Coker wheel - how big?

I need to know the diameter of a mounted, inflated, Coker tire. (About 18" isn’t close enough)

Thanks in advance,


More specifics would help


Perhaps if you let everyone know the purpose of your measurement, that would be helpful. For example, there was a lengthy discussion a while back about the rollout distance (in other words, what circumference do you put in your computer to accurately determine speed and distance).

I am guessing you might be wondering about clearance for a frame or perhaps a brake, but these are all just guesses. There was also another thread that discussed minimum inseam to ride a Coker, if that is what you would like to know. Sorry I can’t help directly, still breaking in (or maybe just breaking) my 29.


The radius is 18 inches; the diameter is 36 inches.

On mine, with the tyre fully inflated so that it assumes its proper shape, it is 36 inches in diameter.

The circumference will be Pi x 36 inches = 113.1 inches or 2873 mm.

If you’re worried about the correct size from the point of view of fitting a computer, even 1/2 inch of ‘squish’ at the bottom of the tyre due to the weight of the rider will only make 1/36 difference - that’s 2.8%. That’s negligible.

Typical speedo error on a motor cycle or car is 5% - 10%!

If you need timings or distances to closer than 3% accuracy, you must be doing speed trials, time trials etc. ? In that case, the accuracy would only matter if you were comparing results with a different machine - otherwise any computer error would be constant.

If you’re worried about frame clearance, 36 inch diameter and 2.25 inch width are the measurements of the tyre, fitted and inflated. 1 inch = 2.54 centimetres.


I’m working on a frame…

Cheers, Greg

sorry this is kind of of topic, but without making a new thread i just wanted to ask a couple questions.

-How fast do these things really go?

-Are they easy to learn to ride? I have only ridden 20" unicycles.

I had my first go on a Ken’s Coker in the weekend. It was awesome! I figured out how to freemount it on my third attempt, and riding it was easy even though Ken had changed his 150mm cranks with some 125mm ones (which are faster and harder to control apparently). I really like the Coker and I want one. I would recommend it to anyone who has lots of money and spare space. It would take a while to adjust from a 20" to a 36", but as the balance concept is the same, I’m sure you could get it easily if you can ride a 20" competently. The Coker has an enormous amount of momentum, and gives you a satisfying high-up, cruising, swooping feeling as you ride it. Some people had a lot of difficulty riding it, so results (of how easy it is) could vary between different individuals. I imagine Cokers would be somewhat frightening to ride down steep hills without brakes.

How fast does it go?

Last year I did a lot of serious training on my Coker.

For comparison, I’m 40, male and 145 pounds. My Coker has 150mm cranks, and the standard steel wheel.

The best I managed was 12.95 miles ridden in exactly an hour. I also managed approx. 22 miles in 2 hours, and several times beat 20 miles in 2 hours. Once, I rode 20 miles in under 2 hours without dismounting at all.

(13 miles = 20.8 km. 22 miles = 35.2 km.)

‘Peak’ speed recorded on the computer was around 16 mph.

This was on generally flat terrain.

On rougher ground, it is possible to average anything from about 8mph (13 kmh) to 10 mph (16 kmh).

On shorter cranks (e.g. 125 mm) the Coker will go just that bit faster, but at the expense of fine control. People who ride on 110 mm cranks (or even shorter!) have hit speeds in excess of 20 mph (32 kmh).

based on my one Coker experience, i’d say it takes longer to re-adjust to your 20 after u got used to the Coker
it feels like u’re trying to balance on a pencil floating down a river!