Help with Cassette combining (13-25 and a 12-27 or 16-27)?
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  1. #1
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    Question Help with Cassette combining (13-25 and a 12-27 or 16-27)?

    After sorting through several posts, and realizing that I would like to have a 27 as my easiest gear (to complement my standard double up front)...

    I was thinking of using my current 13-25 cassette, and either adding the 21-24-27 from the 12-27 cassette to get: 13-14-15-16-17-18-19-21-24-27

    or taking the 21 and then the 23-25-27 from the 16-27 to get: 13-14-15-16-17-19-21-23-25-27

    Is there any reason why one setup would be more preferable or mechanically feasible than the other?

    On paper it seems the 23-25-27 end cog would be better.......but was also thinking on those sharper ascents/switchbacks that having that 3 tooth jump would actually feel better.

    Any and all advice/criticism/etc is welcome.

  2. #2
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    Kinda comes down to the central question of "How much do you use that 18t cog?".

    If you use it a lot, then the first progression you mention will be better. If you don't, then the smaller jumps between climbing gears of the second setup is better.

    It really comes down to individual needs.


    /Interesting associated thread: http://forums.roadbikereview.com/com...es-272670.html
    Last edited by SystemShock; 04-07-2013 at 05:07 PM.
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  3. #3
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    Quote Originally Posted by quickjab27 View Post
    After sorting through several posts, and realizing that I would like to have a 27 as my easiest gear (to complement my standard double up front)...

    I was thinking of using my current 13-25 cassette, and either adding the 21-24-27 from the 12-27 cassette to get: 13-14-15-16-17-18-19-21-24-27

    or taking the 21 and then the 23-25-27 from the 16-27 to get: 13-14-15-16-17-19-21-23-25-27

    Is there any reason why one setup would be more preferable or mechanically feasible than the other?

    On paper it seems the 23-25-27 end cog would be better.......but was also thinking on those sharper ascents/switchbacks that having that 3 tooth jump would actually feel better.

    Any and all advice/criticism/etc is welcome.
    It's hard for me to imagine why losing the 18t would justify closer large cogs. You expect bigger jumps in the shifts when you are in the biggest cogs because your cadence is lower. Just as an example if you were pedalling at a typical climbing cadence of 70 rpm on a steep hill, shifting from the 24 to the 27 would increase your cadence less than 9 rpm. Hardly a big change when climbing the steep stuff. It would be about 6 rpm going from the 25 to the 27.

  4. #4
    feelin' Freddie Mercury
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    Quote Originally Posted by Kerry Irons View Post
    It's hard for me to imagine why losing the 18t would justify closer large cogs. You expect bigger jumps in the shifts when you are in the biggest cogs because your cadence is lower.

    Just as an example if you were pedalling at a typical climbing cadence of 70 rpm on a steep hill, shifting from the 24 to the 27 would increase your cadence less than 9 rpm. Hardly a big change when climbing the steep stuff. It would be about 6 rpm going from the 25 to the 27.
    If it were me, I'd certainly keep the 18t, yep.

    Gears that are in the middle of the cassette do tend to get used a lot. 50/52/53x18 is a great cruising gear for solo riding on the flats for a lot of ppl.

    That said, 2-tooth jumps in the climbing gears sure do feel nice (so long as you're not giving up having a low enough bottom gear to get 'em).
    Monkhouse: I want to go like my Dad did peacefully, in his sleep, not screaming in terror like his passengers.

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  5. #5
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    Some bright and insightful guy posted this in an earlier thread:

    "At that end of the cassette, cadence is usually low and I don't notice the gap that much. It's a ~15% change in gear inches compared to ~11% change between the 17 and 19, where I'm more likely to notice it.

    From an analytical perspective: When climbing, the power required is proportional to speed. When the main resistance is air drag, the power required is proportional to the square of the speed. For example; when climbing, if you maintain the same cadence and shift to a 10% higher gear, you will need 10% more power to maintain that cadence. If you do the same on the flat, you will need ~20% more power to maintain the same cadence.

    For this reason, you want small gaps between gears you will be using on the flats whereas it's less important in climbing gears. For descending, you usually don't do it for long so can tolerate non-ideal cadence for the short time needed. So ideally, you want the small gaps between gears you use on the flats. "
    ... 'cuz that's how I roll.

  6. #6
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    Talking

    Thanks for the input. When looking down at my cassette when riding the flats, the 18t is being frequently so it seems from you all are saying, having a tighter spacing makes more sense

    .....and on the uphill climbs especially when the gradient periodically pitches up, the 3 tooth jump would be more welcome and noticeable (good thing) in contrast to a two tooth jump.

    So the first progression I listed of: 13-14-15-16-17-18-19-21-24-27 is the way I'm going to go.

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