On 08/22/2013 06:41 PM, William wrote:
40 x 26 is plenty. Run the numbers with any normal cassette. Compact
double is all most people need. You need a triple carrying or hauling
lots of weight, and maybe need it for serious off road riding. But if
you lay out the numbers, an intelligently selected compact double
gives you everything you need and nothing you don't need.
On Thursday, August 22, 2013 3:32:06 PM UTC-7, Michael wrote:
Would it take a triple crank?
I am just thinking that a 40t x 26t. double crank seems like it
needs a middle ring.
40 53.8 % 26
11 98.2
63.8
18.2 %
13 83.1
54.0
15.4 %
15 72.0
46.8
13.3 %
17 63.5
41.3
11.8 %
19 56.8
36.9
10.5 %
21 51.4
33.4
9.5 %
23 47.0
30.5
8.7 %
25 43.2
28.1
12.0 %
28 38.6
25.1
14.3 %
32 33.8
21.9
OK, here's the 40/26 with an 11-32 10 speed cassette. The range is
just fine: 22" low, 98" high. Can't be bettered. But what happens
inside the range?
In the terrain I ride most, I'd stay on the big ring all the way down
the block until I was forced to shift -- and I would be forced to shift
every time it got steep, because 39" is not enough for me on 9-10%
grades. What happens then? Let's say I go from the 40 to the 28T chain
ring. Now I'm in a 25" gear, and that's so low I'm going to think I
dropped the chain. I'll be looking for a gear lower than 38 inches,
something in the mid to low 30s. Whatcha got?
Upshift 4 and you get a 37", just about the same as where I was. Upshift
3 in back and I get a 33. I can live with a 33 -- but can I live with
having to upshift 3 each time I cross over? I don't think so. That 54%
difference in the chain rings means you can't ever just shift the front
and keep on truckin', the jump is just too much. Unlike, for example,
the 10-tooth difference between my 36 and 46T chain rings. There, if
I'm feeling lazy or the terrain is steepening fast, I just shift the
front and go from a 52" gear to a 40.5 -- something you can live with --
or I can upshift 1 and get a 46, next in sequence.
What about up at the top end? 98" is a nice top end, in fact it's what
I have now. But where's that 88.7" I have? Missing. Next gear is 2
teeth down, an 83. That's a hole I'd trip on often.
For reference, here's my gearing with a 9 speed 13-30 cassette:
46 36 24
95.5 74.8 49.8
88.7 69.4 46.3
82.8 64.8 43.2
73.1 57.2 38.1
65.4 51.2 34.1
59.1 46.3 30.9
51.8 40.5 27.0
46.0 36.0 24.0
41.4 32.4 21.6
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