I’ve been hanging around this forum for a long while now and at a gut-feel level some of the claims of coker speeds that I’ve seen just didn’t seem right. I’m not trying to call BS or anything and I have the utmost respect for the distance riders out there. I have high hopes of one day joining your ranks. I’m approaching this with an open mind so if you can convince me otherwise, great. So here goes: I did the math and I just don’t believe that 20 mph is attainable. Period.

I’m an experienced road bike rider who does thousands of miles per year. I ride a lot and have a very good, smooth spin. I can go all day long at 90 - 100 rpm. I’m more of an endurance rider and I totally spin out at about 140 rpm. That’s bouncing in the saddle, hips about to fly out of their sockets spinning out. Sprinters really have some strict training regimens to get the highest rpm possible. They train to be able to spin in the 150 to 180 rpm range. 180 is the top rpm I’ve been able to find in searching the internet. And everything I’ve read says that this is with a significant bounce in the saddle. And toe clips to keep the feet on the pedals. Given all that information, I’m guessing that with a ton of focused training towards smoothness and speed, that a unicyclist might, on his very best day be able to get a spin of about 150 rpm.

According to my calculations given a 36 in. wheel:

I threw in 180 because I might be able to believe this with short enough cranks but I’m still a bit skeptical. 200 rpm I’m just not buyin’.

Computers will sometimes throw an erroneous number at you. I’ve had mine show a max speed of say, 30+ mph on a ride where I know I never exceded 25. Calibration is also important. I’m anal retentive enough to have my wife measure the radius from the bottom of my tire to the axle with my fat ass on the bike (smaller radius than with no load) and use this number to calibrate my computer.

Anyway, I’ll pretty easily buy 16 mph or so as a top coker speed and verrrry skeptically 19 mph. It’ll be real hard to convince me of 20.

I ran some numbers and I got that at 19.4 mph you would be spinning 163 rpm or so. This is with the diameter or a coker wheel being 40". Does that sound about right with a 36" wheel along with a tall tire. Maybe you forgot to take into account the tire into the equation?

This can be easily calculated. Racing is done on 24" unis. The maximum allowed size is 24.3333" and you can be sure that this is the size that is used. So the circumference of such a wheel is
then 24.3333" * pi. That’s 194.171cm.
The top swiss and german unicyclist are in the range of 13s (and below) for 100m.
100m : 1.94171m = 51.500 wheel lengths

51.500 : 13 = 3.961 rps (rounds per seconds)
which is approximately 240rpm

Given a Coker wheel and for example Christian Hoverath on top of it:
30mph seems to be possible (for short periods of time)

I think you discount the different that short cranks make. Compared to 170mm cranks. with 125 mm cranks the diameter of your pedal circle is 90mm shorter (27%). Even if you take just your 140 rpm example, 27% higher cadence puts you right at that 180rpm you note above. I don’t think your average Coker rider can spin that quickly, but it seems entirely feasible for the top athletes in the world.

It may seem counter-intuitive, especially if you’ve ridden a Coker a little but not a lot. But I personally can tell you it is very possible to ride a Coker at over 20mph. I’ve done it and know many others who have as well, some way over. But we are not talking about sustaining these speeds for very long.

I’ve read of Olympic cyclists training on wind trainers at 300rpm - do the math and see what Coker speed that translates too. Never say never.

Christian’s nearly 30mph was done with 125mm cranks. I watched Zack ride 24mph a week ago with 140mm cranks. Personally I think 110mm or shorter is what you want to go fast. But who’s to say - it’s personal preference.

One other thing - if you carefully measure the diameter of a Coker wheel, you’ll find it’s less than 36". This means that the speeds are harder to attain than if you’re using 36". My cyclometer measurement is 2776mm in circumference which gives a diameter of 883.6mm or 34.8".

One thing Nathan fails to mention here is that the tremendous centrifugal forces at those speeds make the Coker tire bulge and increase in effective diameter while decreasing in effective width. You may safely be able to add on another 0.01" to the diameter.

I think the thing you are forgetting is that on a bike, the crank length is a lot longer than what is typical on a Coker when reaching the 20+ MPH speeds. So on a bike with 170 mm cranks versus a unicycle with 114 mm cranks, you are moving your feet about 50% further on the bike, so you are going to bounce a lot more with that much more movement.

Another thing is that on a bike you are bending over more and that may contribute to more bounce in comparison to sitting up straight on a uni. Try walking while bending forward in comparison to standing up straight and you’ll notice more bounce.

Go measure it Bob: unicycle wheels seem to be “nominally” based on the
outside diameter of the tyre and NOT the rim. My coker is nominally 36"
measured at the tyre, give or take a couple of tenths.

A summit frame aint worth 300 bucks. One word: total complete rip off!!! I feel sorry for your relatives who payed for it. Now that is worth nothing. Too bad, you should have given it to me for a frame!

On Wed, 25 May 2005 15:34:03 -0500, “tholub” wrote:

>I think you discount the different that short cranks make. Compared to
>170mm cranks. with 125 mm cranks the diameter of your pedal circle is
>90mm shorter (27%). Even if you take just your 140 rpm example, 27%
>higher cadence puts you right at that 180rpm you note above.

Even more. You have to calculate 140 * (170/125) which equals 190.4.

I have maintained (several times, during one minute average) a cadence
of 164 on a 20" with 125 mm cranks. And I’m only a mediocre rider.

On Wed, 25 May 2005 15:51:30 -0500, “nathan” wrote:

>My cyclometer measurement is
>2776mm in circumference which gives a diameter of 883.6mm or 34.8".

I have had my stock Coker for a little over a year. I’ve measured my RPM by counting and using a 1 minute timer on my watch. I can only get to around 110 RPM.

I recently changed to 125 mm cranks that came off of a 20" uni, and my top RPM so far is only 115 RPM.

Don’t look at RPM or Cadence. It is less relevent on unicycles than it is on Bikes. Bikes don’t very the length of their cranks, we go from 170 down to 89mm. What is actually more relevent is the distance than the speed that the foot is moving. I have a spreadsheet somewhere you I did comparisons with different sizes of crank and top speeds (including bikes).

Personally I’ve recorded (with my wrist mount GPS) 18.5mph on my Coker with 125s and 14.5mph on my 24" MUni with 125s; these were both relatively short bursts. Based on my 24" rpm I think I worked out I ought to be able to do something like 19.5mph on my Coker, so not too far out, and I haven’t recorded my speed very many times nor do I consider myself a fast rider.

Has anyone compared the accuracy of a cycle computer to a GPS? I’m looking at putting a cycle computer on my Coker to see how they compare.