Hey Terry - probably wasn't the tyres, more likely the hinge in the middle of the frame on the Z1 needed oiling.........
I had a GPZ1100 from new for a short while (very short) back in the 80s and Kawasaki were still installing the factory hinge then - a good thing in a straight line, but evil in the hills. After that brief defection from Honda I returned!
No doubt your mate Tom not only changed his undies, but also changed to a Honda....if he was smart.
I've got a mate here who is a pretty good rider, has a couple of modern sports bikes and a perfect Z1 like new, and when he takes it out he scares the crap out of himself and shakes his head at how they were ever considered to be the "best". Our roads weren't designed for Z1s. Nice grunt though. 
Peter.
G'Day Pete, yeah you're right mate, I had a 1975 Z1 900 which was supposed to be the best handler of the lot, but it was crap. Marzocchi shocks, progressive fork springs, fork brace, steering damper, and new Pirelli Phantom tyres made no difference at all, it was scary. I actually sold it to buy a Harley Sportster, and I'll tell you right now, to all the wankers who will tell you Harley's don't handle, well, they don't, but they still handle better than Kawasaki Z1's, ha ha!
By contrast, Suzuki blatantly copied the Z1's engine for the GS750-1100 range, (some engine parts are supposedly interchangeable) but totally redesigned the frame, and the big Suzy's were lauded as probably the best handling Jap bike of the 1970's, and the overall best bike in the world, at the time. I've got several GS Suzuki's and even now, they are still great bikes, with the same "Grunt" as the Z1, but still fun to ride fast once you get off the freeway! Cheers, Terry.
