Topic: Repositioning Rear Shocks?

[KB02]

Admitantly, I am not an engineer. However I do have a really cool idea for a rebuild of an old bike that I would like to do, but I have a question as to whether part of my idea is doable or not. For what I want to do, I need to move the rear shocks.

Now, the bike I am thinking of working on is a '74 (I believe) KZ400. I know, it's not a honda, but this IS the technical board, so I figure my best place to get an answer is here. It is currently sitting in my cousin's field, rotting away. I basically have a blank canvas for whatever I want to do. (I'm thinking Cafe racer/street fighter lookin' thing, yet small enough - it is a 400 after all - for a beginner to ride on). For the image I want, I need to reposition the rear shocks.

Basically, I want to lay the top end of the shock down toward the front of the bike. So intead of them sitting sitting at about an 85 degree angle, they'd be closer to 40 or 45. Would this be possible (pronouced, "Ridable") with the stock shocks? Or even at all?

Let me know what you all think.

[SteveD CB500F]

You can get shock lowering kits for the Hondas so no reason why not for Kawis.

Rather than move the top forward, they work by moving the bottom back.  Search on "lowering kit" or similar to see where to buy and what others have done.

I've moved this to "Other Bikes"

[crazypj]

If you lay them down that much a couple of things happen
1. you put a bending stress on shock shaft
2 you in effect lower the spring rate
3. the damper doesn't work properly
I know it has been done on dirt bikes (ATK) but they used a very expensive shock with correctly positioned mountings to prevent bending of shock shaft.
The other who did it used linkages(Buell, etc)
You probably want to google frame/chassis design
PJ

[Geeto67]

with the amount of fab work involved it is probably easier to go grab a dirt bike rear swingarm and monoshock and monoshock the thing.

[CBGBs]

Is it really possible to monoshock a bike like this??? I really want to convert my CB to a monoshock so that I can mount an under tail exhaust. Is this Reasonably possible? I mean, I'm not a real engineer and I don't have a lot of money but I'm resourceful.

[crazypj]

Mono shock is much easier than a laydown system. find a swing arm/shock you like the look of and a reasonablly close fit width wise then weld some plates onto frame. Its a good idea to find out what its off and take measurements of shock location before you start cutting. You can remove everything behind the shock mounts/link and build a much lighter new subframe. It only has to support rider weight plus a bit for safey, instead of all the forces involved holding the shocks and wheel etc.
( OK so maybe its not quite as simple as I make it sound but it is pretty easy)
I've done CB400f with a Yamaha RD350 back end but dont have any pics (it was a long time ago ) That was a little more involved as parts had to be removed without damage and re-fitted after shock mounts were welded into frame and it needed special swing arm bushiings to fit Honda frame
Pic is Yamaha XS650 with Suzuki forks and monoshock. Rear end is getting some more 'trimming'.
PJ

[KB02]

You can get shock lowering kits for the Hondas so no reason why not for Kawis.

Rather than move the top forward, they work by moving the bottom back.  Search on "lowering kit" or similar to see where to buy and what others have done.

I don't really want to lower the bike, so much as just change the looks and make people say, "What the heck is that?"

[KB02]

Alight, after a bit of research and a brief education in shock design, structer and frame design, I have come up with an idea how to make what I want work.

I would like to thank cafe75-550 for the use of the picture of his bare frame. It was perfect for "mocking it up" within photo impressions.

Basically, The whole rear section is removed. I have added a basket on the swing arm to hold the bottom of the shocks in a different loaction, and added a small perch for a seat. (for the seat, I am planning on having just the bare frame with a wicker-like seat woven in place - different, huh?)

The bottom pic is the bare frame. The top pic is with my modifactions. What do you all think? Keep in mind that I am planning on using both rear shocks. This will not be a mono shock setup.

[Bob Wessner]

Interesting look. Will the shocks you have be correct for this type of load and geometry change, that is the change in angle I would think change the load? Just a thought in looking at it. Not sure how one would determine the correct load unless it were somewhat infinitely adjustable and some trial an error testing.

[KB02]

Well, bascially, my theory is that since they are the stock shocks that I plan on using, they should be fine as far as load goes. As for geometery, this design should retain the same directional forces as the stock set up (compresion still going from top to bottom with no real change in tortional forces), so I don't see why it wouldn't work.

[Bob Wessner]

You're probably right, it was just a thought. Let us know how it works, because it is an interesting look.

[bill440cars]

                   I'll be watching this also because I've got some ideas kinda along the same line but,
        different approach. LOL

                                                          Later on, Bill

[scunny]

I am not an engineer.
from looking at your pic of how you would do this, the only difference would be that for every movement of the rear wheel via the pivot point(being the swingarm pivot) would mean less travel of the shocks. I don't know if this would mean a harsher ride or not. If you want to try it why not.
that will be $00.02 for this sage advice

[crazypj]

You need to work out the linkage ratio if your mounting shocks as you describe.
 Its probably going to be way too soft as you have in effect moved the mounting points much further forward, from around 1:1 (vertical over axle) to 3:1 for example, 3" vertical wheel travel is only 1" shock movement, or you get real soft 9" travel
 You want to stay at 1:1 for stock shocks and around 2:1 or less for most other set ups which means you need double the spring rate ( and dampers to match)
PJ

[KB02]

Hmmm... Looks like my math was off in the wrong direction, I was thikning that it would stiffen up the suspention a bit. Re-looking at it, though, You're right. I would say it is a little closer to 2:1 as the drawing sits, though. But you're right. I would (will) have to look into that.