mismatched tires on a Subaru outback? | GTAMotorcycle.com

mismatched tires on a Subaru outback?

wonderings

wonderings

Well-known member
I have a 2013 Outback. About a month or 2 back I hit something and punctured my front left tire. It was not repairable, huge gash in the side. Thankfully (possibly conspiracy) this happened right in front of a tire shop. I rolled right in and had 2 new front tires put on. They were not the same tire I had on the rear as they did not carry those tires and I needed to get back on the road ASAP.

I never thought much of it after that, I do not drive the car a whole lot and most is in town. Recently I noticed that on the highway around 110 kmh there is a shudder I feel in the seat. I read somewhere that AWD cars need to have all 4 tires matching and that this could be the reason for my shudder. Anyone have any ideas or knowledge on this? I would rather avoid replacing the rear tires, but if that is the problem I will do it.
 
2013? Owners handbook is probably out of date. I will ask strangers online for you.
 
wonderings said:
I have a 2013 Outback. About a month or 2 back I hit something and punctured my front left tire. It was not repairable, huge gash in the side. Thankfully (possibly conspiracy) this happened right in front of a tire shop. I rolled right in and had 2 new front tires put on. They were not the same tire I had on the rear as they did not carry those tires and I needed to get back on the road ASAP.

I never thought much of it after that, I do not drive the car a whole lot and most is in town. Recently I noticed that on the highway around 110 kmh there is a shudder I feel in the seat. I read somewhere that AWD cars need to have all 4 tires matching and that this could be the reason for my shudder. Anyone have any ideas or knowledge on this? I would rather avoid replacing the rear tires, but if that is the problem I will do it.
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I would start by making sure all 4 wheels are balanced. Generally tires are recommended to be replaced as a set on AWD cars like this because the more worn tire will likely have a smaller rolling diameter, and will require wheels to roll at differing rotation speeds to be at the same vehicle speed which ends up chewing up the differentials or transfer cases.
 
Even identically labelled tire sizes from different manufacturers are not the same size.
 
inreb said:
Even identically labelled tire sizes from different manufacturers are not the same size.
Click to expand...

Indeed, for the exact same width, profile and rim size, from two different sets of tires, the rotations/mile can differ quite a lot, again why with AWD cars they recommend replacing all 4 as a set.
 
There's an allowed tire diameter variance on AWD vehicles, I think it may be up to 1/4". The centre differential will take a beating if there is too much variance, best to replace quickly with a matched set.
 
Put a chalk mark on the tires, drive forward (100M?) then compare where the marks are.

Yes, tires on an AWD should be similar circumference/diameter.
 
DJM said:
There's an allowed tire diameter variance on AWD vehicles, I think it may be up to 1/4". The centre differential will take a beating if there is too much variance, best to replace quickly with a matched set.
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I believe the industry standard is you want to be somewhere under either it was 2 or 3% difference in distance covered per rotation, or number of rotations per mile as opposed to one made on diameter.
 
Well, being the pedant that I am, I went to the Owner's Manual for the 2013 Subaru Outback. On page 338 it specifically states:


– All four wheels should be
fitted with tires of the same
size, type, and brand. Further-
more, the amount of wear
should be the same for all
four tires.
– Keep the tire pressure at the
proper level as shown on the
vehicle placard attached to
the driver's side door pillar.
– Use only the specified tem-
porary spare tire to replace a
flat tire. With a temporary
spare tire, the effectiveness of
the Vehicle Dynamics Control
system is reduced and this
should be taken into account
when driving the vehicle in
such a condition.

 
Furthermore;

The Vehicle Dynamics Control sys-
tem may be considered normal when
the following conditions occur.
– Slight twitching of the brake
pedal is felt.
– The vehicle or steering wheel
shakes to a small degree.
– An operating sound from the
engine compartment is heard
briefly when starting the engine
and when driving off after starting
the engine.
– The brake pedal seems to jolt
when driving off after starting the
engine.

Sounds like you need a new set of tires.
 
Just to add to this, My audi needs a rolling diameter on all four wheels within 2% before quatro isnt happy and will eventually burn out the center dif
 
Rob Star said:
Just to add to this, My audi needs a rolling diameter on all four wheels within 2% before quatro isnt happy and will eventually burn out the center dif
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I wondered about this. Torsen center diffs are purely mechanical. It does not have clutches to burn. I would be more inclined to believe tires will get shredded before the diff gets destroyed... but dunno.
 
overinflate the worn tires to increase the diameter, underinflate the new tires to decrease. Only half kidding, if you only have to go a few psi each way to get the same diameter, I would do that.
 
daught said:
I wondered about this. Torsen center diffs are purely mechanical. It does not have clutches to burn. I would be more inclined to believe tires will get shredded before the diff gets destroyed... but dunno.
Click to expand...

AFAIK, some if not all gens of Torsen have friction plates.
 
You sure those are not haldex? Torsen on longitudinal engines, haldex on lateral engines.

Sent from my Z826 using Tapatalk
 
I could be wrong, I would have to look at all the diagrams of each generation Torsen, I'm pretty familiar with the 1st gens though, a crazy Finnish neighbor had an 86ish Audi Quattro for rallying up in Sudbury, used to help him with mechanical repairs on it when I was a teenager. Pretty sure it had friction plates.

Torsens will handle mismatched tires far better than a Haldex will, that I am sure of.
 
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