Any motorcycle history/suspension gurus?

[evolutionmovement]

What is the best anti-dive system for a telescoping fork motorcycle? I don't want it to be over-stiff under braking as roads are terrible and I want the ride to be as impressive as the rest of the vehicle. How does the Goldwing stack up as far as brake dive? According to some rough calculations, those forks should easily handle the weight I'm looking at (I'm in the preliminary stages of a design, so haven't gotten into cornering yet and that may sink this idea).

[555BCTurbo]

Anytime I've seen a Goldwing under hard braking, they dive like a sonnbitch...


You would probably be best off with an inverted setup off like a Busa or something

[evolutionmovement]

Thanks. Good suggestion, though those bikes are much lighter than what I'd be using it for. Now that I start figuring it out, I'd have to go to a custom setup and it's all an academic exercise anyway as I don't have the resources to develop this idea. I could effectively eliminate unsprung weight, but the cost would be understeer that would have to be dialed out somehow and I'd want to make sure it had good steering feel. This would be a perfect idea for an electric with wheel-motors. Oh well, at least I can eliminate unsprung weight in the rear.

[suba]

Are you building this bike from scratch, or working with what you have? I know the early (2nd gen for sure) ninja had an anti dive system. It was kinda weird but essentially it was a proportioning valve type system that used air pressure to react to rapid changes in the fork length and closed the valve to slow compression of the fork. Something along that lines (emulators?) could be of use.

[evolutionmovement]

It's actually an enclosed reverse trike (picture a P-40 Warhawk with the wings and tail removed, bigger cockpit, rear wheel under the bodywork, front wheels on outriggers, and you'll have an idea). I'd like to eliminate unsprung weight as much as possible, so I was thinking of having rigid upper and lower control arms like main spars in an aircraft, running laterally across and attached directly to the chassis. The suspension would be incorporated into the wheel spindle itself. At first I was thinking of using telescoping forks over the front wheels as they'll be enclosed by enveloping fenders anyway and I could mount the fender to the suspended portion of the fork, allowing the fenders to rotate with the wheels, but isolate them from the vertical motions. That way I can mount headlights to them AND all of it would be sprung weight. However, there's the issue of brake dive and, of course more importantly, what lateral loads would do.

So then I figured I could just incorporate the suspension into a car-like spindle design itself, even being able to isolate the steering from the vertical movement (no bump steer, easier optimization of geometry), but that requires fabrication out of my budget and would make suspension tuning difficult as I wouldn't be able to draw from other peoples' experiences. Understeer would likely be miserable, but perhaps the right geometry could be found to reduce it. Doesn't matter, looks like I'll be going with a boring double wishbone design.

[206er]

sounds like you are describing what is known as a plunger suspension.

see also: morgan

this setup is really antiquated and has not been used on a production motorcycle in probably 50 years or more. it is prone to play, flex, binding, and it basically sucks at tracking. not something you would want to incorporate into your design on purpose.


don't overthink the unsprung vs. sprung weight issue. it's only critical on race cars and such. to avoid a few pounds unsprung you will be adding a bunch of extra weight and complication that will not work as well as easier and better designs. dont reinvent the wheel with some crazy setup that may or may not be any fun to drive. use something proven like a arm suspension from a sport quad. strong and light. pretty much ready to go, build your crossmember with adjustable attachment points at whatever track width you want. a arms will provide the best camber curve, bump steer, etc. I would focus on dialling in your suspension geometry with something proven like a arms. there are a few books on race car chassis design which will help you out a lot. roll center, instant center, ackerman angle, etc. these are much more important than having a light unsprung weight imho.

[evolutionmovement]

Are the suspension arms on the Morgan fixed? That would be the same concept. Unsprung weight is, unfortunately important when considering a 1500 lbs. vehicle with enveloping fenders attached to the spindles and in which I also want to incorporate headlights (marker lights front and rear at the least). The lighter you go, the more every unsprung pound matters. I intend the vehicle to be long-distance capable, so ride is also important.

Normally I agree with you about unsprung weight, but this particular application is unique. In any event, my concept is too much for budget and time to explore, so the original plan of boring pushrod aero-profile double wishbones is the way I'll go (possibly using a Prowler font end, if I can find one), but I'm still worried about the weight of the fenders+wheels. Aero is a major point of the vehicle, so the fenders have to stay and they have to be mounted to the spindles so that they can turn with the wheels. Otherwise, the fenders would have to be excessively wide to allow the tires to turn, increasing turning circle, frontal area, and what will be an already wide track. Here's an earlier version (the changes are mostly detail).

[N1446]

i had an 88 ninja 600r with an anti-dive front , very effective , grab the front real hard and the a$$ end goes up real quick
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