The concept needed a little work.

Oh wow, is that for real ! I've never seen that before.....WILD !


Joe

Wankel crank!

That manufacturer was into wheelsets, too;

wonder how that rides

Heh, a Reuleaux Triangle. The same shape can be used to make drill bits that drill square holes. Unfortunately I'm too drunk to grasp why this would be good for a crank.

And I was thinking I was too sober to figure it out.

I've had enough to drink I think it'd be fun to try and make a copy and see what it does...

This one rode like fresh poo-poo. My guess is that the triangle one is worse...

In this article............ https://sheldonbrown.com/biopace.html ..........Sheldon claims to have run biopace/fixed gear on personal bikes with success.

Personally I'd like to have M.C. Escher make me a chainring.

Huh, so that is how the square taper is started. Does anyone know the whole process for making those?

i built a fixie one time, and it had a biopace chainring... no problems

Heh, the first thing one needs to know about BioPace is that the big ring is always almost round, only 3.5% radius variation, I measured it.

Next thing is that most of the later BioPace variants that Shimano sold had the same, mere 3.5% variation, which played nice with front derailers and could be SPUN. These were named BioPace II, BioPace HP and BioPace SG, in that chronological order iir.

The smaller ring(s) of earlier BioPace cranks had fully 8% radial variation, which made any downshift from the big ring seem like a bigger drop in gearing than it was. This was pretty awful.

I've raced almost exclusively on BioPace HP rings since 1997. I cannot detect any BioPacing once I've ridden one lap on them, the effect is so subtle.

The pictured triangular chainring is very odd in that the left and right leg seem to get opposite effects from it. It would thus seem to be difficult to adapt to and of course very difficult to spin.
Ever try to pedal a cotter-cranked bike with both cotters installed pointing in the same direction?

I think that BioPace is helpful when you get stuck in a much too high gear, as the torque peak is spread out over a larger number of degrees of crank rotation, i.e. is less peaked. This helps prevent stall-out in any bog-down situation.

The late Edmund Polchlopek, noted French funnybike pioneer, created his own specially shaped rings by modifying (hot-forming iir) standard alloy chainrings. These were actually made in small production batches in the early 1980's.

why do you use them if you can't detect a difference? and it seems you can tell a difference?

I prefer round rings but have a biopace ring on my single speed (mostly because i had the ring on hand and don't have any spare round ones right now) I'm not sure if it makes much difference but if it is beneficial in instances where you're in a too high gear, then it would be useful on a single speed i suppose.

Nice, nice, nice. I'm sober at 10 in the morning, but really need another cup of coffee to wrap my head around this triangular concept.

I've got this early elliptical ring. NOS, too. Had to have it because it was so odd. It's a 144 BCD, in case anyone has any info to share.

While your chainring looks vintage, there is a rather contemporary chainring that looks very similar; here's
The Curious Case of Osymetric Chainrings

https://www.competitivecyclist.com/wh...rings.415.html

Somewhat the same topic: Back in the 80's, I bought a bike fitted with the Houdaille ExO PowerCam. It used a cam drive to spread the torque to maximum at the 3:00 and 9:00 positions and least at the 12:00 and 6:00 positions.

Sounds like a great idea, no? In theory, yes. In practice, it forced me to have a much slower cadence...almost killed my knees. Tried to like it but couldn't, although great fun at parties - the pulsing was quite pronounced, more than any small ring Biopace. I wound up selling it for cheap and shouldn't have...they're collector's items now.

I use them because of the mechanical (front derailer) setup on the Pedersen as it relates to gearing.

My front derailer cannot be lowered below the height for a 52t round big ring.
With BioPace rings, I am using a 50t big ring, which is the one ring I use for almost all of my time spent racing and road riding.

While BioPace HP rings escape my notice while I'm riding, I have noticed a slight improvement with them (in situations where I might stall out and have to unclip to save a fall). I just hang in there and pedal with some extra confidence that I can pull out of tight situation, as when re-mounting awkwardly in technical terrain.

In shorter mass-start events like cyclocross, a strong start is more important. Here, I appreciate the ability to shift earlier without feeling the spike of too much resistance at the pedals (and my knees). The earlier shifting gets me up to speed faster since it eliminates the sharp fall-off in pedal torque as the cadence gets too high. This is exaggerated by the lag in the actual ratio change from when each upshift is initiated, so each upshift gets me another half-bike-length ahead of the guys at each of my elbows. My STI-using competitors have it even worse, because their upshift isn't initiated until they have pressed and released their STI lever, while my thumbshifter moves the cable more immediately.