Advice on Derailleur Size

daffyavfc
daffyavfc Posts: 237
edited September 2010 in Road buying advice
I've got a Spesh Allez Elite http://www.evanscycles.com/products/specialized/allez-elite-2010-road-bike-ec019407

and want to upgrade the rear mech to a 105.

I've found one but not sure if I need the small cage or medium cage as in the following link http://www.chainreactioncycles.com/Models.aspx?ModelID=13595

which one do I need?

thanks

Comments

  • Mad Roadie
    Mad Roadie Posts: 710
    there is a school of thought which says a longer cage is less stress on the chain and therefore more energy efficient - seem to recall an article on longer cages still being used by the Pros on the tour
  • daffyavfc
    daffyavfc Posts: 237
    i've a tiagra 4500 on at the moment and if I knew which one I had on I'd do a straight swap for the same size, any way to tell??
  • father_jack
    father_jack Posts: 3,509
    What's the biggest cog on the cassette?
    Say... That's a nice bike..
    Trax T700 with Lew Racing Pro VT-1 ;-)
  • daffyavfc
    daffyavfc Posts: 237
    50/34 compact and a 12-25 on back
  • topdude
    topdude Posts: 1,557
    Short cage is fine for your chainset and cassette.
    You only need a long cage if using a triple chainset.
    The one pictured on your link is the medium / long version.
    Go for the short "SS" one.

    Why are you changing the mech ? The 105 one is just a few grams lighter and won't make any difference to gear shifting unless your Tiagra one is damaged ?
    He is not the messiah, he is a very naughty boy !!

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