Saw Tooth tyre wear is just normal wear for the non driven wheels, ie rears on a front wheel drive car.
It occurs especially if the tread pattern has non connected blocks in the inside of the tyre.
If the tyres have a non-directional tread pattern then you can switch tyres from left to right to even up the wear.
Here is a description from Continental
What is heel and toe wear?
“Saw-tooth” wear is a wear pattern caused under normal usage with normal suspension settings. This is the outwardly visible (and audible) manifestation of various distortional forces at work on the tread. To explain this, it is better to first say something about ”tread design”.
Tread grooves and sipes – a source of noise – are absolutely essential in ensuring safety on wet and flooded roads. In the case of low-profile tyres in particular, a higher percentage of tread void is necessary to take up the water and to improve the protection against aquaplaning. Cross-grooves for water drainage form “free-standing blocks” in the shoulder area. These shoulder blocks can wear to leave the “sawtooth” pattern as a result of rolling mechanisms under certain operating conditions. These operating conditions include: Long, straight journeys at constant speed Moderate driving style Suspension geometry (alignment/camber).
As the tyre rolls along the road, the free-standing blocks deform as they near the tyre‘s contact patch. They are compressed as they come into contact with the road. As they lose road contact they “rub” the surface while snapping back into their original shape.
The result is higher wear on the block run-out edge. This wear pattern is more likely to occur on non-driven wheel positions. A minor amount of “saw-tooth” pattern wear is normal and has no discernible effects on comfort. More conspicuous wear of this kind points to specific operating conditions (improper inflation, excessive toe-in, low-wear applications).
Tip: In order to gain even tyre wear, the position of the tyres on the car should be changed at regular intervals (unless otherwise recommended by the vehicle manufacturer). The position of the tyres should be changed in good time, at the latest when changing summer/winter tyres.
