Bottom Bracket Info
Bottom Brackets
The current selection of bottom brackets is kind of confusing. Trying to figure out what your frame has can be a daunting task. There are a lot of different choices and different specifications, applications and installations. I am going to try and put together a somewhat comprehensive list together here, it will be an ongoing project though - If you see any I missed please email me and I will get them added.
First let's go through the different types -
1-Piece Bottom Brackets
The crank arms on these are a single forging, usually with the chain rings either welded or press fit on them and not serviceable. They are extremely heavy and easily spotted by the bend in the crank arm as it comes out of the bearing cage (see red arrows in pic below). The frame has a rather large diameter opening to accommodate pressed in bearing cups. They have to be large diameter to "snake" the crank through the frame and screw everything together tightly. These are present on some older bikes worth saving as this used to be pretty common on mid level bikes. They flex a lot, they creak, the bearings are usually not sealed off very well so the grease gets washed out and dirty. The only reason they still exist is they are extremely cheap to produce, which is why they are always on landfill bikes. Unlike other cheaper bottom brackets that have threaded bracket shells, these are not really upgrade-able to anything decent. There are adapters out there, and they do offer improvement, but they are expensive and heavy and still creak and groan for not much gain.
3-Piece Bottom Brackets with cage bearings
This Bottom Bracket consists of bearing cups with caged (usually) bearings that screw into threaded bracket shells on the frame. The crank arms are pressed onto square tapers an the axle shaft and bolted into place. These are very common in bikes from the 70's and 80's on higher end bikes. They were once the go-to standard. While not too bad to use, the bracket shells are most commonly either English or Italian thread patterns with standard 68 or 72mm widths so it is usually very easy to update these to cartridge bearings or even outward bearing systems. The major downside with these is the bearings often get contaminated with anything that falls down the seat or head tube and when installing them the tension on the bearings needs to be set correctly - it's not difficult, but it is another adjustment to make.
Square Taper Cartridge Bottom Brackets
These are very similar to the brackets above with cage bearings except these screw in as a single sealed assembly with a lock ring screwing in on the opposite side to hold it in place. This type of set up offers a few key upgrades. The bearings are higher quality and sealed, so dirt and grit cannot contaminate the bearing. The thrust tension on the bearing is also set from the factory so there is no need to adjust it. These are currently the standard for commuter and utility bikes as well as some entry level road bikes. They work great and I use them all the time as a cost effective upgrade to an older frame- they can be purchased for less than $30 for a decent one.
2-Peice Cranks With Threaded Outward Bearings
2-peice crank sets with threaded outward bearings are the new standard for high end bikes. This system consist of larger bearing pressed into threaded cups that screw into the frame, These larger bearings don't actually fit inside the bracket shell though, the ride just outside it. There are some large advantages to this. The bearings are again sealed, but more importantly they are a much larger diameter. This means the crank axle can me much larger and the bearings more robust so the whole assembly is much stiffer leading to a more efficient transfer of power. The crank set is also much simpler as one side has the axle, chain ring(s) and one arm and is pushed through the bearing and the other arm is simply bolted on the other side of the axle. This makes it very easy to swap a crank set on the fly or repair the bottom bracket if anything ever needs replacing. One of the best features in my opinion is how backward compatible they are. These bearing cups can be found in standard English and Italian thread patterns so it is possible to add these modern features on very old bikes - My 1985 Schwinn is actually running this setup and it works as well there as it does on my 2024 Trek seen here. The easiest way to spot this system is to look for the bearing hanging out between the shell and the crank arm on both sides.
Press Fit
The last type are Press Fit Bottom Brackets. These are very similar to the outward bearing type above except they are not threaded, they are pressed into the frame. This type of BB is found mostly on carbon fiber frames made in the last 10 years. They can be found on aluminum frames but are not as popular. The major advantage with these is they can make manufacturing much easier and allow for an even larger bearing. The downsides however are that they often creak and are very easy to install incorrectly if you do not have the proper tool for it - which is quite expensive. There are also many variations on these so there are many different sizes and variations, finding the one you have can be difficult. The bike industry as a whole is starting to move away from these. It was once thought they would be a great cost saving measure, but the number of warranty claims on them quickly nullified any savings manufacturers gained in the short term. They are not to be avoided though if you can afford the tool to service the. They can be reliable and work great- but I prefer the ease of threaded shells myself.
