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What things do I have to consider when planning to switch parts from one frame (old one) to another frame (new one)? Will all the parts transfer? What items may need replacement because they won't fit?

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up vote 11 down vote accepted

Areas that you need to check and consider are:

  • Bottom bracket size and type - the bottom bracket shell on a frame can vary in overall width, and in the type of bottom bracket that it is machined for.
  • Headset diameter - different frames can have different headset diameters. I think the common ones around at the moment are 1 1/16", 1 1/8", 1 1/4" and een 1 1/2". Some frames have different sizes at the top and bottom.
  • Length of head tube - important if you are swapping the fork over and have trimmed the steerer tube to length on the original bike.
  • Brake mounting type - obviously cantilevers have a different mounting type to calipers and disc brakes. Additionally, there are a number of different disk brake mounts out there (although this is much more standardised these days).
  • Seat tube diameter - these can be different between bikes and will affect whether you can transfer the seat post across.
  • Drop out spacing - this differs between road and mountain bike frames (120mm and 135mm if I recall correctly), but should matter if you are keeping to the same style of bike.
  • Length of cable runs - depending upon how each frame routes the brake and gear cables, you may need new cables and/or outers. I'd suggest replacing these anyway as they are pretty cheap, the replacement will improve your shifting and braking performance and you can get the outer lengths just right for the new frame.
  • Front derailleur mounting and pull direction - does it clamp to the seat tube, or to a braze-on on the seat tube? Is it a top pull or a bottom pull derailleur?
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+1 very nice list. – Gary.Ray Oct 19 '10 at 22:43
Thanks. My commuter is descended from a mountain bike that I destroyed the frame on and ended up buying a second hand frame to rebuild it on. – deemar Oct 20 '10 at 1:28
Typically, 120 mm spacing in the rear is for track frames, 130 mm for road, and 135 mm for mountain. I think 135 mm is becoming more common on road with frames that accommodate disc brakes, larger tires, etc. – Paul H Sep 16 '14 at 0:01

Some of the key considerations off the top of my head in addition to what @deemar has said (must be a faster typist) :

  • Do derailleurs attach with braze-ons or clamps, and are those compatible?
  • If it's a road bike, will there be sufficient clearance between the tire and the frame or brakes? Many touring bikes use tires/rims that are too wide for a frame targeted at racing or more aggressive road riders.
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