After careful consideration I ordered three replacement chainrings; 24, 26, and 50 teeth. My current crank is a Sugino MTB/Touring triple 28/38/48. The current gears inches chart is below. I color matched the gear numbers that are within 1 gear inch to show the overlapping redundant gears.
| Front | |||
| Rear | 28 | 38 | 48 |
| 11 | 68.7 | 93.3 | 117.8 |
| 12 | 63.0 | 85.5 | 108.0 |
| 14 | 54.0 | 73.3 | 92.6 |
| 16 | 47.3 | 64.1 | 81.0 |
| 18 | 42.0 | 57.0 | 72.0 |
| 21 | 36.0 | 48.9 | 61.7 |
| 24 | 31.5 | 42.8 | 54.0 |
| 28 | 27.0 | 36.6 | 46.3 |
| 32 | 23.6 | 32.1 | 40.5 |
Notice how the middle and high gear don’t overlap much, but the low and middle overlap a lot. There’s even a low gear that only overlaps only a high gear. 21 unique gears. 20 tooth gear difference.
The two low gears are experiments. They are actually French TA Cyclotouriste gears while the 50 is a Sugino. On interesting point on why chainrings over 50/53 are rare is that they get to soft at that size as to bend and warp. You can find rings to 60 if you look. The 50 is for riding the tailwinds. Actually, both gears could be for that. The low for the headwind and the high for the return trip.
| Front | |||
| Rear | 26 | 38 | 50 |
| 11 | 63.8 | 93.3 | 122.7 |
| 12 | 58.5 | 85.5 | 112.5 |
| 14 | 50.1 | 73.3 | 96.4 |
| 16 | 43.9 | 64.1 | 84.4 |
| 18 | 39.0 | 57.0 | 75.0 |
| 21 | 33.4 | 48.9 | 64.3 |
| 24 | 29.2 | 42.8 | 56.3 |
| 28 | 25.1 | 36.6 | 48.2 |
| 32 | 21.9 | 32.1 | 42.2 |
The overlap here is a really consistent stair step pattern. Three gears are across all three chainrings. 20 unique gears. 24 tooth gear difference in high to low.
| Front | |||
| Rear | 24 | 38 | 50 |
| 11 | 58.9 | 93.3 | 122.7 |
| 12 | 54.0 | 85.5 | 112.5 |
| 14 | 46.3 | 73.3 | 96.4 |
| 16 | 40.5 | 64.1 | 84.4 |
| 18 | 36.0 | 57.0 | 75.0 |
| 21 | 30.9 | 48.9 | 64.3 |
| 24 | 27.0 | 42.8 | 56.3 |
| 28 | 23.1 | 36.6 | 48.2 |
| 32 | 20.3 | 32.1 | 42.2 |
Only nearby chainrings overlap. Compare the low set with the installed and it’s really shifted down. Provides 2 gears lower than currently. 22 unique gears in this combination. Question is can the front derailleur handle a (50-24) 26 tooth difference with a 24 low and 50 high.