TOPIC:

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.

 

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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?

wrote:

The fork length numbers aren't particularily helpful ...

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....

 

Pretty much what I am thinking at the moment. I think I'll be pretty well sorted if I can get away with a small increase in fork length (15mm) without need extensions for the outer tube. Add the shock mount change for more progressive rear shocks and I'll have a pretty good base to refine over the years. I'll end up with a bit more trail than I had on my hornet, with much better suspension and a bit longer wheel base. As long as the suspension is set up properly, I think I'll manage to have fun riding it
BTW: thanks for the numbers. 

@kzstreetfighter71: I'd quite like a list of good swaps as well. Seems the ZRX front end is pretty popular - just need to get the top of the triples about flush with the stem nut  - but I'd be interested to know which modern front ends are being used (USD forks). BTW: you need to find that little red button so you reply doesn't always end up in the quote

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.

The excerpt I posted is for Sanctuary's street bikes with 18 inch wheels, it says so in the excerpt, the pic was meant as a guide or reference, they would adjust that according to the track, I should have stated that.  97 mm is pretty good for trail using the measurements mentioned, if that's the case, I haven't run them through my calculator, I'd want exact measurements for that, or at least a full set of numbers.  The old Honda fours only had 94mm of trail and weren't known to be "twitchy, the Triumph triple i got my forks off had even less, Rake,  22.9°, trail 91.44 mm (3.600 in). Its not only trail that bike nervous, its the combination of all four, rake , trail,  wheel diameter and offset...  The ZRX numbers are for 17 inch wheels, Calum is using 18's which require slightly more rake than a bike using 17's, around 1 degree.  I absolutely agree with the fork length, Calum needs to factor in the differences, that shouldn't be too hard.
I'm setting my frame up with the wheels on at the moment to determine shock length and swingarm angle, my triples are 40mm offset, ideally they would be 45mm  but i'm changing to 17's in the future and 40mm offset is spot on, i'll have to raise the rear a touch to lose 1 degree of rake, or lower the front or a combination of both,  and it will be very close to perfect, I'll then fine tune it on the road....
 

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...!!!
 

You see you hit the nail on the head there and I’m dealing with something similar in a bike i have in my possession that was built by a KZrider member that was built with information gained here and it’s all off. Iv done what I can but the whole front end needs a lot of work in the near future, more than I had hoped for. It would be a real help if the was a sticky thread at the top of the project that properly illustrates what bolting a non stock front and back end does. I’m a graphic illustration artist as part of my job and would gladly illustrate it some one would do the math side and push for a sticky thread so more builders don’t jump and buy and bolt on the first front end that they come across and do their selves s proper injury without knowing what their choices do to the handling of the bike..
 And I use the quote to much... sorry... 

wrote:

You see you hit the nail on the head there and I’m dealing with something similar in a bike i have in my possession that was built by a KZrider member that was built with information gained here and it’s all off. Iv done what I can but the whole front end needs a lot of work in the near future, more than I had hoped for. It would be a real help if the was a sticky thread at the top of the project that properly illustrates what bolting a non stock front and back end does. I’m a graphic illustration artist as part of my job and would gladly illustrate it some one would do the math side and push for a sticky thread so more builders don’t jump and buy and bolt on the first front end that they come across and do their selves s proper injury without knowing what their choices do to the handling of the bike..
 And I use the quote to much... sorry... 

PM sent..

@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

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.

Thanks, that's what I wanted to hear Now I just need to check the overlap on the fork tubes so I can decide if I can just extend them internally or whether I need to make extensions for the uppers.
The shocks are öhlins   was a hard decision but they were cheaper than the wheels! They have 10mm of adjustment (365mm +8/-2). They're for the ZRX1100 which is why I'm trying to find out what angle the stock ZRX shocks are at. From pictures it looks like the 62° will be pretty close.
 

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Thanks, that's what I wanted to hear Now I just need to check the overlap on the fork tubes so I can decide if I can just extend them internally or whether I need to make extensions for the uppers.


 

On all the forks i have internally extended the figure has been a constant 32mm.
This has been achieved by a simple screw on damper rod extension.
Forks with damping adjuster on the bottom of the leg need a 3mm hole through the length of the extension for the passage of the fork oil.

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