21mm or 23mm: Which is the main inner width of 700c carbon rims?

 The times are flying. In our memory, the mainstream inner width of carbon wheel sets is still at 19mm, and the tires are still 23mm. We have always believed that the narrower the road tires, the faster the tire pressure, but the fact is that wide tire pressure not only provides comfort but also lowers rolling resistance. With the popularization of tubeless tires for road cycling, low tire pressure has completely changed the world of road bike.The most obvious thing is that road bicycles have become more versatile,pneumatic road bike can also ride rocky roads, and endurance road bicycles can be lightweight and pneumatic.
The influence of image wheel rim and tire width on aerodynamics
There is a trend of mainstream road tires transitioning from 25mm to 28mm. In order to accommodate wider tires, the inner width of road wheel sets has officially entered the 2-character range (2x millimeters). 21mm has become a new threshold (buying wheel sets with inner widths less than 21mm is not appropriate now), while 23mm inner width has a later upward trend, in addition to 22mm and 25mm inner widths. It can be said that the current road wheelset is divided into two genres: 21mm and 23mm inner width. How should we choose? Which is the mainstream wheel set inner width?
From the perspective of international top tier wheelset, Valve, Vision, and Shimano are in the 21mm inner width genre, while Pontrager, Enve, and Zipp are in the 23mm inner width genre (with 25mm inner width in the no hook wheel group), and Campagnolo is transitioning from 21mm to 23mm. Basically, the inner widths of 21mm and 23mm each account for half.
More emphasis on aerodynamics (stability) is the main reason for this change, from initially only focusing on coil weight and carbon spokes, to now pursuing more comprehensive performance. But overall, the width within 21mm is still much wider than 23mm.
From 19mm to 21mm: A magical change
If you want to enter the era of tubeless tires, then a 21mm inner width is the starting point. Not only does a larger inner width allow the tire to expand wider, resulting in lower tire pressure (which is the biggest advantage of vacuum tires). More importantly, it is important to avoid tires resembling light bulbs and provide better lateral support, which can prevent tire lateral twisting when using lower tire pressures. Initially, when using a 19mm inner wide carbon rim with 25/26mm tires, when the tire pressure was below 75psi and fully rocking the car, the tire would feel twisted. However, when using a 21mm inner wide carbon bike rim, the tire pressure was as low as 60psi and there was no such twisting sensation. This is the magical change that occurred from 19mm to 21mm.

From 21mm to 23mm: The tires have become wider
The increase from 21mm to 23mm is also 2mm, but the change is not as miraculous as from 19mm to 21mm. From the perspective of tire lateral support, the difference between 21mm and 23mm is not significant, but the inner width of 23mm can allow the tire to expand by 1-2mm more, which means that a lower tire pressure of 5-10psi can be used to achieve greater comfort without losing rolling resistance. For example, for the same 25c tire, the actual width of a wide wheel set installed within 21mm is 28mm, and the actual width of a wide wheel set installed within 23mm is 29.4mm, which is 1.4mm wider. This is equivalent to obtaining a wider tire without increasing weight.
The inner width of 23mm in the picture can make the tire expand wider
For players who do not want to use vacuum tires, Bola recommends a 23mm inner wide wheel set. Because the inner tube takes up a certain volume, the air capacity of the open tire and inner tube is smaller than that of the vacuum tire. Therefore, for the same driver's weight and tire width, a tire pressure of 5-10psi higher needs to be used. Compared to 21mm, 700c 23mm wide carbon bike rim can make up for this deficiency in most cases (the tires expand wider), but of course, ultra-low tire pressure cannot be used like vacuum tires because it can cause snake bites and tire blowouts.
23mm inner width is more suitable for 28mm tires
The maximum tire pressure of the non hook wheel group in the picture is 72.5psi, and a lower tire pressure can be used with a width of 23mm
Not long ago, only endurance road vehicles used 28mm tires, but now 28mm has become a race road vehicle tire, which is more comfortable compared to 25/26mm tires, and sometimes comfort means speed. Compared to 21mm, a 23mm inner width is more suitable for 28mm tires. Generally, a 23mm inner width wheel set has an outer width of 30mm or more, which is more aerodynamic when paired with a 28mm tire.
To summarize
Picture: The combination of 21mm wide wheels and 25/26mm vacuum tires complement each other perfectly
Overall, the width of the 21mm and 23mm wheel groups is evenly matched. If using vacuum tires, both 21mm with hook and 23mm without hook are acceptable, but the actual difference is not significant. If it is an open tire, a 23mm inner width can be used with a lower tire pressure than a 21mm inner width vacuum tire, resulting in better comfort performance. If you are a heavy weight driver and want to use tires of 28mm or more, a 23mm inner width is more advantageous.