Introduction
When it comes to buying your new bike there are so many different options when it comes to spec choice that it can be quite the minefield. Bicycle gearing is perhaps the biggest and most complicated one of those mines with different brands, all with different groupsets, all at different speeds,mechanical or electronic, etc - if you don't already know the key differences between groupsets then it's easy to get lost.
In this blog we strip back those complexities and offer a simple and basic guide to modern bicycle gearing.
The Basics
The basic principles of gearing are really quite simple. When you pedal you turn cranks which have a chainring. The chainring is attached to the chain which transfers the power from your legs to the cassette on the rear wheel. How fast the wheels turn depend on how fast you pedal (cadence) and the gear ratio the bike is in.
A gear ratio is simply the ratio of the number of teeth on the chainring versus the number of teeth on the cassette sprocket. For example when pedalling a bike with a 50 tooth chainring and the chain is on a 25 tooth sprocket on the cassette the gear ratio is 2.0. The implication of this is that for every 1 full turn of the pedals the wheels will complete 2 rotations. A high gear ratio is used when riding at high speeds such as on descents, but it is also important to consider how low a bikes gear ratios go, as this will impact how easy or hard it is to cycle uphill.
Understanding gear ratios can be useful when looking at buying a bike or changing the gears on your bike. It is important to consider the range of gear ratios on a bike, as well as how many gears the bike has, and how close together the ratios are. Matching the gearing to your needs will maximise the ease with which you ride, maximising your enjoyment.
Gear Range
The gear range refers to the difference between the highest and lowest gear ratios, in other words the easiest gear to climb uphill and the hardest gear to hit the fastest speeds. The range of gears is dictated by the difference between the smallest and largest cogs on the cassette and the difference between the largest and smallest chainring. Most modern road bikes are fitted with 2 chainrings, however with the rise of gravel bikes single chainring bikes are becoming more popular.
By having a single chainring a bike loses some gear range, but bike companies compensate for this by fitting a wider range cassette. A great example of this is the Specialized Diverge S-Works we currently have in stock which features a huge 10 to 50 tooth Sram AXS cassette which provides its rider with all the gear range they could ever need. For road bikes roughly the following classification applies: (11-25) = narrow range, (11-28 or 11-30) = normal range, and (11-32 or Sram’s 10-33 AXS) = wide range.
Gear Spacing
Sadly you can’t have it all. A larger range cassette comes at the expense of close gear ratios, meaning there are larger more noticeable jumps between gears. On a single chainring gravel bike such as the previously mentioned Diverge this is fine, as the priority is reliable simplicity and not outright efficiency like a road bike. Road bikes tend to have 2 chainrings and a smaller range cassette as this allows for a wider range of gears whilst maintain close gear ratios, something that a single chainring setup cannot quite achieve.
Number of Gears
It’s easy to assume more is better when it comes to gears as more gears provide a greater range and close gear spacing. A decade ago triple chainsets (3 chainrings up front) were a very common sight, however in more recent years almost all bikes are fitted with either 2 or even 1 chainring. This is because a multiple chainring systems results in a lot of overlapping ratios, or more simply put different gear combinations that result in the same effective gear. The bike industry has tried to simplify gearing to improve shift quality, chain security and ease of maintenance.
The vast majority of the road bikes that we sell feature Shimano or Sram gearing. Both of these companies offer 11 speed groupsets though Sram have recently began offering their 12 speed ‘AXS’ groupsets. Shimano’s 11 speed Ultegra and 105 gears are the most commonly sold gearing systems that we sell at Cycle Exchange, as they deliver a great combination of shift quality, reliability, weight and value for money. Additionally Campagnolo have just released a single chainring 13 speed groupset for gravel riding which allows for a wide range of gears, but closer gear spacing than other 11 or 12 speed 1x groupsets.
Electronic vs Mechanical Gears
Bicycle technology has moved on greatly in the last 20 years, with electronic shifting being a major development. Shimano introduced its ‘Di2’ electronic shifting way back in 2001 and has continued to refine the system over the last 20 years. Campagnolo also introduced its version of electronic shifting ‘EPS’ in 2005, and Sram released it’s ‘eTap’ wireless system in 2015, with both systems also being updated over the years.
Electronic shifting brings the benefits of consistent high quality shifting performance along with low maintenance. Almost all high-end race bikes employ electronic shifting. The key downside is expense, as these systems cost significantly more than their mechanical (cable operated) systems. Another drawback is that the batteries and motors to power the shifting add a few hundred grams of extra weight to the bike. Mechanical shifting has been refined to provide fast, crisp gear shifts and has the benefit of being lighter and cheaper than electronic systems. The cables that control the shifts are however prone to stretching and corrosion over time, meaning mechanical systems require more regular adjustment and maintenance to function optimally.
Conclusion
We hope this guide has been useful and somewhat demystified the extensive and complex world of bicycle gearing. If you have any further technical questions feel free to call or e-mail us here at Cycle exchange for advice and support.
