Tires-How big can I go on police wheels?

I got metzlers (880 and 88) on now, but how big can go on without mods?

The metzler 880's and 88's are about as good a tire as you can get for what you've got.
You probably have a 110 or 120-18 tire on the back and that's as big as you want to go with the original rims. you might be able to get a 130 on there but that's pushing it. That tire was specifically called out for in the design of that bike so that it will maintain it's lateral stability in the twisties with the extra weight the cop bikes usually carry. A fatter tire will give you more of a power patch and help with the braking, but the narrower tire will give you more control in the curves and in the rain. if you go over a 120 witdth you might want to consider new wheels to go with it. check out the police motorcycle forum for more cop bike specific information. Those guys know their cop bikes like these guys know their regular KZ bikes. autos.groups.yahoo.com/group/kz1000p

Thanks,
Yep I got a 120 on the back.
Just to note: I have nothing but good things to say about them. They are wearing like regular Levis ( will be around for a while and perform great), but the grass is always greener isn't it?