Compact vs. Standard Cranksets
This entry was posted on February 18, 2014.
Compact or standard? That is the question.
The difference between these two types of road cranksets comes down to gearing. There are advantages and disadvantages to both along with obvious reasons why you should consider one or the other.
Standard cranks are often called racing cranksets because they offer the fastest common gearing (bigger chainrings are available but must be bought separately). Standard cranks have 53/39 gearing, meaning they have a 39-tooth small ring and a 53-tooth big ring. Ring is short for chainring, which is what the front gears are called that are bolted to the cranks. The bolt circle diameter (BCD) of standard cranksets is 130mm.
Compact cranks have a smaller BCD, 110mm, which allows for smaller chainrings. Compacts have a 50/34 gearing, so losing three teeth on the big ring and five teeth on the little ring compared to a standard. Compact cranksets are preferred for climbing races or for people who like to ride fast but not race. There are many people that race compacts, but for most people it's not the preferred crankset for flatter races or any with limited climbing.
Combined with a wide-range rear cassette, like an 11-28, compact cranksets offer a wider range of gearing and -- as mentioned earlier -- are really designed to maximize one's efficiency to climb or travel at lower speeds. More recently, long-caged rear derailleurs have been more common in use with compact cranksets and 11-32 cassettes, such as SRAM's WiFLi system. This wide range of gearing means a wider range of comfortable speeds and decreases the gearing overlap (when different combinations of front gearing and rear gearing have the same gearing ratio such as a 50/25 and 34/17, both of which are 2:1 gear ratios).
Standard cranksets have more gearing overlap, which can be preferred for racers so they have similar options in the middle of the cassette for both chainrings. This allows for things like shifting into the big ring early if they think an attack might happen so they're prepared to jump to faster gears. Conversely, they can be going at a pretty fast speed in the little ring when approaching a climb and shift to easier gears as necessary. Racers have a tendency to want more options in a certain range of gearing; that's also why some racers elect to use an 11-23 close range cassette instead of something with a wider range, because the gap between gear choices is smaller for certain shifts. This makes it easier to maintain a preferred or optimal cadence which maximizes efficiency.
By the numbers: comparing compact and standard
A standard 53-tooth chainring paired with an 11-tooth rear cog (fastest rear gear) gives speeds as follows when using a standard 700x23 tire. All of the speeds were calculated using a free software app from Bareknucklebrigade called Rabbit.
In the same table we'll compare the fastest combination for a compact crankset, a 50-tooth front matched with the 11-tooth rear.
|Standard 53x11||Compact 50x11|
|Cadence (rpm)||Speed (mph)||Speed (mph)|
As you can see in the table, very high speeds can be obtained with a standard crankset, but you can still get moving right along with a compact crankset. Most people are not going to be able to travel at those speeds riding solo, so a compact is a good choice for those who do a lot of solo riding. You will also notice that at 120 rpm you're only giving up 2.6 mph, which is not much at all. Pedalling down a hill or in the final sprint of a race is when this would become a factor. Most people would have stopped pedalling at this point and would just enjoy the free speed.
How slow can you go with a standard crankset, though? I'll show tables using a 39-tooth ring paired with a 26-tooth rear cog, which is very common (25-tooth also being very common for racing cassettes) and a 28-tooth cog which is the largest rear cog you will see on most road racing bikes and is generally reserved for races some decent climbing. We'll do the same with the compact crank using the 34-tooth front ring matched up with the same size rear cogs.
|Standard 39x26||Compact 34x26|
|Cadence||Speed (mph)||Speed (mph)|
|Standard 39x28||Compact 34x28|
|Cadence||Speed (mph)||Speed (mph)|
So on the slow side, the difference between a compact and standard using an 11-26 cassette is 0.9 mph at 60 rpm (grinding up a hill) or 1.2 mph at 80 rpm (seated climbing). For an 11-28 cassette we have a difference of 0.8 mph at 60 rpm and 1.1 mph at 80 rpm.
Full-range comparison at comfortable seated cadences.
|Top Speed w/ 11t (mph)||Low speed w/ 26t (mph)|
|Standard||41.4 (110 rpm)||9.4 (80 rpm)|
|Compact||39.1 (110 rpm)||8.2 (80 rpm)|
To put this into perspective, that's a 12.8% difference at 80 rpm in your ability to go slower, but only a 5.6% loss in your top speed at 110 rpm, if you can even get to those speeds. You can see why compact is appealing to those who spend a lot of time climbing hills or those that rarely spend time over 30-35 mph.