During my bike's tuneup on June 6th 2008 (I note these things down to keep track of them somewhere), not having the bike chain changed for over two years and 10,000 km finally caught up to me and I got a completely new drivetrain, including a new crank set and cog set. Which changes the gear ratios, for the obvious reason.
(For discussion and formulas, see Umbria100Gearing.)
The crank set (front gears) is a 22/32/42 Shimano Alivio, and the cog set (rear gears) is a Shimano 11-34T MegaRange. Sheldon Brown's gear calculator says that the freewheel version of the 11-34 MegaRange is 11-13-15-18-21-24-34, and I am pretty sure that I have a freewheel based rear wheel (the bike is not that expensive, and besides I once saw the bike shop people working quite hard to get the rear gears off the wheel).
So, handy chart time, using the same notation as Umbria100Gearing. The gear ratios (front to rear), with my guess at okay combos bolded:
| front 1 | front 2 | front 3 | |
| rear 1 | 0.65 | 0.94 | 1.24 |
| rear 2 | 0.92 | 1.33 | 1.75 |
| rear 3 | 1.05 | 1.52 | 2.00 |
| rear 4 | 1.22 | 1.78 | 2.33 |
| rear 5 | 1.47 | 2.13 | 2.80 |
| rear 6 | 1.69 | 2.46 | 3.23 |
| rear 7 | 2.00 | 2.91 | 3.82 |
(Good combos are only a guess now, since the gearing changed. I extended it by one on what it used to be out of general principles, plus I wanted the numbers for other things.)
It's clear why Shimano calls this a MegaRange set; the high to low ratio is 5.88, compared to the old gearing's 3.43.
A by hand chart mapping the gears I actually used from the old gearing to the closest gear on the new gearing:
| (old) | (new) |
| 1-2 | 1-4 |
| 1-3 | 2-2 |
| 2-2 | 2-3 (a bit lower) |
| 2-3 | 2-4 (technically 3-2 is closer) |
| 2-4 | 3-3 |
| 2-5 | 2-5 |
| 2-6 | 3-4 (low) |
| 3-4 | 2-6 (high) |
(I almost never used 1-4, choosing to upshift to 2-2 instead.)
There is no even vaguely good mapping after 3-4. I spent most of my time in the middle gear of the front chainring, and in the new gearing this has significantly wider range, going from 1.33 (2-2) to 2.46 (2-6) instead of 1.58 to 2.38; I'll call this a win.
km/h for cadences in various gears, based on a wheel size of 2170 mm:
| rpm: | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 |
| 1-1 | 2.5 | 3.4 | 4.2 | 5.1 | 5.9 | 6.7 | 7.6 | 8.4 | 9.3 | 10.1 |
| 1-2 | 3.6 | 4.8 | 6.0 | 7.2 | 8.4 | 9.5 | 10.7 | 11.9 | 13.1 | 14.3 |
| 1-3 | 4.1 | 5.5 | 6.8 | 8.2 | 9.5 | 10.9 | 12.3 | 13.6 | 15.0 | 16.4 |
| 1-4 | 4.8 | 6.4 | 8.0 | 9.5 | 11.1 | 12.7 | 14.3 | 15.9 | 17.5 | 19.1 |
| 1-5 | 5.7 | 7.6 | 9.5 | 11.5 | 13.4 | 15.3 | 17.2 | 19.1 | 21.0 | 22.9 |
| 2-1 | 3.7 | 4.9 | 6.1 | 7.4 | 8.6 | 9.8 | 11.0 | 12.3 | 13.5 | 14.7 |
| 2-2 | 5.2 | 6.9 | 8.7 | 10.4 | 12.2 | 13.9 | 15.6 | 17.4 | 19.1 | 20.8 |
| 2-3 | 6.0 | 7.9 | 9.9 | 11.9 | 13.9 | 15.9 | 17.9 | 19.8 | 21.8 | 23.8 |
| 2-4 | 6.9 | 9.3 | 11.6 | 13.9 | 16.2 | 18.5 | 20.8 | 23.1 | 25.5 | 27.8 |
| 2-5 | 8.3 | 11.1 | 13.9 | 16.7 | 19.4 | 22.2 | 25.0 | 27.8 | 30.6 | 33.3 |
| 2-6 | 9.6 | 12.8 | 16.0 | 19.2 | 22.4 | 25.6 | 28.8 | 32.0 | 35.3 | 38.5 |
| 2-7 | 11.4 | 15.2 | 18.9 | 22.7 | 26.5 | 30.3 | 34.1 | 37.9 | 41.7 | 45.5 |
| 3-3 | 7.8 | 10.4 | 13.0 | 15.6 | 18.2 | 20.8 | 23.4 | 26.0 | 28.6 | 31.2 |
| 3-4 | 9.1 | 12.2 | 15.2 | 18.2 | 21.3 | 24.3 | 27.3 | 30.4 | 33.4 | 36.5 |
| 3-5 | 10.9 | 14.6 | 18.2 | 21.9 | 25.5 | 29.2 | 32.8 | 36.5 | 40.1 | 43.7 |
| 3-6 | 12.6 | 16.8 | 21.0 | 25.2 | 29.4 | 33.7 | 37.9 | 42.1 | 46.3 | 50.5 |
| 3-7 | 14.9 | 19.9 | 24.9 | 29.8 | 34.8 | 39.8 | 44.7 | 49.7 | 54.7 | 59.7 |
Now, for my own use, the useful bits of the same information, namely the speed bands for each gear and my target speed in the gear:
| (gear) | (80-120) | (90) |
| 1-1: | 6.7 to 10.1 | 7.6 |
| 1-2: | 9.5 to 14.3 | 10.7 |
| 1-3: | 10.9 to 16.4 | 12.3 |
| 1-4: | 12.7 to 19.1 | 14.3 |
| 1-5: | 15.3 to 22.9 | 17.2 |
| 2-1: | 9.8 to 14.7 | 11.0 |
| 2-2: | 13.9 to 20.8 | 15.6 |
| 2-3: | 15.9 to 23.8 | 17.9 |
| 2-4: | 18.5 to 27.8 | 20.8 |
| 2-5: | 22.2 to 33.3 | 25.0 |
| 2-6: | 25.6 to 38.5 | 28.8 |
| 2-7: | 30.3 to 45.5 | 34.1 |
| 3-3: | 20.8 to 31.2 | 23.4 |
| 3-4: | 24.3 to 36.5 | 27.3 |
| 3-5: | 29.2 to 43.7 | 32.8 |
| 3-6: | 33.7 to 50.5 | 37.9 |
| 3-7: | 39.8 to 59.7 | 44.7 |
Some experimentation suggests that 1-1 and probably 1-2 are too low for anything except the most exceptional circumstances, as I wind up tired from frantically spinning at many RPM.