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Crank arm length? Triple Specialized Sirrus??

harpoharpo Posts: 173
edited January 2010 in Workshop
I've got a Specialized Sirrus 2008 elite which the frame broke and I am getting a new frame under warranty. I'm getting the expert frame which is an upgrade on mine. I just got a new set of wheels and cassette (9speed) so along with the new frame I thought I'd get a new better crankset. VAT is about to go up and there are some decent sales on so want to get it now.

I've decided on a Tiagra triple to replace the triple that is on it. I don't want to go up to 105 or to 10 speed as the set up is fine for what I need it and would rather invest any more money elsewhere.

So what crank arm length do I need? 170mm or 175mm? Can anyone with the same or similar Sirrus measure their crank arm and tell me? I can't find this level of detail on the specialized website or on the specific crankarms that I know are on it (Sugino Comp, five arm). My bike is still at bike shop awaiting the new frame!

If noone knows how can I decide between the two lengths that are available?

Cheers

Posts

  • maddog 2maddog 2 Posts: 8,114
    crank length should be based on your inside leg length

    stand in socks against a wall, jam a book into your crotch (gently) and hold it against the wall, step away, measure the distance from the floor to the top of the book.

    Report back and I'll advise.

    CRC have Ultegra triples for £100 at the moment:

    http://www.chainreactioncycles.com/Mode ... elID=11789

    Quite a bit better than Tiagra. Don't worry about 9/10 speed. Any 10spd c/set will be fine.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • harpoharpo Posts: 173
    33inch inside leg. Frame is a large which is about a 57cm virtual seat tube. I'm 6 foot tall. Think the original crank length was 175. I've got a 172.5 crank on my other bike. What do you think?
  • maddog 2maddog 2 Posts: 8,114
    probably 175

    but you could easily run the 172s though if you like to spin, or have dodgy knees/hips/ears. I'm 5'11" and prefer 172s on the roadie.

    Either will be fine in practice.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • harpo wrote:
    33inch inside leg. Frame is a large which is about a 57cm virtual seat tube. I'm 6 foot tall. Think the original crank length was 175. I've got a 172.5 crank on my other bike. What do you think?

    Will you notice the difference between 175mm and 172.5mm? Probably not.
    The 172.5mm will give you a bit more ground clearance when cornering (roundabouts etc.)

    What sort of pens?
  • harpoharpo Posts: 173
    Think I'll just stick with the tiagra and get the 175 mm crank. The ultegra is a good price though.


    mmacavity - Any pens that have had a good chew.
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