Downtube shifters have advantages over other shifter styles, including Shimano’s STI. Admittedly, I am old-school and downtube shifters fit right into that characterization. Nonetheless, Shimano continues to offer downtube shifters for both 9 and 10 speed (cassette) bicycles. They provide state of the art, indexed shifting, as well as friction shifting for the real old-school folks.
The case for downtube shifters starts with fatigue relief. By training yourself to shift ‘up’ in gear with your right hand and ‘down’ with your left hand, both hands get reasonably equal time off the bars, allowing blood to flow back into them. This is a counter-intuitive argument, since the advantage of STI is to keep your hands on the bars, increasing stability. Certainly, this is a sensible argument, but I am much more aware of hand fatigue than I am with accidents due to downtube gear shifts.
My first state of the art bicycle in recent history was a 2005 Trek 520 touring frame. Touring frames are traditionally sold with barcons (bar end shifters). I rode several thousand miles with barcons, all the time accepting left hand fatigue as toll for riding for hours in a day. Then one very lucky afternoon, I was riding out of my neighborhood and stopped when I noticed a bicycle for sale at a garage sale. It was an ’86 Trek Elance 400 in near perfect condition and priced nicely at $40. Two things happened that day. First, a love affair for mid-80 Trek bicycles was born. Second, I began enjoying mile after mile on a six speed, downtube shift bicycle. I quickly noticed the absence of hand fatigue, which eventually prompted me to convert the 520 to downtube shifters. As I had hoped, moving my hands off the bars for shifting is just what I needed to eliminate hand fatigue for rides up to about 50 miles, and helped to reduce it for longer rides.
Other advantages of downtube shifters include reduced weight, and higher accuracy. I don’t race, so the extra 125~200 gram cost for STI does not get me excited, but I mention it for the competitive racers. It is documented that Lance Armstrong uses a downtube shifter for the hill climbing stages of the Tour de France. This saves and redistributes weight off the handlebars.
Downtube shifters provide more accurate shifts since the cables are shorter, reducing stretch. Also, they require only minimum housing, reducing cable friction. Reliability is increased for two reasons. Since the front chainring shifter is friction-based, the chance of slapping (dropping) the chain is reduced. The second reason speaks to the simplicity of downtube shifters. Since their design is much less complex as compared to STI, their failure rate is reduced.
The last argument for downtube shifters is price. Shimano Ultegra STI shifters cost approximately $500, while the Ultegra downtube shifters garner 1/5 the price.
While I appreciate the advantages of downtube shifters, I have recently decided to convert my tandem to STI. Keeping that rig in a straight line is higher priority for me than hand fatigue or cost. I believe most stokers would agree.