The Triple has fallen out of favor in the past several years. SRAM has been leading the way, first by entering the road market without offering it as an option, and then by introducing the 2x10 to the mountain bike world (more recently the 1x11). The proposed compromise has been the compact, a smaller spidered road crank most frequently featuring a 34/50 ring combination. Combined with a wider range cassette, the compact--with just two rings--produces a gear range that offers the same high and low end. On paper, it makes sense. Right?
In practice, this can work very well on a road bike where speeds are usually above 20mph. This puts the rider in the large chainring and a good position in the cassette. The shifts are consistent, with small percentage changes, and the chainline is relatively straight. The small chainring is then reserved for extremely steep or extended climbs. Now, let's consider a rider who spends more of her or his time between 17mph and 19mph. Assuming an 11-28 cassette and a preferred cadence of 90rpm, you will either find yourself in the 50 tooth ring using the 17, 19, and 21 cogs, or in the 34 tooth ring using the 12, 13, and 14 tooth cogs. In the case of the former, it means 10.5-14.3% jumps (sort of defeats the purpose of cramming more gears in the back) between gears and a poor chainline. In the case of the latter, the percentage changes are a much more desirable 7.1-8.3%, but the chainline will be poor, with the likelihood of the chain rubbing on the inside of the large chainring being somewhere between "high" and "near certainty". Furthermore, SRAM does not offer a trim position that allows for the use of those gears without negatively affecting the lower gears.
So, back to the triple. For many people, it is still a much more desirable option than a double. It offers sufficient options both at the high and low end, with the middle chainring positioned optimally to provide tightly spaced gearing and a good chainline.
I've recently converted my commuter/touring machine to the new 10 speed, Shimano Tiagra triple drivetrain. It is one of a handful of remaining options, and considered a mid-level option. I intend to post an ongoing series documenting my experiences with it in terms of functionality and durability.
- The feel is a bit "softer" than other, higher end Shimano shifters that I have used, including 10 speed Dura Ace and Ultegra. Shifting is still reliable and responsive. It's primarily a sensation at the lever to which one quickly acclimates.
- Each chainring has two trim positions, so nearly all of the gears are accessible. I still try to shift responsibly, but it's nice to be able to quickly eliminate the sound of a rubbing front derailleur.
- Many of the new Shimano road derailleurs are equipped to handle a 30 tooth cog. I am stretching its limits a bit with an XT 11-32 cassette, but everything is working great.
- This version of Tiagra uses the somewhat annoying 92bcd inner chainring that bolts to the middle chainring. This trend began several years ago with Dura Ace, and has since worked its way to Ultegra and Tiagra (Dura Ace is no longer offered in a triple configuration). This limits the inner ring to a 30 tooth, and requires proprietary stuff. Tsk Tsk. I'd prefer a more normal 74bcd with the inner ring attaching directly to the crankarm.