There is plenty of space to put a wider tire in to about a 170, but as you have already learned you need a wider rim.
What is it that you want to gain other than tire size? or just tire size. Your limitations will be that you have a 16" rim on the front as I do.
Your options:
1. Order custom rims from PVM or Dymag 16" and 18" combo. They are the only ones that I am aware of that will make this combo and they are of the 3 spoke variety. Most expensive option, but you will have extremely lightweight rims which will help give the bike the ability to ride faster.
2. Go to a 17" rear from a 89-90 Kawasaki ZX-7 profile would be 170-60-17. Issues with that will be that your front end will be very touchy to any ride height changes. Keep in mind that a 16" front changes and turns very quickly and is tempermental to ride ht changes. (170 leaves about 4mm each side - would suggest a 150-160 tire better.
3. Find the forks of a newer zzr600 or ZX600r and change the front end and rear end. I've seen other mods similar that have worked, but it depends on how patient you want to be at getting the ride set up right.
or as Qkenuf4u stated, you could have Kosman do spacers etc etc.
Come by the Gpz forum and several mods are listed for what you want to do and by people who have done it. I chickened out for now and went with option #1, but I also wanted to lighten the bike and this was one of the quickest ways to do it.
Daron
www.gpz900r.org
