There’s much discussion these days on a subject that continues to be a technological gray area for many cyclists – tire size, width in particular. What’s the fastest size? Wide or skinny? A growing number of riders are adding their own anecdotal experience to the discussion. It largely corroborates what the wind tunnel technicians and armchair scientists have been proclaiming for years; wider tires are faster. Here are a few reasons why.
1. Wider tires offer less rolling resistance. They have a shorter contact patch resulting in less hysteretic loss. That’s a fancy way of saying that they roll over bumps better without being slowed by the impact, allowing you to go faster over less than perfect surfaces. I don’t know of any perfect surface other than a wooden velodrome track.
2.Despite their extra size, 25c tires are at least as aerodynamic as a skinnier tire when mounted on the correct rim.
3. Wider tires are more comfortable. We should not forget that comfort is a factor of efficiency.
Current designs are backed up by quantifiable data proving their efficacy, but I do shake my head and chuckle when I think of how it was in the ‘70s and ‘80s. I remember magazine adverts from Avocet - featuring Jobst Brandt, no less – showing Brandt leaning into a fast corner on 19c tires! We mature riders cut our teeth on Specialized Turbo 19c and 20c clinchers. We all thought that narrower was faster; it was intuitive, wasn’t it? Well, perhaps not.
A patent co-owned by Hed and Zipp dating back to the mid 90’s let the cat out of the bag; wider tires mounted on wider rims produced better airflow and were thus more aerodynamic. It should be stated, however, that “wide” rims in ’95 were not the 25-27mm wide examples we see now, but the principle was proved nonetheless. For optimum performance, a wider tire mounted on a wide rim offers less rolling resistance and gives the rider greater feedback, especially when cornering. The small increase in weight is easily mitigated the advantages of speed, comfort and control that the design offers. I see just one problem for some riders seeking this improvement; their frames don’t have enough clearance on the fork, chain stay, or both.
If you'd like to investigate all manner of questions regarding tires, rims and rolling resistance, I recommend two places to begin your self-education. My friend Tom Anhalt runs bikeblather.blogspot.com; he has listed exhaustive data on a large variety of tires. Another place to seek enlightenment is Jan Heine’s blog, Off the Beaten Path. It’s good for lots of stuff.