postby Steve Climber » Mon May 06, 2013 11:35 am

Don't worry about running your donut. Just go steal someone's full size.

viewtopic.php?t=39627&p=480966#p480966
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Re: Spare Tires on AWD cars

Postby MountainHiker » Mon May 06, 2013 11:43 am

Or you could replace your donut with a real spare and do 5 tire rotation. With all the other safety stuff that’s mandated, it’s a wonder those things are still legal!
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Re: Spare Tires on AWD cars

Postby XMULE » Mon May 06, 2013 11:45 am

It'd be nice if you could cut and paste the relevant discussion here. The group's content is only for members and I'm sure not many would want to join the group just for this discussion. --TheOtherIndian

It's a long discussion. But here is the opening comment. (And yes, per Greg's comment, one disables the AWD via the fuse box see #2)

1) Since so many people here drive Subarus and other AWD vehicles I thought it would be worth it to mention this. Yesterday I had a flat. When the AAA guy arrived he asked for my car's manual and explained that he needed it to see how to deactivate the AWD. He said that the transfer case could burn out trying to even out the torque, rotation speed and power distribution between the remaining good tire and the stupid donut temporary spares supplied on most new cars these days. (It turns out that rather than a switch it requires taking a spare fuse and inserting in someplace that does the deactivation.) Well, like many, I left my manual at home, not thinking it would be needed for any emergency road side service, so he could not switch to the donut. He was kind enough to do a tire plug repair for me so it worked out OK for me. But the lesson is to at least carry your manual with you at all times. I'm going to look into whether there is enough room in the wheel well to put a real spare in there. (I know it will swallow at least some trunk space and raise the cover over the wheel well.)

I'm not sure whether this (the deactivation thing) is a bug or a feature on the part of Subaru. He said that Subaru was the first to require the deactivation but it sounded like other AWD makes are following. It certainly makes sense that a transfer case would struggle with two wildly different tires, they even discourage two regular tires that vary too much in wear. But maybe Subaru transfer cases are more vulnerable than others? After all you are not supposed to drive very far on the donuts.

In general I'm starting to wonder about whether Subaru is starting to depart too much from their established rugged outdoor oriented reputation. No real spare? Really? What about all the ads about people hundreds of miles out in the desert (apparently). What about all the kayak adds now that they use keys that can't be allowed to get wet? Oh I forgot. They don't do those ads anymore. Now its about a comfortable back seat for grandma and grandson. Very sweet but not what I'm interested in. A women at the Boston bike trail parking where I was stuck with the flat said that she was in marketing and advertising and the ad switch was designed to appeal to women since they make many of the major financial decisions in families. I'm all for empowering women but I think Subaru needs to stick to its knitting if it wants to retain market share. I may be getting a Rav4 next time. Or even a jeep if Chrysler keeps improving its once horrible reliability.

2) Yes it is in my manual on page 9-3 under "in case of emergency":: Precautions for AWD models with automatic transmission: "... if your vehicle is an AT model, before driving your vehicle with the temporary spare tire, deactivate the AWD capability of the vehicle as follows. 1. Turn the ignition switch to the LOCK position. 2. Pull any one spare fuse out of the spare fuse holder in the engine compartment. Spare fuses are attached on the back side of the fuse holder cover. You may pick up any one fuse in the spare fuse holder. 3. Put a spare fuse inside the FWD connector located in the cabin and confirm that the AWD warning light "AWD" illuminates. The AWD capability of the vehicle has now been deactivated." Then it goes on to say to switch the fuse out when the regular tire is on and replace the spare fuse in the spare fuse holder.
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