Cranksets are the heart of the bike. It holds the chainrings in place and rotates within the bottom bracket. Crank arms can be made of carbon fiber or aluminum depending on your preference and budget. Most high-performance cranks today have a thru-axle permanently affixed to one crankarm. The spider can be integrated into the right arm or a separate piece secured to the arm. There are one (1x), two (double), or three (triple) chainring options, each designed to excel at different disciplines of biking.
In addition to specialization by niche, cranksets also come in different lengths. They range from 80mm for kids to adult lengths: 160, 165, 170, 172.5, 175, and 180mm. Thanks to wide rear ends, for things like fat bikes and super-boost spacing, the Q-factor, or the distance between the left and right arms, can vary to accommodate widely-set chainstays.
The road bike crankset gets used for fitness riding, racing, touring, commuting, gravel, and cyclocross. Road bike cranksets are often designed with an integrated spider though it has become less frequent.
With 1x systems for road riding, a 1x-specific ring can be sourced, as can a crank that accepts direct-mount 1x rings. Direct-mount cranks can often accept a power-meter spider, which racers often say makes for the best crankset for road bikes.
Mountain bike cranks might be the most diverse. Mountain bike crankset types include triples, doubles, and 1x’s, with five and four-arm spiders in different BCDs, as well as direct-mount options. The best MTB cranksets are the ones that fit your bike, give you the gearing you want, and mesh with the rest of your drivetrain.
Shimano offers all the options, which should be expected as the largest component producer. Their high-end cranksets are either double or 1x, and they have both integrated spiders and direct-mount options.
SRAM pushed 1x in MTB. Their off-road offerings skew heavily toward 1x, with both spider and direct-mount versions. SRAM also offers double- and triple-cranksets. They’re fans of on 1x for the road but sell more doubles as they are still popular options for road riding.
Stages was the first company with a crank-based power meter that did not attach strain gauges to a purpose-built spider. The design is smaller, simpler, lighter, and cheaper. They fix their meters to many different brands' arms—Campagnolo, Cannondale, FSA, Shimano, and SRAM—with single and double-sided options. The basic option mounts the meter on the left arm. Many think the best MTB power meters are crank-based because they’re small, light, and easy to access.
4iiii (four eyes) followed Stages. They make a crankarm-based meter that takes readings off the left arm, the right arm, or both. 4iiii meters are arguably the smallest and lightest and are compatible with Campagnolo, Cannondale, FSA, Praxis, Shimano, and SRAM. 4iiii has an extensive selection of mountain bike power meters. They can be mounted on both carbon and aluminum cranksets, to create both road and mountain bike power meters. 4iiii makes both coin cell and rechargeable models.