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Mixed tires on AWD Legacy


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15 replies to this topic

#1 lhrocker

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Posted 09 December 2003 - 04:10 PM

I checked my tires today and the fronts are different from the rears. The fronts are 205-70R14 while the backs are 185-70R14. I know the first number is the tire width, so is this okay since the second and the wheel size are the same? Should I change them back to the same size (185) or can I change them to all 205?

Thanx,
Peter

#2 NWScooby

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Posted 09 December 2003 - 04:25 PM

I think you would be better off having all four the same size. You can choose which size to go with (185 or 205), with price and gas milage factors being the decision points.

just my .02

#3 alias20035

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Posted 09 December 2003 - 04:55 PM

With that substantial of a tire size difference, the odds are that you have done substantial damage to the AWD system. I would expect there to be noticable problems now or shortly in the future.

All four tires MUST be the same make, model and size, and be properly inflated on EVERY four wheel and all wheel drive vehicle.

I would not use 205/70-14, they are too big.

The sizes that can be used are:

185/70-14 - this is the stock size for 14" rims
195/65-14 - acceptable size for more treadwidth on 14" rims, but not stock
195/60-15 - this is the stock size for 15" rims
205/55-16 - this is the stock size for 16" rims

I recommend four new 185/70-14 tires, you CAN NOT just buy two more to match, because your two existing 185/70-14 tires are worn and the new ones will be larger. The 185/70-14 should be the standard tire size which is indicated on the information plate on the drivers door B pillar.

How did you end up with two different tire sizes to begin with? Most tire shops are smart enough to not install different tire sizes on AWD cars.

#4 lhrocker

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Posted 09 December 2003 - 05:10 PM

That's what came with the car when I bought it. I never bought a used car before, so I guess that's something to check in the future. I didn't find out about this board until after my purchase.

I'll change the tires and have the car checked out.

Thanx again,
Peter

#5 theotherskip

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Posted 09 December 2003 - 05:15 PM

manual or automatic? if it is manual, it seems to tolerate a difference in tire diameters a bit better. automatics can get screwed up real fast...

#6 lhrocker

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Posted 09 December 2003 - 05:51 PM

It's an automatic. I don't know how long these tires have been on the car since it was sold to me by a dealer (Subaru dealership, no less). I will have it checked out though.

Thanx,
Peter

#7 Hocrest

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Posted 09 December 2003 - 06:00 PM

The damage may already be done...

But if I was you I would IMMEDIATELY put the FWD (front wheel drive) fuse in place.
Do this before driving it again.
The fuse holder is under the hood, against the firewall on the passenger side. It is labeled FWD, and takes a 20 amp fuse.

This will disengage the AWD and prevent further damage from happening before you get the tires straightened out.

If my explanation wasn't quite clear enough, check the owners manual in the area about using the spare tire.

#8 cookie

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Posted 09 December 2003 - 06:02 PM

measure the tires with a piece of sting or a tape very carefully.
If they are actually the same size in diameter you may be OK.
As Alias says they should be the same size and make and even then they could be off if the wear is a bit diffferent.

#9 Hocrest

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Posted 09 December 2003 - 06:08 PM

I just ran the tire sizes through the Tire Size Calculator;

185/70-14 = circ.- 76"
205/70-14 = circ.- 79.5"

#10 northguy

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Posted 09 December 2003 - 06:09 PM

There has been voluminous talk about this topic in the last few months and the rsident expert on the potential for damage seems to be Alias 20035. Check the threads for the write ups on damage to the awd system. I'd change the tires then go out and rally it to check the awd system; see if it still works properly. Hope so.

#11 cookie

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Posted 09 December 2003 - 06:10 PM

Get that fuse in.

#12 lhrocker

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Posted 09 December 2003 - 06:24 PM

How can I tell if the car is in AWD while driving, other than putting in the fuse? I know that the AWD is automatic in Subaru's, so is it safe to assume that from the time my foot releases the brake, all the wheels are in "drive"? Will AWD it feel any different than FWD in terms of handling?

Time to find a fuse,
Peter

#13 Hocrest

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Posted 09 December 2003 - 06:33 PM

The easiest way in this area at this time of year is to get onto some of the slippy stuff and hit the gas. At that point it will be fairly obvious.

Once you get 4 matching tires, and you remove the FWD fuse. Find a large, dry, paved parking lot and make tight turns. If you feel a jumping or binding, that isn't a good sign. Do a search for "torque bind" and you will find a lot of interesting reading.

Go get that fuse in.:-)

edit: Yes the car is in AWD all of the time, unless the FWD fuse is in place.

another edit: What year is the Legacy?

#14 tcspeer

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Posted 09 December 2003 - 09:27 PM

Ihrocker, have faith, not fear. I have broke alot of Subaru rules, and my 97 Subaru is still going with 268,000 miles. I torque my crank pully with only 90 ft. lbs. and get blistered here for it all the time. (However I will torque it to at least a 100 Ft. lbs next time) not because I have had any problems, but because these people are wearing me down.

#15 alias20035

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Posted 09 December 2003 - 10:17 PM

The problems you will experience with the AWD system will be either torque bind or no/little power on the rear axle.

First things first though, get four new identical tires on the car, and get that FWD fuse in until you get the new tires.

Torque bind occurs when the AWD system does not allow slippage between the front and rear axle. In turns the rear axle always turns at a slower rate than the front axle, if the AWD system has a torque bind problem you will note a rumble, vibration or braking effect in low/medium speed tight turns. This effect is identical to what happens when you do tight turns on pavement with a shift on the fly four wheel drive vehicle. 4x4's have no center differential or other provision to release torque bind like Subaru does.

If the clutch pack is worn out you will get delayed power transfer to the rear axle or way too little power transfer.

In snow and ice the power transfer to the rear axle should be seemless, if you feel the rear axle kick in this is a delayed power transfer and usually indicates that something is wrong with the AWD system, in most cases you should not feel the power transfer. Also if you are able to spin the front tires only, there is probably no or little power transfer to the rear axle. Subaru's will spin tires, but it should be a maximum of one tire per axle (one front tire and one rear, not both fronts).

Subaru's automatic transmission system sends power to the rear axle during acceleration regardless of traction conditions, it does not wait for the front wheels to spin like the Honda CRV and Element. Subaru designed their system so that the power would be at the correct wheels to prevent wheel slip in the first place, and is one of the very few AWD systems to do so.

Subaru's AWD system is "precautionary" while most of the others are "reactionary".

#16 RyDoggy1

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Posted 10 December 2003 - 01:17 PM

Originally posted by alias20035


All four tires MUST be the same make, model and size, and be properly inflated on EVERY four wheel and all wheel drive vehicle.


195/60-15 - this is the stock size for 15" rims

uhmmm......ive been driving on 205/60/15 for a very long time with no problems.......:rolleyes: and they are all different makes......




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