If you want the PR3, you will have to get a 170/60 rear, which works fine (it is ST13 size) - the 160/60 makes the rear sit a bit too low for my liking. If a 110/80 x 18 front is not available, a 120/70 x 18 works fine as well (later ABS bikes uses the wider front tyre anyway, but has a wider rim as well)