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2009 Outback RE diesel
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Discussion Starter #1
I've recently bought a 2009 manual transmission diesel RE outback from a Subaru main dealer. It had well worn 205/55/17 Geolandars on the back, and new Nexens on the front.
I've got round to reading the manual and the warning is to keep tyres to same make, same tread pattern and above all same rolling circumference to stop confusing/prematurely wearing the AWD system.

The manual suggests if I had auto tx an AWD light would operate to tell me if the tyres were of sufficiently different circumference to cause the AWD system to think a wheel was slipping. As I have manual tx how will I know if the AWD system is operating - I can't figure out if the VDC light would operate or not? (too complicated for an old boy).

I've now fitted 4 old 16" wheels with half worn winter tyres, my plan is to wear these out then fit new winter tyres for next winter - so I'd like to be sure about this premature wearing of the AWD components.

Thanks in advance for any help.
 

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03 H6 OBW & 06 WRX Sportwagon
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I'd LIKE to believe a Subaru dealer would not offer a car with a set of tires that are improper. But, you are wise to be concerned. One 'test' would be to find flat, dry pavement (not gravel/dirt) and see if the car will easily idle through tight circles, then tight 'figure 8s' without any/much gas input and most importantly, without jerking/bucking.

for a long time, Subaru has recommended all 4 tires be within 1/4" of each other in CIRCUMFERENCE. That equates to between 2 or 3/32" in radius I believe. Even use of the 'donut' spare tire comes with caveats about distance/speed I think.

search and read about 'torque bind' for more info.
 

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Lawn ornament XT
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Wow. That's not exactly a good or safe setup they sold you.

Mismatched tires on a Subaru is a great way to wear out the AWD system in a hurry. The system expects all wheels to turn at the same speed. When they don't, it assumes that wheelslip is occurring, and fights to correct it. If the wheels aren't actually slipping, the AWD system loses the fight.

Beyond that, having good tread on the fronts and poor tread on the rears is a bad idea in any car. If you are driving on wet or icy roads, the rear end will lose traction before the front, and you'll more frequently be going into skids and having a harder time recovering from them.
 

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The manual suggests if I had auto tx an AWD light would operate to tell me if the tyres were of sufficiently different circumference to cause the AWD system to think a wheel was slipping. As I have manual tx how will I know if the AWD system is operating - I can't figure out if the VDC light would operate or not?
Can't say if the non-North American models are different, but as far as I know, no one has ever seen the AWD light flash when there was a tire of sufficiently different circumference. See http://www.subaruoutback.org/forums/66-problems-maintenance/18223-awd-warning-light-flashing-odd-size-tires.html?highlight=AWD+light

It's possible that the VDC light might flash or otherwise signal when a tire is of a far different circumference and the VDC isn't able to bring the wheel speed into sync with the other wheels, but, again, I haven't read this or seen any reports that this is the case.

In regard to the AWD function on the manual transmission cars, if the car wheels are on a slippery surface, and one or more front wheels spins but neither rear wheel is spinning, then the AWD viscous coupler is not working. (This requires additional observers to see what all four wheels are doing. It's important to be sure that neither rear wheel is spinning when at least one front is.)

A typical malfunction of the viscous coupler is that it binds all the time (i.e. including when it shouldn't be functioning). This can often be detected by the circle test suggested by 1 Lucky Texan. But it can also fail in the opposite way, that is, not work at all. In this case, the circle test won't reveal the situation.

In regard to tire circumference, see: http://www.subaruoutback.org/forums/66-problems-maintenance/30110-tire-circumference-spec-confirmed-subaru-techtips.html?highlight=confirmed
 

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01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
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assuming your manual trans is like those in the US,

the tires need to be with in 1/4 inch in circumference. it is possible different brand tires meet this requirement. but it is also possible that long term they would wear at different rates. so if you end up running them you should probably check each time you rotate them.

this size tire rotates about 700 times per mile. a 1/4 inch difference times 700 equals about 175 inches or 14 feet.

you may be able run the mismatched tires by putting the matching ties on the diagonal (ie: LF & RR). this will work to make the average axle speed of the front the same as the average axle speed of the rear, IF, IF, IF, you do not have a limited slip differential. a LSD will require a matched set of tires.

(you mentioned VCD, i did not know that was available on a manual trans car.)
 

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2009 Outback RE diesel
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Discussion Starter #7
Thanks for all replies.
FYI I measured the new Nexens, 74" circum. and the worn Geolandars 73" = 4X the recommended tolerance.
I rang the Subaru main dealer I bought the car from, worryingly the service manager said he'd never heard that tyres should all be the same circumference, when I read the relevant section in the owners manual to him, he told me not to worry about it! I called another Sub dealer and he told me it would be OK as long as I changed the tyres one axle (ie 2 tyres) at a time. Be good if these guys could all sing from the same hymn sheet!
I'm inclined to believe you folks more and have ordered 2 new tyres to match the 2 new ones supplied with the car and ditch the worn Geolandars.
- and I'll swap them round to even out the wear.
Thanks again for your replies.
 

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'14 3.6R Outback
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Thanks for all replies.
FYI I measured the new Nexens, 74" circum. and the worn Geolandars 73" = 4X the recommended tolerance.
I rang the Subaru main dealer I bought the car from, worryingly the service manager said he'd never heard that tyres should all be the same circumference, when I read the relevant section in the owners manual to him, he told me not to worry about it! I called another Sub dealer and he told me it would be OK as long as I changed the tyres one axle (ie 2 tyres) at a time. Be good if these guys could all sing from the same hymn sheet!
I'm inclined to believe you folks more and have ordered 2 new tyres to match the 2 new ones supplied with the car and ditch the worn Geolandars.
- and I'll swap them round to even out the wear.
Thanks again for your replies.
Wow. :gasp:

Just.... WOW. If it were me I'd give all the info to SOA. It sounds like it time to retrain some people. :28:
 

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03 H6 OBW & 06 WRX Sportwagon
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Thanks for all replies.
FYI I measured the new Nexens, 74" circum. and the worn Geolandars 73" = 4X the recommended tolerance.
I rang the Subaru main dealer I bought the car from, worryingly the service manager said he'd never heard that tyres should all be the same circumference, when I read the relevant section in the owners manual to him, he told me not to worry about it! I called another Sub dealer and he told me it would be OK as long as I changed the tyres one axle (ie 2 tyres) at a time. Be good if these guys could all sing from the same hymn sheet!
I'm inclined to believe you folks more and have ordered 2 new tyres to match the 2 new ones supplied with the car and ditch the worn Geolandars.
- and I'll swap them round to even out the wear.
Thanks again for your replies.

those guys are either too ignorant or too dishonest to ever touch your car again.
 
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