Tire mismatch???

[Rob2193]

2005 3.0R VDC Outback

The initial alignment was off and the outside edge of my two rear
tires wore down to nothing in only 8000 miles. I noticed it when I
did a tire rotation...funny thing, I had the rotation done at the
dealership and they didn’t notice it!?!

Anyhow, they’re covering two new tires, but won’t replace the
originals that were on the front...I now have 12000 miles on the
tires. The originals are only rated for ~40,000 miles (V speed
rating) and they show decent wear. What is the maximum acceptable
mismatch in diameter between tires...front-to-back??? (.2 inches???)
I have to think that the current mismatch will exceed what is
recommended, and why is the dealership telling me not to worry???

 

[Edward Hayes]

Subaru says the maximum CIRCUMFERENCE DIFFERENCE should be no more
than 1/4 inch. I believe this is ideal but, with so new a car if your
not within the recommended tolerance of 1/4 inch I would push for 4
new tires. I would expect that they remaining tires would be pro-rated
so you may need to share some of the cost like 8000/40000?

 

[Edward Hayes]

The maximum diameter difference for my 215/60/16 tire that is very
close to 3/16 inch or 3/32 in tread depth difference. If you have a
much different tire diameter than my 216/60/16 then a recalculated
number must be done. The magic diametion is 1/4 inch CIRCUMFERENCE per
Subaru.

 

[y_p_w]

Subaru says the maximum CIRCUMFERENCE DIFFERENCE should be no more
than 1/4 inch. I believe this is ideal but, with so new a car if your
not within the recommended tolerance of 1/4 inch I would push for 4
new tires. I would expect that they remaining tires would be pro-rated
so you may need to share some of the cost like 8000/40000?

Just want to make it clear, this really only applies to the current
auto tranny models. The manual tranmissions use a mechanical center
diff that is tolerant of different tire sizes.

 

[Carl 1 Lucky Texan]

2005 3.0R VDC Outback

The initial alignment was off and the outside edge of my two rear
tires wore down to nothing in only 8000 miles. I noticed it when I
did a tire rotation...funny thing, I had the rotation done at the
dealership and they didn’t notice it!?!

Anyhow, they’re covering two new tires, but won’t replace the
originals that were on the front...I now have 12000 miles on the
tires. The originals are only rated for ~40,000 miles (V speed
rating) and they show decent wear. What is the maximum acceptable
mismatch in diameter between tires...front-to-back??? (.2 inches???)
I have to think that the current mismatch will exceed what is
recommended, and why is the dealership telling me not to worry???

I bet if YOU had put tires on the car like that, ever, and they knew
about it - they'd deny any drivetrain warranty claim.

I say, get 4 new tires or have them shave the new ones down to match the
older ones. THEY are the ones that should've delivered a new car to you
that does not chew up tires.

Carl

 

[Edward Hayes]

y.p.w: I have never read anything from Subaru that the maximum tire
circumference difference of 1/4 inch was different for AT and MT/ What
is your source for that information? Ed

 

[y_p_w]

y.p.w: I have never read anything from Subaru that the maximum tire
circumference difference of 1/4 inch was different for AT and MT/ What
is your source for that information? Ed

There's no FWD fuse in the manual transmission models and a
compact spare in the trunk. The reason the FWD fuse is there is
to disengage the electronic AWD system that will might go batty
if you use the compact spare, thinking that there's excessive
wheel slip.

<http://www.cars101.com/subaru_terms.html>

"Continuous AWD: Subaru manual transmissions use Continuous AWD,
normally 50/50 front-to-back power split and use a mechanical
viscous center differential to vary the power split when there
is a loss of traction."

Apparently the viscous coupling in the manual transmission models
is more tolerant of tire size difference than the electronically
controlled clutch pack in the automatics. Apparently the clutch
packs can wear out prematurely if the system constantly thinks the
wheels are slipping. There are advantages to the electronically
controlled system, but sometimes simplicity has its advantages.
Check out the following thread.

<http://forums.nasioc.com/forums/showthread.php?t=260363>