The bottom bracket is an unseen but crucial component which sits at the heart of your frame.
Bottom brackets enable your cranks to spin on a secure and balanced bearing interface. As with any rotational component on a mountain bike (chainrings, hubs, cassettes), the bottom bracket works hard for a living and can be exposed to trail contaminants.
Rotational components also have a more crucial mass profile for mountain bikers, due to the additional energy required to keep them turning over. Grams saved on any rotational component yields a generous energy saving.
On a bottom bracket the actual rotation mass is not really an issue, it is a bearing system, so the most important consideration is friction. A bottom bracket which manages to be both strong in its structure and reduce resistance when spinning, is the ideal.
Reconciling these two concepts can be problematic. Engineers are challenged by producing a bottom bracket which is robustly sealed and has large enough bearings to balance rider weight when standing on the pedals.
The solution would naturally be to use the biggest possible bearings, allowing for excellent weight load distribution, but there are limitations in terms of the frame design. A bottom bracket shell can only be so big before it starts to disrupt the tube profile and geometry of any mountain bike. Crank arm spacing is also an issue.
Bottom bracket design is a compromise between environmental sealing, low friction bearing integration and frame specific packaging.
How to choose the best mountain bike bottom bracket for you
There are an exhaustive array of mountain bike bottom bracket standards and specifications. Perhaps the most elementary – and important – classification is whether your mountain bike frame runs a press fit or threaded bottom bracket.
Although the mechanical bearing functions between a press-fit and threaded bottom bracket are similar, the way they secure to your frame are crucially different.
The press-fit bottom bracket is easier to manufacture, as it can be machine pressed and offers frame designers the ability to meet lightweight specification requirements. For riders who want a narrow q-factor (lateral crank arm spacing), press-fit bottom brackets make a difference.
Unlike a threaded bottom bracket, there is no requirement for an aluminium insert to secure the press-fit system. Therefore, a press-fit bottom bracket frame can be lighter than one of the same dimensions and tubing profile, with a threaded bottom bracket – which requires an aluminium insert.
It should be noted that the weight difference is marginal and comes with a probable irritation coefficient, as press bottom brackets are prone to creaking. This is caused by environmental contaminant ingress, and the annoyance of play developing over time, as the bottom bracket is not screwed into a securing thread. The press-fit bottom bracket works a treat on carbon road bikes, but for the more challenging contaminant environment frequented by mountain bikers, it has its detractors.
Threaded bottom brackets are the more traditional and robust configuration, ideally suited to mountain bikes and retain a legion of supporters who value durability.
Beyond your choice of configuration – either threaded or press-fit – the most important bottom bracket specification feature should be bearings. Remember that the bottom bracket is effectively carrying your full weight when you stand on the pedals.
If you are descending technical trail in the attack position or pedalling out of the seat on a steep climb, all your weight is resting on the bottom bracket’s moving parts.
Any bearing wear will be exacerbated by your standing weight on the pedals, so running the closest manufacturing tolerances and best material bearings are crucial. Bottom brackets with a lower functional friction are most desirable, as they save energy and prevent unnecessary fatigue.
With bearing material, you have steel or ceramic as your choices. Ceramic bearings are more expensive but offer numerous advantages over steel.
The ceramic material can be shaped to a better manufacturing tolerance, which lowers friction by creating the most spherical possible shape. This allows a bearing to seat in a cartridge with narrower tolerances and less friction. All those factors combine to reduce the overall energy you require to turn the crankset through a bottom bracket.
Ceramic bottom bracket bearings are also less susceptible to structural flex, under load than steel. This means that the bearings will retain their shape, even if you are cranking at maximum power up a climb, and therefore provide near-perfect energy transfer when you need it most – instead of friction build-up.
Most bottom bracket bearings are steel, but even here, there is a distinction in the market between stainless and standard steel bearings. You could have a quality steel source material but machining it to the perfectly round shape is what makes for a great bearing – and this requires engineering discipline.
Certain bottom bracket manufacturers prefer to machine their own bearings, for optimal quality control. This also gives them the ability to produce bearings which are perfectly aligned with their overall bottom bracket design specifications.
The best mountain bike bottom brackets
Chris King Threadfit
The best from a boutique bottom bracket maker
Weight: 89g | Bearings: Steel
If you desire a cycling component which runs on bearings and must last virtually forever, the most trusted name is Chris King. The former frame builder has been a pioneer in producing some of the very best hubs and headsets imaginable since 1976. Chris King’s bottom brackets are of the same calibre.
Although they aren’t cheap, the cost of your investment can be amortised over a very long time – as these bottom brackets tend to outlast most frames they are built into.
The secret of Chris King’s low friction performance and impressive durability are exceptionally tight tolerances, due to the labour-intensive manufacturing process involved with its bottom brackets. Unlike many rivals, Chris King fabricates its own bearings and packages the cartridges in-house, at its Portland factory, to ensure unsurpassed quality.
Wheels Manufacturing threaded angular contact
A specification for heavy weather riding
Weight: 101g | Bearings: Chromium
If you are the kind of rider who does not avoid mud or hundreds of miles cranking along in choking dust, this is the bottom bracket for you.
Differentiating the Wheels Manufacturing bottom brackets from most others are their bearings, which are all Enduro standard. Environmental sealing is exceptional too, with Enduro silicone dust seals to protect your bottom bracket’s moving bits from contaminant ingress.
The use of angular contact bearings also decrease load wear and Wheels Manufacturing goes to substantial lengths to shape them as perfectly as possible. The individual bearings are made from military-grade chromium steel and shaped to a roundness standard of 5/1,000,000″.
Hope MTB stainless
Need a mud-proof bottom bracket? Try this proven British design
Weight: 110g | Bearings: Stainless steel
The British brand’s bottom brackets have a deserved reputation for foul weather riding durability.
With Hope’s design, prototyping and manufacturing all being proudly located in Barnoldswick, muddy English riding conditions have shaped engineering priorities with all of the company’s components.
The stainless steel bearings are specific to Hope’s exact specifications and they are double sealed. A non-contact labyrinth seal protects the bearings externally, whilst internal sealing is provided by O-rings.
Beyond this comprehensive double seal structure, Hope’s bottom brackets also have direct contact with the crankset’s axle, which negates the presence of shims or spacers, further reducing complexity and potential maintenance issues.
Unequalled performance – at a cost
Weight: N/A | Bearings: Ceramic
If you desire to sacrifice the least wattage of energy and get the most mileage out of your bottom bracket, CeramicSpeed has what you need.
By using ceramic bearings and custom steel races, the Danish brand claims to reduce drag by 50% compared to a conventional bottom bracket design. Less drag means more efficient power transfer and a greater gain of performance per pedal stroke.
The efficiency gains are only part of CeramicSpeed’s product appeal. Ceramic bearings also manage to be 60% longer lasting, although they are certainly not cheaper than steel. A significant investment is required to buy into CeramicSpeed’s design, but if you compound the efficiency gains and longevity, this is the bottom bracket to have for mountain bikers who are going to be tallying huge cross country and climbing mileages.
The bearings masters make their own bottom bracket
Weight: 168g | Bearings: Steel
We’ve mentioned the benefit of running superior bearings in your bottom bracket, and most of those upgrade kits are supplied by Enduro. Since 1996, this company has been the supplier of choice for many mountain bikers. As such, you’d expect them to build a pretty decent bottom bracket of their own and the TorqTite is exactly that.
This cleverly engineered bottom bracket combines the creak-free fit of a threaded bottom bracket and makes that attribute applicable to frames with a press-fit bottom bracket shell.
Enduro makes their own bearings in Oakland (California), and claim superior tolerances due to the skill of their machinists. Their bearings are also fabricated from nitrogen-infused steel which has better longevity than stainless. With a TorqTite bottom bracket, you can have a creak-free fit in a press-fit frame.