SF:   to tell ya the truth, I don't know what's been done to the motor but it was changed A LOT before I picked it up and USED to be one of the featured bikes on website exileturbo.com.
The website appears to be gone now but I've done a lot of "UN-Modifications" to make it a little more street friendly as it was a lot different that it looks now - but I didn't change the motor
at all. When I got the bike, there was little or no suspension (great for drag racing but no too street friendly).  There was a long extended 4 point swing arm and nicely done wide rear
wheel, an extra 15 degree rake  (which still exists) and a few electrical "mods".  According to the website (if I recall correctly) max boost was 30psi and 1/4 miles were mid 9s. I've removed the boost adjusting  handle  and passenger foot pegs to try and counter any possible temptations I might have on a nice day.
    For street use it should probably have an oil cooler. 

Hope the weekend is good!

wrote:

The early GSXRs used a tube profile like that. I don't know if it would be cheaper to cut up a frame to get the tube but its an option. sub-frame tubes are 20 x 25, main down tubes are 27 x 30. this is a proprietary alloy similar to 7005.

 

Funny you should say that, I actually have a 1988 GSXR1100J  Frame {last of the slabby's}, I won't be cutting it up though, they are starting to fetch good money....

The early GSXRs used a tube profile like that. I don't know if it would be cheaper to cut up a frame to get the tube but its an option. sub-frame tubes are 20 x 25, main down tubes are 27 x 30. this is a proprietary alloy similar to 7005.

 

wrote:

wrote:

Thanks zed, I'll come back to this when the forks are apart but that means I can go to 20-25mm and have some room to move on the rake. I assume you haven't noticed any extra flex in the forks? I'll probably be putting a brace on so it shouldn't be an issue anyway.

EDIT: Removed brain fart

No extra flex or any other issues.
Have done this to both RWU and USD forks into Z frames.
I have used GSXR, RF600, ZXR ,ZX7R, 9R, ZX10R, FJR1300 forks to name a few with their matching yokes and all handle very well.
Despite the differing offsets etc the main factor is keeping the frame stance and consequently the rake close to stock.
Having the back end jacked too high or the front to short results in shopping trolley handling that will tank slap to death and try to kill you once you are approaching 100mph.


 

Not trying to be argumentative but its a balance, The rakes used in the 70's and early 80's were all over the place, Kawasaki went from relatively normal, with poor offsets on their clamps, early 900's and especially the first Z1R's, to majorly conservative with the early GPZ's, 1000R's, 1000J's  and the like, they were much more stable,  but pigs in stock form to get around corners quickly, that's why most people who raced those bikes altered the frame rake. I helped a racer here recently take 4 degrees out of his GPZ1100B race bike by cutting the frame and repositioning the headstock, this was a common mod. His stock rake was 29 degrees. As long as the bike is set up properly there will be no "shopping trolley" effect, that happens when trail becomes dangerously small, raising the rear, or lowering the front is usually done to get the weight balance right, or more weight on the front wheel, you can reduce rake marginally and improve swingarm angle at the same time, again, you have to know what you are doing and stick between the accepted parameters... .....

Your numbers are looking ok, I think the swingarm is a bit long but it should work, we are only talking about 10 to 15 mm, this shouldn't make too much difference on a road bike, Your rake trail and offset are very similar to mine. I'm using Yoshimura's angle for the rear shocks at 54.5 degrees or 35.5, depending which way you look at it, apparently that was the ideal measurement Yoshi came up with on his late 70's, early 80's superbikes, I got that from a PDF file about his GS1000 superbike raced bike raced by Wes Cooley, Moriwaki used similar angles.  Just note that when you lay a shock down, you'll need heavier springs. The spring has less resistance the more angle is used.    What brand of shocks are you using, they look like Ohlins, or are they the Chinese replica's , If they are the multi adjustable Chinese shocks they are insane value for money, My friend pulled a set apart and they are very well made ?  I still haven't bought my shocks yet because I haven't set the swingarm angle , I want to be able to utilise the extra height adjustment on the shocks I'm buying, so i want my shocks to mount in their shortest position so I can raise the back a little when I eventually switch to 17 inch wheels, just to bring the rake back a bit.

@kzstreetfighter71: you don't use the quote too much, your posts are just wrapped up in the quote which makes them hard to find (I have enough problems with reading as it is!). The sticky is a really good idea. If I'd known what I know now (or rather, known what I didn't know) I would have been a lot more specific when ordering parts. As it was I went with the recommendations of the people I was getting the parts from (who really do have enough experience, but maybe haven't really spent the time getting these things to their full potential). One of the places definitely goes for form over function, the other place left me with the impression I wasn't really being taken seriously. Without you guys I'd be screwed!

@750R1: I'd really appreciate it if you could give me one last opinion on the current state of things. If I extend the forks and move the shocks as stated I'll end up with the following (with the rear axle at the front of its adjustment range):

• Rake: 24.5°
• Trail: 100mm
• Offset: 40mm
• Wheelbase: 149.5cm
• Swingarm angle: 11°
• Swingarm length: 520mm
• Shock angle: 62°

I figure this is an OK starting point- I can always lengthen the shocks or the forks depending on which way it needs to go and could even deal with swapping out the triples for a set with a drop if I needed to (though extending the forks may be cheaper). Changing the wheel base/swapping out the swingarm is something I'd like to avoid. The longer swingarm will give me more clearance - but probably more than I need.
Bear in mind this is for a street bike with the occasional track day and I'm not really one to push the limits. I like the corners but don't often get right up on the edge (although I haven't really spent any time at the track). I also don't really do high speed straights - comes from learning on the roads back home, much prefer the corners

wrote:

wrote:

The wheelbase is at 151cm so may offset the steep front end 

Unfortunately it doesn't work like that, its all about balance between the two, lengthening the swingarm a little can be beneficial to handling, but too long and the rear is wanting to react slower to turn in while the steeper front wants to turn faster. these older Kawasaki's have been developed for racing for well over 40 years, there's plenty of info online and I've posted some here, don't guess, do some research, you'll find the information you're looking for...

So not to come across a cheeky asking the question and only asking it for the hundreds of wanna be bike builders and myself.. that will want to do a front and rear end change for a variety of reasons.. what is the model or models swap to a modern running gear system that would best suit the big four?  Taking away rear shocks from the equation, this is something I have been pondering on since I have in my possession 2 frames, engine and bodywork sets that I will be building at a later date to a resto mod finish. I have 2 maybe 3 bikes in mind but what are your thoughts on it?

The biggest problem with a lot of these type of builds is people just bolt on what looks good, as you can see, there's far more too it than that. first you need to know what the stock rake of your frame is, for the Z900's, it was common practice here in Australia to use the Z650 triple clamps on these bikes, it made a noted improvement in handling, I think the 650's had a 45mm offset, I  do have a set of 650 clamps but they aren't here at the moment. They liked a slightly longer swingarm as well, Yoshimura and Moriwaki worked this out quite early on.
As I've said above, it also matters what size wheels are being used, and of course what your expectations are, do you want a lazy high speed bike, or do you want a race orientated suspension, or one that does both relatively well?   A lot of development of these bikes was done in the late 70's, early 80's, I've read that much stuff my head spins at times, luckily I have a couple of well know vintage racers to work off, these guys really know their stuff, my friend, where I work on my bikes, is a multiple Australian champion and a genius with engines and suspension, You guys would love the triple plug head he designed and built for a FJR1200 engine running on methanol, it runs 2 ignition systems to fire the plugs slightly at different intervals to burn fuel that's pushed to the outside of the piston crown, even with 2 plugs there was still unburnt fuel in the combustion chamber , so the 3 plug head has 1 central plug that fires first, spreading the flame front out from the centre where the second two plugs burn off the rest either side, its ingenious and worked brilliantly, it also gave a substantial HP boost. 
Maybe I just get caught up in the challenge, I'm a classic over thinker...!!!
 

The fork length numbers aren't particularily helpful because the don't factor the difference between the top of the fork and the top of the headstock. Drop and thickness of the top clamp have an effect. You could have a set of forks that are 800mm with a 30mm thick flat top clamp and end up at 770mm total or you could have a 770mm forks with a 30mm thick clamp with 30mm drop and end up at 770 total. There is only something like 10mm difference between stock KZ forks and ZRX forks but the stock triple has 30mm drop

Assuming a 25.3" front wheel diameter that Sanctuary bike is at 97mm of trail. That is probably at the lower limit of what is good and I wouldn't be surprised if it was a little twitchy coming out of turns as many race bikes are. That's fine for racing where the ragged edge is expected but most people, myself included, want a little more stability for highway cruising. Remember you are building a street bike.

I think if you massage what you have you can end up with a bike that handles well, even if it isn't optimized to perfection. I would tackle the things that will be the hardest to change once the bike is complete first (shock mounts) This way if you need to make changes to dial it in its not a huge pain later on. I ran the stock swingarm and stock ZRX triples on my 1000 for a year before designing and building the custom suspension. Part of the fun in building bikes (for me)  is slowly refining the bike, I just went threw a slew of smaller changes to my KZ1000 and it just keeps getting better and better.

These ZRX 1200 dims are all I have. I believe the 1100 has a slightly shorter wheelbase and some other small changes. These numbers are what I based my target on. I rode a friends ZRX1200 and was impressed with how it handled. I figured that was a good goal to aim for since its overall design and construction is similar to the KZ.

 

Thanks for that, some really good info there.

wrote:

don't guess, do some research, you'll find the information you're looking for...
 

It's less guessing and more trying to get the most out of what turned out to be less than ideal advice. Not really bad advice, just less informed than I assumed - and we all know what assumption is the mother of I should have posted more questions about the chassis here as I did with the engine 

More numbers:
I went back to the garage and adjusted the rear axle as far forward as it would go - 520mm pivot to axle.
Offset is 40mm
Forks are 770 (according to the internet, haven't actually checked)

My forks will end up sitting at a point about flush with the top yoke on the Sanctuary bike you posted - giving me about the same height as a 790mm fork on that bike (plus a bit more due to shorter offset).
I lifted the front about 14-15mm off the ground today to simulate lengthening the forks. Put me at about 24.5° (rough measurement, will do some trig later). Swingarm was at 11° and the shocks would sit about where the silver cross is in the picture below (pretty close to the sanctuary bike and where pretty much everyone else seems to put them). This would put the shocks at about 28° to vertical, as apposed to 18° with the stock mounts.
Lengthening the forks by 15mm and moving the shocks should sort things out. Wheelbase will be pretty close to the sanctuary numbers you posted (10mm longer swingarm, 5mm less offset), albeit with both axles about 5-10mm closer to the rear of the bike. Rake will be at 24-25° and trail will be a few mm longer due to the shorter offset. Should be a pretty good starting point though (still have room to move with fork height in the triples and adjustable shock length).

@DoctoRot: do you have any numbers for the ZRX rear suspension/geometry? The shocks are for a ZRX so I'd like to base things off that, couldn't find any numbers though.

 

wrote:

I think you should try a combination of several things
1. internally extend forks - 12- 20 mm I'm not sure but i think you can extend them a little without needing the top caps.
2. Mill bottom of top triple clamp. 15-20mm That sucker is way over engineered. You could cut it in half and it would be OK
3. Lower rearend till swingarm is at 10 degrees. 

Other things to consider:
Shorter swingarm? New swingarm is much longer than stock which means to achieve desired angle you need the rear end to be relatively higher.
Low profile rear tire
High profile front tire.

I sorted out point 2 today - it was more of a question of MOT paperwork. Milling out 15 mm leaving about 15 mm around the top bolt. Not going right across the bottom, just a 60mm circle around the bearing cap and nut. Will then cut a M28 x 1 thread in the stem and use a nut instead of the top bolt - will be easier than shortening the stem. This change will put me at around 23°/95mm rake/trail.

Point 1 is now on the backburner until I get the forks apart and see what is required. I'm pretty sure I can't just put a spacer at the bottom and use a longer damper bolt as the compression settings will get messed up (I think...). I think I'll look at adding about 15mm to the top of the damper rod [EDIT: that won't work ]. As you said, there should still be enough overlap between the uppers and lowers when fully extended.

I can shorten the shocks a bit (gets the swingarm to about 10.5°) but I probably won't bother moving the shock mounts to bring it up any more. May consider the mounts that scrirocco posted a while back just to lay them down a bit.

The wheelbase is at 151cm so may offset the steep front end - or it may just make things worse
Basically, once I've had the top yoke milled and decided what to do with the forks I think I'll just get the bike together and see how it rides (before I pull it apart again and paint it). If it's dodgy once I get it on the road I'll look at moving the shock mounts and/or putting a Zephyr swingarm on it. 

Thanks for the suggestions! I'm really hoping the changes at the front will get me where I need to be.