Mountain Biking - sizing up bottom bracket

Could somebody give me a quick run through on bb sizes? I'm just trying to get my head round it all.

I just bought cranks and bottom bracket off ebay for my Zaskar frame, I thought I'd got the sizes right but clearly I haven't. The shell measured up to 73mm, the bb said it did 68 and 73 so I didn't worry about that. It's also got the measurement 113mm which I'm assuming is the complete width of the bb, I was buying the cranks and bb as a pair so I didn't worry about that. The problem is that it physically won't fit in the shell, the diameter of the bb is too large, but I can't find any measurements regarding diameter. Theres a label in the bb which talks about the FD type, then lists 'Clamp' and 'E-type' and it says that if yours is E-type and 73mm then this bb won't work. What is this FD type and is that whats causing the problem?
I'm just trying to determine what size to get, I'm building this bike on a budget and don't want to mess up again.

Thanks in advance, Steve

Does your bb mount on the seat tube of your frame or on the bottom bracket?

The diameter of the bottom bracket is pretty much a standard.

Also, you do realize that one of the bottom bracket cups are reversed thread right?

Sorry LowCel I don't understand the question. Does my bottom bracket mount on the seat tube or on the bottom bracket? It all looks pretty standard, bottom bracket shell welded in where the down tube and seat tube meet.

Does your bb mount on the seat tube of your frame or on the bottom bracket?



he meant to type


Does your front derrailer mount on the seat tube of your frame or on the bottom bracket?


E type means your front derailer mounts with your BB. It should have no impact on your supposed lack of bb shell diameter.

BB shell diameter is pretty standard. Sure your not screwing the cups in the wrong sides like LC intimated?

pics would help

Yeah, whatever you do, dont try and force it in. You will totally ef yourself.

Oops...sorry. Yeah, meant front derailleur. :o

I'm afraid I haven't got any means of taking pictures right now, but the thread of the cup is still a good 15mm away from reaching the thread in the shell. About half of the bb will fit in, in that the shell comes half way up the bb, but then it's just blocked from going any further.

Sizing of the srew-in cups on almost every bottom bracket made nowadays is called 'English thread' whick is 1.37" x 24 threads per inch. the left or non-drive side has left-hand threads; the drive-side or right (chainrings) side is right-hand thread.

It's true that some 73mm BBs will not work with an E-type front derailleur (FD). That is because the derailleur has a mounting ring that goes behind the drive-side cup and takes up some space which throws off the chain line. It's usually not an issue if you have a 68/73 BB with a 68mm shell. If you have a FD that clamps to the seat tube, you needn't worry about this.

The 113 is the overall spindle length and is normal for a standard three-chain-ring drive setup. If you have a single-ring DH bike and need to run a chain guide, then you need to start looking at longer spndles, llike 118s and such.

I'm afraid I haven't got any means of taking pictures right now, but the thread of the cup is still a good 15mm away from reaching the thread in the shell. About half of the bb will fit in, in that the shell comes half way up the bb, but then it's just blocked from going any further.You should take the frame in to a shop that has the taps to chase the threads in your shell; there is probably a burr in there. If you try to force past the burr with alum. BB cups, you run a real risk of buggering the BB threads.

Yeah I think its gonna have to go into the shop. I'm not actually planning on using this bb anyway (it's a RaceFace SRX), but I just wanted to make sure I got the size right. Thanks for the help tho chaps.

Yeah I think its gonna have to go into the shop. I'm not actually planning on using this bb anyway (it's a RaceFace SRX), but I just wanted to make sure I got the size right. Thanks for the help tho chaps.That's a good thing to do with a RaceFace BBs (not use it). Better use for it would be to attach two large treble hooks and use it to jig for Ling Cod.

Easy now.........they also make great paper weights. :D

For the record, I've only had about five of them go out on me. :rolleyes:

I'm having alot of luck with my Diabolous external bb.

External is a different story all together. My experience was with ISIS.