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Guest Message by DevFuse

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Tire replacement

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8 replies to this topic

#1 zooma37


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Posted 07 December 2003 - 09:52 PM

Hello again,

I'm a new Subaru owner and I noticed in the owner's manual to the 2003 Forester that Subaru recommends I replace all four tires at the same time. What's wrong with replacing two at a time instead of all four? Replacing all four gets expensive. By the way, how often should I rotate the tires, align the wheels, and how long should the standard tires on the 03 Forester last? In case you haven't noticed, I'm a rookie at automotive issues.

#2 Hocrest


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Posted 07 December 2003 - 10:03 PM

Due to the All Wheel Drive system the circumfrence of the tires must be within 1/4", this works out to be about 1mm of thread depth. If they vary by more than that, you can end up cooking the center diff.

This is the reason for the FWD (Front Wheel Drive) fuse located in the engine compartment. If you need to run with different size wheels, for example, using the spare. You need to install the fuse to prevent damage to the tranny.

Do you have only two tires that are worn? I have noticed that the tires on my Legacy wear more evenly than any FWD or RWD car I've ever had. Even with my heavy foot, my tires have always been ready for swapping at the same time.

#3 zooma37


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Posted 07 December 2003 - 10:19 PM

I have an automatic 03 Forester with 6000 miles on it, and I've noticed that it drifts slightly to the right on a straight and level road. I guess it needs a wheel alignment, but can tires that are slightly off really throw an entire transmission out of whack? The system seems really sensitive to me, although this is the first AWD car I have ever owned.

#4 Hocrest


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Posted 07 December 2003 - 10:39 PM

Check your tire inflation. Sometimes one low tire can pull your vehicle to the side. If not, then you probably want to check the alignment.

Do a search on this board for "torque bind" and you will find the effects of various sizes of tires.

#5 adge_082


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Posted 08 December 2003 - 12:10 AM

Does the tire tread thing apply to manual transmission cars as well?

I have a 96 Lx AWD 5MT, the rear tires, although the same brand and model of tire are worn a lot more than the fronts, looks as though they were replaced/ fronts moved to the rear, and fronts replaced with new tires.

The wear would easily be more than 1mm worth of tread depth difference, will this affect my car? looks like its been this way for a while now. dont want to kill the thing, or do any more damage.

Another point, i bought the car from quite a good used car lot, that only deal in subaru. They gave me a warranty, i had the vehicle inspected, which they were happy to do. Very friendly, didnt hide anything etc.
One would think that if it were a problem, they would have fixed it, they did do a major service on the vehicle when it entered their lot.

I also had another inspection just prior to the warranty running out and nothing was said about it.

Im a little confused.

#6 alias20035


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Posted 08 December 2003 - 12:13 AM

Subaru will perform one free wheel alignment in the first year or 12000 miles (or 20,000 km in Canada)!!! Check your warranty and service book. This is a little known but TRUE fact.

Wheel alignment is not always correct from the factory, and it can be knocked out quite easily in transit.

It is absolutely essential that you regularly rotate your tires for even wear which will mean even circumference. Subaru's tend to wear out the rear tires a little more than the fronts.

#7 Setright


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Posted 08 December 2003 - 02:46 AM

I am actually quite surprised by how even the front/rear wear is. Like Hocrest, all my tyres tend to be ready for replacement at the same time.

#8 Ranger83


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Posted 08 December 2003 - 05:24 AM

If your car is drifting, first thing to check is tire pressire, especially with the cold temps.

I think they mean a difference in Diameter of .25". no?

The diameter of a Michelin HydroEdge 205/70x15 is 26.1" Michelin says that gives 797 revolutions per mile. Circumference is 2 x Pi x R = 81.954

They show a P215/65x15 has a diameter of 25.8 - 0.3". That tire goes 806 revolutions per mile. That's 81.012 in circumference.

This is a difference of only 1.1% - and that's for a tire .3" different. Guess I better start checking my tire pressure every day....

#9 Commuter


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Posted 08 December 2003 - 01:09 PM

Subaru's website states 1/4" on circumference. If the tire's circumference is 80" (for argument), then that is only 0.3%!

Everything I've read indicates that the VC used with the manual transmission Subaru's is not as sensitive as the clutch pack used on the automatics, but Subaru does not make a distinction between them. You cannot disable the VC center diff, hence the warnings / limits about speed and distance when using a donut spare tire with a manual.

Liability being as it is, the 1/4" spec is probably conservative. How conservative, I cannot say. But I've seen a few reports of people burning up their clutch packs in short order by running an oddball tire. And one guy that fried 2 VC's, then found out that he had 1.5" difference between front and rear tires.

Some AWD systems are more forgiving (Torsen based ones) than others. I'm not versed in the various systems currently out there though, so I can't comment further. Even Subaru has 3 (or is it 4?) variations with the VDC stuff, etc.

Just one of those "the beauty of AWD" things we have to acknowledge and live with.


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