Gear ratio

Barts
Barts Posts: 15
edited June 2014 in Road beginners
Hi my first post and just after a bit of advice, I'm currently riding a cannondale synapse with a triple chain set and would like a compact or standard double ( could some one explain the difference ) on my new bike. I think the ratios on my current bike are 50/39/30 12-26 and would ideally like as close to this as possible so does anyone have any advice as what's close to this on a compact or standard double ? P. S need a low bottom gear for all the hills where I live.

Comments

  • Dave_P1
    Dave_P1 Posts: 565
    It sounds like a compact would be best as they use smaller chainrings compared to a standard.
    Compact 50/34
    Standard 53/39
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  • meagain
    meagain Posts: 2,331
    "50/39/30 12-26" gives a lowest gear inch of approximately 31". A 50/34 with same cassette approx 35". Plenty of gear calculators on line that will let you make a comprehensive comparison e.g. Sheldon Brown.
    d.j.
    "Cancel my subscription to the resurrection."
  • dj58
    dj58 Posts: 2,222
    Firstly is your new bike a 10 or 11 speed?

    Your current low gear is F/30T - R/26T = 30.4 inches

    If you change to a compact 50/34T, with a 12/30T 10sp cassette, your lowest gear will be F/34T - R/30T = 29.9 inches, short cage RD.

    If you change to a compact 50/34T, with a 11/28T 11sp cassette, your lowest gear will be F/34T - R/28T = 32.0 inches, short cage RD.

    If you change to a compact 50/34T, with a 11/32T 11sp cassette, your lowest gear will be F/34T - R/32T = 28.0 inches medium cage RD.
  • ai_1
    ai_1 Posts: 3,060
    As above. Go with a compact NOT a standard if you want to keep a similar small gear for the hills.
    A compact has the same big ring as your current triple with 50 teeth so nothing changes at the top end if you still have a 12 tooth small sprocket. Many broad range cassettes will have an 11 tooth small sprocket which gives you a slightly bigger biggest gear which can be handy if you like decending fast but won't matter much if you don't.
    Since the small ring is changing from 30 to 34 teeth the rear tooth count required to get you a similar gear ratio will go up in the same proportion.

    26x34/30 = 29.47 teeth.

    Obviously you can't get a sprocket with 29.47 teeth. But you can get them with 28 or 30.

    So a compact double (34/50) with a broad range cassette (11-30 or 12-30) will give you a nearly identical range of gearing to your current triple. If you could live with a slightly bigger smallest gear then an 11-28 cassette will be fine too.
  • markhewitt1978
    markhewitt1978 Posts: 7,614
    Barts wrote:
    Hi my first post and just after a bit of advice, I'm currently riding a cannondale synapse with a triple chain set and would like a compact or standard double ( could some one explain the difference )

    Why do you wish to change? Any specific reason? It's quite an expensive thing to change over.

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