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Another gearing question

carls10carls10
in General Training Discussions

 I realize that there are a few others threads about this but in the interest of not hijacking I will start a new one.

I am getting into IM training for IMLP and am considering getting a new cassette.  My current set up is 50/34 with 12-27 cassette.  The crank length is 170cm.  My current indoor FTP is 144W and I'm 5'4" racing at 105-110#.  I am not a strong cyclist and I raced Placid in 2010 and never was able to spin up the hills, I was working too hard just to keep the bike upright.  Im considering a 12-29 as I believe this will give me more easier gears.  I'm not really concerned about losing top gears.  

Thoughts?  Waste of money?  I have read the great Wiki posts and think I am interpreting all of this correctly but I am still learning so please pint me in the right direction if I am way off base.

Comments

  • GMAN 19030GMAN 19030

    A 12-29 might make for some funky RD adjusting. Maybe or maybe not.



    You also might think about a shorter crank as 170's are kind of long for someone of your height. Shorter cranks generally yield a higher cadence.

  • Cary BlancoCary Blanco
    Carly - are you on 650 wheels or 700s?
  • Cary BlancoCary Blanco
    Fwiw - with an outdoor FTP of 150 @ 110 lbs you're looking at a solid 3 watts/kg I'm assuming that the first number will go up a bit and the 2nd will go down a little by race day. I think with your current gearing you should be somewhat comfortable on the hills at LP. That being said, almost all uf us can always use an "easier gear". I'd say try a race rehearsal at LP camp with the current setup and if you're still looking to spin more then try the cassette more teeth afterwards.
  • Michele CellaiMichele Cellai
    Carly-
    I switched from 172 to 165 crank arm length about 1 month ago. I am using a 12-28 for IMSG, same as I used for IMWI.

    If you can spring the money, go for the shorter crank length. It changed my FTP ( I dropped at least 10 watts between tests done on different crank lengths), but I am definitely spinning a higher cadence and in my RR, it felt like I was flying when my watts were actually too low.
  • Al TruscottAl Truscott

    Since I am in the process of going from 172.5 to 167.5 cranks, I have been doing some research on the implications. Several possible reasons are noted for the benefit, specificaly to TT riding. As Michelle notes, it enables a faster cadence more easily. But probably more important is the change in position which results. With the cranks shorter, the saddle needs to be raised to allow the same angle at the knee when foot is at the bottom of the pedal stroke. There is a consequent increase in the hip angle at the top of the stroke. With appropriate adjustment to fore-aft position and tilt of the saddle, these alterations usually allow a "flatter" (lower) posture over the top tube, affording an aero advantage compared to the longer cranks.

    At any rate, that's the theory, and we'll see once I make the change and get re-fitted.

  • Coach RichCoach Rich

    I went to 165mm cranks last season for the same reasons that Al described. However, it had been almost 3yrs since I had ridden my tri bike so I wasn't able to feel many of the differences that Michele described.

    Since you're going to the LP camp, I suggest you maybe find a cheap/loner cassette and try it out? Takes just a couple minutes to swap cassettes.

  • carls10carls10
    @ Cary I am riding 700 wheels
    @ Rich that's a good suggestion, might see what I can hook up with the LBS and try it on some hilly terrain locally
    If I do go with the shorter cranks how difficult of a swap is that? Likely I can do it on my own?
  • mgraffeomgraffeo
    Carly, a swap out is very doable. The only thing that requires its own tool is if you have to change a bottom bracket, and even that is pretty straightforward. Helps to have a book like the park tool blue book, but the Shimano instructions that come with cranks are pretty good.

    I would second the shorter cranks. Not sure a 12-29 is going to get you what you're looking for, just because there's not a huge difference between a 27 and a 29. It will help a little, but a few rpm at a given speed. Another option would be to look at getting a SRAM Apex rear derailleur. They can accommodate a much bigger rear cassette, supposedly giving you more range than a triple would. Of course, you could also look into a triple...
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