Installing Donor Suspension (good Idea Or Bad Idea?)

Tmod

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Hi Members,

This is my opinion and I am using issues that I had working for Race Tech dealing with riders that had decided to install suspension from other bikes and applications on their bike.

If you read across the web you may find riders that are installing or recommending suspension components from different bikes/applications and installing them on bikes they were not intended for. While this is fine if you do some home work what I had found is that a majority failed to do the home work and ended up calling in so we could guide them in the right direction as they ran into issues.

I will break this down into individual notes for those that are interested in grafting suspension components from one bike to another to try and make the transition a little less painful and safer as the wrong suspension on the wrong bike may be unsafe to ride. I am going from my memory so I may have to come back and add to this list as times goes on.

(1) Don't assume that because the center to center length of the shock or the fork length is the same that it will work fine, Shock bodies/Fork sliders as well as shaft/fork travel can be different even though they are the same length so you end up with either too much or too little travel. Too much travel is worse then less as the tire may hit the underside of the bike at the most inopportune time.

(2) Because it has clickers it has to be better then what I have syndrome, While this may hold true in some instances let's keep in mind that 90% of the performance of the shock/fork is the valving on the piston, The other 10% is the clickers. All the adjustment in the world is not going to make up for the lack of the correct valving inside the shock/fork. If this were true we would not have pistons with shims on them but only clickers that would take us back to orifice damping.

(3) Bigger shock bodies are better as they hold more fluid, While there is some truth to this one several of the aftermarket companies use small body shocks and they work perfectly fine as long as you use a very hi quality suspension fluid with a hi VI (Viscosity Index). Usually the higher priced aftermarket shocks come with clickers as well and they are far more adjustable then maybe the standard shock that the bike came with.

(4) Geometry changes, This is the one that will bite most riders as it is hard to find a donor shock/fork that will maintain the exact same geometry numbers as stock. Sometimes a geometry change is beneficial and other time it causes issues. I have had riders install a shock that is 30mm longer then the OEM shock and running the numbers you end up with very little trail as the back end is jacked up so high, This leads to instability up front as well as less traction in the front. How many riders want less traction in the front tire, Not many I hope. The same can be said if the forks are shorter as it will cause the same issue. Now if the shock is shorter or the forks longer it will cause the opposite affect and make the steering very slow and feel heavy and tends to run wide on corner exit.

(5) Upside down forks are superior as they have less unsprung weight then a conventional fork, Not true as I took a set of 41mm USD forks and a set of 41mm conventional forks with a cartridge and the conventional forks were lighter all the way around and had less unsprung weight. If you want better aesthetic values then no doubt that the USD look far better then a set of conventional forks.

(6) Better brakes on USD forks, Can't argue this one as there are many more options for the radial systems then there are for the conventional brake system. However I have seen conventional systems able to pull off a stoppie.

Well that is the start of my little rant and if you agree or dis-agree I would love to hear it. If you have any questions feel free to ask away and I will do my best to answer you and add it above.

Terry
 

DaveM

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There really does seem more to doing this than I thought, some interesting points you have noted in your post.
 

keystiger

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Good information. I swapped shocks on Dirt Bikes back in the "day" without much thought. However that was 30 years ago. Now I wouldn't think about snagging a used (or new) suspension without consulting a pro for sure.
Technology and engineering have advanced AMAZINGLY since the 70's Dirt bike era I learned in ;)
 

DaveM

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Back then it was very common to use what ever parts you could get hold of and I have also done a few jobs like that along the way.
 

dearborn

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I have a thread in the Hinckley Triples section on using a '94 through '97 Kawasaki ZX9 shock on my '96 900 Thunderbird. I would highly recommend this swap for this bike to anyone looking for a cost effective replacement for the horrible OEM Thunderbird, (not "Sport"), shock. It will quickly point out that you'll need to spend about $300 on your FRONT end though!
 

dearborn

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I am VERY pleased with the ZX9 shock swap on my '96 Thunderbird. BUT.... you're right about changing the rear ride height. The ZX9 shock raised the rear about an inch. This was remedied by a set of adjustable "dog bones" which restored the proper ride height. The travel for OEM vs ZX9 shock was VERY similar, (yes, I measured it) and the overall difference in length, as I remember, was only about 1/2 inch. Setting proper "sag" was essential. The weaknesses in the front end were remedied with addition of .85kg/mm RaceTech springs and 15wt fork oil at the proper level recommended. Did NOT add "Gold Valves" as they seemed to be more useful on a race bike and an unnecessary expense for a street bike "cruiser" that gets ridden "briskly" occasionally. I'm happy with just the springs. The ZX9 shock spring seems to be OK, too. I'll play with that and possibly revalving the shock later, but for now, I have had ZERO negative issues with the shock swap; rides better, even my 100lb passenger has remarked on how much better it feels, the awful harshness of the OEM Triumph shock is gone, it handles and feels way better solo, too. The stiffer fork springs made a BIG improvement, too. Adding a couple of "clicks" in compression damping adjutment when carrying my admittedly light weight passenger DOES make a difference. I can't speak to any other shock swaps folks might try, but this one works
 

dearborn

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Hi Members,

This is my opinion and I am using issues that I had working for Race Tech dealing with riders that had decided to install suspension from other bikes and applications on their bike.

If you read across the web you may find riders that are installing or recommending suspension components from different bikes/applications and installing them on bikes they were not intended for. While this is fine if you do some home work what I had found is that a majority failed to do the home work and ended up calling in so we could guide them in the right direction as they ran into issues.

I will break this down into individual notes for those that are interested in grafting suspension components from one bike to another to try and make the transition a little less painful and safer as the wrong suspension on the wrong bike may be unsafe to ride. I am going from my memory so I may have to come back and add to this list as times goes on.

(1) Don't assume that because the center to center length of the shock or the fork length is the same that it will work fine, Shock bodies/Fork sliders as well as shaft/fork travel can be different even though they are the same length so you end up with either too much or too little travel. Too much travel is worse then less as the tire may hit the underside of the bike at the most inopportune time.

(2) Because it has clickers it has to be better then what I have syndrome, While this may hold true in some instances let's keep in mind that 90% of the performance of the shock/fork is the valving on the piston, The other 10% is the clickers. All the adjustment in the world is not going to make up for the lack of the correct valving inside the shock/fork. If this were true we would not have pistons with shims on them but only clickers that would take us back to orifice damping.

(3) Bigger shock bodies are better as they hold more fluid, While there is some truth to this one several of the aftermarket companies use small body shocks and they work perfectly fine as long as you use a very hi quality suspension fluid with a hi VI (Viscosity Index). Usually the higher priced aftermarket shocks come with clickers as well and they are far more adjustable then maybe the standard shock that the bike came with.

(4) Geometry changes, This is the one that will bite most riders as it is hard to find a donor shock/fork that will maintain the exact same geometry numbers as stock. Sometimes a geometry change is beneficial and other time it causes issues. I have had riders install a shock that is 30mm longer then the OEM shock and running the numbers you end up with very little trail as the back end is jacked up so high, This leads to instability up front as well as less traction in the front. How many riders want less traction in the front tire, Not many I hope. The same can be said if the forks are shorter as it will cause the same issue. Now if the shock is shorter or the forks longer it will cause the opposite affect and make the steering very slow and feel heavy and tends to run wide on corner exit.

(5) Upside down forks are superior as they have less unsprung weight then a conventional fork, Not true as I took a set of 41mm USD forks and a set of 41mm conventional forks with a cartridge and the conventional forks were lighter all the way around and had less unsprung weight. If you want better aesthetic values then no doubt that the USD look far better then a set of conventional forks.

(6) Better brakes on USD forks, Can't argue this one as there are many more options for the radial systems then there are for the conventional brake system. However I have seen conventional systems able to pull off a stoppie.

Well that is the start of my little rant and if you agree or dis-agree I would love to hear it. If you have any questions feel free to ask away and I will do my best to answer you and add it above.

Terry
 

dearborn

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Well TMOD, you make some good points. And being sufficiently "lawyered-up", your advice to those considering suspension modifications to "do your homework" is good advice. BUT... I am a licensed Master Motorcycle Mechanic and the modifications I described to a '96 Thunderbird, if done as directed, with the components described in the multiple posts and threads here, detailing the various experiments done, WILL absolutely achieve the results noted. And those results will be vastly superior to the OEM rear suspension unit fitted to a '96 Thunderbird. (The fact that the rear suspension unit is now 24 years old and likely worn-out junk is also a significant factor!). Taking measurements BEFORE modification is addressed and issues AFTER modification- ride height changes, affects on steering, etc, selection of components, spring choices, setting proper "sag", properly addressing issues with the front suspension arising from modifying the rear, etc, etc, are all covered in my posts/threads on the ZX9 rear shock swap to a '96 Thunderbird.
From new, (I worked as a mechanic in a Triumph/Ducati/Japan dealer when Triumph re-entered the US market), owners complained about the harsh, non-adjustable rear shock, (and many other things-spongy front brakes, hard starting, etc). The proof that the OEM shock fitted to the T-bird was poor was the widespread use of adjustable, much improved shocks/suspension fitted rear and front, to many other models in subsequent years, including the Thunderbird "Sport" models.
Caution is a good thing. A lack of experience and knowledge, and not doing the proper research before doing things can get a person in deep trouble.
I really don't want to sound like an old crank, but it's folly to assume that because the vast majority of folks who post to enthusiast forums like this are "newbies" asking "what oil" questions and the like, that sometimes, folks who really DO know things and have a good bit of experience, may also join in.
Folks here who have done the modification as described, universally report good results
 
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