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25 vs. 23: Is Wider Really Faster?

From the Pro’s Perspective: Michael Barry

For ages, cyclists assumed that narrower tires were better. Time trial bikes were fitted with 19mm tires, as we thought that they would slice through the air better than a 23mm. The rider cautiously rode to the start line, avoiding any bumps or road grit, for the fear that the tires might be punctured. We’d pump them rock hard, as we thought that harder tires created less rolling resistance. We also thought that narrower and harder tires were more aerodynamic, rolled faster, and were more responsive. Well, they aren’t.

In the last five years, all of our old theories have been proven wrong. Wider tires and tubulars are now the norm on almost all professional team bikes, including time trial bikes. Not only do wider tires roll faster, but they’re also more resilient, comfortable, and aerodynamic when paired with the right rim.

At the start of each new year, professional teams provide their riders with a supply of clincher tires and tubes to get them through a season of training. During my 14-year professional racing career we went from riding on 21- or 23-millimeter tires to 25s. The wider tires allowed us to venture off of the smooth tarmac and onto bumpier gravel roads. I rode up into the mountains, discovering new areas and climbs. I would arrive home without neck and back pain.

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On the cobbles, which are the ultimate test for a wheel and tire, professional teams have used wider tires at a low pressure for decades. In Paris-Roubaix or the Tour of Flanders, finding the right tire and pressure is crucial to performance, as a good tire will make the difference between winning and losing. Mechanics, directeurs, and riders talk about and test the tires and pressures in the hope of finding the magical combination. They’ll keep notes (that won’t be shared with rivals) on what worked and what didn’t for the following season’s races.

The latest and fastest aerodynamic wheels have wider rims that are shaped more like a “U” than a “V.” A wider tire creates a curved teardrop form. Not only is the air turbulence around the U-shaped rim less, but the bike is also easier to handle in crosswinds, given that the wind curls around the surface. Older deep-V sectioned rims were almost always a struggle in a crosswind. With them, I’ve even been blown off of the road. Friends of mine have been carried into the air and come crashing down. That doesn’t happen with wider rims and tires.

Whether riding a time trial or tearing down a gravel mountain road, there is no reason not to ride on wider tires. Without them, you’ll be at a distinct disadvantage.

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The Nerd’s Perspective: Jeff Stewart

It’s been said that tires win races, and after you win races on 23mm tires, I understand that you’ll probably be reluctant to change a single thing. It’s worth noting, however, that there’s a distinct difference between winning at the Giro and winning at your local crit. And if you’re like most of us, your tire selection for said crit race was most likely influenced by what was won on at the Giro. This isn’t to say that we’re all disciples of pro worship, but it’s inevitable that there’s going to be some bleed over on the page. However, this isn’t a complete negative. After all, there’s a big difference between wearing an Astana team kit and riding Astana’s team tires.

At the end of the day, the facts are the facts; a 25mm tire experiences less rolling resistance than a 23mm tire at the same air pressure. Without cutting too deep into the science of the matter, it all comes down to the contact patch. To paraphrase an insightful discussion on the matter between Jared Gruber and Wolf Vormwalde for Peloton, at equal pressure, a 25mm tire has a “wider but shorter” contact patch, while a 23mm tire has a “slimmer but longer” contact patch. The increase in the required deflection of the latter example equates to spending more energy “into deforming the material.” This is pretty well demonstrated by this chart from Continental:

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Photo Courtesy of Continental 

As you can see, less energy will be wasted on material deformation with a 25mm tire at equal pressure. And in more elementary terms, this means that you’ll go faster. Speed, comfort, and handling — not bad.

However, this isn’t to say that 25mm tires are without any drawbacks. For one, there’s weight. In the aforementioned interview, Vormwalde estimates that 25mm tires come with a 40gram average weight penalty per wheelset. Obviously, added weight at the perimeter of a wheel isn’t something to cheer about. The real question is where this negative trumps the positive of decreasing overall rolling resistance? People smarter than myself have said that only top-level sprinters and climbers have anything to fear in this department. And given the amount of teams riding 25mm tires at the 2012 Giro, I’d say that even they have little to worry about.

Then there’s aerodynamics. Depending on the wheel, say a Smart System ENVE for example, a 25mm tire will better compliment the rim profile. But if you’re riding an aluminum clincher with a 19mm rim width, the bulbous profile won’t be so favorable. Lately, though, it’s been reported that some teams have been riding 25mm rears with 23mm tires up front, albeit, I greet this with some skepticism. In fact, given that ENVE’s SES front wheels are wider than the rears, this makes little to no sense. Admittedly, I could be wrong.

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Lastly, there’s a slightly hidden flaw at play in the perception of the science. If you’re observant, you probably noticed that I’ve been referring to 25mm benefits with the clause, “at the same pressure,” throughout this piece. This is important, because most users have the tendency to drop pressure on these tires. The reason for this is an increase in comfort, but this comfort slightly impacts the benefits of lowered rolling resistance. With a 25mm tire, you can replicate a 23mm pressure feel at a significantly lower pressure, which effectively removes much of the sour notes from the tarmac. At this lower pressure, however, you’re accepting a heavier tire while denying yourself much of its benefits — outside of comfort that is. But as Vormwalde states in the Peloton piece:

“That’s part of the beauty of the wider tire. You can run it at lower air pressure, and it feels softer and gives you more comfort. When you race, you just pump it up a little more. If you go by the numbers in the lab, if you have a 19mm tubular tire and a 25mm tubular both ridden at 9 bars in a 40km time trial, you would win with the 25mm tires by 50 seconds. That’s all just from the reduction in rolling resistance. “

I can accept that nothing is more personalized on the bike than our tires, whether it’s our air pressure, tread pattern, casing TPI, or width. If your frame has the tolerance for a 25mm, though, I recommend that you give it a chance. Norms are not laws, after all, and a brief look into tire width’s history will confirm that opposition always comes before change. Ultimately, though, results will always sway the masses.

Words: Michael Barry and Jeff Stewart

Citation:

Gruber, Jared, “Wolf Vorm Walde.” Peloton Magazine

http://www.pelotonmagazine.com/Chatter/content/18/849/Wolf-Vorm-Walde