high speed geared Coker

HandyAndy beat me by a minute. :slight_smile:

I’m a bit confused about the gear ratios. Is it 1:1.5 or 1.5:1? Which way means that it’s geared up?

Kris brought der uber-Coker out to a MUni ride at Simon Fraser university yesterday. I was pleased that he had wisely drilled a hole in the frame of a standard Coker to attach the torque arm rather than use one of the kluge clamps I had brought for the purpose.

I was pleased that I was able to ride it at all and found that I was in fact able to freemount it after several tries. A good running freemount was easier than starting with a prop to mount. Mike Rocks was also able to ride it.

It is a fast machine and very dangerous. You can’t tell how fast you’re going and you have to get up a good bit of speed before it bomes stable enough to be comfortable. When you’re stable you know you’re going too fast to run out a fall. But it is fun.

The hub was built into the wheel by Dave Stockton (U-Turn) and it is a beautiful piece of work. The axle is of an unknown, magnetic material and is probably the weakest part of the entire setup. Kris had 6" cranks on it when it when we tried it out. He claims he’s going to commute with it but he’s a real rider, unlike hacks like myself.

There are or will be some phots available.

What diameter wheel is Blue Shift then? Not a Coker? I think Brown Streak would be a good name for a unicycle that can do those speeds :wink:

That’s an interesting concept. I think I’d be a little uncomfortable with a good bit of speed on a geared up Coker. :slight_smile:


Doesn’t sound like a city riding machine. Not stable enough. It does sound well suited to long, straight, boring country roads, though.

The ride at SFU was also very fun. We had about 10 show up including one bicyclist. It was a rideable descent with a few toys and we ferried the ride so there was no initial climb involved. We had eight for dinner afterward so it was a good group outing. Rare for the relatively lame Vancouver riding group who need to be prodded firmly to get their unicycles out.

Byron got some digital uber-Coker shots and Kris and I used his camera with perhaps some success. Dave Stockton has some photos of the finished wheel that I hope he will post soon.

Watching someone ride by on it is unbelieveable. I would really like to see Christian Hoverath on the thing.

I found it to be more stable than Blue Shift or Uni.5 primarily because of the huge rotational inertia of the Coker tire. Getting started is a different story, though. I was always able to mount uni.5 more easily than Blue Shift but, again, I found the Big Apple on Blue Shift more stable in motion because of the inertia. Some found the opposite to be true.

Kris was kind enough to share his new toy with all present who were interested even knowing that huge UPD’s were probably to be expected. There was no disappointment there. It seemed to escape undamaged.

i think i have it backwards, one revolution of the crank to provide 1.5 revolutions of the wheel

Thanks again to Greg and Kris for allowing me to participate in this project. There are a few photos in the first album here, entitled, “Building the KH Coker.5”.

Harper, how close is the Harper hub to being available? And any idea about how many $$$$ I would love to have one as soon as they are available.

I went out for a longer ride this afternoon. In general the Super Coker (or whatever you want to call it) is fantastic for gentle terrain, and hard for hills. Climbing hills is like going uphill in 10th gear on a bike, or putting 100mm cranks on a Coker- in other words it’s definately hard work. Unless you were going for a speed record on completely flat terrain, I don’t think you would want to go shorter than 150mm cranks (which is what I have on there now). I don’t have a speedometer to measure speed, but I’ll try to find someone to drive alongside me next time I’m riding, to measure an average cruising speed.

Stability is really good though. I find that I hold the saddle handle more because I have to push harder with my feet compared to a normal Coker, but it’s not that bad and I don’t think it would be any problem concentration-wise to keep it up for a long time. The only paranoia I have is that I’ll be cruising along at high speed and the planetary hub will break down and send me onto my face. Hopefully that won’t happen!


Do you have a GPS? I find that a GPS works well for measuring your current speed as long as you can get good satellite reception. And the best part is that you don’t have to calibrate it to the size of the wheel.

That’s great Kris!

I suppose you’re using a brake with the sort of momentum it’s generating?

I just received my no-tubes kit today- perhaps that might be an interesting addition to a geared up Super Coker to make it easier for acceleration and deceleration?


Try to weigh the wheel before and after the No-Tubes application. It will be interesting to see just how much weight is actually saved by going to No-Tubes.

I can tell it will save plenty already- but yeah, I’ll weigh the different kits if I can get my mums kitchen scales to work. The rim strip (required for the no-tubes set up)- weighs next to nothing compared with the beefy Coker innner tube. And the sealant shouldn’t weight that much- a couple of scoops- probably 100mL/s 100g I would suspect. I’ll let you know tomorrow.

First. I think this is a good time to ask for name suggestions.

Second, clearly it’s been a long time since Kris rode a bike. I think my 24 speed is years outdated. I don’t know if 10 speeds exist anymore but tenth gear on a modern bike is not that high.

if i’m not mistaken, i think most road bikes still have 10 speeds. but i could be completely wrong. i do know lance’s bike has 18 speeds.

ill be trying to think of a name. someone mentioned supercoker, i like that. or perhaps “the 36 inch grinch” :stuck_out_tongue:


I’m having very poor response from overseas production firms right now. The version Kris has was reworked from a sample from an overseas manufacturer. The gears in it are imprecise but strong. The pins, bushings, cage, and bearing system are very strong and precise because they were reworked by me. It is more likely to twist under high torque but not catastophically. The hub is sound and is unlikely to seize. The low tolerance manufactured gears give der uber-Coker about 1.25 to 1.5 mm backlash at the pedal axle center on a six inch crank. That is my estimate, not a measurement. Blue Shift and Uni.5 were both about 1mm or a bit less. I had hoped for 0.5mm. The sample hub Steve Howard has is probably the worst but I dont know what the measured backlash is on that one. I saw it in Moab and it was sloppy. He has not reworked the hub too much. He would probably have to replace the gears with a higher quality set.

The axle on der uber-Coker is questionable but unlikely to break under regular use. If it twists, the production prototypes are seviceable so Kris just has to yank the guts and ship those to me. I will cut off the axle and machine one out of 17-4PH, weld it to the planet cage, heat treat it and ship it back to him.

The sample was made very inexpensively but was useless as delivered. that was number two of three and a half samples. They never got it right and I went to two other firms with higher minimum orders so it requires a large, risky upfront investment.

The high end road bikes (the ones used for competitive racing) are now using 10 sprockets on the back wheel which gives them 20 gears.

For mountain bikes the new standard is 9 sprockets on the back wheel which gives them 27 gears. But not all of those 27 gears are usable because in some combinations the chainline is too out of whack.

Tenth gear on a mountain bike would be the big sprocket on the back and middle ring on the front. That’s a fairly low gear on most bikes. You can certainly climb many logging road grades with that gear.

i like “der uber coker” if you call it the super coker it makes my Super 29er seem not so super…

at the very least,anything with the “Super” tag sould have splined cranks.

being afraid of speed I don’t think I would be interested in more than 1.25 ratio
I would really appreciate ratio such as O.75 and down to handle
steep terrain…
does that make sense?
I am also wondering wether continuous ratio change would not be better than discrete values… (but I am no practical techie)