There is a great accessory for your bike called a bike computer or cyclometer. Like a cars dashboard it can tell you many things about your speed, average, time and even get into more detailed things like cadence*, heart rate or incline. The computer works on your bike by either a cable running from the computer head unit on your handlebar/stem area down your bike to a sensor that zip ties on. Then a magnet is placed on your wheel, every time the magnet spins past the sensor it sends a transmission to the computer head. It computes how many times per minute or second the magnet goes around, does some math and tells you your speed/distance. The wheel diameter is very important as that is part of the calculation to get the right speed/time so make sure to set your computer head unit for your wheel and tire size. If you change tire sizes, reset the settings.
There are many ways to separate computers, especially if you start getting in to a lot of data capturing. For this article we will start basic, wired or wireless.
Wired Versions :
Entry Level :
Basic featured include speed, time and average speed. Utilizing a cable that runs from your handlebars down to your front fork on the bike. They range from $24-35 and many type or colors are available. The Trek 6i and Cateye Mity 8 are my picks in this category. For this category, go down to your local bike shop and buy what they recommend. This way they are familiar with set up if you need any help at all.