Buyer’s guide to road bike groupsets
Groupsets are the collections of parts that makes up a bike's gearing and braking. This comprises the shifters, crankset, front and rear derailleurs, chain, rear cassette and brakes.
Components of a groupset Crankset There are four types of front crankset found on road bikes. The first is a standard double, as used by pro riders. It consists of two front rings one large 53-tooth outer ring and a smaller 39-tooth inner ring. The second and most common type of crankset is a compact. This uses a smaller inner ring (34-tooth) to allow for a lighter bottom gear to make climbing steeper slopes easier.
There's also a halfway house between standard and compact gearing, in the form of Pro-Compact (aka Semi-Compact) crankset, which use a ring combination of 52 and 36. The last type – and one that has fallen a little out of favour since the introduction of the compact crankset – is the road triple. This usually combines a 50-tooth outer ring, a 39-tooth middle ring, and an inner ring that has just 30 teeth. Road triples offer the widest and lightest bottom gear but nowadays they are only really found on lower-priced entry-level road bikes, although they are still favoured by touring cyclists riding bikes laden with the extra weight of luggage. The crankset spins on bottom bracket bearings that are housed or threaded into the bicycle frame. Bottom brackets are available in a staggering array of configurations;
Cassettes Cassettes come in a huge range of sizes. Professional riders and time triallists favour a rear cassette with as few jumps between gears as possible, because it makes it easier to maintain a consistent pedalling cadence as you accelerate or climb. These close ratios are most commonly 11-25, although they do go as low as 11-23, where there will be a maximum of two teeth between jumps. Most people favour a cassette with a slightly wider spread of gears to make climbing easier. The most commonly found setup on standard bikes is a 11 or 12 to 27 or 28.
Recently, all of the gear component companies have released even wider cassettes, designed for serious mountain climbs. SRAM has its WiFli cassettes, which go as large as 11-32, Shimano offers a 32 in its 10-speed systems and a 30 in 11speed, while Campagnolo offers up to 30-teeth. To put this in context, mountain bikes commonly use 34 or 36t as the largest cog.
Chains The groupset brand and number of gears dictate the chain. The more expensive chains often have smoother, more durable and corrosion resistant coatings than their cheaper counterparts. Additionally, some more expensive chains have the pins and plates drilled to remove weight. A chain is a wear item though, and is cheap to replace, so the one included with a bike isn’t worth stressing about.
Derailleurs Derailleurs are the components that move the chain between rings at the front and across the gears of the rear cassette. Each different brand offers its own design, but the principle is generally the same, with a cable connected to the shifters doing the pulling. Both Shimano and Campagnolo offer electronically-actuated derailleurs.
Shifters
Road bike gears are changed using gear levers that are integrated with the brakes. Each company offers its own design, and while all shift gears, they each have a particular way of doing it. By far the most common is Shimano's STI (Shimano Total Integration). The STI design uses two levers – one sits just behind the brake lever and the brake lever itself, which doubles as a gear shift lever.
Swing the right-hand brake lever inwards on Shimano and the rear mech shifts the chain upwards on the cassette (to a lighter gear). When the inner lever is pushed inwards the chain is shipped down the cassette (to a harder gear). STI is designed to allow multiple upshifts at one time, so the further you push the brake lever, the more gears you'll shift (up to a maximum of three). The left-hand shifter operates the front derailleur, the brake lever swings inwards to move the chain onto the larger chainring, the small lever moves it to the smaller ring. Cheaper Shimano shifters, such as Sora or Claris, offer a slightly different setup, with the small lever moved to the top of the hood and operated by the thumb.
SRAM's system is called Double-Tap. Double-Tap has one lever on each side (just behind the brake lever). Push the righthand lever in until its first click, and the chain will drop into a smaller gear on the cassette, but keep pushing the lever until it hits a second click (or double tap) and it'll rise up the cassette to a lighter gear. The left-hand lever's first click shifts the chain to the smaller front ring, and the second click moves it up onto the bigger chainring.
Campagnolo's Ergopower uses a combination of a lever sitting behind the brake lever and a small button shaped lever on the inside of the hood (the rubber coated housing is referred to as the hood). The right-hand lever swings inwards to make the chain rise up the gears, while pushing the button shifts the chain into harder gears. Pushing the lever further or the button through more clicks allows Campagnolo users to shift multiple gears at a time. The left-hand lever lifts the chain onto the bigger chainring while the button trigger drops it onto the smaller chainring.
Brakes Until recently, brakes were simple items – cable-operated rim brakes were your only option. Now there’s the choice of cable-operated rim and disc brakes, or hydraulic (fluid based, like a car or motorbike) operated rim or disc brakes. Brake choice will be dictated by bike choice, and cable-operated rim brakes are still the most common at all price points. SRAM has all four options available, while Shimano offers all but hydraulic rim brakes. Campagnolo currently only offers cableoperated rim brakes.
Resources: http://www.fibica.com/road/groupsets.html http://www.bikeradar.com/gear/article/buyersguide-to-road-bike-groupsets-41610/