Does anyone make a Bike Computer/odometer that works on the 36" tire?
There are a fair number of computers that will work with a coker. Some are also very inexpensive. The best way to tell if a cycle computer will work is to remove it from the packaging, read the instructions for set up and then try and set the wheel diameter to coker size. The limit on the size you can set the diameter to is fairly arbitrary and vaires from computer to computer. Some allow entry of sizes up to formats like 999. As long as you can enter the diameter of a coker wheel in you should be fine.
The other alternative is to buy a second magnet and mount it directly opposite the first, using half the wheel diameter as your setting.
I can state from experience that the Cateye Enduro 8 and the basic Schwinn computers both can be programmed for the Coker wheel size.
There have been threads on this…you might try a Search for more info.
You can go to the web site for a cycle computer manufacturer and download the manual for a particular model to find out the specs and how big of a wheel they’ll let you enter. You’ll have to do the manual configuration instead of the presets that are on some computers.
The wheel circumference for the coker is going to be in the 2775 mm to 2800 mm range (or 277 cm to 280 cm range). Most computers have you enter the value in metric (either mm or cm). There are a bunch of computers that will let you enter numbers that big or bigger for the wheel size. More info on the numbers is here on Klaas Bil’s site: The rollout of a Coker wheel
I don’t know the good computers are for a Coker. The models change and I haven’t kept up. The one I used to like is a one button Schwinn computer that you could get at Wal*Mart for around $10. But that model has been changed to a two button version and I don’t know if the new one is still good for a uni or not.
One problem some computers have is that some of them register a new speed after only one revolution of the wheel. Other computers require two or maybe three revolutions before they’ll register a new speed. Computers that update the speed and max speed after only one revolution have problems with false readings when the magnet flips by the sensor during a mount or an idle. They can give you false readings for max speed that you know are way too high. That’s one reason I liked that Schwinn because it doesn’t have a big problem with false readings. You aren’t going to know how a particular cycle computer behaves until you actually try it. It’s not something that you can find out in the manual.
I’ve lost 2 Cateye Enduro 8s in 4 rides from not clipping them in properly… push them right in so it clicks twice!
The Schwinn 2 button works great. Available at Walmart.
For about $10 
Re: Bike computer for Coker?
Would these bicycle computers work on a smaller unicycle? for example,
my 20" Nimbus?
Yes it would.
One other issue with selecting a cycle computer for a Coker is that the stock Coker spokes are fat. Some of the sensor magnets that go on the spoke won’t fit the Coker spokes and others will require a little bit of modification to get them to fit. The Schwinn computer that I use required a little modification with a fingernail file emory board to widen the slot that fits around the spoke. Was very easy to do and only required a minimal amount of filing and the disposable emory board was completely up to the task. It’s something to look at to see how well the sensor will fit on a larger diameter spoke.
Another approach is an item like the Trainer from Timex.