Inner width of most road wheelsets is either 21mm or 23mm. Still under debate, though, is the prevailing exterior width. We can be sure that wheel width from outside is growing in line with inner width. Better knowledge of the aerodynamics of the wheelset helps to improve aerodynamics and stability by means of this increase in exterior width.
Reason 1 For Increased External Width: Improved Aerodynamics
Originally designed like a knife blade, the pneumatic wheelset has a very flat V-form with a narrow outside width rim. This minimizes the frontal windward area, therefore lowering air resistance when the wind strikes at a 0° angle. Still, in the real world, wind usually blows from several directions. To maximize the performance of the wheelset, the rim form is changed; the external width is raised to improve its "sail effect." This allows the wheelset to achieve a negative wind resistance effect and function quite effectively even in cases of up to ±15° of angle of attack. Major brands have so enlarged the external width of their wheelsets to 28mm (with an inner width of 21mm), 30mm (with an inner width of 23mm), or more.
Reason 2 For Increased External Width: To Improve Stability
Bicycle wheel design has always sought to strike a compromise between aerodynamics and stability. Originally designed just for increased aerodynamic performance, high-frame pneumatic wheelsets proved difficult to operate on windy days. Since wind might be erratic, it became essential to increase wheelet stability. Stability is occasionally more crucial than aerodynamics for amateur riders, particularly in conditions of high wind gusts.
Using a wavy rim is one of several techniques to increase stability, but widening the rim externally is more successful. The Roval Rapide CLX is a head start with an "astonishing" 35mm external width in the front and a frame height of 51mm, which is a significant truncation. The duller the rim, the more stable it is; thus, the only way to improve stability is to keep increasing the external width until you get to a very exaggerated 35mm, which of course only needs to be used in the front, where the force on the front wheel affects the steering rudder. Over the CLX50, the (quite sharp) profile offers a 25% increase in crosswind stability.
Reason 3 For Increased External Width: Wide Tire Fitment
Mounted on wheelsets with inner widths of either 21mm or 23mm, 25/26mm and 28mm are the most often utilized tire sizes at current. The tire width in reality could go from 27 to 30 mm. It is advised that the variation between the tire width and the rim width should be within ±5% if greater aerodynamic performance is sought. While some like somewhat smaller tires, others contend that wider tires compared to the rim are ideal. Still, one should also take much thought into the rim's external breadth. The exterior width of a rim with a 21mm inner width is 28mm considering the inner width of the rim and the thickness of the tire lip hook; the external width of a rim with a 23mm inner width is 30mm. The style of the rim will also affect the outward width; some have a more noticeable central bulge for extra width.
28mm External Width Genre
Cyclists often choose the Shimano Dura-Ace wheelset since its internal width of 21mm and external width of 28mm. Shimano designs and analyzes the wheelset using artificial intelligence (AI) and computational fluid dynamics (CFD). The artificial intelligence looks for wheel shapes that a human designer might not have considered in great detail. Fascinatingly, the artificial intelligence searches for "ordinary" wheel forms, although in actuality the Dura-Ace wheelset performs anything but ordinary.
Typical of the Zipp 404/454, hookless rims lack a lip hook, so the sidewalls are straight, and the 23mm inner width is 28mm external width. The actual width of the tires will be rather wider than that of the rims since hookless rims utilize at least 28mm tubeless tires.
With an internal width of 23mm and an external width of just 28.4mm, the new Bora Ultra WTO wheelset produces a tiny rim sidewall with 21 G3 spokes and a lightweight construction. Although you might object to the style of the Campagnolo wheel set, its technology—including the hubs and rims—is indisputable.
30/31mm External Width Genre
Designed to be both aerodynamic and stable, typical of the Bontrager Aeolus RSL, the rims have 23mm in inner width and 31mm in external width. Because the front and rear wheels have the same profile, the tire-rim connection is smoother and aerodynamic drag is lowered, therefore saving power at high speeds.
With a bulbous center rim and an inside width of 21mm but a maximum outward width of 31mm, the Vision Metron 45 SL The Vision Metron 60 SL follows the same design principle, with a maximum external width of 33mm due to the 60mm frame height; the key to the Vision wheelset design is airflow modeling and wind tunnel testing, which is best achieved with a 25–28mm external tire. With a 60mm frame height, the Vision Metron 60 SL employs the same design principle and has a maximum exterior width of 33mm.
Different Designs For Front And Rear Wheels
The unique design of the Roval Rapide CLX emphasizes stability and speed in a high-frame aerodynamic wheelset. By means of tremendous efforts to maximize the design, specialized engineers have produced the best interpretation of the aerodynamic concept. With a 35mm width, a robust rim sidewall, and a hollow form guaranteeing lightweight construction, the front wheel is remarkably exterior.
Because the airflow at the front of the bike is different from the airflow at the rear of the bike, ENVE Ses wheelsets are made differently at the front and rear. All SES wheelsets have frame heights and forms especially intended for the flow field in which they are installed. Whereas the rear frame height is taller, sharper, and more streamlined to maximize power transfer and minimize drag, the front frame height is less than the rear and has a more rounded shape to maximize crosswind stability and control. The external widths are the same, independent of the varying wheel types and frame heights. ENVE SES 3.4 and SES 4.5 have an internal width of 25mm and an external width of 32mm, respectively.
Conclusion
Wheel set external width is not a typical pattern; designs span traditional to radical to pie-in-the-sky. Still, the emphasis is primarily on aerodynamics and stability. Generally speaking, 28mm external width is the beginning point; 30mm external width is the majority; manufacturer boldness determines the range of width you can use.
