changing sprockets

OK, guys, I need some advice. Back in my younger days my big red hotrod wasn't red enough, loud enough, or fast enough. In my twilight years I'm looking for something slightly less obvious, and fast over the long haul. So the GPz will be painted a tasteful platinum pearl and fitted with a Rifle Sport fairing and soft bags.
The GPz1100 is thoroughly in pieces on my garage floor. It needs a new chain and rear sprocket, so # of teeth is open for discussion. Calculations show that the stock 15/41 ratio gives me about 4100 rpm @65 mph, 4750 rpm @ 75 mph. As I recall from my days of riding the bike (last ridden in March of 1990) it always seemed to be buzzy on the highway, and downshifting was unnecessary to pass. On the other hand, changing the rear sprocket to 35 teeth would mean 3500/65mph, 4050/75mph, and a 32 teeth would give me 3200/65mph, 3700/75mph. So, how low can I go? Where do I lose the torque curve?

I can't imagine running a small rear sprocket on a GPz, especially a 32 tooth. The stock 15/41 will easily take you all the way to 155 mph and not even redline. IIRC it's maybe 7500 rpm.

I put in a 42 tooth rear today on mine. It's not much of a difference, but WTH right?

My opinion - you'll regret going too low.

I think the problem you will run into by going with to great a ratio change is taking off from a stop. I think it will be real hard on the clutch.

Going from a 41 rear to a 35 rear is about like going up two teeth on the front, and I suspect that is pushing the limit. Only way to know for sure is to try it.

to GPZ1100: Huh? 15/41 puts 135mph@8500rpm, which is redline, which is the top speed both Cycle and Cycle World observed in '81. OK, Kaw speedos are all WAY off at the top end, but you don't believe yours, do you? The 15/42 actually lowers top speed, and uses up an engine faster. It just allowed the '82 GPz to get better numbers in the Superbike drag war of the early '80s.



To steell: I appreciate your concern. One of the real annoyances about my GPz was the goofy shifter mechanism that doesn't allow you to start up in second. When the rear wheel is stopped you can only get first or neutral. So I never accidentally started up in second. But I always thought it had enough torque to do it. But I've got to tell you, this bike is going to rack up some miles on country roads at 65-75 mph. I guess I'll try the 35.

Understand that I weigh 235 lbs so it takes a little more to get the bike moving with me on it than it does with a 100 lb rider

When you order a chain you should get one with enough links that the axle will be in it's rearmost position with the 35 tooth sprocket, that should give you enough room to go to the next larger size sprocket if 35 is not enough.

If you have the cases split, it's a simple matter to remove the "Neutral Finder"

Post edited by: steell, at: 2006/09/04 01:21

About the 135 @ 8500 - my statement was from recollections of about 8 or 9 years ago when I used to top out a 83 GPz1100 regularly. I didn't do the math. Redline on my 83 is 9500. I remember it doing a stated 155 at quite a bit less than redline - maybe it was more like 8000 or 8500. Sorry for any confusion or incorrect statement.

I went from 15/41 to 15/42 because I want a slightly more usable power band. I don't hit the century mark too much any more so the top speed doesn't matter much.

My opinion is that 32 or 35 teeth on the rear sprocket is going too far - you'll be lugging a lot.

Good luck with your Kaw and let us know how it works for you!

I don't remember the RPM's or the tooth count after 23 years but on my 80 KZ1000 I changed to the biggest front sproket that would fit without grinding the case and the smallest rear sproket and I could still smoke the tire or bring the front end up with ease depending on where I sat(+/- a inch or two). Droped the Hiway RPM's and made for a much smoother ride.I saw only benefits and NO draw backs. If it were a smaller bike/less power then you might get in trouble changing the ratio.

<--agrees with mikes82kz1100:whistle: