One of the most hotly debated aspects of road bike technology is the question of whether tubular tires are better than clinchers. In practice, the debate centers on speed and comfort, with tubular aficionados stoutly maintaining that "tubs" score highly on both.
There is one area where tubular tires unquestionably outperform clinchers on the road. Whereas a clincher, once punctured, is highly likely to come off the rim, a flatted tub will stay in place, glued to the rim. This is the primary reason that tubs are still favored for racing by professionals and the best example of the benefit to be had is arguably that provided by Spaniard Abraham Olano. Olano won the 1995 World Road Race Championships in Colombia with a lone break on the last lap from a group that included his team mate Miguel Indurain. Olano punctured with about 2 1⁄2 miles (4 km) remaining. Although his rear wheel could be seen moving around on the tire, he retained enough control to be able to keep riding to the finish for the win.
Braking from high speed puts a lot of heat into a bike wheel rim. On a long descent, this can raise the temperature of the air inside a clincher, increasing its pressure and blowing the tire off the rim. Or, it can soften the cement or glue holding a tubular tire to the rim; in the worst case, the tire may creep around the rim or even roll upside down, leaving the cyclist riding on the base tape. Here, honors are about even.
Many proponents argue that tubs are less likely to suffer a "pinch" flat when rolling over a sharp edge. When this happens, the inner tube gets caught between the rim and the edge of, for example, a hole, usually leaving two and occasionally four telltale holes in a "snakebite" pattern. The rounded edges of the tubular rim are considered to pose less of a risk to the tube than do the raised sides of the clincher design.
Superior ride comfort is also claimed for the tubular when fitted to a classic box-section sprint rim. Again, the culprit is held to be the clincher rim's raised sides, which make the rim deeper and less easily deflected in the radial plane.
The use of rigid deep-section rims of either format renders this argument null. Although the combined weight of a clincher tire, inner tube, and base tape is usually within a few grams of that of a comparable tub, the clincher rim is, inevitably, heavier. This is especially true of older deep-section clincher rims fitted with an aluminum sub-rim to hold the tire.
At the root of the tubular versus clincher debate, however, is the question of rolling resistance. According to their advocates, tubs roll faster. It's a difficult question to resolve, since there are so many variables involved. Tire width, tread depth, carcass quality, inflation pressure, inner tube thickness, whether the inner tube is made of butyl, rubber, or latex, and even the type of base tape fitted to a clincher rim may affect the outcome. It is hard to find directly comparable clincher and tubular tires, where tread depth, pattern and compound, carcass construction, and tire width are the same.
The best evidence suggests that a road clincher rolls slightly faster than a directly comparable tubular and the reason is that the cement, tape, or glue holding the tub to the rim is soft and compressible but not very elastic. It allows the tub to flatten against the rim at the point passing over the ground but slows its return, so some of the energy absorbed as the tire compresses is lost to slow recovery.
Any difference is small and outweighed by the many other considerations. Ultimately, the convenience and ease of repair offered by clinchers makes them the more popular choice. The debate will surely widen to include tubeless tire technology as it improves and becomes more widely accepted.
This is an excerpt of The Bike Deconstructed: A Grand Tour of the Modern Bicycle by Richard Hallett, published by Princeton Architectural Press. Reprinted here with permission of the publisher.