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Guest Message by DevFuse

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Replacing tires: just two okay?

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9 replies to this topic

#1 bohuslav


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Posted 07 November 2004 - 01:28 PM

Hi friends of all wheel drive,

I am new owner of 97 Outback. Shortly after purchase of my car I realized that car is pulling to the left. Alignment was okay, and when I rotated tires, car pulled to the other side. Diagnosis: one of the front tires is bad.

Tires look pretty new though, and have only about 8K miles on them. I think about buying only front tires, and keeping rear tires, as those look even better than the front tires. That way I may save some $$$.

Now the question is: is it good for all wheel drive to have on each isle different (slightly) tires? In fact, after some driving the front tire look differently than rear (if you do not rotate them really systematicaly).

Thanks for your thoughts.

#2 Setright


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Posted 07 November 2004 - 03:51 PM

The correct and official answer is no.

The law-suit-avoiding answer is also no.

Finally, from a personal, car-caring, long-term wise-ness point of view: No.

Saving a few dollars now will only see you wasting a big sum of your hard-earned on a major repair further down the line.

Rotate the new tyres every 6k miles if you have the energy. I find that every 12k keeps them well within specs, and this also means I only rotate when I swap over from winter to summer tyres and back again!

(Hold on to the good tyres, they might come in handy as spares later on.)

#3 coloradosubarules



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Posted 07 November 2004 - 08:14 PM

How about NO! Even if you live in FresNO. Not even in NOvember.

I think you get what we are trying to say here. If you like your AWD...just say no.

#4 SevenSisters


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Posted 07 November 2004 - 08:44 PM

Comment. Not a recommendation:

I bought a wheel and full size spare and do a 5 tire rotation every 6K.
I have not experienced problems with this method and always have a workable replacement in the event of non repairable tire damage.

8K isn't too much differnt than 6K and I don't suspect the rears are worn much.

HOWEVER. Get a cloth sewing tape measure and compare the circumference of the rear tires with the same brand and model new tires. They must be within 1/4" if I recall correctly.

If that fails, the tire dealer should be able or know some one that can buff or true the new tires to the worn tires' size.

#5 Dangerdave


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Posted 07 November 2004 - 11:06 PM

Its already been said a few times, but it is a really dangerous thing to do. My younger sister had a tire blow out on her 93 legacy turbo, and replaced it with a used tire as a "temporary" thing. She wrecked a rebuilt transmission in 4 months. She's since replaced all four tires and the car still shudders terribly on corners etc. Seriously dude NOT WORTH IT

#6 Ranger83


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Posted 08 November 2004 - 10:07 AM


The new tire tread depth is usually 11/32" of an inch. After 8,000, you might have worn 1/32" - probbly not even that. There would be a miniscule difference in rolling diameter, which is very likely less of a difference than a tire with low inflation pressure, not to mention rounding corners.

I was overdue for rotation of my tires and found the difference front to rear to be more than 1/32".

As long as you replace them with the same brand and size - or at least, the same rolling circumference - you will not have any problem at all.

Michelin and some others have diameters and rolling circumferences listed on their websites. The math is very simple and you can easily prove to yourself that there's no issue. I forget the spec that Subaru specifies, but it's a lot more than 1/32" (0.03125"). A human hair is 0.001 to 0.002" for comparison.

#7 Setright


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Posted 08 November 2004 - 11:31 AM

Yes Ranger. Your math is fine, and the dimension difference tolerated is 1/4 of an inch in circumference.

However, what we are doing is judging by the size of the potential repair bill, compared to the expected saving up front. Risk vs. Consequence. The risk is small, but the consequence is large.

#8 Glenner55


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Posted 08 November 2004 - 12:55 PM

What the car (transmission and drivetrain) "sees" is diameter of the tire not the brand or even tread type. I used differnet brand snows on my son's 92 Legacy Turbo. Tires were paired so that the same make and model were on the front axle, different brands on the back. I carefully measure the tire circumference and they were within 1/8 inch. Car ran just fine with no bucking in the transmission which is what you need watch for. Previous owner had mismatched tires (different diameters) on the rear and there was a noticable bucking as the drive system tried to account for the different numbers of revolutions per wheel. In essence it thought the car was always turning even when running at 80 MPH on a highway.

Subaru transmissions especially on the older Turbos were known to have problems handling the torque created by the turbo engine. The car still runs fine at 198,000 miles and will be turned into an ice racer this winter as the body is shot.
If you can match the diameter of the two new tires to what you have alraedy the car will not "see" any difference.

Your math is fine, and the dimension difference tolerated is 1/4 of an inch in circumference.

However, what we are doing is judging by the size of the potential repair bill, compared to the expected saving up front. Risk vs. Consequence. The risk is small, but the consequence is large.[/QUOTE]

#9 Commuter


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Posted 08 November 2004 - 04:52 PM

In general, one does not want to replace just one (or 2) tires on an AWD vehicle.

Now, let's be practical. At 8k miles, the tires are less than 1 yo I'm guessing. As pointed out, the wear would most likely be minimal. This depends on the tire and driving though. Eg - is it a 700 wear rating tire, or a 200?

Given that the tire is probably very new, it is also probably current. That is, you can go out and buy another exactly the same. Now the question is whether the 8k miles has made more than a 1/4" difference in the circumference. You can get an idea of this by measuring tread depth and comparing to new. Note that this is difficult though, because 0.040" (1 mm) tread depth variation equals the 1/4" circumference variation. Still, you have a starting point.

I had to replace a tire after 6 months and 25k kms (15k miles) due to a sidewall puncture. I was using a 700 wear rated tire. I jacked the car up and measured the circumference with a tape as previously mentioned. I was just under the 1/4" allowance.

If the variance is too great, you still don't have to buy 4 new tires. You should be able to find someone to shave the new tire down a bit (again, as previously mentioned).

One thing I would personally be wary of though is to put a different brand, or even different 'model' of tire on the car. Even if the circumferences measure the same, the "rolling circumference" might be different (different sidewall stiffness, etc.). (Do the charts actually give this? That is, a tire under load? Perhaps they do.) Also, there is the issue of different tread patterns and compounds etc resulting in different grip. Not the best for staying out of trouble.

My 2 cents.


#10 richierich



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Posted 08 November 2004 - 05:31 PM

The answer is YES, if you use the exact same brand and model of tire. And with 8k on them I would expect them to replace the tire for free.

If you use a different brand and model of tire, then it is best to replace all 4 because even though they say the same size on the side they can be more then a 1/4 difference new.

Most of us have more than 8k difference in tires because we are bad and don't rotate our tires regularly enough.

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