Tire Circumference

[Edward Hayes]

I contacted Subaru at www.subaru.com and ask the following question. What is
the maximum allowable circumference difference for AWD Subaru's??? Their
response from J. Mergen was. "All four tires on AWD Subaru's must be within
1/4 inch circumference of each other" I love my Subaru Forester but that
difference is ridicules on a car sold to the general public. I wish Subaru
made a 2 wheel drive version of my Forester. Eddie

 

[cc0113830]

I contacted Subaru at www.subaru.com and ask the following question. What is
the maximum allowable circumference difference for AWD Subaru's??? Their
response from J. Mergen was. "All four tires on AWD Subaru's must be within
1/4 inch circumference of each other" I love my Subaru Forester but that
difference is ridicules on a car sold to the general public. I wish Subaru
made a 2 wheel drive version of my Forester. Eddie

Simple arithmetic says that this translates into a difference in radius
(i.e. tire wear) of about 4/100 of an inch. Are manufacturing
tolerances even that tight?

 

[Jim Stewart]

Simple arithmetic says that this translates into a difference in radius
(i.e. tire wear) of about 4/100 of an inch. Are manufacturing
tolerances even that tight?

As much as I like my Subaru, I think it is a ridiculous spec
as well. Does anyone out there actually measure their tires
on a regular basis? Is it in the maintenance schedule?

If there is a danger of destroying the viscous coupler from
like type tires that are slightly different in dimensions,
I'd think that the reasonably thing to do would be to provide
an overtemp light for the coupler. Then at least, you could
stop and let it cool down then get the situation fixed.

 

[Edward Hayes]

Good point nltplk: "lets them off the hook" I don't think so if a customer
gets really aggressive with them since it's not in the maitaince book or
stated ANYWHERE that I can find.

 

[someone]

A quick look at 215/60/16 tires (my Forester) showed that difference can be
slightly exceeded between manufactures of that size tire.

That's why you're supposed to go with 4 tires of the same size/brand/model.
I've seen BIG differences in true size in tires of different brands labeled
in the same size.

 

[Ken Gilbert]

I contacted Subaru at www.subaru.com and ask the following question. What is
the maximum allowable circumference difference for AWD Subaru's??? Their
response from J. Mergen was. "All four tires on AWD Subaru's must be within
1/4 inch circumference of each other" I love my Subaru Forester but that
difference is ridicules on a car sold to the general public. I wish Subaru
made a 2 wheel drive version of my Forester. Eddie

little brouhaha on this over here:
http://forums.nasioc.com/forums/showthread.php?s=&threadid=381351

ken

 

[Edward Hayes]

I reviewed the comments on nasioc forums Ken Gilbert and some were
interesting and informative but some by self appointed experts. It does
appear reasonably important that AWD vehicles(MT or AT) should have tires
rotated regularly. I measure tread depth with a 3 dollar auto parts gage at
my 5,000 miles oil change and rotate when fronts or back have worn to 1/32
inch difference. 1/32 inchX 2 + OA tire dia. = slightly less than the 1/4
inch max circumference difference recommended. My driveling style and
Michelin Xone require a rotation at ~10,000 miles while the Yokohamas
required a rotation at ~ 6.000 miles due to different wear rates. Now I am a
car buff and in my earlier years I would view this as a neat good thing to
do. Now that my life's priorities have changed, it is a pain in the butt.
Eddie

 

[Decimal Cat]

Subaru is always overstating the sensitivity of the drive train components.
To read my Loyale's manual, you'd think the transfer case would be toast
every time you put the car in 4WD and had one low tire, or were driving
along icy roads with the 4WD on and had to go over a dry patch stretching
about a hundred feet before you got back to the slippery stuff.

It's like someone else said, it's just so they can insulate themselves
against paying for major drivetrain work if they feel like it.

--Decimal Cat