I am running a cateye velo 5 on a 26" wheel. However i am unsure that it is reading correctly. I cant have it near the outside of the wheel as there is to much gap between magnet and sensor so i have shifted it into the middle more. to be exact its 13cm form the centre of the hub. I am just not sure how to set it up so it reads correctly.
Here are the instructions. I really just dont understand how to set it up 
thanks alot
are you having trouble physically mounting it or problems programming?
The distance from the hub isn’t important as long as the magnet is within a couple of mm from the sensor. Every time the wheel goes round, you would have ridden a set distance (around 2050mm), and the sensor will pick up one pass of the magnet. The distance from the hub doesn’t come in to that equation.
STM
so, i simply measure the circumference of the tire and put that in and i can move my sensor and magnet anyway along the fork?
Oh and is 24mph a speed I could reach on a b*ke on straight tarmac?
Yes, that’s right
Probably. You’d have to be gunning it a bit, but it’s achievable though. You won’t get anywhere near that on a 26" uni though 
STM
its worth measuring the circumference by rolling the uni with your weight on it, you flatten the tyre a significant amount and it effects the circumference
Depends on your gear ratio. I have a fixed gear bike with a 42 tooth chainring in front and a 15 tooth cog in the rear…that’s very do able. I also have a single speed mtb with 40 teeth in front and 19 in back…that’d be a lot harder to get up to that speed. Figure out your gearing ratios and teeth on your chainrings/cogs and throw them in this nifty little calculator:
http://www.sheldonbrown.com/gears/
Select “speed at 120RPM” and itll tell you about how fast you can comfortably go at that gear ratio since 120RPMs is pretty brisk for a b*ke cadence
This is a good starting point, but it might require fine tuning… or at least it might if you’re as pedantic as I am.
If you’ve a bike path in the area that has mile (or kilometer) markers you may want to use that to double-check your computer’s settings. Luckily, I have a path nearby with lines drawn across the way every 1/4 mile. Now my compy’s dialed IN!
Very nice, i presume this is to reduce measuring inaccuracy by averaging, and to take in to account that unicyclists don’t go in straight lines.
Yes, the straight line issue is definitely something you’d want to know about if you plan on using your computer for very accurate rides. I’ve noticed on my cycling computer last year at RAGBRAI that the final measurements for a 70 mile day would be 1-3 miles off due to the path that the wheel follows with its natural wobble. Some of that was likely due to the settings being slightly off due to tiny differences in rollout too.
Actually, that might be a great way to improve on one’s wobble… to calibrate their computer using such a method, then re-calibrating later and going for less error (from a straight-line path).
Dunno how one could measure their error, though. Any thoughts?
The straight line issue is as much a matter of calibration accuracy, as it is a matter of definition. You can perfectly well argue that the distance you ride on your unicycle is the distance that the centre of the tyre contact patch has travelled, including all the wobbling it does. In my own measurements, wobble is on the order of 3% (depending on rider, wheel size, speed, etc), which coincides quite well with 1 to 3 miles on a 70 mile trip.
I’ve written some more blurb on the various ways of defining distance and speed on my Coker Rollout Page. Keep in mind that this page was written in 2004, there are a lot more 36" options now. But the distance definition issue hasn’t changed.
IMHO, wobble should not be considered in cycle computer calculation. You want to add a built-in “lie” to the numbers your computer puts out? Better to be aware of the wobble and work to ride straighter, if cranking out miles/kilometers is your main goal.
All of my wobbles count!
If cranking out miles is your main goal and all of your wobbles count, then why would you want to work to ride straighter? The more you wobble on a given course, the more miles you crank out.