forester tire rotation

[Richard Chang]

Subaru recommended [...] keeping the tires within ¼ inch circumference
on all wheels. [...] Within 10K miles my 4 main tires would be worn enough
that there would be more than ¼ inch difference between them and an
un-used spare. Thus making the spare unsuitable for putting on the car.

Isn't this too paranoid. My interpretation of the issue with different
tire sizes is that you don't want to drive around with different tire
sizes because of wear and tear on the central differential. I would
think that a short drive with a spare tire is not going to cause
problems.

Richard

 

[Tom Forsha]

Correct.
What I meant and could have said is ...
Thus making the spare unsuitable for putting on the car [as a permanent
replacement] (if you give any credence at all to the 1/4 inch rule).

I reread my post.
I think my comment about using a well worn tire as a permanent spare covered
that issue (not afraid to use an off-sized tire for short periods of time).

Nice to know some body is actually reading this stuff ;-)

Tom

Subaru recommended [...] keeping the tires within ¼ inch circumference
on all wheels. [...] Within 10K miles my 4 main tires would be worn enough
that there would be more than ¼ inch difference between them and an
un-used spare. Thus making the spare unsuitable for putting on the car.

Isn't this too paranoid. My interpretation of the issue with different
tire sizes is that you don't want to drive around with different tire
sizes because of wear and tear on the central differential. I would
think that a short drive with a spare tire is not going to cause
problems.

Richard

 

[Richard Chang]

Thus making the spare unsuitable for putting on the car [as a permanent
replacement] (if you give any credence at all to the 1/4 inch rule).

I reread my post.
I think my comment about using a well worn tire as a permanent spare covered
that issue (not afraid to use an off-sized tire for short periods of time).

Agreed. So, the only incentive is economic --- extending the life of
the tires. But, including the spare in the rotation is a one-time
savings. You can't do this with the second set of tires you have on the
car, since the new tires will have much more tread than the spare ---
even if you buy the Geolanders again. If you buy 5 tires, then you
negate the savings achieved from including the spare in the rotation.

I'm guessing that Subaru and others think this one-time savings is not
significant enough for them to have to print 2 sets of instructions for
tire rotation --- one set on instructions for when the spare is new and
another set for when the spare is worn down. (Supposing that a worn down
spare is OK to use during an emergency. Otherwise, you would have to buy
5 tires each time.)

Richard

 

[Tom Forsha]

I agree that the primary reason I elected to include the spare in the
rotation was for economic reasons.
The economic predicament that that this fellow has is the one I hope to
avoid.

Posted to: http://autos.groups.yahoo.com/group/subaruforester/
a couple of days ago.

Subject: 1 dead tire means replace all 4???

"2002 Subaru Forrester 5 spd withlimited slip diff. 17k miles. I hit
a pothole and the right rear Geolandar bought it.
I go to tire shop and they say i need to replace all 4 because even
a tiny mismatch in circumnference front to back introduced a bind on
the transfer case (or whatever they call it).
I've read that only a variance of 1/4" in circumference is allowed.
This translates to about 1/32" tread wear difference.
Hard to beleive."

Now you could argue that he did not need to buy 4 new tires (or even three
if the spare was a match).
But it would still go against the 1/4 inch rule, and at 17k miles (per the
example) the difference may be worth the risk.
But what if it was 20K, 25K, 30K? (rhetorical question).

Tom

Thus making the spare unsuitable for putting on the car [as a permanent
replacement] (if you give any credence at all to the 1/4 inch rule).

I reread my post.
I think my comment about using a well worn tire as a permanent spare covered
that issue (not afraid to use an off-sized tire for short periods of

time).

Agreed. So, the only incentive is economic --- extending the life of
the tires. But, including the spare in the rotation is a one-time
savings. You can't do this with the second set of tires you have on the
car, since the new tires will have much more tread than the spare ---
even if you buy the Geolanders again. If you buy 5 tires, then you
negate the savings achieved from including the spare in the rotation.

I'm guessing that Subaru and others think this one-time savings is not
significant enough for them to have to print 2 sets of instructions for
tire rotation --- one set on instructions for when the spare is new and
another set for when the spare is worn down. (Supposing that a worn down
spare is OK to use during an emergency. Otherwise, you would have to buy
5 tires each time.)

Richard

 

[John Varela]

Agreed. So, the only incentive is economic --- extending the life of
the tires. But, including the spare in the rotation is a one-time
savings. You can't do this with the second set of tires you have on the
car, since the new tires will have much more tread than the spare ---
even if you buy the Geolanders again. If you buy 5 tires, then you
negate the savings achieved from including the spare in the rotation.

Suppose that a tire lasts 40,000 miles. (The argument below works equally
well for any other number you prefer.)

After a 4-tire rotation, at 40,000 miles those tires are used up. If new
tires can be bought to match the unused spare, then only three have to be
bought and one of the four used ones becomes the spare. Thereafter four tires
must be bought every 40,000 miles.

With a five-tire rotation, the originals will last 50,000 vehicle miles, after
which four tires must be bought (no longer constrained to match the original
equipment), and four more at each 40,000 miles thereafter.

SO:

_______Number of tires purchased_______
Vehicle miles 4-wheel rotation 5-wheel rotation
Total Total
40,000 3 0
50,000 0 3 4
80,000 4 7 0 4
90,000 0 7 4 8
120,000 4 11 0 8
130,000 0 11 4 12

Which way is cheapest depends on how long you plan to keep the car. Note that
if the replacement at 40,000 miles is 4 tires instead of three, either because
tires to match the spare can't be found or because the buyer just wants
something different, then the 4-wheel rotation is never better than the
5-wheel rotation.

HOWEVER: the 5-tire rotation has the advantage that, if one of the tires is
destroyed by a road hazard during the first 50,000 miles, only one, not four,
new tires must be bought. After that, it doesn't matter because either way
the spare won't match the road tires.

I'm guessing that Subaru and others think this one-time savings is not
significant enough for them to have to print 2 sets of instructions for
tire rotation --- one set on instructions for when the spare is new and
another set for when the spare is worn down. (Supposing that a worn down
spare is OK to use during an emergency. Otherwise, you would have to buy
5 tires each time.)

It might not be a bad idea to rotate 5 tires and buy 5 new ones each time.
Here's the above table expanded to show the 5-tire repurchase:

________________Number of tires purchased_______________
Vehicle miles 4-wheel rotation 5-wheel rotation 5-tire repurchase
Total Total Total
40,000 3 0
50,000 0 3 4 5
80,000 4 7 0 4 0 5
90,000 0 7 4 8 0 5
100,000 0 7 0 8 5 10
120,000 4 11 0 8 0 10
130,000 0 11 4 12 0 10

It looks like if you plan to run the car until it falls apart you're better
off rotating and buying 5 tires every time. This has the advantage that if a
tire is destroyed, only one new one is needed, regardless of mileage.

Anyway, the cost of printing two sets of instructions should hardly be a
deciding factor.

 

[Jeff Lackey]

TireRack offers tire shaving. So you could get a new tire and have it
shaved to the proper tread depth. Jeff
el3.net...

 

[John Varela]

TireRack offers tire shaving. So you could get a new tire and have it
shaved to the proper tread depth.

Yes, that's an alternative, but you can only do that if they can match brand,
model, and size of the tires on the car, and even if so you'll pay 100% of the
price of a tire that has only a fraction of its tread life left. The decision
on whether to do this would depend on how much life is left in the three good
tires. If they're almost new, buy the shaved replacement, but if they are
near their end of life, better to replace them rather than ruin a new tire.
And if your tires are intermediate, neither new nor at end of life, flip a
coin?