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I'm still not understanding the whole 4WD vs AWD thing. Tire shops say they have to replace all 4 tires on AWD vehicles, but not 4WD, is this still true for full time 4WD cars? I have a bulge in one that needs to be replaced, I bought the tires 6 months ago, and I don't want to have to buy a full set of tires, but I don't know how to argue the point to the tire shop.

I believe what they mean is for vehicles that only use 4WD offroad it may not be necessary to replace them all like it would be if you use AWD on the road like a subaru.

That's just my guess.

Your tire circumferance needs to be within 1/4" of each other. So if the tires you bought 6 months ago provide that, you should be able to buy just one tire.

Legacy777 wrote:Your tire circumferance needs to be within 1/4" of each other. So if the tires you bought 6 months ago provide that, you should be able to buy just one tire.

ok, cool, so it is essentially(or exactly?) the same as an AWD system? At least as far as tires are concerned? I just wasn't sure if Subaru using the term 4WD meant it was different.

Technically, Subarus are 4WD. The difference between a 4WD vehicle and an AWD vehicle is that 4WD is switchable between 4WD and 2WD. AWD basically means that the car is always in 4WD and cannot be switched out of it.

Thanks for the info!

They ended up replacing all 4 because they had somehow worn down half to nearly 50% in 10k miles so they couldn't just do two.

Under warrenty they did it?

ericem wrote:Under warrenty they did it?

Under us bitching about it. It was a combination of the fact that the dumb cunt that was such a prick the last time we were there didn't want to replace the tire at all because she said I hit a curb, and that the tires that have a 50k mile warranty were already half worn out. Didn't ask for 4 free tires, an adjustment would have been fine, but I think they just wanted to get rid of us.

I Though AWD was used to descride a system that uses a center diff rather than a transfer case with solid connection between front and rear?

awd means you dont decide when all 4 wheels are going or not the car does, possibly by tcu or viscous center diff...

4wd means you can push a button or pull a lever like on a pickup and choose 2wd or 4wd and when you choose 4wd it locks all 4 so all 4 wheels are going no matter what the traction is.

there are scenarios like with the sti where you can pick the bias from 50-50 to 80-20 or something but you cant pick 2wd so all 4 are still driven and therefore its still awd not 4wd.

since you can pick 2wd with a 4wd vehicle if the front and rear tires dont match its no big deal as long as its in 2wd mode. because only 2 wheels are driven so there will not be any stress on the drivetrain.

having said that i've seen awd vehicles have 4 different tires for the life of the tires with no issues on the drivetrain. but i still wouldnt reccommend it.

-Alex

[quote="mexicanzero"]
having said that i've seen awd vehicles have 4 different tires for the life of the tires with no issues on the drivetrain. but i still wouldnt reccommend it.
[/quote

True. The problem is that some tire manufacturers don't actually size their tires the same. A 205/55-16 by Goodyear may be more than 1/4" taller than the same sized tire made by Bridgestone. I own a car that was the "victim" of mismatched tires- I had to replace the center differential as soon as I got it.

Apex3 wrote:Thanks for the info!

They ended up replacing all 4 because they had somehow worn down half to nearly 50% in 10k miles :shock: so they couldn't just do two.

Get an alignment right away. Do some searching around here for full background, but start with this:

0 toe, all four corners
Front: max. negative camber, same left and right.

If you had really bad tire wear you may have suspension issues. Having the alignment will either fix it or will help find the source of the problem. Either way, you don't want to kill your new set of tires over the next few thousand miles.

Subarus seem pretty tolerant of tire size abuse and being towed with one axle on the ground, etc... The 4wd system in my VW Syncro would be ruined in short order by any of these. It's a single viscous coupling in the front diff.