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Bike Question - close ratio cassette 11-21

Hi all - in this months 220 the off season bike training mentions to use a close ratio cassette 11-21 for your indoor turbo session.

Can anyone explain to me what that means exactly and does it mean having to change a piece of equipment on the bike?

I have a specialized allex 08 if it helps!

Thanks in advance!



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    Jason NJason N Posts: 36
    What this refers to is the rear sprockets on your back wheel. A close ratio 10 speed casette would have the following cogs 11-12-13-14-15 etc all the way to 21. (There is often a 2 teeth difference between the bigger cogs) The numbers refer to the amount of teeth on the sprockets. I think the allez probably goes 11-28 on a 9 speed system. This basically means that there is greater difference when shifting from one gear to the next. This makes it more difficult to maintain a constant cadence (leg speed) when shifting up or down.

    It is relatively easy to change the cassette. I`m no bike mechanic but approx £15 gets you the right tools to remove the lock ring and slide off the cogs. (I do this every now and then for a major clean). Although to be honest I reckon your local bike shop would do it FOC if you bought the cassette from them.

    Hope that helps
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    treefrogtreefrog Posts: 1,242
    Close ratio casette is the rear cogs with the smallest having 11 teeth and the largest having 21 teeth - each cog will have 1 more/ less teeth than the previous/next one. 21 teeth is quite "tight" as stanard rear casette has 23 as the biggest cog. The tight ratio is reccommended for the turbo because these is nowhere to hide ire you will always work hard. It is not essential, Generally I nly use 2 cogs for intervals (11 and 23 top and bottom!) and 1 cog for prolonged sessions (14 I think) and always keep it in the big one (53) at the front.

    As regards the turbo I keep it simple for the bulk of the Winter I do 60kM as fast as possible, and then as competition time approaches I do appropriate intervals

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