Q. I was getting my GSX-R out from hibernation and I’ve noticed some stepped wear on the front tyre, it probably occurred with that end of the year track day and 300-mile ride I did last October.
A. There are obviously no engine forces acting upon the front tyre – after all, it simply rotates to keep up with the rear wheel. But one of the two main forces acting upon the front tyre is braking.
Much of your braking is done on the entry to corners, from upright to the initial angles of lean. This throws much of the bike's and rider's weight onto the front wheel.
While you are leaned over in the corner your bike would like to throw you into the hedge, but the combination of the tyres and the suspension acting upon the tyres to keep them in contact with the road, prevent you being spat off.
As you can imagine, with a significant amount of weight on the front tyre, and with that tyre trying to prevent the bike heading for the hedgerow, there are big forces at work here - hence a greater degree of tread wear on a front tyre’s shoulders than in the centre of the tread.
Tread pattern design has been refined over the years so that irregular wear characteristics are far less of a problem than they use to be, but ultimately there is only one perfect tread pattern design that avoids irregular tread wear totally and the tyre manufacturers cannot all use the same design, so they use variants of this pattern.