Hot!Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2x.

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2018/11/27 00:36:52 (permalink)

Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2x.

http://bit.ly/2x4fastbents

Enjoy!
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    Crit Rider
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/11/27 00:54:31 (permalink)
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    Doc Dan
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/11/27 13:42:55 (permalink)
    Gearing for my terrain (mountainous):
    58/42 x 36/11 for my Ti Aero -- Mostly for training, regardless of terrain.  
    50/34 x 36/11 for my CA2 and CA3.  
     
    The big pizza pan cassette in the back makes all the difference.
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    Crit Rider
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/12/04 17:53:00 (permalink)
    Doc Dan
    Gearing for my terrain (mountainous):
    58/42 x 36/11 for my Ti Aero -- Mostly for training, regardless of terrain.  
    50/34 x 36/11 for my CA2 and CA3.  
     
    The big pizza pan cassette in the back makes all the difference.




    Both 650c? 
    Even if it is, a 42/36 is not small enough for me. 
    Cadence?
    #4
    Doc Dan
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/12/04 21:09:04 (permalink)
    Crit Rider
    Doc Dan
    Gearing for my terrain (mountainous):
    58/42 x 36/11 for my Ti Aero -- Mostly for training, regardless of terrain.  
    50/34 x 36/11 for my CA2 and CA3.  
     
    The big pizza pan cassette in the back makes all the difference.




    Both 650c? 
    Even if it is, a 42/36 is not small enough for me. 
    Cadence?


    The CA2 is a 700.  
     
    The 58 x 11 is only useful on some of the long descents.  https://www.youtube.com/watch?v=VDmNCAU9tvE&t=600s
     
    Given the mountainous terrain and dearth of flat roads my cadence is really variable.  But when I am on flat terrain (WTTC, etc) cadence with the 50 is in the 85 - 90 range.  I typically train with the Ti Aero with the 58t.  But when I'm at an event I'm back to the double up front.  
     
    I'm likely to put a 55/42 up front on the CA2 shortly.
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    Crit Rider
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/12/05 17:47:32 (permalink)
    You are really handicapping your performance by climbing at such low cadence and high force. 
    Its not so good for your joints either. 
    I'd put the 50/34 on the 650c bike and a 46/30 on the 700c one. Thats what I would do for myself.
    That would give me low gears equivalent to what I use now (27x32, 700c). I live at sea level, and my power to weight ratio is likely different from yours. I'd do even more if I were you, but at least this gets you in the right direction. 
     
     
     
     
    post edited by Crit Rider - 2018/12/05 17:48:49
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    Doc Dan
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/12/05 19:26:07 (permalink)
    85-90 is a low cadence!?? Especially with my climbing gear setup?
    post edited by Doc Dan - 2018/12/05 19:28:10
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    Crit Rider
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/12/05 20:29:06 (permalink)
    Dan, I love you. But.....
     
    You are in denial. 
     
    Looking at the speed you get with those gears at 90rpm with 23c tires:
    42x36 650c: 7.6mph
    34x36 700c: 6.6mph
     
    Assuming you are 180# and have an FTP of 150W at the elevations you are training at, you can hold 90rpm at FTP on these grades:
    42x36 650c: 4% (so if its 8% cadence drops to 45rpm, if its 12% cadence drops to 30rpm)
    34x36 700c: 4.7% (so if its 9.4% cadence drops to 45rpm, if its 14.1% cadence drops to 30rpm)
     
    If you are doing a tempo ride that is at about 80% of FTP, or 120W:
    42x36 650c: 3.1% (so if its 6.2% cadence drops to 45rpm, if its 9.3% cadence drops to 22rpm)
    34x36 700c: 3.6% (so if its 7.6% cadence drops to 45rpm, if its 10% cadence drops to 30rpm)
     
    If you are doing an easy ride that is at about 66% of FTP, or 100W:
    42x36 650c: 2.5% (so if its 5% cadence drops to 45rpm, if its 10% cadence drops to 22rpm)
    34x36 700c: 3% (so if its 6% cadence drops to 45rpm, if its 12% cadence drops to 22rpm)
     
    Math does not lie. If your weight is over 180#, or your FTP is under 150W this all gets worse. 
    I do not know about all the climbs around you but I bet there is lots of 5% and steeper. 
    Yarnell is 5-8%.  
     
    Some riders think that because they feel more tension/pain in their legs at low rpm in bigger gears that they are doing the right thing. They are not. 
     
    The fact that you ride 85-90rpm on the flats when you are not gear limited means you know how to pedal like an experienced cyclist. If we measured your FTP as a function of cadence, we would likely see a flattish area between 75-95rpm, outside of that range, it drops. You are less efficient. That is why you need gears to keep your engine in its sweet spot at a power level that is sustainable for the duration and in line with your desired power level for that part of the ride.
     
    With such big gears, you can get into a situation where you can't leave town unless its an FTP day. With enough gears, you can maintain an efficient cadence and dictate your own effort level, rather than having the terrain dictate it. You will also have more choices of where to ride on easier days. 
     
    I have a powertap wheel I can loan you for a while, courtesy of Willie. Interested? 
    #8
    Doc Dan
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/12/06 06:34:43 (permalink)
    Jim ... and I very much respect your experience and expertise. 
     
    I'm gonna study your post and reply later.  (Odd for me not to jabber first and think about what I'm jabbering about later.  Ready. FIRE.  Aim.)
     
    #9
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    Re: Double chainrings finally practical for fast bents: 12s, XD drive, and super-compact 2 2018/12/06 16:37:21 (permalink)
    Yeah, I do that too from time to time. 
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