What happens when a bottom bracket fails?
Eventually your bearings will disintegrate and your BB will lose its ability to hold the spindle centred withing the BB shell, that will result in the crankset becoming wobbly, your chain will come off, your chainring might even go hit your chainstay and if you’re lucky it will happen at low speed.
What is the standard size bottom bracket?
Bottom Bracket Standards
| BB Standard | Frame BB Shell Inner Diameter | Common Shell Width |
|---|---|---|
| BBRight (Direct Fit) | 42mm | 79mm |
| Specialized OSBB Alloy | 42mm | 68mm (Road) 84.5mm (Mountain) |
| Cannondale BB30a | 42mm | 73mm 83mm (Cannondale BB30A-83) |
| PF30 | 46mm | 61mm (Specialized OSBB/FACT) 68mm (Road) 73mm (Mountain) 83mm (Downhill) 100MM (Fat Bike) |
Do bottom brackets matter?
The bottom bracket or ‘BB’ is the engine room of your bike’s chainset and one of the two most important bearings on your machine (the other being the headset). A good-quality BB, correctly installed, should serve you with years of trouble-free riding, but bearings can wear out or the BB can become loose.
What causes bottom bracket failure?
The fail by water and grit entering the bearing and causing the cartridge bearings to get loose. This is felt by poor shifting or chain rub, and finally the bearing can get very stiff if the balls jam up inside. External bearings can be cleaned and adjusted. Most have some sort of seal that can also be replaced.
What does a bad bottom bracket sound like?
Most surprisingly, what often sounds like a bottom bracket creak is usually something else. Most of the time, the true cause is a loose chainring bolt. Tighten ’em up and that’ll quiet most creaks. Sometimes even when a bike is new from the factory, the BB isn’t tight and it creaks.
Is a creaking bottom bracket bad?
While the poor bottom bracket gets blamed for creaking, very often the cause is found elsewhere. In order to turn frowns upside down, a mechanic needs to go on a scavenger hunt. Checking off boxes and eliminating options. Many creaks on a bike sound very similar to a creaking bottom bracket.
What should I replace the bottom bracket on my UN52?
My bottom bracket has started to develop play so I need to replace it. The obvious choice is the UN54 but what else should I consider. Priority is fit and forget, the 52 has done 4 years of commuting all year round, the last 2 years being off road. I don’t mind paying more to get something lighter but not if it won’t last.
What are the numbers on a Shimano bottom bracket?
Shimano cartridge bottom brackets are typically coded with a model designation and two numbers: shell width and length. Square Taper: CT21, LP27, UN40, UN51, UN52, UN71, UN72, UN91. These are all interchangeable if the other numbers match. Listed in order of quality, CT21 is worst, UN91 is best.
Is there a replacement for a Shimano UN52?
Yes you could spend out on Royce BB but the UN54 does the job great…all my bikes have Shimano UN52/3/4 BB and I can’t even remember when I lasted replaced them as they have been transplanted from bike to bike for years. Standard splined BB tool my fitting and removal like this…
Can a un54 be used as a replacement for UN52?
@joolsburger: I’ll have the un54 for a fiver if you’re still selling. The topic ‘Replacement for UN52’ is closed to new replies.