Hi again. I have a question. What is a Bottom Bracket on a Bike ?

Is it the part the crank goes through?

I've seen pictures and I'm guessing what it does.

Is it important for me to understand it's use and how to maintainwhen to replaceif it ever needs replacing, or is it something that isn't really needed to be considered.



  • Yes,

    Rarely needs replacing. Some are sealed units some require stripping and greasing. Buy a good bike book or take your bike to a local bike mechanic.

  • If your bike is fairly new then it could be one of a number of standards (press-fit, threaded, bb30, ...) so its probably easiest to leave to the bike shop mechanic unless you are confident and have bought the correct tools.

    Coming from a mountain biking background, where they tend to suffer due to being a moving part at the bottom of the bike, if its worn you'll notice that the cranks don't rotate as smoothly as before.  The best check is to hold the pedal ends of both cranks and push/pull towards the frame - if its good then there should be no movement, but if the bearings are worn then you'll see a little bit of play. 


  • Relatively cheap and easy fix really, plus, the longer you leave it the less easy it is to do, without the aid of soaking it in coke and heating the frame with a heat gun or similar! image

  • It's not something I need to look at as my bike is new.

    I was just in the pub when my one of my bosses was chatting about it and I didn't know what it was.

    When I asked him what it was he just looked at me funny and told me to google it.

    So I thought I'd ask some strangers on a forum as I was bound to get a better reply than from that t*sser.

  • Generally my experience of it is they are expensive. I have a habit of destroying them sooner than anyone would think. And they are best left to the man at the shop.

    I would just mention to your boss that you get through BBs after about 3000miles which is sooner than you would expect but it is probably due to over gearing and putting too much power through the crank arm. You've considered titanium ones but aren't sure if the extra cost would give you more wear/£. Then ask him if he thinks the new carbon buttons for Di2 that save 0.002g are worth £100 and voila you are a triathlete!

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