I have a gearing problem on the Vendetta. I am running 160 cranks on 39/53 chain rings coupled to a 12-25 cassette, which has 12, 13, 14, 15, 16, 17, 19, 21, 23 and 25. I run a cadence of about 101, which is the same foot speed as running a cadence of 92 on 175 cranks and which is somewhat standard.

At a cadence of 101 and in the 53 ring, the 17t sproket yields 39.5 kph while the 19t yields 35.4. This means if I want to go from the 19t down to the 17t I have to make about (39.4/35.4) squared more force, (24%) or about (39.4/35.4) cubed more power (38%). If the most power I can make has me sitting at 37 or 38 kph then the cadence is either too fast or too slow. I need an intermediary gear.

The lowest gear is a gain ratio of 3.25 which I do need. I don't care for running full tilt down hills, it doesn't help the average speed, so the highest gain ratio of 9.19 is more than enough - its 56.0 kph at 101 cadence.

Better would be compact double on 160s with 34/50 and a 12-23 cassette (which has 12, 13, 14, 15, 16, 17, 18, 19, 21 and 23), yielding a gain ratio low of 3.08 which would be welcome to a high of 8.67 = 52.8 kph at a 101 cadence. Most importantly it would give very close ratios from 33 kph to 45 kph, right where its needed, spacings of 5.5%, 5.9%, 6.3%, 6.7% and 7.1%. I think I'd more easily find the right gear. Comfort is critical for sustaining higher performance. If there is always a gear available that gives a comfortable cadence, that is the most efficienct for you to sustain your highest level, this is a good thing. Some athletes might be looking to position the spread of ratios a little higher than me, so for them, the jump to a 53t/39 would make perfect sense. For the rest of us the proposed gearing is possibly ideal for a time trial or go-your-hardest bike.

Hmm, by the way, the Dura-Ace range includes an 11-21 cassette!

The presence of something as seemingly inconsequential as an 18t sproket instead of a 17 or 19 turns out to be quite critical.

Current configuration, note the jump from 35 to 39 in the second blue shaded area.

Proposed configuration, note the smooth steps through that second blue shaded area.