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There is a trend in today’s road and triathlon wheels – they’re getting fat. What’s the reason behind this seemingly unstoppable expansion of girth? Depending on who you ask, there are many benefits from using wider rims. First and foremost, you can use a wider tire at little-to-no aerodynamic penalty. When the rim’s width more closely matches your tire’s width, the airflow around this system tends to be smoother than the lightbulb shape of a wide tire and narrow rim.
But why would you want to use a wider tire? For starters, they reduce your risk of pinch flatting at a given tire pressure. As well, you can use a lower air pressure which absorbs more road shock, and tends to have...
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a reduced Coefficient of Rolling Resistance (Crr). For those not in-the-know, Crr is like a golf score – lower is better (and faster). Lastly, wider tires tend to have better grip on wet or irregular road surfaces. Gone are the days of road racers using 21mm tires at 150 psi (10 bar) for everyday usage. By 2012, we’ve seen nearly a universal adoption of click here and 25mm tires by the Pro Peloton, at pressures ranging from roughly 90 to 115 pounds. For the cobbled Spring Classics races, they often use up-to-28mm tires and even lower pressure.
On to the more subjective benefits of click here some say they improve handling or cornering, due to the resulting casing shape of the tire. There is also a loosely thrown-around idea that wider rims unilaterally reduce rolling resistance – in and of themselves. At this time, I say the jury is out; nobody seems to be able to back it up with real numbers. For example, suppose you have a 23mm tire. You mount this tire on both a 19mm wide and 23mm wide rim. Your tire’s contact patch on the 19mm rim is long and narrow, and with the 23mm rim is short and wide (relatively). The wider rim increases air volume slightly, and makes the tire’s sidewalls more vertical. In theory, the tire casing has to deflect less to make the same size contact patch – easy enough.
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