Cranks are the crucial levers that turn pedal pressure into propulsion and upgrading this transmission keystone is always a cosmetic and performance temptation. But what do you need to know to arm yourself with the right road crankset – cranks, axle, spider and chainrings – for your bike and riding?
Before you even start thinking about budget or clever design, you need to check which ones will fit your bike. Even though we tried to limit the axle types on test as much as possible, the sheer number of bikes we had to rope into our testing regime to find a home for all the different variants shows it’s no simple task. Even on same diameter axles, different details mean that different brands often need their own specific bearings to work. Adaptors and converters have made things easier recently but different bearing sizes and fitting standards are still a potential minefield so it’s still essential that you double check your chosen crankset will fit your frame before you part with any cash.
Don’t assume that bigger axled cranks are stiffer, either. Overall stiffness is governed by the entire structure, from the chainrings, through the spider and crank then across the axle to the offside crank. While they look fancy, don’t assume that carbon cranks are automatically stiffer than alloy ones either, as both materials use a range of manufacturing methods for a wide spread of results.
Don’t get hung up on weight either – cranksets sit in the most central, lowest point of your bike possible. This makes their weight the least obvious of any component in dynamic or handling terms, and it’s why most pro bikes use torque meters or even extra heavy axles to bulk their weight up to the minimum legal lever. Conversely, a lightweight crank that flexes so much it feels like your feet are bending under your bike is really demoralising when you’re trying to claw your way up a climb.
Key crankset components
Crank length: Cranks – the ‘arms’ – come in different lengths to match different length legs and leverage preferences. The average is 172.5mm but 170 and 175mm cranks are relatively common on complete smaller and larger bikes respectively, and you can get as short as 160mm or as long as 180mm.
Axle: Most road cranksets use an axle permanently fixed to the driveside crank and a left crank that bolts/clamps into place. Some brands still use a separate axle, while Campagnolo uses two half axles that join in the centre on its Ultra Torque designs. Most come with 24mm steel axles or 30mm alloy ones.
Spider: The four or five-arm piece that connects chainrings to axle. Some are moulded into the arms, some made separately but permanently attached, others are removable. Standard (53/39) chainrings generally have a 130mm bolt circle diameter (BCD – the fitting pattern for the rings), compact (50/34) 110mm.
Chainrings: Most chainrings are made from a single-piece reinforced disc with teeth cut into the edge. In many cases brands are interchangeable or replaceable with aftermarket options. Shimano’s ‘blended’ chainring/spider design demands specific replacements to keep aesthetic and functional form.
Material: Solid forged alloy cranks are the cheapest option but generally the heaviest. Drilled or hollow moulded alloy cranks then follow in the fashion (but not necessarily function) hierarchy. Carbon wraps on alloy armatures look good but don’t always perform well and even ‘full’ carbon cranks have to use alloy pedal and axle interfaces.
Bearings: As well as different axle diameters, different bearing shoulder dimensions mean most cranks will only run in bearings from the same brand or specific aftermarket options, though converters are reducing the number of ‘impossible’ combinations. None of our test cranks obviously lost spin smoothness during our test period.
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Article Source: http://www.bikeradar.com/road/gear/article/best-road-bike-cranksets-44316/