A crank is one of the crucial and functional parts of a mountain bike. Without it, your bike is useless. It is the only piece of equipment that attaches you to your frame via pedals and the rear wheel via a chain. A crank can make or even break your cycling experience. A smooth crank allows better power-to-speed delivery and keeps your bike running smoothly.
When looking for a new set of cranks, you can find a decent pair for well under 100$ or pay even up to 1000$ for the most premium pair you can find. Why are these premium cranks so expensive? To put it simply, it’s weight, the lack of weight, to be more precise. As with so many bike parts, the more you spend, the lighter it gets. While weight is the main reason, there are other benefits along with these pricier products, such as stiffness and durability, which we will try to explain further in this article. You can see the video first.
Do I need 1x or 2x?
In the early days, bikes had a single front chainring and only a rear cog to change ratios. The bike industry developed and innovated increasingly, providing a greater range by adding double and even triple chainrings to road bikes. Mountain bikes quickly adapted to the same system and even added more rear cogs to enhance the range further.
Over the past few years, 1x drivetrain systems have become the industry standard. This means you will only find one chain ring on your crankset. Due to its simplicity, this system gained a lot of popularity. A front derailleur adds weight, cost, maintenance, and complexity to the shifting with multiple chainrings.
On top of that, rear cogs have gotten larger, with wide-range cassettes going from a 10 to a 52-teeth ratio. The greater gear ratio makes double and triple-chain rings almost redundant. Although some riders still swear by a double chainring, with enough range on the rear cog to handle all your local climbs and descents, a single chainring is perfect.
Gear ratios and chain rings
We already mentioned the term gear ratio before. If I explained it, I'd say this: gear ratio determines how hard you work to turn your wheels. The ratio is determined by considering the number of teeth on the front chain ring to the number on the rear cog. For some of us, this is very confusing as the term higher gear refers to both the bigger front chain ring and the smaller rear cogs. On the other hand, lower gearing refers to a smaller front chain ring and a bigger rear cog. Higher gearing generates more power and speed, making it ideal for downhills and flats. Lower gearing generates less power but takes less energy, making it ideal for difficult climbs. When selecting cranksets, you'll be looking at the range of sizes of chainrings available and comparing them to your rear cog and the clearance you have in your bottom bracket area. The most commonly used chainring sizes are 30, 32, 34, or even up to 36 teeth.
On top of that, you'll also want to check that the crank arm is compatible with your desired chainring model and brand. The main consideration is how the chainring is mounted to the crank. Some brands use a proprietary direct-mount system or BCD (Bolt Circle Diameter). Any modern 1x chainring uses an alternating narrow/wide tooth profile to improve chain retention.
How long should my MTB cranks be?
There are a few sizing measurements to remember when looking for the best mountain bike cranks. First, there is the length of the crank arm. The three main crank lengths are 165 mm, 170 mm, and 175mm. Traditional logic dictated longer cranks mated better with longer legs, so larger bike sizes often used 175mm. Remember that crank arm length can impact your riding style and bike fit, but mostly, riders just run what comes pre-installed on their bike.
However, it would help if you remembered that longer crank arms risk striking rocks and trail debris with your pedal or crank arm. These days, clearance is king, and 170mm is popular to increase the gap between the ground and crank tips at the bottom of the pedal revolution to reduce strikes on rough trails. Though a pedal strike might lead to a crash, it rarely damages the part to the point of disrepair. When looking for a new crankset, you need to consider the type of bike you ride; an XC-bike will have its bottom bracket placed higher than an enduro bike.
What bottom bracket do I need?
When fitting new cranks, check what bottom bracket design you need. Most crank manufacturers use their bottom bracket sizing, meaning that if you're upgrading to a different brand, you'll need to replace your bottom bracket. Conversely, there are also a couple of standards used by frame manufacturers, limiting which bottom bracket you can use and, therefore, limiting your choices of mountain bike cranks.
The best way to find out what cranks you can choose is to identify what is currently fitted onto your bike. The easiest way is to check your frame manufacturer's tech specs. If you're not bike-literate, ask your local bike shop for advice. In most cases, you'll either have a 24mm or a 30mm diameter axle. Some brands, like SRAM's DUB system, use a propriety axle diameter (28.99mm for SRAM), which requires a bottom bracket from SRAM's DUB ecosystem. But for most regular cranks, you can choose any third-party bottom bracket as long as you have the correct axle diameter.
Construction
Cranks are forged from one of these three materials – aluminum, carbon, and titanium. Each has its various pros and cons. The cheapest cranks are made out of aluminum; they are also the heaviest and have a bit of flex. The top of the bill alloy cranks is forged to align the aluminum's grain structure, rather than machine, with some brands also using sophisticated forged hollow arms to save weight. Carbon bike cranks are the next step up; they are much stiffer and shed a lot of weight compared to their aluminum counterparts. The extra stiffness should improve power delivery and reduce flex to increase responsiveness in driving the bike with feet through turns and features. Lastly, titanium cranks, which are ultra-firm and efficient, are a first-class upgrade. Although most riders likely wouldn't feel the difference from a top alloy crank. The biggest advantage of titanium is its durable construction. But as with all premium products, it comes with a sky-high price tag.
Consider the discipline you’ll most likely ride when choosing a new crank. If you ride a lot of XC, a lightweight carbon crank is your best option. You’ll have the lightest component possible and get the maximum performance out of it.
An alloy crank might be the better option for a more downhill-orientated riding style. In case of a rock strike, there is less risk of breaking your cranks than a carbon crankset.
Final thoughts
Cranks should be a fit-and-forget product and only require a minimum of maintenance. For such a simple bike part, getting the right choice for you is quite complicated. Choosing the best crank depends mainly on your budget, riding style and personal preference. Hopefully, this article helped you narrow down your choice.
