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compact or double

kurtkurt Posts: 18
I'v been advised to swap my 53/39 for a compact on my triathlon bike - I have 12-25 on the back

is this a good idea??


  • ZacniciZacnici Posts: 1,385
    Oh goody - not had this topic for a while - time to dust off the old almanac.

    Well Kurt, entirely dependent on your physical setup, training and anticipated events. I am making a presumtion that a compact was recommended as you were not using the outer ring i.e the 53 fully as was the case with me. I swapped from a 53/42 to a 50/39 and also mix and match with a 36 and 34 as the whim takes me.

    The best solution is where you csn swap out the 'standard' with a 'compact' chainset and vice versa using the same BB. It took me about 30mins to swap or therabouts. The only fiddly bit was adjusting the front derailleur height as it was a collar fixing and changing the chain length, look here: http://sheldonbrown.com/chains.html#length

    This may be of use to you and explains why I went down the compact route:
  • AvoneerAvoneer Posts: 174
    Good idea if you find yourself peddaling too fast when you're on the big front and little back rings, or don't have really powerful legs.

  • diddsdidds Posts: 655
    what was the reason given for changing your setup.

    THIS is the most crucial aspect.

  • kurtkurt Posts: 18
    Firstly - thanks for the replies

    My usual training ride on the tri-bike is always completed on the 53 - I very really use the 34 (my training ride in the Outlaw route so undulating and flat). The only "race" conditions I have used the tri-bike under was the GNBR (taken on the club riders and getting abused!) which I completed with an average cadence of 72/mph of 19.2 - the GNBR is mostly the Outlaw route. My road and cross bikes have compacts. But even with the compacts my "natural" cadence does seem to be 70.
    The 12-25 is a recent change from 11-23 - I felt a little under geared with the 11-23.
    My slight worry is when fatigue starts to set in towards the end of the bike leg the 53 feels a bit cumbersome plus staying aero even when going over undulations, would it be less of a strain with a compact??
  • ZacniciZacnici Posts: 1,385
    I would normally point you in the direction of Sheldon Browns calculator whcih is a fascinating site:

    Unfortunately it doesn't have a calculator @ 70 cadence but it does for 60 and 80; so pulling off the figures for:
    53/11 @ 60 and 80 we have theoretical speeds of 37.4km/hr and 49.8km/hr.
    53/12 @ 60 and 80 we have theoretical speeds of 34.3km/hr and 45.7km/hr

    50/11 @ 60 and 80 we have theoretical speeds of 35.3km/hr and 47.0km/hr.
    50/12 @ 60 and 80 we have theoretical speeds of 32.3km/hr and 43.1km/hr

    It seems simple to conclude that the 53/11 has it, but ... that is not the whole story. You are obviously concerned about the latter stages and maintaining the workload with the 53. Yes a 50 would help in some instance but I wonder if it is the inner ring you may want to tweak?

    You mentioned 34, that seems to be at odds with the 53. Is it a 39?

    My thoughts are that if you are happy with the 53 for a susbtantial part of the course and rarely using the inner ring might I suggest using a 53/42, with the 12/25 that would give you greater overlap and dare say would reduce tiredness as presently you are using the 53 almost exclusively. With the 53/42 there will be more overlap and allow you keep 'in the zone'. As a tradeoff you would lose a couple of kph off your theretical top speed. If that seems OK you may want to revert back to the 11/23 for compariuson.

    If pushed for time and not able to 'field trial' the permutations try playing with the gear calculator to see what I mean.
  • AvoneerAvoneer Posts: 174
    That's a sh*t hot reply.

    Well done that man.

  • kurtkurt Posts: 18
    Thanks Z! Very good reply and understandable!!

    Maybe I'm getting pre-race nerves or the windy conditions (always seems to be head-on!)of late or the training have been taking their toll on me??
    The inner chain ring is a 39 and not 34. So I'm going to give my current set-up a go at the outlaw and see what happens but the 42 inner does sound interesting....

    Thanks again for your time, much appreciated!
  • ZacniciZacnici Posts: 1,385
    Well thanks chaps, kind words, most appreciated.

    Kurt may see you at the Outlaw, but from the sound of things only when you lap me

    When the bib mumbers are released must do a post for all to declare.

    Good luck and thanks once again.
  • kurtkurt Posts: 18
    I suppose its better late than never...

    How did you go at the Outlaw??
  • ZacniciZacnici Posts: 1,385
    Oh man - completely screwed my hydration.
    Lost my electrolyte tabs (big lesson - fundemental error split them so you have built in redundancy) and got a cramp about gosh 3hrs I think into the bike in right calf. Stopped a couple of times to rub it away and even pedalled on left leg only for about 30 mins, an hour later one of the gals from Leicester Tri gave me a rub down at their feed station. I was almost in tears watching all these people I had steadily worked my way through over 4 hours zipp on past but positive side it enabled me to complete the bike and even pulled a few places back. On th ereturn leg still fragile and at one point my vision started to blur which was a bit unsettleing with cars whizzing past.

    I had done several recces of the bike route and planned on a 6:00 - 6:15 bike time taking it nice and steady with a max of 6:45 if the weather was lousy/had to do any stops etc. I eventually got in at 7:09 but still in the game.

    Kicked off on the run started OK, no cramp, no tightness, on target for my run time but it was clear after 30mins that I was still not right, I ate crisps and banana to try and get the electrolytes sorted but no go. So just settled into survival mode to finish.

    Coming diwn the chute was amazing; helds held out and High 5'd it all the way down to those words 'John Williamson you are an Outlaw'

    Primary goal was to finish, job done, secondary under 15, 14:47 job done, tertiary goal sub 13 - next year.

    As if to remonstrate me for my stupidity the official photo actually shows the electroltes and myself parting company - talk about rubbing salt in!
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