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The basics of bike gearing systems - size matters!


When it comes to bike gearing system size matters! I am sure you are also aware of some other cases when size matters (easy tiger!) but here we are talking about bikes! A lot people have been asking me about how to decide what size of chainring or cassette they need when they decide on a groupset. Obvious answer is it depends on how you intend to use your bike. Is it simply for commute? Is it for racing or is it simply for casual riding? But without knowing the basics you still won't be able to make a decision. Here I would like to post some basics about the gearing system to help you make the right decision! For a bicycle to travel at the same speed, using a lower gear (larger mechanical advantage) requires the rider to pedal at a faster cadence, but with less force. Conversely, a higher gear (smaller mechanical advantage) provides a higher speed for a given cadence, but requires the rider to exert greater force. Different cyclists may have different preferences for cadence and pedaling force. Prolonged exertion of too much force in too high a gear at too low a cadence can increase the chance of knee damage; cadence above 100 rpm becomes less effective after short bursts, as during a sprint. The most common gearing setup on new road bikes is a 50/34 chainset with an 11-28 cassette. This means that the big and small chainring have 50 and 34 teeth respectively, and the cassette’s smallest cog has 11 teeth and its largest cog has 28 teeth. Taking the example of riders maintaining the cadence of 90 rpm; this setup has a good range in which the shortest (easiest) gear combination, 34-28, has a speed of 14.1 km/h at a cadence of 90 rpm and the tallest (hardest) combination, 50-11, has a speed of 52.8 km/h at a cadence of 90 rpm. How does Cassette size matter? Carry on using above example, what if you can’t sustain 14.1 km/h while climbing and you don’t want to drop your cadence too much? In that case, the easiest change to make is to swap your cassette to one with larger cogs. Switching the cassette to an 11-30 decreases the speed from 14.1 to 13.2 km/h and switching to an 11-34 decreases it to 11.6 km/h. These cassettes have the same 11 tooth small cog, so maximum speed is not affected. How does Chainrings size matter? Shimano chainsets currently come in three chainring configurations: 50/34 (compact), 52/36 (mid compact), or 53/39 (standard). All of these sizes are compatible with the same cassette and derailleur combinations. So carrying on with the above example, if your bike has a 53/39 chainset and a 11-30 cassette, your easiest gear, 39-30, has a speed of 15.0 km/h at 90 rpm compared to a speed of 13.2 km/h with a compact chainset (50/34) and the same cassette. Chainring size has a large effect on speed. For most people, a chainset with compact 50/34 chainrings provides a gear range that suits all their needs. Most new endurance and entry level road bikes are specced with 50/34 chainsets, racing bikes with 52/36, and time trial bikes with 53/39. This is good news for most riders as the gearing corresponds to the type of riding for which the bike is intended. However, this wasn’t always the case. The compact 50/34 chainring combination only gained popularity about 10 years ago as an alternative to triple chainring chainsets and the mid compact 52/36 has only been around a few years. This means that if you have an older bike or a racing style bike that you use to train in the mountains you may have bigger chainrings than you’d like. Depending on your chainset it can be easy or impossible to switch chainring sizes. Shimano 11 speed chainsets feature fully interchangeable chainrings. A few other newer chainsets have this feature, but with most other chainsets it’s not possible to change chainring sizes. In these cases the entire chainset has to be changed if different chainring sizes are desired. This is due to the mounting of the chainrings on the crank arm spider. How does No. of Gears matter? Road bikes normally has 9,10,11 speed. What differs among these three is the size of the step between each gear. A 9 speed cassette has larger steps between gears than an 11 speed, which means that you may need to pedal at a faster or slower cadence to maintain your speed or pedal a bit harder or softer to maintain your cadence than you would with an 11 speed cassette. So hopefully after you read my boring long essay you know a bit more about bike gearing systems and this will help you making the right decision about what sizes you go for. But don't worry if you still has more questions please feel free to shoot them over. Remember size matters! 😄


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