1977 KZ650C Resto Mod Question

I am starting to look at parts to do a resto mod to my 77 650, is a 2004 GSXR750 a good donor bike for the suspensions front and back? Thanks for any and all assistance!

It all depends on what you expect the bike to do post modification. The GSXR swingarm will be at least 6 inches longer, the Front end will have a 30/35mm offset triple clamp set giving you much more trail, the bike will handle like a pig, probably ok in a straight line, because of more trail and longer swingarm, but if you like canyon carving then straight up bolting on these parts will make it handle worse, if you are just going for looks then go for it, if you want it to handle, talk to people that know what they are doing...

Yup! Before screwing up the bike's handling by putting the wrong stuff on the bike I highly recommend the following video be watched. I seriously doubt the KZ650 bikes shown would break the 750cc records if the handling sucked. Other than replacing the rear shocks with S&W units I don't think they made suspension changes. Ed

Yes, but a big oval doesn't test but so much with regards to handling. I can tell you that my KZ650 handles, rides, stops, etc. way better than stock.

What have you done to your 650, and to what do you compare its "handling" ?. As far as that video goes, it definitely tests aspects of the bikes handling...

I didn't say it didn't. I have stiffened the frame with bracing, added '95 ZX6R front and '92 GSXR600 rear monoshocked. I did go through the stock bike first with progressive springs in the forks and new progressive shocks for the rear with a boxed steel swingarm. I have owned mine for almost 20 years and continue to tweek it now. I built it for me, and I do think that with the weight saving in rotational, unsprung weight, the ability to adjust rebound and compression for my weight, and a massive upgrade in braking power and feel, that it does all of what I have claimed. I do have reservations about the seat for long rides however.

Unfortunately, we lost a lot of the photos in Bdog's build thread (link in his signature). It would be a good thread for the original poster to read through since it sounds like he is looking for a similar project.

You buy a brand new ZX-10R, what improvements could you make to the stock setup that would make a significant difference in performance on the street for an average rider?

Part of what makes modding these old bikes so much fun is there is a lot of room for improvement because our understanding of chassis design and metallurgy has come so far. The KZ650 were good for their time, but to think that motorcycle suspension design peaked in 1978, or that new knowledge cannot be applied to old bikes is absurd. Kawi didn't change many things on that record setting bike because that would have made them unable to pursue the record. Proper race bikes of the day most certainly ditched the stock forks, look at Dr. Gamma's period racer.

I'm not advocating slapping any USD fork or mono shock on either. There are many different routes to improve the performance of these bikes. It takes research and an understanding of suspension design to get good results but they can most definitely be had.

Stock KZ650 seat is great. I rode from Chicago to Denver on a straight shot several years ago. 16 hours in the saddle no problem!

DoctoRot wrote: ........................... It takes research and an understanding of suspension design to get good results.................

Exactly! Unfortunately there are many folks who think any newer suspension setup will work fine for any older bike without considering such things as the bike's geometry, weight, etc. Gaining a real understanding of suspension design takes more time and energy than those folks are willing to apply. Done correctly can bring excellent results; done based on what can be obtained cheaply and/or quickly without regard for the physics and geometry can easily lead to a bike that handles worse than when it left the showroom floor. Ed

Bdog wrote: I didn't say it didn't. I have stiffened the frame with bracing, added '95 ZX6R front and '92 GSXR600 rear monoshocked. I did go through the stock bike first with progressive springs in the forks and new progressive shocks for the rear with a boxed steel swingarm. I have owned mine for almost 20 years and continue to tweek it now. I built it for me, and I do think that with the weight saving in rotational, unsprung weight, the ability to adjust rebound and compression for my weight, and a massive upgrade in braking power and feel, that it does all of what I have claimed. I do have reservations about the seat for long rides however.

On the track, a stock 650 would go round better than your bike with its modifications. Not trying to be an ass here but, Handling isn't about better brakes. You've altered every aspect of the bikes suspension without knowing what each change does or effects. Rebound , preload and compression are only adjustments, fine tuning, its the geometry that sets up a great handling bike. What is your fork length, {centre of axle to fork top} what is the triple clamp offset, what is the front wheel and tire diameter, what is the length of the swingarm, what is the angle of the swingarm ? ALL of these things have an effect on "handling", whilst I have no qualms with the new braking ability of the bike, and it probably looks great, It won't "handle" better than the stock bike. I'm in the middle of building a bike at the moment, I have spent hours doing the calculations for the new suspension {this isn't the first time I have done this}, I have had new fork tubes made to the correct length i need, I am using an 18 inch wheel set so the wheel with tire measurements, along with rake and offset are all used to calculate the correct geometry, I will end up with a different rake and offset which will give me about 100mm {4 inches} of trail, an ideal number for this bike with this set up. At the back I am using an alloy swingarm, twin shock at 500MM in length, the same length Moriwaki used on his Moriwaki Kawasaki monster from the early 1980's, that bike was a giant killing machine and started of Wayne Gardners international career, I then have to calculate shock length, Both with and without rider, to establish not only the correct swingarm angle, but what effect the rear has on overall rake, as this effects rake and trail at the front as well, measuring suspension "sag" and spring rates are also part of this equation. If I were to use 17 inch wheels I'd have to start calculating all over again as the smaller diameter wheels turn in quicker the the 18's I'm using. I'm not trying to talk down your bike, Its just that far too many people think that by simply bolting on more modern parts it makes the bike "handle" better, in all reality, that's just not correct... For well set up older bikes just look at AC Sanctuary's bikes, they are built to a formula that they know works. I'd also like to point out that even Kawasaki got it all wrong with the first Z1R, they simply bolted on a 18 inch wheel and did nothing about the triple clamp offset which produced real small trail numbers and a poorly handling bike, all the race bikes of that era used 18 inch front wheels, so Kawasaki simply bolted one on, it didn't work, a simple change of triple clamp offset would have made all the difference, they went back to a 19 inch front on the next model.

DoctoRot wrote: The KZ650 were good for their time, but to think that motorcycle suspension design peaked in 1978, or that new knowledge cannot be applied to old bikes is absurd. Kawi didn't change many things on that record setting bike because that would have made them unable to pursue the record. Proper race bikes of the day most certainly ditched the stock forks, look at Dr. Gamma's period racer.

Great comment in defense of the video.

To say that continuing to turn left doesn’t take handling to make it go faster is wrong. Technique and geometry are what separates speed from HP.

750 R1, I have found that when someone prefaces any statement with “I’m not trying to be an ass” they are about to be an ass. Your remarks are being made, at great length, without knowing the dimensions of my bike. I did a lot of reading from Tony Foale when I was younger and did take measurements when I was setting the bike up. Now, it has been a divorce, a heart surgery, a new marriage, and a child later so I’m not entirely sure off the top of my head what they are. But I will go measure the bike this evening and see what’s what. I can tell you I went through three front setups and 2 rear before I found what suited me 12-13 years ago when the project was mothballed.

To the OP, be prepared to weld any brackets you may need if you are going to change foot placement, the ‘77 has a goofy foot peg mount from the factory that was changed one year later.