This is a purely personal opinion, so I would appreciate it if you read it lightly.
Major premise: For those who ride at speeds of 50km/h or above
It is true that double chainrings are advantageous for those going 50 or faster.
Introduction
In road cycling, it is a proven fact that double chainrings with closely-spaced gear ratios are advantageous for maintaining speed on flat terrain, so double chainrings utilizing SRAM's 12-speed sprockets are an excellent choice. However, many people do not know that single chainrings are also not inferior in terms of gear ratios. However, the single chainring I mention here is a somewhat smaller 36t single chainring.
Main discussion
Based on the standards of general amateur riders aiming for maximum speeds of 50km/h or less, I will compare the speeds according to gear ratios in two SRAM 12-speed setups in the most frequently ridden speed range of 25km/h to 40km/h (based on 100 cadence). For the double chainring, the sprocket was set to the 10-28t sprocket known to be the most closely-spaced.
1. Single chainring (36t) combination
Sprocket: 10-33t (10-11-12-13-14-15-17-19-21-24-28-33)
Speed variation in 25~40km/h range: 38.3(12t) ➔ 35.3(13t) ➔ 32.8(14t) ➔ 30.6(15t) ➔ 27.0(17t) ➔ 24.2(19t) (km/h)
2. Double chainring (46/33t) combination
Sprocket: 10-28t (10-11-12-13-14-15-16-17-19-21-24-28)
When using outer (46t): 39.1(15t) ➔ 36.7(16t) ➔ 34.5(17t) ➔ 30.9(19t) ➔ 27.9(21t) ➔ 24.5(24t) (km/h)
When using inner (33t): 38.3(11t) ➔ 35.1(12t) ➔ 32.4(13t) ➔ 30.1(14t) ➔ 28.1(15t) ➔ 26.3(16t) ➔ 24.8(17t) (km/h)
Looking at the data, it is true that the double chainring using a 10-28t sprocket includes a 16t cog with a very closely-spaced gear ratio. However, if you look closely at the single chainring (36t + 10-33t) data, you can discover an unexpected fact.
The SRAM 10-33t sprocket is closely configured in 1t increments from 10t to 15t, and due to the nature of the 36t single chainring compared to the outer 46t chainring, smaller t-number cogs are used. Therefore, when cruising at constant speed on flat terrain, the speed variation of the single chainring combination in the most frequently used 30km/h to 38km/h range is 38.3(12t) ➔ 35.3(13t) ➔ 32.8(14t) ➔ 30.6(15t), with a gear ratio difference between gears of only about 2.2~3km/h.
On the other hand, let's look at when riding with the 46t outer on a double chainring. Since the front chainring (46t) itself is larger than the single (36t), even if the sprocket cogs change by the same 1t, the range of movement in gear ratio becomes larger. In fact, when using the 46t outer, the speed changes from 39.1 ➔ 36.7 ➔ 34.5 ➔ 30.9, and despite using the supposedly closely-spaced 10-28t sprocket, due to the chainring size, the speed difference between gears actually becomes larger than the single 36t setting.
The 33t inner chainring certainly provides a closer gear ratio in that range. However, using the 33t inner chainring as the main option has the problem of chain cross-chaining, and if you use up the 33t inner chainring in this range, the 46t chainring's reason for existence is greatly reduced since it is used for higher speeds.
Ultimately, to fully utilize the closely-spaced nature of a double chainring, you need to frequently make additional shifts by raising the front chainring while simultaneously lowering the rear sprocket as speed changes. If you keep alternating front and rear derailleurs to get an extremely close gear ratio, the pedaling flow is interrupted during the shifting process and power is lost, which actually reduces overall riding efficiency.
Moreover, with this single chainring combination, you can secure a respectable gear ratio of approximately 1.09 with the combination of a 36t chainring and 33t sprocket on climbs, providing more comfortable uphill gearing than the double chainring combination mentioned above.
Conclusion
SRAM's 12-speed 10-28t double chainring is an excellent combination boasting closely-spaced gear ratios. However, a single chainring combining 36t and 10-33t also demonstrates closeness in gear ratios in the most needed speed range comparable to double chainrings.
For general amateur riders not exceeding maximum speeds of 50km/h, a single chainring can be an equally attractive and rational choice, offering more intuitive and clean riding without shifting problems, weight savings of at least 300g, and cost reduction.
