Suspension component interchangeability

How the heck do you figure out whether you can use shocks, springs and forks from other models of bikes? Obviously you could become the wreckers best friend and swap parts for a few months, but I'm after more realistic suggestions.
Springs must be very easy to match since as long as it fits in the tube (perhaps with a custom spacer) and has the desired spring rate it does the job.
Rear shocks are more difficult as the linkage ratios vary between models and mounting and packaging is more complicated. But there are still interesting options e.g. apparently the GPX600 shock is a good upgrade from the GPX250 one.

What it boils down to is; how can I upgrade my GPX's suspension without forking out $$$ for new components and without buying used components from overseas (e.g. EX500 springs).

Very good question!
I'm interested in some ideas from people as well.
I have my stock ZX7 rear shock I'm wanting to squeeze into my ZXR400 trackie, which I've heard could be possible.

How the heck do you figure out whether you can use shocks, springs and forks from other models of bikes? Obviously you could become the wreckers best friend and swap parts for a few months, but I'm after more realistic suggestions.....

Most of this stuff is trial and error. It helps if you do have a friendly wrecker, no doubt about that. A lot of research into whatever you want to swap is also needed - google every biker website, chances are that someone *somewhere* has already done the changes that you want to do (unless it is a really obscure swap of bits). Checking with suspension experts is the first place you should try, just to determine if the rear shock you want to use is any good for its intended new use .....

You can make anything fit, and work, on anything you like, if you throw enough money at it, and this is ultimately what determines the success or otherwise of your swapped suspension bits....

ummmmm get out the tape measure and measure up the old one and then anything up to 10 mm longer should be okay so long as it has gas in it and doesnt have oil pissing out of the seals.

A spring is a spring they come in a few different lengths and diameters get one that is the right lenght and diameter to makle it easy to adjust.

you can fiddle with rebound and compression but i find that so long as you can get enough rebound you ccan change compression charictaristics by changing the spring....IE a heavier rate spring will require more rebound dampening and less compression dampening than a lighter spring you just have to try one.

ohh and punisher i recently had a fiddle at a zxr400 shock it has a funny clicker on the back with 4 settings and i would be looking for something else as well maybe a second hand ohlins out of something kawasaki.

I have a second hand penske in the back of my six, i have been told it was originally supposed to fit a 6r but will also fit a 7r/9r...its approximately 10mm longer than a stock 03/04 6r shock but works just fine all that linkage rate stuff refers back to spring rate.

How the heck do you figure out whether you can use shocks, springs and forks from other models of bikes?

In a lot of case, by inspection.

You don't need to be John Holmes... no, wait, that should be the other Holmes, the one with the hat and the pipe... either way, you don't have to be that guy to look a 2000-model ZX6 parked next to a 2000-model ZX9 and go, "Those bikes are wearing the exact same shock and forks. It'll only be the internals that are different."

Beyond that, you twig to the fact that recent Japanese bikes come fitted with suspension supplied by one of only two manufacturers; Showa and KYB (pronounced Kayaba, after the Japanese vocalisations representative of the three letters; Ka Ya Ba), each of which has their interpretation of eyelet/clevis dimensions and shock body lengths (if not necessarily the travel). What this boils down to is that two bikes fitted with KYB rear shock sin a similar configuration to another (eyelet-eyelet or eyelet-clevis, bolted to a dogbone-type linkage or a one-piece linkage) are likely going to be cross-compatible... eg. the aforementioned eyelet-clevis 1998-2002 ZX6 and ZX9 KYB rear shocks fit 1996-onwards GSX-R600's and 750's, Showa
eyelet-eyelet rear shocks fitted to Honda VFR800's fit VTR1000's and Blackbirds.

Further, something manufacturers are loath to change are steering head dimensions. Thus, the complete front end from a 2002 CBR954RR bolts straight into a CBR600F from 1988, and the crap rwu forks and soggy brakes on a TRX850 can be fecked off in favour of the fully-adjustable upside-downies and six-piston calipers from a YZF750R.

Ultimately, the best way to find this sort of shit out is to keep an ear on the technical sections of forums like this one... not even through asking direct questions, but just keeping an ear out. If someone does an interesting transplant, chances are they'll do a write-up on it. Once they do, read about it and file it away for future reference.

What it boils down to is; how can I upgrade my GPX's suspension without forking out $$$ for new components and without buying used components from overseas (e.g. EX500 springs).

The problem there is that your bike is a 20-year-old design; so, any compatible parts from higher-spec bikes are going to come from bikes which are also 20 years old and, to put it mildly, 20 years ago, suspension on bikes was unspeakable shite. What's more, whatever you might find in wreckers by way of bits is going to be 20-year-old, worn-out, terminally-shagged unspeakable shite. Specifically, 20 years ago, shocks fitted to bikes didn't take too kindly to being rebuilt, so once they're shagged, they're a bin-and-replace job.

For a concrete answer... you're pretty much, unfortunately, screwed. Fitting the complete front and read ends off a ZZ-R250, which may or may not be possible (the forks'll fit, swingarm not so sure) will give you the ability to run 17" wheels, which opens up tyre choice.

Ultimately, you'll be able to fix the forks with heavier oil and stiffer springs; find out on Ninja250.com what the part number of the Ohlins or Eibach springs everyone fits is, then contact the importer (Eibach have an Australian outpost, and Steve Cramer Imports do Ohlins) and have them order you in a set. You'll be able to fit them yourself and refill the forks with 15W oil inside of a couple of hours unless you're someone who must stay 10m or more away from any and all toolboxes by court order.

Rear end, you're in real trouble, for the aforementioned reasons... a stiffer rear spring would be easy enough, but because the shocks are non-rebuildable (not 100% on that one, but that was the style at the time), you couldn't upgrade the already deficient damping to cope with it and you'd end up with even more of a bouncy-castle ride than you've already got.

As an outside hail-Mary longshot, look into whether a ZXR250 shock will fit; I'll have a can of surprised paint on standby, so I can colour myself with it if they end up cross-compatible.

The short answer is, unfortunately, going to be the usual "Grit your teeth and hold out until your P's expire, and save your experimenting for a bike which'll actually go faster as a result.

[ because the shocks are non-rebuildable (not 100% on that one, but that was the style at the time.

Yeah, it used to be the case that these things were throw away items. However, there are a couple of people around Oz now who claim to be able to not only pull them apart, but also to fettle them and put them back together somehow. I can't remember where they are ATM, I'll dig aroundthe archives in my head over the next few days and try and find who it is.

The rear shock in my GPX decided to stiffen itself up, to the point where it had only about 10mm of travel. I replaced it with the adjustable one from a ZZR250, which is about 10mm shorter but seems to work fine.

Ok, I did some membering and some googling and came up with the following.

Promecha suspension claim to not yet have seen a shock they could not rebuild! promecha.com.au

Hagon do a brand new replacement shock and spring which retails at $699, but who knows what they might sell one for??

And naturally enough, Trevor Manly rebuilds OEM rear shocks also! tmperformance.com.au 0437 071 595

HTH

Thanks for the awesome reply I-K. The info about shock mounting configurations and steering head geometry sounds promising, even if it's still a fair bit of effort (would be nice if there was a pick-a-part style motorcycle wrecker).
I know the springs are easy, I've already changed the fork oil and cut up some longer preload spacers and increased the oil leve, but alas, the springs are so soft that it's still not enough to stop bottoming out.

Rear end, you're in real trouble, for the aforementioned reasons... a stiffer rear spring would be easy enough, but because the shocks are non-rebuildable (not 100% on that one, but that was the style at the time), you couldn't upgrade the already deficient damping to cope with it and you'd end up with even more of a bouncy-castle ride than you've already got.

Yeh but I-K if the thing is deficent in compression but has plenty of rebound a stiffer rear spring would be the go because it needs more rebound and less compression anyway.

The last couple of kawasaki shokies i jumped on felt this way to me a 9r and a 400 one but hey you really have to be there to see whats going on and suspension is a hard thing to get your head around if you dont know whats going on...it comes easy with time and patience and a few dollars spent.

...if the thing is deficent in compression but has plenty of rebound a stiffer rear spring would be the go because it needs more rebound and less compression anyway.

It's a GPX250. It won't have enough of either. Putting in a stiffer spring will just turn it into a more vigorously bouncy castle...

The last couple of kawasaki shokies i jumped on felt this way to me a 9r and a 400 one...

I put an Ohlins rear on both the 9 I sold a couple of months back and the 9 I just put on the road; the issues I looked to correct were the too-low rear ride height (they're a C1 and a C2; no rear ride height adjuster) and the unsophisticated damping, more so the compression side. The stock shock stays too rigid over bumps, but gives way too much under weight transfer due to throttle or brake application.

that's a pretty typical kawasaki set-up,way too much high n not enough low speed damping. The later model stuff is better in this respect.

that's a pretty typical kawasaki set-up,way too much high n not enough low speed damping. The later model stuff is better in this respect.

Yeah, I found out about the low speed side within three weeks of my first ride. I bounced (maybe twice per second, up and down and left and right) around a ~100 km/h right hander after overtaking some cars. They probably thought it was funny. I'm glad I had the presence of mind to not whack the brakes on and drive off into the bushes.

that's a pretty typical kawasaki set-up,way too much high n not enough low speed damping.

To be fair, that's a pretty typical off-the-shelf KYB/Showa thing. Crude bypass circuits with crap flow characteristics are easy (read "cheap") to drill, and the result is excessive high-speed compression damping.

Conversely, a shim stack with fewer thick shims is cheaper to assemble than a shim stack with more thinner shims, and because the thicker shims won't flex as much, they have to be made to offer less damping as a baseline.

Practically every friggin' bike out there has that exact problem; jagged high-speed damping, doughy low-speed. You just feel it more on the compression side.

that's a pretty typical kawasaki set-up,way too much high n not enough low speed damping.

To be fair, that's a pretty typical off-the-shelf KYB/Showa thing. Crude bypass circuits with crap flow characteristics are easy (read "cheap") to drill, and the result is excessive high-speed compression damping.

Conversely, a shim stack with fewer thick shims is cheaper to assemble than a shim stack with more thinner shims, and because the thicker shims won't flex as much, they have to be made to offer less damping as a baseline.

Practically every friggin' bike out there has that exact problem; jagged high-speed damping, doughy low-speed. You just feel it more on the compression side.

Hear Hear!!!! and the quality of the shims does not need to be as high.

Neil