KZ650 - 810cc

T_Dub wrote:

The Duc's were my inspiration for that one, and it should even be stronger than a duc frame, since its wider. I really would like to make the bike I designed around that frame, I have a CBR engine handy, just need some cash. I could have done it instead of the KZ, but I wanted to do the KZ first instead of leaving her sitting. BTW, the thing under the seat in that render is the fuel tank. All you see in front of you when sitting on that bike is a gaping hole with some velocity stacks staring up at you. :woohoo:

That wold look COOL, not to mention the sound of the intake wailing when you twist the throttle.

Think about it like this: if you mounted your frame sideways in a jig at the swingarm pivot ONLY, then stuck a bar in the steering neck and placed a torsional force on the frame, where would the weak points be? If there aren't any, in your engineering expertise, then I should shut the hell up. One thing I was too lazy to do (or impatient?) was to build a fixture for my jig to mount my frame like that and do an initial torsional strength test and a post bracing test and quantify the improvement by measuring the amount of force required to twist the frame a given distance. I may still do that....

It would be a very cool bike, I may start it next spring once I get out of school.

I really do think the engine takes some load, if the mount bolts are tight then the preload tension in them alone will serve to resist torsion. A better test would be to take the engine mounts and some bar stock and make long spacers to go where the engine normally is, and then bolt them in. If they were the same diameter as the engine holes they would simulate the engine being there rather well. They'd probably take less force than the engine would, but it'd be a better way to do it since in the areas where the engine goes there would be a tendency for the tubing to buckle slightly. That can cause a frame to seem MUCH weaker than it really is. I bet I could bend in the downtubes with the engine out, but I can't with the engine in. Since they can bend further with the engine out, it can cause the bending to dominate the stress characteristics in the tube, causing inaccurate results.

I think you're right, a proper torsional simulation should include the engine. I think it would be simpler to just bolt in some empty cases rather than tubes. I would be much too lazy to source a bunch of tubing the proper i.d. to simulate an oversized engine mount. It would be interesting to check the torsional rigidity with and without the engine to see how much the engine ties the frame together.

Thats true. The best test would be with and without engine, both before and after frame mods. Four tests. It's always nice to see hard numbers. I've seen guys go through a spaceframe for a racecar, add all kind of extra bracing, and maybe make it 5% stronger. Sometimes its not worth the weight, especially if its the difference between more than enough and even more.

T_Dub wrote:

Oh I know a lot about frame design, I do it all the time, and do FEA on them to make sure they're strong. I know just from looking at it that the ZRX frame is better in torsion than mine, but then again mine also has triangulation at the neck, hence all the plate welded on. The backbone isn't as good but aside from boxing it in there's not much you can do there. What you're doing with your front down tubes would be the only thing I would think would be worth doing in a KZ frame that already has a triangulated neck.

Here's an example of a frame I designed for a CBR600. It's crazy strong in torsion.

That's freaking awesome!

T_Dub wrote:

Thats true. The best test would be with and without engine, both before and after frame mods. Four tests. It's always nice to see hard numbers. I've seen guys go through a spaceframe for a racecar, add all kind of extra bracing, and maybe make it 5% stronger. Sometimes its not worth the weight, especially if its the difference between more than enough and even more.

Sounds like alot of scientific quantifiable fun.....if we weren't in the middle of building bikes!

Thanks Larry, I really do hope to build her someday.

Adam, you're right, that should be our primary focus!

T_Dub wrote:

I might have a bit more theoretical knowledge, but theres never a substitute for seeing things from a different perspective.
Just because I'm an engineer doesn't mean I know everything.
The only reason I argue is that I don't see where the forces are coming from to make those braces necessary.

the beauty of the z1 is ,The work has been done for us , long ago. we dont even have to understand it (although it would be nice). all we really need to do, is trust that the guys that raced these things, did a lot of trial and error (many were engineers too) and learned where the frames flexed.
once you understand the torsional loads applied to the frame during lean, it is a little easier to see where the issues lie.
looking at your frame u can see that the neck area is well braced. its behind that that this issues start. now u have to think about twin shocks vs mono.
as the questions, why did they switch, what were the twins failures, and limitations? if u understand the twins weaknesses , u can aid the frame in that direction.
nothing can be gained by saying i dont understand why there is a need for more bracing so i'm not going to do it.
obviously we cannot tell u why, u are not interested, in hearing it from us.
u must learn this on your own.
I can get u started , if u want some pics and info about bracing, PM me your email addy.
I dont know much about the subject,i have been triing to learn. Mostly, I just trust that the Legends before us, did.so i will simply copy them.
if u choose to peruse this, hopefully u will share your finding, and educate us.

Keep it twisted
Mark.

Yeah I have no problem with looking into it, I would love to actually. Anything that might tell me where the forces re coming from would be good. I know the racers back in the day had reasons for what they did, but I don't see a lot I can do to my frame to make it more torsionally strong without adding a lot of weight or really getting into serious frame mods.

I pm'ed you my address, look forward to seeing what you have.

T_Dub wrote:

Oh I know a lot about frame design, I do it all the time, and do FEA on them to make sure they're strong. I know just from looking at it that the ZRX frame is better in torsion than mine, but then again mine also has triangulation at the neck, hence all the plate welded on. The backbone isn't as good but aside from boxing it in there's not much you can do there. What you're doing with your front down tubes would be the only thing I would think would be worth doing in a KZ frame that already has a triangulated neck.

Here's an example of a frame I designed for a CBR600. It's crazy strong in torsion.

But if u don't truly understand frame geometry u cant expect it to perform any better than whats out there, so it just becomes a beautiful frame.
I will certainly say that it is beautiful. Well done

Oh, sure Ty, tell me to eff off, but listen to Mark?? :laugh: :laugh: :laugh: I hope that there is some useful information there for you

Hahaha I can tell him to eff off too if you like! Actually we just moved into PM's.