What has caused this wear in tyres?

[MOA4B9]

Today I took the winter wheels off and swapped for summer ones. I noticed these thin grooves close to the outside and inside edges of the tyre. They are about 0.5-1mm deep and they are present on all this winter tyres. I'm pretty certain they were not there when I put them on. I've done about 2 weeks of driving around London and then 1700 mile trip to Switzerland. My initial thought was that the tires might have been under inflated and that's the place the rubber was folding over. I went with tyre pressures from the sticker on the door for the same size tyre and S+M next to it. The Dunlop Winter Sport 3D also has the S+M making on it.
Have you ever seen this type of wear? What do you think has caused it?

 

[Jimbbobw1977]

They are fine. Google tyre sipes

 

[Nickfrog]

LOL. This has to be a wind up and I fell for it for a few seconds!

 

[WM Jon]

Take it you’re talking about this continuous groove running round the circumference of the tyre? Looks unusual to me and can’t comment on what caused it but it’s not immediately clear from your image, I’ve circled it in red to help highlight it.

 

[WM Jon]

Present on this image of a new Dunlop M+S tyre. I have these in my garage but hadn’t noticed it before.

 

[MOA4B9]

Take it you’re talking about this continuous groove running round the circumference of the tyre? Looks unusual to me and can’t comment on what caused it but it’s not immediately clear from your image, I’ve circled it in red to help highlight it.

Yes, that's the one, thanks for highlighting them, probably didn't make myself clear about which grove I ment. I didn't notice them when I was putting the wheels on but looks like they were there from the begining.

 

[Nickfrog]

Sorry about my post ! I too thought you meant the sipes.