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Front derailleur technical assistance
NB: Originally posted elsewhere on the Global Riders Network and appears via syndication.
Looking to upgrade FD to XT from entry level Deore. I have worked out the difference between top swing and conventional swing but can anyone explain the difference between a 28.6mm and 34.9mm Dual pull v's 31.8mm and 34.9mm Dual pull
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The measurement in millimetres is the band width of the FD ( not to be confused with band width on a radio, your bike cannot pick up AM or FM ) so you can either measure your frame tube where the FD will sit or read the inside of the old FD.
Often the size is the same as the seatpost clamp size. For many dual suspension bikes 34.9 is the size.
In fact, all mtb FD's will be 34.9 and then a spacer kit is supplied for the other two sizes....
in simple terms, it is the diameter of the tube which the derailleur will clamp to.
Most derailleurs come with some spacers.
If it's ~32mm, get the 31.8.
If you want to measure the diameter of a tube and don't have a set of callipers then try this method:
Tear off a straight edged strip of paper about 30mm wide. (eg end of an A4 sheet of paper)
Wrap the paper around the tube and mark where it starts to overlap.
Now measure from the edge/corner to the mark - this is the tube circumference.
Now grab your calculator and divide this measurement by "Pi" (Or 3.1415 is accurate enough)
This is then the tube diameter!
For a 31.8mm tube the circumference measurement will be ~100mm. For 34.9mm tube the circumference will be ~110mm.
Cheers
Jon
Already done but I just used a bit of string instead of paper