The Bike List

Compact Chainsets – The Complete Guide

What is a compact chainset?

A compact chainset (the crank arms and chainrings combined) always has two chainrings. The big (outer) ring typically has 50 teeth and the small (inner) ring most commonly has 34 teeth although it may sometimes have 36 teeth, providing a 50/34 or 50/36 combination. A 48/34 is another less common compact chainring combination that is sometimes used on hybrid or town bikes.

A compact chainset offers a middle ground between the more race-oriented standard road double and semi-compact chainsets with two larger chainrings (typically with 53/39 or 52/36 tooth chainrings) and heavier road triple chainsets with three chainrings that offer a wider range of gears (typically 50/39/30 teeth).

A road triple will offer more gears and may be a better option for less able riders on consistently hilly terrain. A compact chainset however offers a similar selection of gears for a lower overall weight. With two chainrings there is also the advantage that the chainline (how straight the chain runs from the chainrings at the front to the sprockets on the rear) will be straighter more of the time, which is mechanically more efficient.

What bikes do compact chainsets typically feature on?

A compact chainset is one of the most versatile chainsets, which is why you'll find them on a wide range of bikes. Many recreational road bikes feature a compact chainset as the gear ratios (range of gears) offer a middle ground between the more race oriented standard road double and semi-compact chainsets and the wide-ranging road triple chainset. This middle range offers 'best of both worlds' ratios that make compact chainsets ideal for recreational or commuter road bikes, some cyclocross bikes (those typically designed more for commuting and general purpose riding rather than racing) flat handlebar road bikes, touring road bikes and some more road oriented hybrid or town bikes.

Click here to see all bikes that feature a compact chainset.

What is a semi-compact chainset and how is it different to a compact chainset?

A semi-compact chainset (typically 52/36 teeth) offers gears that are in between those found on a standard road double (typically 53/39 teeth) and those on a compact chainset (typically 50/34 teeth). Where as a compact chainset is a good all-rounder option found on a wide range of bikes, semi-compact chainsets are typically found on road racing and time trial or triathlon bikes. This is because the larger chainrings on a semi-compact chainset (typically 52 big outer and 36 small inner chainring) are better suited to riding at higher average and top speeds.

Click here to see all bikes that feature a semi-compact chainset.

Ideal for climbing.

Compact chainsets aren't just for recreational cyclists and those new to cycling. Strong riders such as professional racers will use compact chainsets in hilly areas and on hilly stages of long distance races such as the Tour de France.

Compared to a standard road double chainset a compact chainset will allow you to spin your cranks faster uphill (thanks to the easier gears available) which will make climbs feel easier to pedal up. This is especially useful for long or steep inclines where spinning up hills with a higher cadence (revolutions per minute - RPM) is generally considered to be more efficient, although perhaps slower. A higher cadence also means it is much easier to stay seated whilst going uphill.

Top speed.

The downside however is that on the downhills or on fast stretches of road you may run out of big gears and be unable to go any faster than gravity will allow or you will need to spin your cranks at a very high cadence to generate power.

For example, using a 50 tooth (big) chainring and a 11 tooth rear cog (a common smallest cog size on the cassette) you'll be travelling at 29.36mph at a cadence of 90 RPM (revolutions per minute). Most people will naturally pedal at a cadence of between 80 and 90 most of the time, unless it's a particularly hilly ride in which case this number might be lower.

From our experience with a typical compact chainring ratio of 50/34 and a smallest rear cog with 12 teeth you'll need to be going over 35 mph before you run out of gears. In most places you'll need a good hill to get up to those sorts of speeds and even then you'll probably need to be pedalling fairly hard.

Bike List Top Tip: it pays to look after your components

Keeping your chainset, cassette (the group of smaller cogs on your rear wheel) and chain clean and well-lubricated can make a big difference to how efficient your bike is. If your chain is dirty it can be up to 7 or 8% less efficient - the equivalent of being 5 or 6 kgs heavier on a climb. Source - The Obree Way, A training manual for cyclists, Graeme Obree.

Converting your compact chainset to a standard road double.

Shimano 22 Speed Dura -Ace FC-9000

Whilst we are comparing compact chainsets to standard road double chainsets it's also worth pointing out that it's much easier to change from a compact or semi-compact to a standard road double or vice versa than to a triple chainset as this merely requires a change of cranks and in some cases simply just new chainrings (such as with Shimano's 22 speed Dura-Ace FC-9000 chainset, pictured on the right, where the Bolt Circle Diameter is the same on all cranks). A longer (new) chain will also be needed when swapping from a compact or semi-compact to a standard road double chainset or vice versa.

What is BCD and why is it important?

BCD stands for Bolt Circle Diameter and is the diameter of the circle created by, in this case, the five holes at the end of the arms on the spider - the multi armed piece that connects the chainrings to the crankset.

BCD 110 And 130

The BCD number must be the same for both the crankset and the chainrings otherwise they won't be compatible.

A point worth noting is that the BCD on the majority of compact and semi-compact chainsets is 110mm whereas the BCD on the majority of standard road double chainsets is 130mm. This is significant as each BCD places restrictions on the maximum or minimum size of the small chainring. The small chainring must have 38 teeth or less on a 110mm BCD chainset and must have 38 teeth or more (usually 39) on a 130mm BCD chainset. This means you'll need a 130mm BCD if you want to run a 52/39 or 53/39 or 54/42 racing / triathlon / time trial specific chainring combination and if you want to run a 52/36, 52/38 or 50/34 etc you'll need to opt for the 110mm BCD crankset.

Converting your compact to a road triple chainset.

Changing from either compact chainset or standard road double to a road triple or vice versa will typically require a new left shifter, front derailleur, chain as well as chainset which means this type of change is usually not cost effective.

The Bike List Top Tip: replace instead of converting

Price up a conversion from two to three or three to two chainrings, and include labour costs as well as the parts mentioned above, as in some cases it can be cheaper to replace the bike with one that has the setup you want and sell the one you have.

What cassettes are compact chainsets typically paired with?

Compact chainsets are typically paired with cassettes (the group of smaller cogs on your rear wheel) that have an 11 or 12 tooth small sprocket as the smallest cog giving you a 50 + 11 or 50 +12 biggest gear.

They will also typically come with a cassette that has one of the following sprocket ranges: 11-23, 11-25, 11-26, 11-28, 11-30, 11-32, 12-23, 12-25, 12-28, 12-30.

To work out gear ratios, speed at cadence or cadence at speed visit BikeCalc.com for more information.

Changing A Cassette

Changing a cassette is a cost effective way of adapting your bike to make it more suitable for different terrain. For flatter terrain where smaller incremental gear changes are an advantage choose a cassette with a close range such as 11-23, 11-25 or 12-25. A simple change to a cassette with a wider range of sprockets such as 11-26, 11-28, 12-28, 12-30 or 11-32 etc will make the same bike noticeably easier to pedal on hillier terrain.

If you shop around you can usually find a good cassette such as Shimano 105 (which strikes a good balance of value and quality) for around £25-£35. A like for like cassette replacement will usually be around 3-4 times cheaper than a like for like replacement chainset.

Read our guide to changing a Shimano 10 speed cassette here.

The Bike List Top Tip:

Most rear derailleurs will be capable of running a number of different cassette ranges. If the largest sprocket on the cassette is changing significantly in size make sure your rear derailleur can accommodate the larger sprocket. Most road bike rear derailleurs are available in a short cage (small gear range), mid cage (middle gear range) and sometimes long cage (wide gear range) designs.

Summary of compact chainset:

  • 50/34 or 50/36 are the most common chainring teeth combinations.
  • Will have either 10, 12, 14, 16, 18, 20 or 22 gears.
  • Ideal for the recreational road cyclist, those new to road cycling and those riding in hilly areas.
  • The most common chainset and therefore features on a wide range of bikes
  • Weighs less than a triple chainset.
  • More efficient when pedalling up hills compared to a standard road double or semi-compact chainset thanks to the easier gears on offer.
  • The smallest cog on the cassette will typically have 11 or 12 teeth.
  • Can run out of big gears on fast roads and descents but typically only over 30-35mph.
  • Shares the same 50 tooth large outer chainring as a road triple chainset and therefore shares some of the same gears.
  • The chainline will be straighter more of the time than on a road triple and therefore more efficient.
  • Much easier and cheaper to change from a compact or semi-compact to a standard road double chainset than it is to change to a road triple chainset.
  • A good all-rounder for the majority of road cyclists.
  • Compact and semi-compact chainsets typically have a 110mm BCD where as standard road double chainsets typically have a 130mm BCD.
  • Changing from a compact or semi-compact to a standard road double only requires a new chainset and chain.
  • Changing from a compact or semi-compact to a road triple chainset is often not cost effective as it requires a new chainset, left shifter, front derailleur and chain. So, buying a new bike and selling your old one can be a better option.

To find out more about semi-compact, standard road double and triple chainsets click below to read our comprehensive guides.

Semi-compact Chainsets - The Complete Guide

Standard Road Double Chainsets - The Complete Guide

Road Triple Chainsets - The Complete Guide