This overview provides both a broad and detailed view of the key issues.<\/p>\n\n\n\n
Links to Sections<\/strong><\/p>\n\n\n\n MTB Crankset Development Through Time<\/a> <\/p>\n\n\n\n An MTB crankset consists of<\/p>\n\n\n\n Let\u2019s unpack what each is in terms of what it does. (No mention of bearings: I deal with them in the post on crankset bearings<\/a>) The drive side crank includes a 4- or 5-arm connector we refer to as the spider_to which the chainring(s) attach. Probably _leg<\/em> is a better word but arm<\/em> is conventional.<\/p>\n\n\n\n The non-drive side crank consists of a single shaft that bolts into, or clamps around, a bottom bracket spindle or (integrated) crank spindle.<\/p>\n\n\n\n We measure the crank length \u201ccenter to center\u201d: from the center of the spindle\u2019s hollow point, marking the center of the (here 4-arm) spider, to the center of the pedal threads.<\/p>\n\n\n\n Most MTB crank lengths are printed on the section encircling the pedal threads. You\u2019ll see 72.5<\/em> peeking above the tape measure in the image. Going by the tape measure, we see the crank is 175.2mm in length.<\/p>\n\n\n\n <\/p>\n\n\n\n Whilst bottom brackets<\/a> are a separate category of component, the type of bottom bracket you use largely determines what crank you use, although bottom bracket converters<\/a> give you flexibility in choosing crank\/spindle combinations these days.<\/p>\n\n\n\n An under-appreciated aspect of crankset design is the influence on them of attempts to come up with quick and efficient ways to change the load ie. change the gears.<\/p>\n\n\n\n Chainrings<\/a> are a separate category of component, but play a central role in increasing or reducing crank load.<\/p>\n\n\n\n Similarly, you can write the history of the derailleur by just sticking to derailleurs. But their development has always, ultimately, unfolded in relation to the unstated quest to improve crank efficiency.<\/p>\n\n\n\n <\/p>\n\n\n\n The BCD<\/em> , or Bolt Circle Diameter<\/em>, is printed on the chainring. The Bolt Circle<\/em> is an imaginary circle connecting the 4 bolts of the 4-bolt spider chainring in the example above. The line directly connecting one bolt with its opposite, is that circle\u2019s diameter, the BCD<\/em>.<\/p>\n\n\n\n The structure depends on the number of chainrings to be mounted.<\/p>\n\n\n\n A simple MTB crankset such as a single or 1x drivetrain has a simple mount. The chainring bolts (bolt and matching nut) to the inside edge of each spider arm.<\/p>\n\n\n\n A double chainring crank spider has an extra machined edge beneath the outer, or large, chainring where the second, smaller chainring is mounted.<\/p>\n\n\n\n The large chainring bolts to the outer side; the small chainring to the other.<\/p>\n\n\n\n The most complex mount is the triple crank. The smallest chainring\u2014or \u201cgranny\u201d ring\u2014bolts to an extra platform added to the inside of the second chainring, which then becomes the middle chainring.<\/p>\n\n\n\n The image shows the granny-ring bolt mounts snugged up next to the spindle, with the middle and large chainring mounts extending further out.<\/p>\n\n\n\n Crafting the angles and distances takes complex engineering and several CNC machining sessions (we\u2019ll cover MTB crankset production below<\/a>).<\/p>\n\n\n\n The distance between the granny ring mount (top third, center) and the middle\/large chainring mount (right third, center) is calculated down to 0.001mm. Accuracy is crucial, otherwise shifting will be inconsistent and unreliable.<\/p>\n\n\n\n <\/p>\n\n\n\n The large chainring is sitting below the mounting bracket; the middle chainring is sitting a little to the side on top. The large chainring slots into to the bracket\u2019s lower edge; the middle ring on top.<\/p>\n\n\n\n That\u2019s the aligned position, giving you a view of the granny ring\u2019s bolt holes, which line up between the middle of the crank spindle (imaginary point) and the middle\/large chainring hole.<\/p>\n\n\n\n Add the granny ring at the \u201ctop\u201d ie. the innermost mount.<\/p>\n\n\n\n The nut slides in from the outside. The bolt, from the inside. Bolting the granny ring in position first, before the middle\/large chainrings, works, although you can just as easily put it together in reverse order.<\/p>\n\n\n\n The way is clear to fasten the bolts to torque.<\/p>\n\n\n\n Incidently, you can also see the boss and ramps to the right of each boss. These additions are crucial to efficient mtb crankset functioning by assisting chain movement from a lower chainring to a higher chainring. The chain catches on the boss, then the ramp, lifting into position.<\/p>\n\n\n\n The simplest\u2014and most recent\u2014way to fix chainrings to cranks is to go spiderless.<\/p>\n\n\n\n Check out our post on Direct Mount Chainrings<\/a> for the complete discussion.<\/p>\n\n\n\n <\/p>\n\n\n\n MTB history is fairly well known\u2014we\u2019ve all come across Gary Fisher, or maybe even posed for a photo with him, at Sea Otter, or Interbike when it existed.<\/p>\n\n\n\n The thing to remember about bike component innovation and development is that most of whatever has been invented or envisaged (I\u2019m thinking of all those patent diagrams of technology that never actually rolled off a production line) happened in the 1890s or the following decade.<\/p>\n\n\n\n Is this the first mountain bike? Vernon Blake on his1930 bike. At a glance, it certainly appears so.<\/p>\n\n\n\n Vernon\u2019s bike consists of a simple double-diamond frame structure with wide tires. And is that a double chainring on the crank? There\u2019s also what could be a derailleur shifting lever on the seat tube, just above the crank.<\/p>\n\n\n\n The bike\u2019s cantilever brakes also marks it clearly in the MTB class. The handlebar\u2019s semi-drop position would make for difficult handling though.<\/p>\n\n\n\n Compared with the original Klunker mountain bikes, the basic features are all there.<\/p>\n\n\n\n But while Vernon\u2019s bike is a good candidate for an MTB, it still falls short. The important point to appreciate is that the historical context is completely different.<\/p>\n\n\n\n The early klunker<\/em> MTBs were all about getting off-road onto the trails, away from traffic, away from the rules complicating everyday life. They were as much an expression pure freedom as much as a particular bike design.<\/p>\n\n\n\n The revolution resulting in 1x drivetrains is probably the biggest recent development in MTB cranksets.<\/p>\n\n\n\n <\/p>\n\n\n\n Original drivetrains had wide chainrings, by default, which narrowed over the years in response to narrowing chain link widths, which was, in turn, a response to continual addition of rear sprockets in the quest for optimum gear ratios.<\/p>\n\n\n\n Here\u2019s a selection of what was around in 1907 for example.<\/p>\n\n\n\n So, was it a simple progression from single crank to double then triple?<\/p>\n\n\n\n A Bernard Cabot design from 1893, the very dawn of the modern safety bike (safe, because of two equal-sized wheels rather than the head high ridiculously dangerous Penny Farthing designs).<\/p>\n\n\n\n Here\u2019s a sketch of an crank double from just a few years later. We can see that the quest for variable gearing spawned single, double and triple cranks from the get-go.<\/p>\n\n\n\n <\/p>\n\n\n\n There are three key stages in creating an MTB crankset: cold forge, CNC machining, finishing. (The chain line is also important . . . more on that here.)<\/a><\/p>\n\n\n\n <\/p>\n\n\n\n While forge processing is the first step in the process, its probably not quite what you have in mind since this means of component production does not require heat. Hence the name \u201ccold\u201d forge.<\/p>\n\n\n\n We\u2019d like to show you the complete forging process, even a little, carried out on a batch of MTB cranks.<\/p>\n\n\n\n Unfortunately, we outsource this to a small workshop specializing in cold forge techniques. They insist all their operations remain off the public record and top secret.<\/p>\n\n\n\n This situation is common in Taiwan where an old-school competitive advantage is seen to come from keeping manufacturing processes \u2018secret\u2019. \u201cAs soon as anyone else learns how we do it, they\u2019ll do it themselves\u201d, they say.<\/p>\n\n\n\n Many bigger companies have no problem with showing productive processes though; Chosen, the hub-maker for example. The example highlights hubs, not cranks, but the process is similar.<\/p>\n\n\n\n Cold forging involves mounting a jig or mold cut to the shape and dimensions of the component into a cold forge press. A component is pressed into existence in one movement taking a few seconds. Nothing to it really.<\/p>\n\n\n\n The extreme pressure shapes each aluminum blank into a form close to the finished wheel hub. Or a crank as the case may be.<\/p>\n\n\n\n Once we have the rough result, we still need to do more refinement as well as adding further functionality. We complete those through CNC processing.<\/p>\n\n\n\n <\/p>\n\n\n\n CNC machining makes it possible for a brand to create almost any component design imaginable.<\/p>\n\n\n\n A combination of cold forge and CNC processing is the most efficient way to produce parts, in most cases.<\/p>\n\n\n\n Manufacturers could make parts only using CNC. But CNC machining creates a lot of excess aluminum waste, and does take time. In creating MTB cranks we cold forge the shape, then refine and add to it through selective CNC machining.<\/p>\n\n\n\n The program is written to the 2D X and Y axes. The third dimension is added with the Z<\/em> value, which orients a cutter head on the vertical plane.<\/p>\n\n\n\n A raw-forged piece appears in the basic form of the finished piece.<\/p>\n\n\n\n We\u2019ll firstly machine the center: that\u2019s what we\u2019re aiming for. Then we\u2019ll do the the spider arms.<\/p>\n\n\n\n A range of cranks fixed onto platforms inside the CNC cabinet ready for processing.<\/p>\n\n\n\n One session completes a sequence of cuts of different depths at various points. As you\u2019ll see in the image, both drive and non-drive cranks are processed together. All sorts of disparate machining can be done at the same time.<\/p>\n\n\n\n The CNC program is loaded; the operator makes sure there are no errors, making a few adjustments along the way.<\/p>\n\n\n\n CNC\u2019s cutting drill bits are the fastest, most precise means to cut complex shapes with pinpoint accuracy. The non-drive side crank here must be cut exactly to the contours of the spindle.<\/p>\n\n\n\n Machining the spindle takes place in a separate batch. Splines are cut into the semi-processed spindle on the right.<\/p>\n\n\n\n An exact fit. No play at all. A later process fuses the spindle to the spider.<\/p>\n\n\n\n The raw-forged spider arm is on the left. The CNC cutter prepares the mount, then goes on to trim the arm\u2019s edges. Once a piece has been machined, you\u2019d never know it had been forged originally.<\/p>\n\n\n\n <\/p>\n\n\n\n The machined cranks next visit a sand-blasting and anodizing expert. The crank surfaces are blasted clean and prepared for immersion into the special solution in which. More details on anodizing in the bike-crank-arm post<\/a>.<\/p>\n\n\n\n <\/p>\n\n\n\n \u201cBest\u201d is always relative. Best depends on:<\/p>\n\n\n\n For most purposes these days, you\u2019ll best opt for a single chainring crankset fitted with a narrow-wide chainring which radically simplifies your drive train through eliminating the derailleur along with its shifter.<\/p>\n\n\n\n The narrow-wide chainring together with a chain guide virtually guarantees no chain drops issues. You\u2019d also be wise to choose a wide range cassette, something along the lines of 11-36 is one to start with.<\/p>\n\n\n\n <\/p>\n\n\n\n The standardization of single chainring cranks in contemporary mountain biking has coincided with the acceptance and rapid evolution of eMTBs constructed around mid-drive electric motor systems.<\/p>\n\n\n\n Your bottom bracket completely disappears on an eMTB, and your cranks are only superficially relevant. Weight is now no longer<\/p>\n\n\n\n Here\u2019s Ali Clarkson and Danny Macaskill getting an absolute blast out of a pair of Danny’s eMTBs on some pretty sketchy, steep, and loose downhill trails.<\/p>\n\n\n\n
MTB Crank Manufacturing<\/a>
What is the Best Crankset for a Mountainbike?<\/a>
The eMTB Effect on Cranksets<\/a>
Are Carbon Cranks Worth It?<\/a><\/p>\n\n\n\nHOW IS AN (MTB) CRANKSET STRUCTURED?<\/strong><\/h2>\n\n\n\n
Although most cranksets (road bike, BMX etc.) have the same elements, MTB cranksets differ in several ways.<\/p>\n\n\n\nCrank Arm vs Crank<\/strong><\/h3>\n\n\n\n
First, no need to talk about a crank arm since the arm is<\/em> the crank<\/a>,<\/strong> i.e. the lever upon which force is exerted. Crank<\/em> is an automotive metaphor describing how an engine\u2019s crankshaft channels energy to a car\u2019s driveshaft.<\/p>\n\n\n\n![\"measuring](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/mtb-crank-measurement.jpg\")
<\/figure>\n\n\n\nCrank and Spider<\/strong><\/h3>\n\n\n\n
![\"Mountain](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/09\/mountain-bike-chainring-r-mh1.jpg\")
<\/figure>\n\n\n\nBCD and Spider<\/strong><\/h3>\n\n\n\n
![\"Crank](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/crank-spider-4-bolt-holes-1024x1016.jpg\")
<\/figure>\n\n\n\n![\"Crank](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/crank-chainring-mounts-4.jpg\")
<\/figure>\n\n\n\n![\"Crank](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/crank-chainring-mounts.jpg\")
<\/figure>\n\n\n\nMounting Each Chainring<\/strong><\/h3>\n\n\n\n
![\"Small](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/small-ring-position.jpg\")
<\/figure>\n\n\n\n![\"Middle](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/middle-large-chainrings-position.jpg\")
<\/figure>\n\n\n\n<\/figure>\n\n\n\n![\"\"](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2020\/05\/middle-large-chainrings.jpg\")
<\/figure>\n\n\n\n![\"Chainrings](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/chainrings-mounted.jpg\")
<\/figure>\n\n\n\nCrank Minus Spider\u2014Direct Mount Chainrings<\/strong><\/h3>\n\n\n\n
MTB CRANKSET DEVELOPMENT THROUGH TIME<\/strong><\/h2>\n\n\n\n
![\"\"\/](\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/1\/18\/Vernon_Blake_%28cropped%29.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/www.torpedo7.co.nz\/wp-content\/uploads\/2014\/10\/klunker.jpg\")
What Was the Original Crank? Single Chainring Spider or Triple?<\/strong><\/h3>\n\n\n\n
![\"1907](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/1907-chainrings.jpg\")
<\/figure>\n\n\n\n![\"Bernard](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/bernard-cadot-1893-1024x397.jpg\")
<\/figure>\n\n\n\n![\"Magnat](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/magnat-debon-1900.jpg\")
<\/figure>\n\n\n\nMTB Crankset Manufacturing<\/strong><\/h2>\n\n\n\n
Cold Forge<\/strong><\/h3>\n\n\n\n
![\"Chosen](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/chosen-cold-forge-1.jpg\")
<\/figure>\n\n\n\n![\"Chosen](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/chosen-cold-forge-2.jpg\")
<\/figure>\n\n\n\nCNC Machining<\/strong><\/h3>\n\n\n\n
![\"Cnc](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/cnc-display-1024x759.jpg\")
<\/figure>\n\n\n\n![\"Spindle](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/spindle-connection-crank-arm.jpg\")
<\/figure>\n\n\n\n![\"Crank](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/crank-spindle-splines-1024x576.jpg\")
<\/figure>\n\n\n\n![\"Crank](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/crank-arms-in-cnc-1024x576.jpg\")
<\/figure>\n\n\n\n![\"cnc](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/cnc-kepad-1024x576.jpg\")
<\/figure>\n\n\n\n![\"Cnc](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/cnc-drill-cutting-1024x576.jpg\")
<\/figure>\n\n\n\n![\"CNC](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/spindle1-1024x576.jpg\")
<\/figure>\n\n\n\n![\"Spindle](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/spindle2-1024x576.jpg\")
<\/figure>\n\n\n\n![\"cnc](\"https:\/\/www.firstcomponents.com\/wp-content\/uploads\/2018\/10\/cnc-machined-crank-arm-1024x576.jpg\")
<\/figure>\n\n\n\nFinishing<\/strong><\/h3>\n\n\n\n
WHAT IS THE BEST CRANKSET FOR A MOUNTAIN BIKE?<\/strong><\/h2>\n\n\n\n
THE eMTB IMPACT on MTB CRANKSETS<\/strong><\/h2>\n\n\n\n