Originally Posted by sakurama
If you're going to offer 17/19 you should consider offering the rear in a wider size of 5-5.5" which is the size of the new 1190 and the water cooled BMW so those sizes will become much more popular. 4.25 is a 150/70-17 which is narrow for the bike and street rubber. I run 160-170 and am waiting for a good 180 option.
Why? A 150 rear tyre is plenty for 100hp.