A unibike is a “bike with the front wheel and fork removed (and possibly with geometry optimized for balancing on the one wheel)” [Tom Holub]. In the past I’ve discounted trying to buy/make a unibike because the violent UPDs I frequently experience would decimate it tout de suite.
A penguin is similar to a giraffe in that it uses a chain but is usually shorter with sprockets with different number of teeth for a gearing advantage. I have long wanted a penguin but have thought it would be too tall to ride effectively on trails.
I was looking at pictures of trials bikes like this one:
I’m wondering if the design of this kind of bike could be used to make something in between a unibike and a penguin. It would be like a unibike because it would be the back half of a bike but my idea is the unicycle seat post would not go where a traditional seat post goes (this trials bike doesn’t even have that) but in line with the bike frame. This makes it somewhat like a penguin except the chainring is not directly in line with the “bottom” sprocket. It’s located very close to the tire so extends the height as little as possible. It also may be protected by saddle handles on UPDs but chain ring protectors may also help.
I’m no engineer and may not have expressed my idea well but I’m throwing it out there to see what others think.
I bought a kid’s BMX from the tip because I wanted the yellow ‘spokey-dokeys’ that were on it.
Ended up doing exactly what you describe with a stick welder; tacked the hub to be fixed gear, cut off the headstock and welded the seat post to the top tube in ‘perma-wheelie’ mode.
It was pretty good fun, a 16" wheel geared up to a 32". Really badly made and fragile, it only lasted a day. I’ll try and find some pictures.
The displaced cranks made it fairly uncomfortable to ride though; a penguin is the way to go. Welding the seat tube to the bottom bracket shell would make all the difference.
Edit: I definitely remember having to make a chainwheel protector so it didn’t get bashed. We used a section of seat post and put a rubber grip over the end. It looked like the silly thing had a boner.
I think sticking a seat so it’s in line with the top tube would almost create a recumbent uni… Your pedals would be further forward than normal alway, I would think.
I made one very similar as well, but out of an old road bike I found sticking out of a dumpster. I laced the front wheel onto a unicycle hub and turned the back wheel and frame into a kind of penguin.
Like Rich, mine was slapped together quick and dirty with really shady workmanship. But my cranks were fairly close to centre line and it wasn’t that hard to ride. The wheel folded when I went down a couple stairs so I stripped off all the useful bits and returned the remainder for a refund.
It was a fun little project but not something I would spend much money on. I would like to have a giraffe or penguin again but would probably make a dedicated frame this time.
If I may offer, the origin of “Penguin” for short giraffes comes from a Penguin-brand unicycle. I don’t know much about them, but there were a few of them in the Redford Township Unicycle Club back in the late 70s/early 80s. I have also seen a Penguin standard uni, but only once.
Tommy Miller of the Unicycle Factory had another name for a geared-up, short giraffe; he called them Travellers. The most efficient/inexpensive way to gear up a unicycle. Keep the crank axle as low as possible, then use ordinary bike sprockets/cogs to run the chain.
It could work great, though I assume Trials bikes have freewheel hubs. You could keep the whole frame, take off the front end and even attach a separate seat tube, maybe where the top of the fork used to be.
That’s what would be cool about it. The stuff doesn’t have to line up for it to be rideable. Just remember that it’s going to be oriented underneath the center of mass of the rider, so that’s how you figure out the angle it will stand up at.
Thanks for the response! I’d love to see your pictures. It doesn’t surprise me that people have created unicycles like this before from regular bikes.
The angle between the seat stays and chain stays in trials bikes is very acute and sometimes nonexistent. My thinking is that this would minimize the crank offset vs. doing it with a regular bike.
Did you take any pictures? The chances of finding a trials bike in a dumpster are nonexistent and they’re expensive to be chopping up for a project. What would be your plan for a dedicated frame?
Thanks, John! I hadn’t heard the term Traveller before. I’ve ridden one of Tommy’s Travellers before and if I ever have the perfect, tested idea for a custom unicycle I’m hoping Tommy will still be available to build it. I want something as low as possible that can withstand significant UPDs. And for my purposes of course it has to freewheel!
I was thinking more of a “build from scratch” when I said I would rather build a dedicated frame next time, but I just came up with what could be a workable idea.
What if you took a normal frame with horizontal dropouts
cut everything off of the seat-tube and bottom bracket
squeezed the seat-stays and chain-stays together to be nearly parallel
welded the resulting flattened rear “triangle” to either side of the BB.
The result would be a giraffe with very short dual legs with the BB doubling as the crown.
I might have to check for bikes next time I go to the dump…
EDIT: if you wanted to use the trials bike frame, you could possibly remove the fork then add a tube coming from the headset and add a saddle to that. You would have to do something to stop the freewheel (crank swap?) and everything could be 100% reversible.
I’ve thought about this some more and ultimately ruled out this design for my purposes. While it may work fine for a fixed wheel unicycle the added height makes it problematic for a freewheel unicycle. It makes UPDs worse for one thing but the bigger issue is balancing while coasting. I do this primarily by tilting the frame forward or backward using the pedals as a base. These are fine, quick movements and putting the pedals outside the wheel doubles the distance required. With practice I could learn to do this on mostly even terrain but I’d rather spend that time gaining proficiency on a traditional freewheel unicycle.
Anyone see a reason why an eccentric bottom bracket (or adapter) wouldn’t work for chain adjustment on a Giraffe or Penquin? I might have an idea floating around in my head…
