This post compares the advantages and disadvantages of carbon and aluminum bike cranks.
The Advantages of Carbon Cranks
- Lightweight
The main advantage of carbon components is that they have the potential to be lighter than their aluminum equivalents.
Weight Comparison
The table below compares the weight of aluminum and carbon MTB cranks.
| Aluminum Cranks | Weight | Carbon Cranks | Weight |
|---|---|---|---|
| Shimano Saint FC-M820 | 827g | Truvativ Descendant Carbon Eagle Boost Direct Mount | 555g |
| Shimano Saint FC-M825 | 828g | SRAM XX1 Eagle X-SYNC | 422g |
| Shimano ZEE FC-M640 | 817g | SRAM XX1 Eagle X-SYNC 2 | 765g |
| Shimano ZEE FC-M645 | 847g | SRAM Force 1 / CX1 X-SYNC | 679g |
| SRAM NX Eagle Direct Mount | 705g | SRAM X01 Eagle X-SYNC | 471g |
| Shimano SLX FC-M7000-11-2 | 789g | Truvativ Stylo Eagle | 555g |
| Shimano XT FC-M8000-B1 | 698g | FSA SL-K Modular BB392EVO | 560g |
| Average: | 787.28g 27.77oz | Average: | 572.42g 20.1oz |
Conclusion: On average, the carbon cranks in the table are 27% (215g) lighter.
215 grams are a lot in the world of professional cycling but don’t mean much to recreational riders.
And while it’s nice to save weight, cranks are among the places where extra grams are difficult to perceive because the weight is very close to the ground and in the middle of the bike.
If suddenly 215 grams are added to your bike’s crankset, you probably won’t even notice the difference.
For that reason, the light weight of carbon isn’t a strong incentive to buy carbon cranks, especially from the perspective of amateur riders.
- Futuristic & Modern Look
Some people like the aesthetics of carbon components and buy them for the looks rather than a functional quality.
- Extra Stiffness (maybe)
Some people claim that carbon cranks are stiffer and thus result in a more efficient transfer of power. In reality, however, most riders will be unable to detect that extra stiffness because it’s very subtle if it exists in the first place.
The Disadvantages of Carbon Cranks
- Lack of Toughness
Carbon is a strong material, but its strength is fragile.
In other words, carbon components offer sufficient resilience when used as intended but cannot handle external and unexpected stress very well. Once the upper layer is damaged, the entire carbon component becomes compromised.
Alloy and steel parts, on the other hand, can handle stress coming from all directions. It will take a lot more than a scratch to make a set of quality alloy cranks unusable.
- Possible Unexpected Failure
When carbon fails, it does so completely and without giving notable signs beforehand.
Technically, the same applies to aluminum but to a lesser degree. Also, the extra resilience of metal alloy greatly reduces the possibility of aluminum failure.
- Extra Vigilance
The soft side of carbon necessitates constant inspection of every carbon component. A scratch may quickly become a crack and then result in total disintegration.
Alloy components do not necessitate such vigilance. Of course, it’s always good to expect the entire bike for weak spots, but metal elements are more resilient and require fewer inspections.
- Expensive
Carbon components are significantly more expensive than their alloy rivals.
Truth be told, a cyclist can buy a fairly cheap entry-level crank (e.g., Shimano Acera) and ride it for years without experiencing any problems. Meanwhile, carbon cranks are not only much more expensive but also unlikely to survive as long due to the nature of the material.
The Advantages of Aluminum Cranks
- Reliability
Aluminum can take more abuse than carbon and is a lot less likely to fail unexpectedly. For that reason, even some professional cyclists use alloy bars instead of carbon ones.
The same applies to cranks. Since alloy cranks are cheaper while also being tougher, many cyclists prefer them over the carbon models.
- Cheaper
As already mentioned, a decent aluminum crank can be had for very little money. This makes alloy cranks more accessible.
- Greater Variety
Aluminum cranks are more common and thus have a greater market share resulting in the presence of more models to choose from.
- Lower Maintenance
Alloy cranks do not need constant inspections for cracks.
The Disadvantages of Aluminum Cranks
- Heavier
At the end of the day, aluminum components cannot be as light as carbon without losing strength. Thus, the vast majority of alloy cranks will be heavier. That said, some high-end alloy cranks weigh as much as low-end carbon models.
- Unexpected Failure
Similarly to carbon, aluminum cranks can also fail unexpectedly. However, this outcome is a lot less likely.
FAQ: Are carbon cranks worth it?
Carbon cranks are worth it only when the rider is competing at a high level and wants to have the lightest possible machine. In all other cases, carbon cranks do not offer game-changing benefits.
One could even argue that they make for a poor purchase because a good set of alloy cranks is cheaper, tougher, and doesn’t weigh a lot more. Thus, recreational riders are better off buying alloy cranks. The saved money can be invested in a component that will make a bigger difference (e.g., fork, tires, rims, brakes…etc.)
Summary: What You Need To Know
- Carbon cranks are lighter than aluminum models. Nonetheless, the weight savings aren’t substantial and thus only professional competitors could benefit from them.
- Carbon cranks are more expensive and yet more likely to fail unexpectedly than alloy models.
- Carbon cranks require more frequent inspections.
- Alloy cranks are heavier but also more affordable.
