'79 Kz650 Project

Onetype wrote: Actually, "them" shocks set anywhere from mid to firm and the bike rides the same, if not better than stock. Reason being the shocks are still mounted on the same arch, just lower, and the only difference in geometry is the swingarm, which had considerably less affect than most who drop the front and take the stock rake out.

What keeps the gemoetry from spreading? Well even before I lowered the upper bars, with 200+lbs on the bike it moved less than 1/8 of an inch (forward movement, not lateral). That's without ANY support to the mounts. What makes you think lateral support is needed? Think about it, where is force being exerted? Sideways? Nope. Will I probably guesset them anyway, yeah. Do I have to? No. You can't deform a triangle without physically changing the length of one of it's sides. Basic geometry. If it fell off a truck or trailer then maybe, but it would first have to destroy the lower mount allowing the shock to have lateral movement (which it has maybe 1/16 when bolted down). After the handlebars, tank, and rearsets take most of the damage. That being said, my new battery and box will act as lateral bracing.

I've been designing hotrod suspension for some time now, and even though this was my first bike build it is the same concept.

Picked up a new plasma today, going to finish my tank soon. Have a few others to test out meanwhile. Have way too many projects taking up my time, and work unfortunately. I hope to have it completely done in the next few weeks.

You sound very defensive. I will try to better explain what I believe is the issue and you can take it, or leave it, or ignore it. In the picture of your configuration below I have circled in red the 2 places on your frame that I believe can move about more than is desirable. While each of their vertical axes does benefit from the triangulation you mention their common horizontal or lateral axis does not. When riding through a turn, especially if the road is bumpy or uneven, or especially when braking or accelerating in a turn, forces are generated which try to twist the swingarm and frame. It appears to me that these forces, and perhaps others, may be transmitted to the 2 points circled in red in a fashion that would cause these sections of the frame to move in a manner that changes the physical relationship between these 2 points, i.e. they may spread or move closer to each other. It does not appear that the battery box will do anything to maintain the physical relationship between these 2 points. However, if an appropriate gauge tube was welded between the 2 points their relationship would be maintained. This would however still leave the possibility that the 2 points could move left or right as a single unit which although an improvement would still not be desirable. This problem could also be easily eliminated by welding diagonal bracing between one or both of the points circled in red and its diagonal counterpoint circled in blue. This bracing would give you the triangulation currently missing from the points in question.

Perhaps none of this is actually relevant to you if you normally practice a sedate riding style, but if you’re ever tempted to run through turns in a spirited fashion I would respectfully suggest you consider these or other bracing options that might improve the stability of your bike. Ed

in that position, wont the shocks bind when the swingarm moves on heavy bumps?

650ed wrote:

Onetype wrote: Actually, "them" shocks set anywhere from mid to firm and the bike rides the same, if not better than stock. Reason being the shocks are still mounted on the same arch, just lower, and the only difference in geometry is the swingarm, which had considerably less affect than most who drop the front and take the stock rake out.

What keeps the gemoetry from spreading? Well even before I lowered the upper bars, with 200+lbs on the bike it moved less than 1/8 of an inch (forward movement, not lateral). That's without ANY support to the mounts. What makes you think lateral support is needed? Think about it, where is force being exerted? Sideways? Nope. Will I probably guesset them anyway, yeah. Do I have to? No. You can't deform a triangle without physically changing the length of one of it's sides. Basic geometry. If it fell off a truck or trailer then maybe, but it would first have to destroy the lower mount allowing the shock to have lateral movement (which it has maybe 1/16 when bolted down). After the handlebars, tank, and rearsets take most of the damage. That being said, my new battery and box will act as lateral bracing.

I've been designing hotrod suspension for some time now, and even though this was my first bike build it is the same concept.

Picked up a new plasma today, going to finish my tank soon. Have a few others to test out meanwhile. Have way too many projects taking up my time, and work unfortunately. I hope to have it completely done in the next few weeks.

You sound very defensive. I will try to better explain what I believe is the issue and you can take it, or leave it, or ignore it. In the picture of your configuration below I have circled in red the 2 places on your frame that I believe can move about more than is desirable. While each of their vertical axes does benefit from the triangulation you mention their common horizontal or lateral axis does not. When riding through a turn, especially if the road is bumpy or uneven, or especially when braking or accelerating in a turn, forces are generated which try to twist the swingarm and frame. It appears to me that these forces, and perhaps others, may be transmitted to the 2 points circled in red in a fashion that would cause these sections of the frame to move in a manner that changes the physical relationship between these 2 points, i.e. they may spread or move closer to each other. It does not appear that the battery box will do anything to maintain the physical relationship between these 2 points. However, if an appropriate gauge tube was welded between the 2 points their relationship would be maintained. This would however still leave the possibility that the 2 points could move left or right as a single unit which although an improvement would still not be desirable. This problem could also be easily eliminated by welding diagonal bracing between one or both of the points circled in red and its diagonal counterpoint circled in blue. This bracing would give you the triangulation currently missing from the points in question.

Perhaps none of this is actually relevant to you if you normally practice a sedate riding style, but if you’re ever tempted to run through turns in a spirited fashion I would respectfully suggest you consider these or other bracing options that might improve the stability of your bike. Ed

Attachment AAbike.jpg not found

gengomerpyle wrote: in that position, wont the shocks bind when the swingarm moves on heavy bumps?

Hard to say. If they are already heavily compressed when the bike is at rest they might. By the same token, if they are not compressed at all when the bike is at rest I'm not sure what limits the upward motion of the swingarm. What is the vertical distance the swingarm (rear axle) can travel when hitting a big bump, and what hits first to stop further upward motion? I'm sure Onetype has run all the numbers during his design phase before setting up this unique suspension. Ed

I'm not defensive. This is my first bike build, so I am open to constructive criticism, as there are multiple ways to do something, some better than others.

Both the shock mounts and down tubes will be gusseted with 3/16 plate. I was referring to the lateral movement which you were talking about, as is there is none. Even leaning with a big boy on it. However, I plan to run some tube support tied into the battery box i'm running, along with the mount for the starter relay, regulator etc... I just won't be running tube stock right at the shock mounts as it's not necessary (maybe 3-5 inches forward, have to build my seat first).

As for binding, the springs only have so much travel, and even on the softest setting around the neighborhood bottom out far before any binding occurs. On the stiffest setting, it rides completely trouble free with minimal travel. Mind you this is on 30+ year old coil springs. Once I'm riding it long distances/more often, if I don't like it I will increase the spring rate.

While I have seen similar designs on other bikes, I have yet to see one on a heavier inline 4 cylinder frame. You can overbuild something unconventional and someone somewhere is going to have doubts. To each their own I guess.

I got the same reaction when I designed my suicide rear suspension on my '31 Ford. And it rides like a dream.

I would hope your finished reame looked something like this. Keep in mind the load on that thing in riding conditions can be 10 times the static load you put on the bike just sitting on it.

Onetype wrote: ...

Am surprised about there being much of any suspension travel at all.

By installing "lowering blocks" to a stock suspension (which moves the bottom of rear shocks slightly further rearward) the suspension feels like virtual struts, with only the slight more laid down angle.

Here, the rear shocks seem more drastically laid down, which would seem to afford even less actual suspension.

If the rear suspension feels too stiff with the laid down shocks, perhaps lighter springs with reduced spring rates might allow improved suspension travel with the laid down shocks.

Good Fortune!

:evil: I really like the look it is one of a kind for sure very nice

Very cool low look to the bike. I would have to agree that the frame needs a little more support for safety reasons. Also, how much ground clearance do you have at the pipes? It looks like you might be scraping those in corners and turns (may just be the angle of the pic). I do love the low look, but functionality comes into play as well. You might be able to fabricate an exhaust that will have a little more clearance if needed.

~Clutch

Haven't has any issues yet, but I haven't really been able to lean into it. Sandblasting the headers right now. If i run into issues in thr future ill build new exhaust.

I'm going to add a little bracing in the shock area and make my seat. I also fried my rectifier somehow, so I need to order a new one.

Narrowed the stock little stubby fender 1 1/4 in. Should work nice.

Haven't accomplished much this past week, I have been way too busy with other projects.

I did however nearly finish my tail light.

It's a vintage microphone, forgot the brand (still has the id tags on the inside, numbered by hand). I just need to finish the red lense for it.



Found a cb200t tank on ebay for super cheap. It was really rusty inside. 2 days soaking in a Muriatic acid solution, and 2 inches shorter, it looks brand new. (picture was before soaking it, and smoothing out the cuts/taking a little more out.



My welder keeps burning through it, so my buddy is going to tig it back together at his shop for me in the next few days.

My ballistic battery showed up (1 lb, 10oz dry cell motorcycle battery.
Ordered my seat pan, need to pick up some leather to wrap it.
And yes I still need to finish the frame bracing, but I'm waiting for the seat pand to get here to mock everything up.

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Got some work done this weekend:

Built a battery box - turned out pretty good, just need to figure out a nice way to mount it.


Added some gusseting, and cross bars for seat. Not sure what the final position of the seat will be. I made a pivot for the front so it will lift up. Basically it's a larger diameter tubing that spins on a smaller diameter. I think I will end up putting the rear on rubber mounts and raising it slightly.


Extended my rear brake line, boxed the pedal mount back up, and installed it.

Wiring still needs work, but I need to figure out where my battery will be first. Chances are i'm going to have to shorten just about every single wire to get it looking good.

finished tail light: