Why can't we buy a sprung unicycle like this?

Take for example the Hatchet. Instead of tilting the frame 15 or so degrees back from vertical, as at present, tilt it back closer to 90 degrees, and extend the goose-neck as needed. You would get a certain amount of shock absorption out of that arrangement. The weight penalty would be minimal. And the buyers’ queue would go down the block and around the corner.

I don’t see a need for that sort of thing. And I have to say; I don’t think it’s aesthetically pleasing.

Assuming it can be done as you suggest I think you would get a unicycle with a squishy feeling and somehow inprecise handling. I would say that you want the “triangle” of contact points on the unicycle (handle, seat and pedals) to be as rigid as possible and then leave the cushioning for the tire.

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If you’re wanting some kind of flex from this arrangement then you’d be talking about making it out of steel (as aluminium would just crack), and even then it’d be a nightmare technically to make it strong and light enough.

You’re adding more material for basically no gain.

Some super cheap unicycles are a bit like this though with the frame at about 45 degrees and the seatpost being at 90 degrees to that and 45 degrees to the ground. It enables the post to be as long as you like and it not hit the wheel, but that’s the only benefit.

I don’t know if adding a guesstimated ~30% extra tubing (and thereby weight) can count as “minimal”…
The stresses where the “goose neck” meets the fork blades would certainly be maximal. A nice and long lever to bend or break the fork legs.

I would be very interested to play around with frame compliance, but either as “real” suspension (which I know would likely be terrible, but I’m curious), or with different tube shapes at the fork legs and reinforcements at the crown. I think I would prefer the oval tubing of most frames to be the opposite - stiff sideways, a bit more compliant front to back. However I’m not sure if I could pick that up in a blind test…

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Maybe a lateral strut with a damper would be a good idea, and reduce the stress quite a bit. It would add to the weight, but then you could make the frame cross section lighter, and claw some material back that way. Anyway, who cares about the weight, except when you are lugging the wheel up or down the stairs?

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Surely anyone who rides unicycles knows that lighter is almost always better. People don’t just buy carbon rims and modern aluminium frames as a way to spend their beer fund.

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I think compliance front to back probably just results in twisting, which is something you don’t want.

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The original idea is like the old Softride bikes, which worked OK. The biggest problem I see is that the handle is on the end of the same flexible beam as the seat. So you couldn’t stand up and pull on the handle for more force; the seat and handle would just come up to you.

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Probably true, but I think I’d notice side to side flex much more (and find it less desireable). I’m not sure if with reasonable tube sizes and thicknesses the difference is noticable anyway, but if I had unlimited budget, I’d love to try it out.

At that point of complication, why not commit all the way and build a lobbybopster style suspension…? Lets see some Custom Uni/Muni Frame builds - #7 by Canapin
Or at least a swivel joint at the back. Suspension members based on bending are very tricky (some modern carbon fiber bicycles have them nowadays, but they have development budgets far beyond what unicycle brands could ever dream of).

I followed that link, those are some nice mechanisms. But the best idea from that lead I got was the cupholder! Nik describes his Disco Uni - YouTube
Having a place to put down the coffee is a definite plus.

Any suspension in a unicycle other than hub based is the same as putting a suspension seat post in from a city cruiser bike, so just make a saddle adapter mount for one of those and keep it simple if you really want more than the tire can give you. I’ve thought about doing this but determined that suspension isn’t necessary for me.

At the risk of this turning into a thread about suspension, the issue with suspension seatposts tends to be that
a) you can’t pull up on them (although I don’t know how @lobbybopster gets around that)
b) they’re not designed to handle the twisting forces that a unicycle saddle puts on the seatpost (especially when it hits the ground) and have quite a bit of slop in twisting side to side.

Ok that makes sense, well perhaps a custom suspension post, maybe one that is make of square tubing and has a four bolt mount welded to the top to eliminate twisting and is designed to be pulled up on. Or just weld bearing holders to the bottom of a mountain bike fork that has locking suspension so you can lock it for street riding or uphill and unlock for downhill. I think this thread was made to discuss suspension, specifically a certain way of having suspension, but certainly other ideas are gonna bubble up, especially since the original idea was determined to be impractical and would have high stress on some parts.

Hi, All I can say is that I have no twist in the frame, they are lighter than some basic uni’s I get better traction because they have standard width tires and they don’t bounce like a fat tire uni because of the dampening in the shock. The travel is straight up and down in line with the axle, plenty of knee clearance and it doesn’t effect hopping like you think. I base these comments on the last 21 years I have been making them for me and some friends. It has led to alot of fun and comfortable riding. Yes it is just a big seat post attached to the axle. Earlier on I tried to suspend the wheel separate from the seat and found that the balance was too tricky to ride. There are several posts here detailing how to build them, The top picture is from the 2008 sandiego muni weekendalso the lower trispoke clipless model on the link was my early attempt at a road specific model, it worked incredibly well but in a moment of weekness I traded it to my son for my original 1962 columbia uni I learned on that I had given to him. Seat post, think Thud Buster.

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On the topic of material-based dampening/spring, there is the axle-side design of the Lauf carbon forks that may translate to unicycles: