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I've been thinking a lot lately about how to re-invent the conventional bicycle frame, especially mountain bike suspension parts.
One idea was to replace a good part of the frame with a curved leaf spring like the kind found on the back axles of most trucks and vans. Of course, it would need to be
fork-shaped in the back to accommodate the rear wheel. Then you can weld or bolt the steering and front fork assembly to the front end of the spring and add a vertical tube for the seat and the pedals in the middle. The disadvantage of this idea is that there is no real place to put shock absorbers, and the spring that makes up the frame will have poor torsional rigidity (the wheels could twist in relation to each other). Also, the front forks will tend to move forwards and back as the suspension moves up and down, throwing off the rake angle.
One solution is to add some control arms to either end. In the back, a single forked swingarm above or below the springs would be enough to add rigidity and a place to mount a shock absorber.
In the front, you would want to have four parallel links to keep the steering at a constant angle. This would act like the duolever system found on BMW motorcycles, with a scissor-shaped linkage connecting the front forks to the handlebars and isolating them from vibration (see link). This makes it necessary to add a horizontal frame tube between the seat post and the handlebars.
The only really static part of the frame would then be two metal tubes welded at a right angle, with all of the suspension parts and the slightly curved leaf spring bolted to this. This design would most certainly end up heavier and less rigid than a conventional mountain bike, unless special materials were used, like the composite leaf springs in a Corvette.
I will try to add an illustration as soon as I can make a sketch and upload it to a host. Until then, ask me any questions.
an article on motorcycle suspension designs
scroll down 3/4 of the page to see a description of the BMW duolever system [discontinuuity, Sep 08 2007]
Picture of an automotive leaf spring
[discontinuuity, Sep 08 2007]
do you think this guy beat me to it? It's hard to tell from just the description [discontinuuity, Sep 08 2007]
Looks possibly baked.
Google Patents has illustration, but it's still confusing. [baconbrain, Sep 08 2007]
Baked and quite tasty
I played with a set of these a few months ago. The owner was over the moon with them, me I'm not convinced yet, but they sure seem the business. [Custardguts, Jun 18 2017]
||You could use Ryan Leaf. At least in San Diego.
||The patent in the fourth link looks a lot like my first version of the idea.
||Well, it worked for the Corvette. It has it's advantages and disadvantages, and it's a love-it-or-hate-it kind of thing.
||I'm sure I've seen leaf springs on early motorcycles. I can't find a decent link right now. If I remember correctly there is a quarter-elliptic projecting forward from the headstock, connected by pushrods to a leading-link front end.