Like the front, it guides the chain from one cog to the next, but it is also responsible for maintaining chain tension and taking up the slack when we move from bigger gears to smaller ones. The rear derailleur is much more effective at switching gears while pedalling hard. It is important to note however, that in order to switch gears the chain must be moving forward. With both the front and the rear derailleur, when the shift cable is pulled, it will move the chain to a larger gear.
When the cable is released, it will move the chain to a smaller gear. Just remember that larger gears at the rear mean easier pedalling but more torque, and larger gears at the front mean harder pedalling but more speed. The key element that will determine how hard you work is the difference in the number of teeth the wee pointy bits that hook through the gaps in your chain between the front chainring at the front and your selected rear cog.
That means the outer ring has 50 teeth and the inner ring has 34 teeth. The rear cassette is 11 speed The combination of your selected chainring and cog determine the gear ratio. The gear ratio, combined with the circumference of your wheel and tyre determines how far you will travel with each revolution of the cranks.
To get our gear ratio we divide the number of teeth on the front by the number on the back:. This is expressed as 4. This is the gear I would use on the flat. It is going to take quite a lot of effort to get it moving, but when I do I will move quickly.
This would be the opposite end, the small ring on the front and the biggest on the back. Vice versa, combining the smallest front chainring size with the largest rear sprocket size results in the lowest available gear, which will help you keep the pedals spinning when the road points steeply up. A bike with 30 or more gears is not an indication of a machine designed to break the land speed record any more than a bike with only a single gear, assuming similar ratios.
Just like a car, bicycles benefit from a low gear to accelerate from a standstill, or to climb a steep hill, and at the other end of the scale a high gear helps you to achieve high speeds without over-revving. Continuing with the car example, using too low a gear at high speed would result in high fuel consumption.
The same is true of your body pedalling a bike. So, quite simply, more gears means more scope to find your preferred pedalling speed. To put this into perspective, in the days of five or six-speed cassettes, a range of teeth could only be achieved by having sizeable gaps between sprocket sizes. Modern speed cassettes with the same spread, , would have only single tooth increments for the majority of the shifting. The result is smoother, more precise shifting, as the mechanical difficulties the chain has to overcome to climb onto the bigger sprocket or drop down onto a smaller one are much reduced with smaller increments, but most importantly, the possibility is there to greatly improve pedalling efficiency.
Cyclists are much more able to fine-tune their pedalling speed to suit the gradient or terrain, often resulting in a lower energy cost. You don't have to ride a bike with gears - some people choose to ride singlespeed bikes.
These still have a gear - which is determined by the size of the front chainring and rear cog. Singlespeed bikes are popular among commuters living in flat areas, because they require little maintenance. They're also used by some racers hill climbers for example who want to drop weight and cut down on any extra complication coming from the shifting process - in this case, choosing the correct gear ratio is crucial. Finally, track bikes only ever have one gear - though again riders will change their set up to suit certain events.
In other words, some gear combinations will result in the same ratio as others using a different sprocket and chainring. For example, 53x19 is the same gear as 39x See the diagram below for an illustration of this. A classic t combination is known as a 'standard' chainset, though it is largely unused by recreational cyclists and very rarely specced on bikes by manufacturers.
A standard double set-up is usually the preferred choice for racing, offering the largest chainring sizes for the biggest gears possible to keep you pedalling smoothly when speeds are high. A compact is essentially a double set-up, only smaller. Both chainrings are reduced in size, usually 34t or 36t inner, paired with a 48t or 50t outer, reducing the gear ratio across the range.
The semi-compact chainset offers a 52t outer chainring one tooth smaller than the standard, but two teeth bigger than the compact paired with a 36t inner ring three teeth smaller than the standard and two bigger than the compact. This combination offers the best of both worlds; the 36 inner ring can be paired with an , or cassette at the rear to offer enough gears to tackle almost every climb, while a 52t at the front offers a bigger gear for fast group riding, descending, and even racing.
Having three chainrings brings the possibility of adding a much smaller gear option. And this is it. Ready for a ride into the unknown? Moving images that make you sit in front of them until the end of time. Or until you are ready to ride out again. This is a difficult question, and those in need turn to Sheldon Brown who, despite his passing in , is […]. This is a difficult question, and those in need turn to Sheldon Brown who, despite his passing in , is still regarded as the greatest bike mechanic who ever lived.
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