What is a Compact Crank
Most road bikes have 2 chainrings. There is a larger, outer ring and there is a smaller, inner ring. Traditionally they are referred to as numbers, for instance, you may see the chainrings referred to as 53/39.
The numbers refer to the number of teeth on the ring. So that set would feature 53 teeth on the larger ring and 39 on the smaller ring. Chainring sizes vary, but the following are the more commonly found sizes, 53/39T and 52/42T.
So what is a compact chainset?
The compact chainset, or compact crank, is simply 2 rings which are smaller than the more traditional sizes. A 50/34 compact has fewer teeth on the larger ring and fewer teeth on the smaller ring, meaning that the diameter of both these rings is smaller.
Assuming the same cassette on the rear, the difference between a traditional chainset and a compact is that in the same circumstances the cyclist can select gears allowing them to pedal faster (higher cadence). In other words, they have lower gearing. This is not necessarily an advantage to powerful cyclists like the pros, but a compact crank is ideal for less powerful and more recreational cyclists. It offers a slightly lower range of gears to choose from.
How about my rear cassette, where does that fit into this equation?
Of course it’s quite possible to vary the size of the cogs on the rear cassette just as it is to do so on the crankset, within reason. However, a general rule it that your chainset is there to stay permanently, the cassette gets replaced more frequently. Overall a compact offers better versatility to the majority of riders that have any hills to climb.
It is often useful to be able to change the rear cassette, if you have rides which feature a lot of climbing, you may choose lower gears on the rear cassette to accommodate the climbing.
So should your bike have a compact chainset?
Ultimately it’s just a matter of choice, depending on the type of riding you do, how powerful you are, and the most common terrain you ride on. As a general rule, the compact is more versatile as a whole, but you do sacrifice a higher top speed.
Also, Read On Other Crankset Topics