frame bracing

Kidkawie wrote: Racing is one thing, I'm talking everyday street riding/cruising. I could easily throw a crapload of gussets on my frame and call it a day, I'm looking for someone to find exactly what the problem is with the older frames. Like I said, riding it seems like behind the engine is the weakest spot, possibly where those triangular gussets are above the swingarm bolt.

I guess the only way to really find out is to put a bare frame/engine in a jig and tray to fold it in half.

AUTO CAD....(COMPUTER AUTOMATED DESIGN) program would let you enter KZ or Z1 frame diamentions and profile into computer. It will let you imput dia of tubing ID and OD. You can apply stresses to frame to see how it reacts. It will show all stress / weak points of frame in a different color with red showing stressed area. It then lets you goto a single stress point and introduce different remidies to correct problems....IE,,, tubing or plates.....when done right the color of area will change from red to blue and tell you the amount of correction.....it is 99% correct and is all done on computer screen....you can move frame in 3 axis and in any direction and look at it.....the whole frame can be done and area corrections printed out. Its an incredable process.....only problem.....the thousands of dollars the program costs and the skill needed to run program. If you never have seen the process.....it would blow your mind. This is the best way period....to access a frame and its weak points....you can see below the stress in red....also the forks and frame are autocad imputs....you can see how real it is....you can design any frame you want and know how its going to react before built.

That's what I'm talking about.

Racing is a different ball game. Yes, if I was going to race a bike, I would gusset the shit out of it. But I think with some fine testing (or that CAD program) someone can figure out the actual weak point/flaw in the frame (if there is one) so the average guy doesn't have to pucker up doing 80mph.

enjoying this discussion guys. In my mind having worked as a mechanical designer/design engineer for years using 3D CAD software. its apparent the factory already did a lot of analysis to the frames from the 70s and fixed everything in the 80s frames and modified everything in a way very similar to what blackbanshee shows in his pics. at least as far as the handling for the street goes. its shows when you look at the frames next to each other...





I wouldnt think to add much more to a factory frame than what they did. Of course if I ever had time enough at work (ha!) I would love to measure out both frames, build some 3D models in Pro/E and get one of the FEA guys to run 'em thru a few of they're analysis programs like Hypermesh and Ansys.

cadmonkey wrote: enjoying this discussion guys. In my mind having worked as a mechanical designer/design engineer for years using 3D CAD software. its apparent the factory already did a lot of analysis to the frames from the 70s and fixed everything in the 80s frames and modified everything in a way very similar to what blackbanshee shows in his pics. at least as far as the handling for the street goes. its shows when you look at the frames next to each other...

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I wouldnt think to add much more to a factory frame than what they did. Of course if I ever had time enough at work (ha!) I would love to measure out both frames, build some 3D models in Pro/E and get one of the FEA guys to run 'em thru a few of they're analysis programs like Hypermesh and Ansys.

That would be awesome if that was done....thanks for checking in on thread. Thanks

Thanks for those diagrams.

The horizontal tubes (that the ignition coils mount to) get a brace from the top tube....looks like to keep them possibly from spreading OUT from forces to the steering tube. I wonder if some sort of headstay could be fitted? Essentially tying in the top of the frame to the engine.

Kidkawie wrote: Thanks for those diagrams.

The horizontal tubes (that the ignition coils mount to) get a brace from the top tube....looks like to keep them possibly from spreading OUT from forces to the steering tube. I wonder if some sort of headstay could be fitted? Essentially tying in the top of the frame to the engine.

that is called a head steady and is quite a usual solution in race bikes.

here's the one in my CB500/4 racer. frame is a bit different but principle is the same

BTW, quite surprised about the heated discussion going on here, soon will rival engine oil threads

so if i may, I will add a road racer's angle: seen with my very eyes braced frames in the winners cycle, for sure, but, surprise surprise, quite a few stock unbraced ones (stock swingarm too) at the top step of the podium.... and no, and they didnt buckle,snap or went off track at every turn.

what am i trying to say here? I did brace both my race bikes frames for my own peace of mind, but there certainly are people out there that are massively fast on non-braced frames or swingarms even. At least one of them told me he simply that likes the "feel" of the bike like that, he doesnt even run a fork brace.... and still wins races.

very nicely made head steady, had a pretty awesome one on my 67 triumph tt chopper i made from plate and heim joints.

I obviously have a view on this since I bought one of Leon's kits and welded it in, with that being said, I recently read an article in Cycle World where they were discussing frame and swing arm ridigity in Moto GP where they tend to spend the money if it makes sense and saves them a tenth on the track. The discussion was that there is a trend coming back to allow more flex then previously at least in the swing arm to allow more lateral movement to help the chassis move withe surface of the road, keeping more tire in contact with the pavement during aggressive lean angles. If they make he swing too stiff, it doesn't allow the tire to follow irregularities in the track surface on high speed corners. Interesting concept, and of course you can go too far the other way as well. I think you'll find it would be hard to find the perfect combination of bracing without adding it all simply because too many variables exist between rider weight, tire size and compound, suspension component selection , etc as they will all play a major effect in how the chassis has the forces transmitted through it. It comes down to simply bracing it how you like and forget the rest...

Just my .02 but WTH do I know!

Cory

Kidkawie wrote: I'm looking for someone to find exactly what the problem is with the older frames. Like I said, riding it seems like behind the engine is the weakest spot, possibly where those triangular gussets are above the swingarm bolt.

I guess the only way to really find out is to put a bare frame/engine in a jig and tray to fold it in half.

Yes, Kosmann did just that back in the late 70's. They mounted a KZ frame in a fixture and measured where and how it flexed. They mounted dial indicators all over the frame and found that most of the flex happens around the stearing head. The two or three short braces that get welded to the three top tubes are very important. When the frame flexes those top tubes flex away from each other. The kit that Leon makes (Z1 Restoration too)has the needed braces to do the job. One of the things I like about these older bikes is I don't have to reinvent the wheel. (Bad Pun)

turboguzzi wrote:

Kidkawie wrote: Thanks for those diagrams.

The horizontal tubes (that the ignition coils mount to) get a brace from the top tube....looks like to keep them possibly from spreading OUT from forces to the steering tube. I wonder if some sort of headstay could be fitted? Essentially tying in the top of the frame to the engine.

that is called a head steady and is quite a usual solution in race bikes.

here's the one in my CB500/4 racer. frame is a bit different but principle is the same

BTW, quite surprised about the heated discussion going on here, soon will rival engine oil threads

so if i may, I will add a road racer's angle: seen with my very eyes braced frames in the winners cycle, for sure, but, surprise surprise, quite a few stock unbraced ones (stock swingarm too) at the top step of the podium.... and no, and they didnt buckle,snap or went off track at every turn.

what am i trying to say here? I did brace both my race bikes frames for my own peace of mind, but there certainly are people out there that are massively fast on non-braced frames or swingarms even. At least one of them told me he simply that likes the "feel" of the bike like that, he doesnt even run a fork brace.... and still wins races.

This is why I think there are other solutions besides bracing. For instance, when I'm riding on the freeway doing 80mph (or any casual riding), there are really no forces on the frame that would cause it to distort. I think alot of the issues is the garbage suspension. Too soft in the front, too stiff in the rear, pretty much zero damping.

I agree for normal riding ,well suit yourself.My z1 at 125mph at the track is perfectly fine but I also have an upgraded front and rear end, as well its only a 1075.Probably good idea too look for a later model kz to fab on.