It maybe, the site also had imaages of the reverse ie a lip on the forward edge of the groove (sipe?) and provided possibilities form the causes of both. Fecked if I can find it now though
Try this one https://www.youtube.com/watch?v=Cqq5dEiADJY
Try this one https://www.youtube.com/watch?v=Cqq5dEiADJY