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I've a giant defy 3, compact. My front chain rings are capput and need replacing. Could u easily change to a triple chain set, they are currently 34 and 50. I've already just re placed the chain and cassette when I noticed the front was a mess when looking to change my bottom bracket.

Thanks for advice.

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    Most likely you would need to switch out your shifter as well, on a road bike with brifters that can get expensive.
    – Jamie A
    Commented Oct 7, 2016 at 17:08
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    Also, see bicycles.stackexchange.com/questions/8192/… and bicycles.stackexchange.com/questions/31030/…
    – Jamie A
    Commented Oct 7, 2016 at 17:11
  • Thanks, I thought other parts might need changing. The easier option, I feel then and much preferred would be a new bike. Not out of the realms of possibility!
    – ItsDanny
    Commented Oct 7, 2016 at 18:36
  • Anyway: triples are out. They were at the zenith in the days of 8-9 rear cogs to extend the range of usable gears. Now with 11 the spread of gears is wide enough for a doubles.
    – Carel
    Commented Oct 8, 2016 at 20:19
  • Interesting Carel. A bigger spread at the back would negate for a total bike overhaul. Ta
    – ItsDanny
    Commented Oct 8, 2016 at 20:53

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In order to change the crankset from double to triple, you will have to replace following things besides triple crankset.

  1. Left brifter to triple from double
  2. Front derailleur to triple
  3. Bottom bracket with longer axle
  4. Rear derailleur with larger capacity if it's short cage

The left brifter (aka STI lever) is the most expensive component. If you don't change the front D, shifting on front is bad if lucky, and the cage may hit the chain. If you don't change the bottom bracket, there is a chance that the inner ring may hit the frame. If it clears the frame, the chainline is bad anyway, so you need a longer crank axle.

For deciding what rear derailleur to use, you need to add up the number of teeth differences of cassette's largest to smallest, and the teeth difference of front's outer and inner ring, and the total has to be smaller than the capacity that the rear D can handle.

So, you'd be looking at at least a few hundred USD dollars with just components, and if you don't do the work yourself, you'll need to pay for the work which is probably another 100+ USD.

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