It creaks. I think I hear this clicking sound when climbing. So, when I was pedaling the other day, I hear this pop once when I hit a pothole. The mysteries of the bottom bracket. It’s quite often other problems on the bicycle are falsely attributed to the bottom bracket. That’s the number one part of the frame that is stressed the most, ‘used’ the most, and generally welcomes dirt and grime to sit and adopt a patch of their own. Everyone has a theory of what’s going on whether it be technical torque specs and assembly prep compounds to the daily commuter on a 1984 steel relic rusting from years of rain, snow, grit, and use.
I am going to share a bit of my own experience and knowledge and hope it sheds light on the subject and speeds up your repair or ends your frustration. Please speak up and contribute any good points I don’t cover. Lastly, common language will be used for the most part, or a photo that explains it better.
There are several types of bottom brackets. There are a couple more after that categorized into what you hear people call ‘proprietary’ components. Some of the time, that makes it more difficult to service or replace. Either way, most of the problems can be remedied by a regular service for the bottom bracket (henceforth called BB) yearly. That is the part that makes us shop people happy. Not because of more revenue (it actually will save you money and frustration), but generally because it makes it easier to fix the part and clean it rather than remove a damaged part and then install a new part. That being said, good information about the subject and a regular check from your LBS, you and your bike will be happier.
Probably to this day, the most common BB is the square taper. There are two types. The difference is how fast the edges taper. The more uncommon (at least in North America) is the ISO taper. I see it mostly on Italian road bikes (for good reason). The most common is the JIS taper. Many different bikes have this BB. Here is a photo of one:
Think about the square edges on the sides holding the crank arms and the pedals. The threads on the edges of the cylinder go with the threads on the frame at the base of the frame.
Most of the time there is something of a seal between the spindle (the darker square taper rod) and the BB cup (the threads of the cylinder). Inside that crazy monster are two rings of ball bearings. On the inside, part of the spindle and part of the cylinder have curved channels that the bearings spin around in. A nice, healthy amount of grease on the threads of the cylinder, the curved channels, and the ball bearings will keep the same one running for years and years. The only thing necessary to replace regularly is the bearings. Most standard sizes run 10 cents each. Nicer ones are about 30 cents. There are usually 18-20 in a bottom bracket. The grease and the fresh bearings allow the energy that you push onto the pedal to propel you easier. Plus, no creaks or pops.
But wait. Dude. My mechanic told me I have this cartridge bearing system and that I have to replace this thing like, around five to ten thousand miles. It creaks between then. If it is the BB, it is usually because the threads of the frame and the threads of the cylinder have gone dry. The grease initially installed on new ones has washed away with the water that enters the frame from rain and temperature and exits through ‘breather’ holes in the frame. Check on the inside of your frame where the rear wheel connects to the bike. One on each side for steel, aluminum, and titanium frames and then another on each side at the fork (where the front wheel connects), and then right at the bottom of the bike where that bottom bracket is. This is why regular service keeps grease inside the bearings and threads and makes it run smooth and quiet as it should. Cartridge bearings last longer and are generally more expensive, but quality loose bearings in the BB like I explained about at the start can last a long time with less expensive but more frequent cost.
That’s a summary of square taper bottom brackets (BB). They are generally the easiest to diagnose and service because they are more readily available at your LBS. They have existed for quite some time and continue to be very reliable BB’s. They can range between somewhere near 30-50 dollars (for cartridge BB) for the majority of bicycles and higher end BBs running around 100-200. Pristine bearings in these bottom brackets are unbelievably smooth and provide an extremely confident pedal stroke and power transfer from you to the bike. It makes it move!
More to come next post for Octalink BBs, other ‘like-minded’ BBs, and outboard bearings. Less like a boat motor and more like a ship propeller.
– SNC
secondnaturecycling 