I'm new to subaru and also AWD. I've taken some tyre tread measurements from the two central groves.. (30psi all round.. looks a little low, I'm going to pump up to 33psi.). Tyres are also all the same brand and make and were on the car when I bought it.

NS Front - 5.2 mm
OS Front - 6.2 mm
NS Rear - 6.1 mm
OS Rear - 6.5 mm

Even accounting for measurement inaccuracy its obvious that the NS Front is wearing faster than the opposite side, especially towards the outside edge.

So my first port of call will be to have the alignment done? as it looks like its out. I don't feel any pulling or anything though.

Next question is I know that the subaru AWD system / diff doesn't like differences in tyre sizes / tread etc.. but how much? The manual just says to not to mix tread depths, sizes etc.. I assume meaning if you have 2/3mm left all round and you get a flat not to just replace the one with a new 8mm tread one?

Also should I rotate the tyres given the current levels or leave for a while, not sure when the last owner did this..

cheers!

 

I've seen posts of some of the US forums staring 1/4" circumference max difference and 2/32" tread difference (which is about 2mm), but I can't find anything official from subaru or in my manual... apart from the generic message about using the same size, tread depth etc.. does this imply no difference at all in tread is allowed?

 

The tracking was well out it seems..

Also got them to switch the rear's with the fronts while they were at it, my logic being that the font's will wear a bit quicker so hopefully even it out a bit.

 

anyone any views about the difference in tread wear, or if it was correct to rotate the tyres front to back in this case?

 

Seems like you found the cause you uneven wear. I'd keep an eye on it in the future and check then.

I would not be worried about 1mm on the tread depth, that difference could be seen in the tyre pressures.