Giant Defy 3.5 BB replacment

[stixmaster1]

I have a Giant Defy 3.5 2010 model - one of these:

http://www.giant-bicycles.com/en-gb/bikes/model/defy.3.5/4861/38961/

I need to replace the BB but last time I tried this I ended up with the wrong threading. I didn't even check the length! (amateur)

I want something that fits exactly right and I'm planning to go with a UN54. How do I find out exactly what I need. Does anyone happen to know already. Will I just have to take it out and check. It would be great to be able to order this today as time is limited on this.

TIA.
stix

[xerxes]

Measure the with of the bottom bracket shell, it will be either 68mm or 73mm, most likely 68mm and almost certainly an English thread, not Italian.

Next, measure the length of your existing bottom bracket axle, which will be anything from 107mm to 127mm.

[stixmaster1]

(08-13-2012, 10:53 AM)xerxes Wrote:  Measure the with of the bottom bracket shell, it will be either 68mm or 73mm, most likely 68mm and almost certainly an English thread, not Italian.

Next, measure the length of your existing bottom bracket axle, which will be anything from 107mm to 127mm.

okey doke. Cheers. In general is there a way to find out exactly what parts are on a bike without measuring?

[xerxes]

Not really, there are now several different types and sizes of bottom brackets and headsets. Sometimes the measurement is marked on parts, sometimes it isn't. It's all a bit of a pain really.

There has always been a variety of standards, different threads, English, Italian and French, plus some peculiar to certain manufaturers, I think Raleigh had there own thread standard for headsets back in the 60s and 70s, for example.

More recently there has been a number of alternative designs, all claiming to be an improvement on the conventional square tapre type, like yours; octalink, ISIS, powerspline, Hollowtech and lately, press fit designs like BB30 and BB90. Some of them may have some advantages, but I think the main benefit of the press fit types is a saving on manufacturing and assembling costs, no threads to cut in the frame or on the bottom bracket parts, and it's quicker to assemble a press fit in the factory with an automatic hydraulic press, than it is to fit threaded parts.