Topic: Finally got suspension done

[greenjeans]

Now I'm looking for a GSXR1000 front end....thanks Twister 

Looks really nice.  I'm usually not a fan of the modern front end / swingarms.    You guys have won me over.
Can't wait to see that beast when it's completed.

[TexasTwister250]

Thanks!!  I am looking forward too, I thought it would be done in a few months but the price of the parts I want are so expensive it will take a long time....fortunately I have a couple of other bikes to ride this spring to keep me going.

[greenjeans]

Thanks!!  I am looking forward too, I thought it would be done in a few months but the price of the parts I want are so expensive it will take a long time....fortunately I have a couple of other bikes to ride this spring to keep me going.

At least you have another bike to ride.   It will be well worth it when you are finished.   Gotta fire some questions at ya -

I may have missed it, but have you posted the bearing sizes that you used in the steering neck ?

How were you able to machine down the bearing surface - in the steering neck right ?   Am I thinking correctly ?  Not on the stem ?

Is the axle diameter on the front wheel 15 or 20mm ?

[TexasTwister250]

Thanks!!  I am looking forward too, I thought it would be done in a few months but the price of the parts I want are so expensive it will take a long time....fortunately I have a couple of other bikes to ride this spring to keep me going.

At least you have another bike to ride.   It will be well worth it when you are finished.   Gotta fire some questions at ya -

I may have missed it, but have you posted the bearing sizes that you used in the steering neck ?

How were you able to machine down the bearing surface - in the steering neck right ?   Am I thinking correctly ?  Not on the stem ?

Is the axle diameter on the front wheel 15 or 20mm ?

I don't remember which bearing they were, but if you go to all-balls racing they have a section called conversion bearing.  If you look up the CB750 they have about a 100 different forks and which bearings top and bottom that will bring the two together.  Most of use GSXR simply because there are so many of them available and it is a cool looking fork set with radial brakes.  I would go with the GSXR 1000 rather than 600, only because the conversion I read on here there was a difference in the stem lenght, where as on the O7 I used it was the same.

Yes I machined down the steering neck bearing lip about .300" so the seal would be down in the neck in stead of sitting slightly above it.  The way I did it turned into a mess.  I used 1 7/8 hole saw to boar down into the lip, then used a drimmel to clean it up and level it.  I would have taken it to a machine shop but without the front wheel it was impossible without tearing the bike down to the frame.  If you could find the right size machining tool like a mill you could perhaps get better results I believe the bore was 48mm.

Not sure about the axle it is a 08 GSXR 1000 wheel and 07 GSXR 1000 Forks.  I could measuare it but it should be able to find it with a google search.

[Lamp]

I just mounted some rc51 rear sets on my frame the same way. You're in for a surprise when go to mount you oil tank. It hits the rear master cylinder. Good luck!

[TexasTwister250]

I just mounted some rc51 rear sets on my frame the same way. You're in for a surprise when go to mount you oil tank. It hits the rear master cylinder. Good luck!

Yes it would be right in the way.  I plan to mount a center mounted oil tank, I do not like the way the side mounted tank looks.

[TexasTwister250]

I've decided that I do not like the way the twin shocks look.  Also, the Ohlins shocks I want are like $1500 and would have to be made to fit, mounting is different.  So, I have decided to convert it into a Monoshock system.  I've ebayed a 07 GSXR rear shock for $25.  I will be easy to weld up the mounts for it, no problem there.  My question is the linkages, I don't see any reason to add the complication, but does anyone know of a compelling reason to add the linkage?

[DonDDR]

Dont the links act as a fulcrum as well as compensate for the arc of the lower shock mount if it was bolted right to the swing arm? With out the fulcrum "math" or whatever wouldnt that possibly jack your spring rate off the chart?

[m in sc]

yes! well, that clinches it. im putting the ZX7 susp/wheels on mine this winter.  nicely done.

[Retro Rocket]

I don't see any reason to add the complication, but does anyone know of a compelling reason to add the linkage?

The suspension is designed to work with the linkage, your suspension will be nothing like the original without the linkage and probably not work very well at all. There's a lot of theory that goes into suspension, you can't just weld a pile of parts together and expect it to work. I would look for a bike with a fairly basic monoshock set up like the early TZ Yamaha's and try replicate that....

[m in sc]

I don't see any reason to add the complication, but does anyone know of a compelling reason to add the linkage?

The suspension is designed to work with the linkage, your suspension will be nothing like the original without the linkage and probably not work very well at all. There's a lot of theory that goes into suspension, you can't just weld a pile of parts together and expect it to work. I would look for a bike with a fairly basic monoshock set up like the early TZ Yamaha's and try replicate that....

^ i have done this, actually quite a few times. you lose lots of real estate doing this under the bike which oyu may not have. you really are saying: 'if i cant have ohlins im not interested'? buy some works shocks. also, going to a monoshock will load the frame different, you will need to address that.. stick w/the twin shocks. if you must go mono w/that arm,  do it right and get a linkage setup in there but its going to be a load of work.

[TexasTwister250]

I don't see any reason to add the complication, but does anyone know of a compelling reason to add the linkage?

The suspension is designed to work with the linkage, your suspension will be nothing like the original without the linkage and probably not work very well at all. There's a lot of theory that goes into suspension, you can't just weld a pile of parts together and expect it to work. I would look for a bike with a fairly basic monoshock set up like the early TZ Yamaha's and try replicate that....

^ i have done this, actually quite a few times. you lose lots of real estate doing this under the bike which oyu may not have. you really are saying: 'if i cant have ohlins im not interested'? buy some works shocks. also, going to a monoshock will load the frame different, you will need to address that.. stick w/the twin shocks. if you must go mono w/that arm,  do it right and get a linkage setup in there but its going to be a load of work.

I looked at the suspension on my Busa, the linkage appears to do only a couple of things:  1) It allows the shock to be mounted vertically and mount to the bottom of the swing arm to save space instead of the old way on top of the swing arm with a forward more longitudinal position, 2) It reverses the motion of the swingarm so that it compresses the spring instead of stretching it (i.e. during a compression load), 3) there may be some bit of cantilever to the motion but at most your getting an 1-2 inch advantage.  I think the modern bike uses the linkage more for space savings than any other reason.

When i look at my Ducati, it's spring is does not have any linkage that I can see it appears to be mounted directly to the mono-swingarm and directly to the frame.  This is why I feel like it will work.

Here is the plan; 1) since I shortened the front of the swingarm and removed the original shockmount which was on the bottom, I will have a 1/4" aluminium plate welded to the top of the SA brace and two bosses welded on top of that to mount the bottom of the shock.  2) Next at the corner where the engine cradle tubes meet the backbone tubes under the tank, I will weld a mount across the frame, brace it and weld on a mount for the top of the shock, this will put the SA force directly in line with the frame backbone.  This will give the shock about 20-30 degree angle for a slight progressive rate.  The spring can be swapped if a stiffer or lighter one is needed, and the shock will have compression and rebound dampening adjustment.  It should be able to be dialed in for the correct sag and performance.

This will make mounting the center mounted oil tank a bit more challenging but I'm sure a solution will present itself for that problem when I get there.

[m in sc]

the linkage changes the forces placed on the shock. It would have been cheaper for the manufcturer to just put a pin across the arm and stuff a shock in there.. they didnt  for a reason. IF you decide to go that route break out the geometry and load calculations. theres a ratio change in that linkage, it wasnt just to position it up and down. its not hard but guess work can be very dangerous in this type of work.  most of the math is simple ratio calculations. good luck with it... its fun to do for sure.

 edit.

that being said... heres a cbr 929(i think, might have used a 945 shock) shock in a 'tz' style 'over-the top' modded swingarm and r1 frontend on my h1 .


 are you going to have enough room in the arm w/out adding too much wheelbase?

[Retro Rocket]

Nice work m in sc, i agree with everything that you have said regarding the mono shocks.  If you use the GSXR1000 swingarm as it is then you will also have an extended wheelbase that will also alter the way the bike handles, just something else to think about.....

[TexasTwister250]

Nice work m in sc, i agree with everything that you have said regarding the mono shocks.  If you use the GSXR1000 swingarm as it is then you will also have an extended wheelbase that will also alter the way the bike handles, just something else to think about.....

The swing arm was shortened 4inches to replicate the wheel base of an RC51, it is about 1in longer than stock.  But again, I looked at the Ducati swingarm where the shock is mounted on the top, as it will be on my bike and it does not have any cantilevered linkages, and this is the second best handling bike I've ever ridden, the best was a Honda RS250 which also did not have any linkage.  The original GSXR has a linkage but I am convinced that it is primarily for the purpose of reversing the direction of SA movement... like a seesaw, since it is mounted to the bottom it has to be reversed to correct the movement. 

There may be a bit of arc that this design creates,  but I do not believe there is any engineering black magic in that, it would just change the load on the spring, maybe creates a slightly non-linear load rate.  The Ducati style is proof of that these shocks will work in a direct fixed position top and bottom, and what ever difference there are in load can be neutralized by a different spring.  Since I shortened the rear SA the moment arm acting on the shock will have changed putting more load on the shock, but the rear of my CB is so light now that I can easily pick the rear of the bike up off the ground (maybe 100lbs), I imagine that if anything the spring rate of the GSXR shock will be too stiff, but cannot know until I can try it.  The good thing is that I can leave the dual springs in place until the monoshock is perfected.  It arrives today so I will be able to start evaluating the specifics of how to best install it on the bike.  More to come...

[m in sc]

dont just try it, figure the spring rate and do the math... im not saying it won't work but you need to get the ratio correct before you just jam it in there.

i also have a ducati, it handles fantastic so i understand. but you arent tying that suspenstion to a ducati frame designed to take the loads either.
just my .02

[scottly]

the shock will have changed putting more load on the shock, but the rear of my CB is so light now that I can easily pick the rear of the bike up off the ground (maybe 100lbs)

Maybe 200 lbs, unless you left the motor out.

[TexasTwister250]

the shock will have changed putting more load on the shock, but the rear of my CB is so light now that I can easily pick the rear of the bike up off the ground (maybe 100lbs)

Maybe 200 lbs, unless you left the motor out.

Yeah, that was a little light.  I measured it last night and it wasn't bad.  177lbs rear and 187lbs front.  That would be 364 with a 51/49 ratio.  Not bad... but that is dry and w/o oil tank, gages or headlight, or battery.

[Retro Rocket]

The swing arm was shortened 4inches to replicate the wheel base of an RC51

I think you need to get a copy of Tony Foale's book on motorcycle suspension and have a bit of a read because , without being a smart arse, your understanding of suspension is a bit simplistic. Replicating another completely different bikes wheelbase doesn't mean a thing. These bikes were made with completely different measurements between the steering head and the swingarm pivot, as well as wheelbase and rake and trail, nothing on either bike can simply be made work properly by mimicking the donor bikes specs. it just doesn't work like that. There are quite complex formula's to determine all these measurements and they can't simply be swapped. For example, the RC51 has a longer swingarm because it has a completely different swing arm pivot point, the overall bike without the swingarm is smaller than the SOHC Honda and has a longer arm to suit its own specific measurements. The linkage on most monoshock suspension is for changing the shock to swingarm movement ratio, or rising rate, most are completely different but are designed that way for a specific purpose, take the linkage off a gsxr and tell me it handles the same and i'll eat my hat.... The linkage is designed to work with the shock and spring and all are designed to work together, take  away the linkage and it completely changes the way in which it all works, this is fact......

Foale's website....     http://www.tonyfoale.com/

[TexasTwister250]

The swing arm was shortened 4inches to replicate the wheel base of an RC51

I think you need to get a copy of Tony Foale's book on motorcycle suspension and have a bit of a read because , without being a smart arse, your understanding of suspension is a bit simplistic. Replicating another completely different bikes wheelbase doesn't mean a thing. These bikes were made with completely different measurements between the steering head and the swingarm pivot, as well as wheelbase and rake and trail, nothing on either bike can simply be made work properly by mimicking the donor bikes specs. it just doesn't work like that. There are quite complex formula's to determine all these measurements and they can't simply be swapped. For example, the RC51 has a longer swingarm because it has a completely different swing arm pivot point, the overall bike without the swingarm is smaller than the SOHC Honda and has a longer arm to suit its own specific measurements. The linkage on most monoshock suspension is for changing the shock to swingarm movement ratio, or rising rate, most are completely different but are designed that way for a specific purpose, take the linkage off a gsxr and tell me it handles the same and i'll eat my hat.... The linkage is designed to work with the shock and spring and all are designed to work together, take  away the linkage and it completely changes the way in which it all works, this is fact......

Foale's website....     http://www.tonyfoale.com/

I also said, "it is about 1in longer than stock".  Sorry, but that was being a smart arse.  Your entitled to your opinion.

This is a cafe racer project trial and error is the fun of it, there are so many variables between the GSXR and a CB750 that it would likely be impossible to do any meaningful calculations to answer endless "what if's".  Seat of the pants will tell me if I've got it right or not.  If I go down in flames because I got it wrong then so be it.  It's called development, the worst outcome is the spring rate isn't right, big deal, there is an endless viariety of springs to swap with. 

In retrospect this was a dumb question because if I used the linkages, the shock would work backwards since it is being mounted to the top of the SA.     Also, I received the GSXR shock, and the reservoir is mounted in such a way that it will interfere with mounting.  I will probably ebay a Ducati or some other shock where the reservoir is mounted parallel or remotely.

Thanks to everyone for your feedback, I will post a pic when it is finished.

[Retro Rocket]

I also said, "it is about 1in longer than stock".  Sorry, but that was being a smart arse.  Your entitled to your opinion.

I was definitely not trying to be smart, believe what you like.  You are basically saying the suspension geometry is smoke and mirrors when in fact there are specific measurements and formula's to get it right, i was trying to help.. Its not an opinion, the link will explain it better than I can, my typing skills are not that great.

This is a cafe racer project trial and error is the fun of it, there are so many variables between the GSXR and a CB750 that it would likely be impossible to do any meaningful calculations to answer endless "what if's".

Thats where you are wrong, the calculations you speak off have already been done, so you could refer to current frame geometry to find out how close you are to getting it right. I have seen many conversions and do them myself, i have GSXR forks and a modded GSXR arm on my bikes, i am changing the offset of the Suzuki front clamps for the very reasons i offer here.

It's called development,

No, the development has already been done, thats why i suggested you have a read. I am sorry f you were offended but i won't loose any sleep over it, you asked questions on a public forum and i answered as i have done this before and so have many others here, some very dodgey and some very good. I am in the school of doing it right, its quite ok that you are experimenting, i was just trying to offer some insight into suspension technology.........

Build away.....