This post compares the advantages and disadvantages of sealed and unsealed bottom brackets.
The Advantages of Sealed Bottom Brackets
- Protection from Contaminations
The main advantage of sealed bottom brackets is that the bearings are protected from dirt and moisture. Consequently, the bearings keep a consistent performance throughout their lifespan.
- No Play
Sealed bottom brackets remain tight and spin just fine for a long time.
- No Bearing Servicing
When the bearings of a sealed bottom bracket go bad, the user extracts them and presses in new ones. In the meantime, there’s no servicing.
There are also cartridge bottom brackets that come with sealed bearings too. Those models are not meant to be serviced, although it’s possible to do so in the case of some models. When a cartridge bottom bracket starts to underperform, complete replacement makes the most economic sense as the units are entry-level and thus cheaper.
- No Adjustment
The sealed bearings do not stress the bottom bracket at many small points like the free ball bearings found in unsealed bottom brackets. For that reason, sealed bottom brackets remain stable for longer whereas unsealed models require periodic adjustment of the cup and cone setting so that the cranks can spin freely without play.
The Disadvantages of Sealed Bottom Brackets
Quality sealed bottom brackets tend to cost more and are rarely found on budget builds. That said, there are also very affordable low-end models.
- No serviceable
Sealed bottom bracket bearings cannot be serviced. When they go bad, they’re simply replaced. In different, the bearings of non-sealed bottom brackets can be serviced for a long time.
The Advantages of Unsealed Bottom Brackets
The main advantage of an unsealed bottom bracket is that it can be serviced for a long time.
The first part of unsealed bottom brackets that usually complains are the ball bearings. Those are either free ball bearings or caged ones. In the first case, the user can replace individual bearings. (Note: You will need a bearing gauge to figure out the size of the bearings.)
If the bearings are caged, the entire unit will have to be replaced.
A problem occurs when the races on which the bearings slide deform to the point where the bottom bracket doesn’t slide smoothly even when the ball bearings themselves are in fine condition.
When the races are damaged, it’s time to replace the entire bottom bracket.
The Disadvantages of Unsealed Bottom Brackets
Unsealed bottom brackets are known to get loose faster. As a result, the bottom bracket develops play hurting the power transfer coming from the cranks.
- Require Periodic Servicing
The advantage of unsealed bottom brackets could also be a disadvantage. In order for the bottom bracket to perform well, it needs to be serviced periodically. This requires disassembly of the unit, de-greasing, re-greasing, and bearings re-packing.
For some people, this is too much unnecessary work. A sealed bottom bracket, on the other hand, is either replaced entirely when it malfunctions (cartridge model) or its bearings are pushed out in favor of new ones.
It’s also worth mentioning that unsealed bottom brackets require the user to adjust the cup and cone mechanism and the lock nut to a setting allowing free rotation of the cranks without play in the bottom bracket.
This goal isn’t insanely hard to achieve and is done with basic tools (cone wrenches, small pliers…etc.) but it requires some practice and expertise. People who want to just ride their bike with minimal servicing might not like this property of unsealed bottom brackets.
- Victim of contamination
An unsealed bottom bracket does not offer sufficient protection from contaminations. When you add the proximity of the bottom bracket to the ground, you have a recipe for a dirty mechanism. That said, it takes a long time for problems to occur if the bottom bracket is packed tightly.
What To Choose?
Truth be told, there’s not much of a choice because sealed bottom brackets dominate the market if the user is looking for variety. Luckily, they can be acquired for relatively little money if the user is fine with a cartridge model.
If the bike is going to be used for commuting, then a basic cartridge unit can provide decent performance for thousands of miles. The main downside of this choice is that you will be limited to square taper cranks.
If you want a more modern set of cranks, the classic route today is to get a bottom bracket with external bearings sitting outside of the bottom bracket shell.
That said if you have an unsealed bottom bracket, and it’s operating smoothly, there’s no need to replace it just yet. I have a very old bottom bracket on my retro road bike that I’ve serviced a few times, and it still operates as intended.