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  1. #1
    mtbr member
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    MATHS... a little help please..

    Can someone just double check that both my maths and thinking is correct.

    According to the SB calculator - my bike which has a 175mm crank; 2.25 rear tires and a single speed 38T x 16t setup - produces approx 62.15 gear inches.

    Now from a year of single speed riding I have become stronger on the hills going up but lazy coming down but as I have got used to these conditions, I figure that when I get an Alfine, that I would be happy with about two gears either side of this but obviously three either side is a bonus..

    Now the question, if I keep my 38T and get a 20t for the Alfine, it seems as if my gear inches ratio are now from 26.4 to 81.0.

    I was hoping to get a bit closer to a range of around 24 gear inches to around 90 gear inches and my maths say I will need a 42T chainwheel if I stick with the 20t sprocket.. whereas that will get me a high gear of 89 gear inches, I would need a 34T chainrin to get a 23.9 gear inches..

    Does this seem about right and also is a 42T chainwheel excessive, especially when everyone here seems to be talking about chain rings in the range of 30-34... will I really suffer that much given that I have been used to hills with up to a 8% - 12% incline. The current setup has me spinning out at around 18mph.

    Comments, pointers, slaps for being bad at maths - all appreciated..

  2. #2
    Bike Dork
    Reputation: themanmonkey's Avatar
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    Nov 2005
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    SS riding and IG riding are different beasts. Do you like the gear size you're running SS? If so than make sure you imitate it. Even slight changes will be noticeable. Would you prefer to have more high end or low end? This will determine where you want your old SS gear size in the line up. Build it up with what you have and ride it and see if you'd like to change anything. Cogs are cheap and easy to swap, so just build it and stop over thinking the process. Nothing will tell you want you need more than riding the bike.

  3. #3
    mtbr member
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    Thanks for the reply.

    I do not know anything else but the current chain and sprocket setup so over the last yr or so I have just got use to it and just fight the hills when I get to them, though this has created a strain on my right knee that is eased with rest.

    I guess I am trying to get the best range out of my options without buying more stuff that I don't need (crankset wise) but you are right, chainrings and sprockets are realitvely cheap, so I may well just suck it and see..

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