With electronic shifting, is there an optimal cassette range for both steep climbing and fast descents?

Question: With modern electronic shifting, is there an optimal cassette range (e.g., 10-34 vs. 11-36) that best suits both steep climbing and fast descents? —Scott R.

RBR’S STAN PURDUM REPLIES: Back in the mid-1990s, when I was preparing for a ride across America, I didn’t have the funds to purchase a touring bike, so I decided to reconfigure my old 10-speed Schwinn Sprint so it would be better geared to handle steep climbs on mountain roads. The bike came with a five-cog 11-28 cassette on the back wheel and a 48/34 crankset. I switched the cassette to a six-cog 11-34 and replaced the double crankset with a triple 48/34/24, which, in the bike lingo of that era, made my bike an 18-speed. I also swapped out both derailleurs with new ones able to embrace the range of the new setup.

Though indexed shifting was becoming common on new bikes by then, my Schwinn had been made in the 1980s and still featured friction shifters. Nonetheless, my rejiggered gearing worked quite well on my cross-nation odyssey. I do, however, remember sometimes having to use considerable force on the shift levers to coax the chain onto the biggest cog, and when using the front derailleur, I often had to do a maneuver called “tuning the shift” (also known as “trimming the front derailleur”) — adjusting the front shift lever slightly one way or the other to get the optimal chain alignment between whatever chainring I was using and the selected cog in the back to minimize chain rub (which sometimes could not be altogether eliminated).

None of that prevented me from having a great time on the trip, but I’ve narrated these details to highlight how far today’s shifting systems have come from where they were 30 years ago. Modern cassettes, having 10, 11, 12 and now even 13 cogs make for many more steps when shifting up or down, minimizing big jumps between cogs. The cassettes and chainrings have ramps, profiles, grooves and pins to make shifting smoother and help the chain move between gears rapidly and easily. And indexing has eliminated the need to “tune the shift.” All that’s true even with mechanical shifting.

Electronic shifting is easier yet, however. It enables shifts with only a light touch of a button, which some say reduces hand fatigue and improves speed, precision and consistency. But in terms of your question, electronic systems also self-adjust to prevent chain rub, which can be a problem with mechanical shifting systems when running wide-range cassettes such as the 10-34 and 11-36 you mentioned.

As most of us know from long experience riding bikes with multiple gears, the cog with the largest number of teeth yields the cassette’s lowest gear while the cog with the smallest number of teeth yields the cassette’s highest gear. 

Thus, if the 10-34 and the 11-36 cassettes both had the same number of cogs (let’s say 12, giving them twice as many steps as my old Schwinn setup), and I were considering them in isolation from my crankset, I’d personally favor the 11-36, simply because I live in a hilly area and seldom ride where I don’t need to do at least some climbing. The two extra teeth would give me a lower gear, and since I’m not that into speed, I wouldn’t miss the slightly higher gear the one less tooth would provide.

But of course, the tooth count of the cassette cogs doesn’t operate in isolation from the crankset, which on road bikes today usually has one or two chainrings, where the number of teeth in the rings works together with the cassette to yield a gear ratio for each cog-chainring combination. And overall, the largest chainring paired with the smallest cog produces the bike’s highest gear and the smallest chainring paired with the cassette’s largest cog produces the bike’s lowest gear.

Hence, there is no single optimal cassette range. The best choice depends on the resulting gear ratios when the crankset and the terrain you normally ride are taken into consideration. That also means that there may not be much difference between the two cassettes you mentioned if paired with different cranksets.

For example, a 10-34 cassette when paired with a 48/35 crankset gives you: 

• a high gear ratio of 4.80 (48 teeth on the big ring ÷ 10 teeth on the smallest cog). 
• a low gear ratio of 1.03 (35 teeth on the small ring ÷ 34 teeth on the biggest cog).

Likewise, an 11-36 cassette when paired with a 52/36 crankset gives you:

• a high gear ratio of 4.73 (52 teeth on the big ring ÷ 11 teeth on the smallest cog). 
• a low gear ratio of 1.00 (36 teeth on the small ring ÷ 36 teeth on the biggest cog).

As the numbers show, both setups provide a wide overall gear range with an excellent top speed potential and a good low gear for climbing. And the resulting ratios are similar enough to be almost negligible to you as a rider. (That .07 difference at the high end is likely to matter only if you are racing competitively.)

You can, of course, run the numbers for pairing each of the cassette ranges with other sizes of chainrings before making a purchase decision.

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Stan Purdum has ridden several long-distance bike trips, including an across-America ride recounted in his book Roll Around Heaven All Day, and a trek on U.S. 62, from Niagara Falls, New York, to El Paso, Texas, the subject of his book Playing in Traffic. Stan, a freelance writer and editor, lives in Ohio. See more at www.StanPurdum.com.