By that time, the first AERON/TPU tubes had been in use on our in-house test benches for about six months. Result: With each development phase, these lightweight tubes showed increasingly strong resistance to punctures and crushing in the tire. In some cases, the tools required four times more force per square millimeter to cause basic damage, using the performance metrics of classic butyl tubes as a reference.

More Insights into TPU Tubes

The results promised a paradigm shift in the bicycle industry, but what looks good on paper and with standardized tools can expose weaknesses in real-world tests that hadn’t been seen in lab conditions. That’s when one of the employees thought of using the automotive industry as a model and pushing practical testing to the limit. The famous professional bike race from Paris to Roubaix in northern France just flashed across the TV screen. The racecourse, known among cyclists as the “Hell of the North,” covers about 200 kilometers of country roads and paved farm roads, plus roughly 55 kilometers of historic cobblestones. 

For professional teams, their riders and mechanics, the race in early April always brings significant stress. On one hand, the race bikes need a setup suitable for cobblestones; on the other hand, the support crew faces a constant flow of breakdowns on race day.

For professional teams, their riders, and mechanics, the race in early April always means immense stress. Often, completely new race bikes are built because the aero bikes don’t offer enough space for the extra-wide tires. In addition, the weight distribution between the front and rear wheels on a less aggressively designed frame geometry better suits the riding technique, which at least gives you a chance to make it through the cobblestone sections—known as “pavés”—unscathed and without whiplash.

As the person chosen to conduct the field test, I unfortunately don’t have a fleet of bikes that would allow me to quickly switch between different models depending on the route. My race bike is exactly that kind of speed-optimized machine with 25-millimeter-wide tires, equipped with two AERON/TPU ExtraLite Protect tires and three more as spares—the TV broadcasts showed a seemingly endless stream of pros on top-of-the-line equipment frantically calling for their service cars. And so far, there has been no public test of modern TPU technology on this ultra-tough course. So this wasn’t skepticism about the product, but a calculated risk.

Despite a less-than-promising start, motivation and morale were at an all-time high—until I, as the test rider, saw the condition of this legendary cobblestone surface firsthand: rough, bumpy, and dirty. According to reports, once a certain minimum speed is reached, the individual cobblestones should blend into a smooth, even surface. And following that logic, a cautious—i.e., slow—approach to the cobblestones wouldn’t make the ride any easier. The conclusion: eyes closed and just go for it.

The roughly 30 sections of cobblestones in the UCI professional race aren’t all equally difficult. Length, and especially the roughness and condition of the surface, categorize them from one to five stars, with the three 5-star sections often serving as the race’s main challenges. And it’s precisely at one of these that my bike and I are standing right now—less euphoric and optimistic than before.

Sector 22 was the first; others with three stars followed, then four, and then comes the Forest of Arenberg—a stretch of the course so daunting that even outsiders to the cycling world know exactly what it means for both rider and bike. More as an afterthought, I briefly press the valve stem of both tubes twice, under the illusion that this minimal pressure adjustment will make everything better. The top teams can rely on charts and experience here; I can only rely on rough guidelines from cyclocross.

I’m genuinely afraid of Arenberg! However, cyclocross might have been the right kind of inspiration. For example, on sand, there’s a riding technique where you shift your weight far back to take pressure off the handlebars. To prevent the rear of the bike from literally throwing me out of the saddle, I shift into a high gear before Sector 21—counting backwards—since putting more weight on the pedals means less on the saddle. The first few meters on #21 Maing to Monchaux-sur-Écaillon are relatively flat and give me an opportunity to try out the rear-weighted position. For a moment, I feel completely satisfied, then I overlook a huge, slanted rock, and suddenly both wheels press one after the other into its raised edge.

You improve, but you never fully get used to it. That’s one way to describe progress on the vibrating plate. There are moments with a flicker of control, but mostly you’re more passenger than pilot. Applied to the sector with the highest difficulty level exactly 200 meters ahead, it means: relinquish control, shift up, take your position, don’t slow down, and just let physics do its thing.

There’s a world of difference between 5-star and 4-star sections. Against the stones in the Arenberg Forest, my wheels feel like they’re from a 20-inch kids’ bike. Like tiny whirlpools in an already choppy sea, entire patches of irregularly placed, tilted, twisted, or simply missing stones stand out. Not only do the wheels take blows from below, but the cobblestones treat the tires like a punching bag. No machine in a lab could do that! And even worse: halfway through the 2,300 meters, gravity pulls me into the left-hand lane. There, hedgerows and thorns lurk, which I cannot avoid. You’re trapped in this lane, mainly because it’s constantly shady and cool in the forest, and the dew stays on the stones for a long time, making them slippery. Puddles have also eroded the joints here; it’s as if the path sometimes turns into a stone desert. This is truly a tire’s life in fast-forward—or rather, two or three. The forces alone that have acted on my AERON/TPU up to this point would not allow standard inner tubes to survive.