Originally Posted by
Barrettscv
Actually, the overlap reduces the need for changing the front chain-rings.
I set up my bikes so that I can use either the large or small chain-ring in the 18 to 23 mph range without cross chaining. I'll think about the next mile or two of route and only use the small chain-ring if I'll be doing more climbing mixed with a few flat sections. I'll also stay on the big chain-ring if I'm mostly descending with a few flat sections coming up.
Overlap is good to have on a drive-train.
I avoid using a compact if I don't need the broad range a compact can provide. A compact reduces the top speed of the small ring and requires the rider to change chain-rings more often than with a standard double. I’ll use a 50 & 39t standard crank-set with an 11-23 ten speed cassette and can use either chain-ring between 15 and 25 mph. I'll also benifit from small, about 7%, changes in cadence from 16 to 33 mph.
You say it's good because you can use both rings for the same speed, I agree but don't you think it's overly complicated for no good reason?
Example:
This is your configuration, 50x39 with 11-23 cassette, MPH @ 90 rpm (170mm arms, 700x23 tyres).
cogs-50----39
11t 32.0 24.9
12t 29.3 22.9
13t 27.1 21.1
14t 25.1 19.6
15t 23.5 18.3
16t 22.0 17.2
17t 20.7 16.1
19t 18.5 14.4
21t 16.8 13.1
23t 15.3 11.9
You like this configuration because you can do 15-25mph on the last 7 cogs in the 50 ring and the first 7 on the 39
That's good, but why do you have 20 gears if 7 are the same? You have 14 different gears in reality.
Ideal scenario:
53x27 crank (insane I know)
33.9 17.3
31.1 15.8
28.7 14.6
26.6 13.6
24.9 12.7
23.3 11.9
21.9 11.2
20.7 10.6
19.6 10.0
17.8 9.0
Absolutely no overlap, 20 unique gears and around 7% average jumps.
I know this sounds crazy but to me that's what 20 speeds should be and I simply don't understand the concept of why overlap is good.