OK, so I've often said that my creative imagination far surpasses my technical ability, but this has got to be one of the wildest and crasiest off the wall ideas I've ever come up with...

The other day I was reading a thread on hardtail struts, and saw the "crowbar" shaped strut, and was thinking how much I loved the look, but wasn't crazy about the potential uncomfortable ride that a rigid frame provides.  That's when it hit me...what if the angled strut that follows the lines of the bike were combined with the "suspension" of a tortion spring similar to seat springs.  You've seen Hardtails, you've seen Softtails...Ladies and gentlemen, I present to you the "Torsion Tail"...

I think the trick would be to have a torsion spring that supports the weight of the bike & rider without having too large of a diameter of coil & being too large of a wire diameter, but I think that it could posibly actually work.

Thoughts?

I understand that it probably would ride like a pogo stick, but that's not the point.  We're not going for the feel of a cadilac here, just an alternative to a hardtail.  With that being understood, the topic of creature comforts went out the window a long time ago.  What I'm going for is the look of a rigid frame, but won't rattle your teeth loose.  And before anyone says "HD has done this, it's called a 'Softtail'..." I know, but that kind of conversion would take a crap ton of frame modification.  My Idea incorporates the shock mounting points, so it would be a direct bolt-on replacement, and could easily be changed back to shocks without any mods to the bike itself.

Pretty simple idea,... yet, I've never seen one...

Probably a good reason for that... ...

Dang it Dave, there you go again smashing all my hopes and dreams with logic.  

The buggie & the patio chair are designed for comfort, and to absorb the compression, and therefore are nice and bouncy.  Torsion springs can be designed to do a number of different things...provide a lot of torque, absorb impact, etc.  All of these things are controlled by a few things: wire dia, wire tensile, coil dia, and number of coils.  For asthetics and space limitations, a single coil with a fairly small dia would be needed.  Also, you're kind of limited on wire dia because of the long canteleiver at the top portion, so it would need to be fairly beefy to keep from bending.  Those variables would force it to be really stiff, so the wire tensile couldn't bee too high, so the spring rate would be slow enough not to "buck".  I think it is "possible", but would have to be done in such a way that it would only take the "sting" out the larger bumps, and not to be a soft cushy ride.  Which takes me back to my original point of it being a "softer" alternative to a rigid frame.

With all that being said, the spring I just described requires the design engineering and special tooling to make that would price it about the same as nice used softtail.

I love the idea! I reckon it would look awesome with some funky chrome hairpin springs, just like your illustration. How about incorporating some friction dampers from a Castle fork into one end? Could work....

I think we have a junk spring tooth harrow out back... More like leaf springs than torsion bars. Might have a junk branch rake section still, the rods are 5/16" diameter by about 3 feet long...  Have to check the forge iron pile.

If you want to be different, make the P in LS650P stand for "Power Plus" knock off...



Solid rod from swingarm to the leaf spring. That bike above is a 1918 1000cc, design debuted in 1916, same year Indian offered an electric starter...

Hardly Runnerson didn't have a full production swingarm Big Twin until 1954... and electric start came out on them in 1965.

Hey, I decided the P in LS650P stood for "Police", and built a scaled down 1950s English police bike out of my 2003...  

A lesson in undamped harmonic motion......

https://www.youtube.com/watch?v=rCukkwWBMDg

https://www.youtube.com/watch?v=ng3hbZk9h50