cross cassette advice

itboffin
itboffin Posts: 20,072
edited January 2009 in Workshop
I'm looking for a cassette for my home build "cheapish" cross project and have found a couple of Shimano models, I'm running a compact 50/34T up front, can anyone suggest a good rear range ideally without large GI jumps, thanks.

# 14,15,16,17,18,19,20,21,23,25
# 15,16,17,18,19,20,21,22,23,25
# 16,17,18,19,20,21,22,23,25,27
Rule #5 // Harden The Feck Up.
Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
Rule #12 // The correct number of bikes to own is n+1.
Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.

Comments

  • andrewgturnbull
    andrewgturnbull Posts: 3,861
    Hi there.

    12-27

    There are plenty of downhill sections in most cross courses, and you will soon run out of gears with a 14. The gaps don't matter so much - this isn't an alpine climb where changing across a big gap will break you rhythm - your rhythm will be chopping and changing continuously anyway.

    I'd also suggest a closer match between big and small rings - otherwise you'll be changing the front dérailleur continuously, which is ok until it cruds up with mud and throws your chain off. Personally I run 39/49. I find If I need anything smaller than 39x27 then I'm faster getting off and running! With the 39 I'm usually in the small ring 90% of the race.

    Your mileage may vary... of course if you're planning something long and looney like the 3 peaks, then 34x27 is ideal.

    Cheers, Andy
    http://www.andyturnbull.co.uk
    http://www.stirlingtri.co.uk
  • itboffin
    itboffin Posts: 20,072
    Thanks for the advice, I've not done any CX races yet, just my own combination of road/off road riding and I loved it. long before I cycled I used to do lots of cross country running and climbing, CX seems like the perfect winter sport for me.
    Rule #5 // Harden The Feck Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
    Rule #12 // The correct number of bikes to own is n+1.
    Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
  • rickhotrod
    rickhotrod Posts: 181
    48/39 is better than 49/39 because you don't get a big jump when you do the double shuffle and only change one cog on the rear cassette. 48/39 is often specified on new cross bikes maybe for this very reason.

    For example, go from 39/19 to 48/21 (ie. a typical change up from the small to big chainring) and that's a 11.4% jump. Do the same with a 49 chainring and that's a big 13.7% jump!

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