Gearing safety question

edited August 2012 in Legacy Products
I have the 24-speed Zoomer and I know you're not supposed to use the big-big or small-small combinations. I usually stay in the middle chainring on the front, but sometimes I need more high gear on straights. I'm just wondering what gears I'm safe to use on the small and big chainrings.

Comments

  • breadstick wrote:
    I have the 24-speed Zoomer and I know you're not supposed to use the big-big or small-small combinations. I usually stay in the middle chainring on the front, but sometimes I need more high gear on straights. I'm just wondering what gears I'm safe to use on the small and big chainrings.


    Well, your highest gear is going to be the largest chain ring up front and the smallest sprocket on the cassette in back.

    Even better is to go to Sheldon Brown Gear Inch calculator located here http://www.sheldonbrown.com/gears/.

    Using stock data from the TT website you get something like this. I know this is hard to read...Looks better at the website.
    Your Gear Combos to avoid are marked as bold
    ChainRing
    30 42 52
    Gear Inches
    Rear Cass
    11 50.9 71.3 88.3

    13 43.1 60.4 74.7

    15 37.4 52.3 64.8

    17 33.0 46.2 57.1

    20 28.0 39.2 48.6

    23 24.4 34.1 42.2

    26 21.6 30.2 37.4

    30 18.7 26.2 32.4

    Gear combos 30/17 or 42/26 give you almost the same GI as 52/30 (biggest-biggest, which requires max stretch on the chain) and 52/20 and 42/15 is equivalent to 30/11 (smallest-smallest, leaving alot of slop in the chain). Also, in both extreme cases, the chain is skewed left/right or right/left to the max ("cross-chaining"). All of which simply means a higher likelihood of a chain, gear, or derailleur malfunction.

    And note that your stock IGH on a Rover is roughly 30/23 in first gear and 52/11 in 8th (probably more like 52/12 or 52/13). Sheldon's puts the GI range of each gear as 23.9/31.2/35.4/40.1/46.2/52.3/59.4/77.4. TT puts it at 24 to 80
  • The danger of using the small-small combination of crank and sprocket, is that there will be too much slack in the chain, and hitting a bump could sometimes throw the chain off one of the sprockets. The danger of using a big-big combination is that if the chain is not sized correctly, this could cause the derailluer to be bent or pulled into the drive wheel damaging both. Again, if this is set up correctly as far as the chain length, this should not be an issue. I tend to use the middle chainwheel in front, and if I need higher gears , switch or the large chainwheel, and for lower gears to the small. Very seldom do I find it necessary to be in a cross-chain situation, but as was already stated, if the trike was set up properly, nothing bad will happen.
  • the chain is skewed left/right or right/left to the max


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