04 Mazda3 - "scalloped" inner tread on rear tires

[wes8398]

I just changed over my fiance's '04 Mazda 3 to winter rims/tires and I noticed that both rear tires are "stepped" on the inner tread. It's like every other tread block is worn down. I googled it and I think the correct term for this is "scalloping". What I gathered from my googling is that weak shocks and/or worn suspension components could be the culprits, BUT I wasn't sure if that's still the case when the 'scalloping' is only on the inner side of the tread. Does that implicate anything else?
FYI the car has about 120,000 km (75,000 miles) on it and is a highway commuter which does a 200km (125 mile) round trip from 2 to 5 times a week.
Any suggestions/ideas would be greatly apprecaited. I don't want my fiance putting a ton of k's on these brand new winter tires and messing them up too.

[Default User]

Under inflated tires mixed with bad alignment.

[Walrus]

Rear alignment off - tires are toed out. This drags the inner treads first and causes cupping of the tread blocks.

[wes8398]

I know for a fact that the tires have never been consistently run under-inflated. The alignment thing is possible though. I had an alignment done last year, but cheaped out and just had the front done, thinking the rears would probably be fine. I guess not!

What about weak shocks, etc? Is alignment more likely the culprit?

[JSI]

I'd say more likely worn out shocks.

Had that happen on a previous car when the rear shocks were wearing out.

[bubba1983]

common issue on the trucks at work with stepping of the tread blocks...weak shocks/some form of alignment prob

[wes8398]

Had the alignment checked today and everything is within factory spec. I guess new rear shocks are in order.