Types of Gearing: Derailleur gears: This is the most common method of changing gear. The chain is pushed between several different-sized sprockets at the front and back by a cage called a derailleur. It sounds crude, and it is, but it does work suprisingly well!
The good thing about derailleur gears is that you can have a very wide range of gears - typically 24 or 27 gears, which gives you a wide range with lots of steps. Derailleurs are also very efficient - typically 99% or more. Hub gears: Used much more often on city bikes, hub gears are fully enclosed in the rear hub. An epicyclic gearbox gives 3,4,5,7 or even 14 gears. The advantage is that the system is very reliable - it is completely sealed away from the elements, and as the chain is not yanked from one cog to another, the chain and sprockets last much longer too.
The downside is that hub gears are not as efficient - 95% or more usually. You usually also don’t have as wide a gear range as with derailleurs (unless you use a Rohloff). Measuring Gearing: So how do you compare gearing systems, and how do you know what gears you might need? There are two measures of gearing: Gear Inches: This is the method used in most English-speaking countries, and it’s a bit old-fashioned! Basically, you compare each gear to the equivalent size of wheel you’d use if there was no gear - it dates from the days of “ordinary” (“Penny Farthing”) bicycles. So, for example, if you say that a gear is “60 inches” then that means that it is equivalent to riding a bicycle with a 60” diameter wheel. Progression Metres: This is the Continental method, and it’s a bit more logical! Basically, this tells you how far you travel for each rotation of the pedals, in metres. You can convert from one system to the other very easily: Progression Metres = Gear Inches x 3.1415 x 0.0254 What gears do you need? The simple answer is it depends on what you’re doing! As a basic guide: City riding: about 35 to 85 inches
Road racing: about 30 to 120 inches
MTB riding: about 20 to 100 inches
Touring: about 20 to 120 inches or more But the whole point of gears is to make sure you’re always pedalling at a sensible speed whatever the terrain, so it’s always a personal choice... Work out the gear ratios on your bike with our Gear Calculation Software. Single Speed: This is an option which is becoming more popular - I have a single speed commuting bike, for example. The big advantage is reliability - there are far fewer things to go wrong! It’s very reliable, and also very efficient and light. The downside, of course, is that you are stuck with one gear (usually about 60 inches). So you cannot go as fast downhill as you normally would, and hills take more technique. I find that I am very fast on my singlespeed when commuting, but for longer journeys I much prefer the flexibility that gears give. Fixed Gear: For hard-core obsessives only! What this means is that there is no freewheel in the mechanism - you have to keep pedalling all the time (unless you take your feet off the pedals, which is not recommended!). Fans say that you get a lot more control, as your legs control braking as well as accelerating. You are stuck with only one gear, of course. Personally, I can’t ride a fixed gear for long without falling off, but some people swear by them (the rest of us just swear AT them!). | 
