Originally Posted by
masterchief
Thanks, I run a triple on my current commuter, but I want to simplify things and be able to use the 38t ring as the primary chainring. I currently find myself shifting very often between the big and middle ring.
11-34t in the back is noted, it's the reason i'm going with the deore rear derailer, since it will accept the 34t in contrast to the long cage tiagra rear derailer. I'm not all set on gearing yet, I've been thinking 38 was too low as well, but I think i'll try this out and see how it goes.
Going from a triple to a double doesn't really "simplify" anything. You still have a derailer to deal with and all you have is one less chainring and less range.
The lower range brings up the other fly in the ointment. If you are currently shifting between the big and middle ring, it means you are using the gears efficiently. Shifting up and down the gear range isn't a "problem", it's the way you are supposed to use the gears.
Also going to a 38/24 crank leaves giant holes in your shifting pattern as it does for
all doubles.
This comparison of the 38/24 vs a 46/34/24 crank illustrates the problem.
First, the triple has a wider range so that you don't end up coasting as often. With the double, you end up running out of gears at around 25 mph while the wider triple allows you to pedal for about 10mph more. Running out of gears gets frustrating real fast.
But looking at the shift pattern closely, one of the things that jumps out to me on all doubles is that the transition from the outer ring to the inner ring is large and jarring. Let's say that you are cruising in the 38/19 combination at about 15mph and you feel you need to shift to the inner ring. You'll need to increase your cadence from 90rpm to greater than 120rpm and you won't be close to the cadence you need to maintain the speed. It feels kind of like you've dropped a chain.
On the triple, the step is smaller (although still a bit too large). You only need to increase cadence to 120rpm to maintain the same speed. If you play with the calculator a bit, you can see that a 46/38/24 offers a nice shifting pattern where a change from the outer ring to the middle ring is smaller more natural jump. If you use a 40 tooth middle ring (hard to find), the change from outer to inner is about the same as a change from one cassette cog to the next. I use this on a road triple for my commuter bike and find it a great shifting pattern. A 44/38/24 would be similar but with a bit lower gearing.