Are 40mm Road Tyres the Future? Here's the Shocking Truth!

Over the last decade, the cycling world has seen a radical shift with road tyre widths expanding dramatically from the traditional 23mm to 25mm, then 28mm, and now inching towards 30mm. At competitions like Paris-Roubaix, riders are even experimenting with impressive 35mm tyres, which ironically push the limits of what's considered 'wide' in the cyclocross realm designed for rugged terrains.

But will this trend continue indefinitely? Are we on the cusp of seeing professional cyclists, such as Tadej Pogačar and Jonas Vingegaard, racing on 40mm or even 50mm road tyres? This question led us to explore the implications of using wider tyres, especially considering recent advancements, such as Pirelli's launch of the P-Zero Race TLR, available in widths ranging from 26mm to a whopping 40mm.

While wider tyres are touted to reduce rolling resistance, their added size could theoretically cause aerodynamics to suffer. Thus, our investigation sought to determine if the performance boost from reduced rolling resistance would outweigh the potential drag penalties, and at what speed the tipping point occurs.

To explore these questions, we visited the Silverstone Sports Engineering Hub, where we employed two key testing facilities: the Pedalling Efficiency Rig and the Wind Tunnel.

The Tests

We used a consistent model—the Pirelli P-Zero Race TLR—across various widths for comparability. The test focused on two wheelsets: the Hunt CGR40, a gravel race wheelset, and the Zipp 303 XPLR SW, chosen to maximize rim width for future-proofing purposes.

A thorough testing protocol allowed us to examine multiple wheel-tyre combinations in a variety of scenarios, including both smooth tarmac and rugged cobblestone surfaces. We conducted 72 runs in total, ensuring thorough data collection for robust results.

Through rolling resistance tests on smoother surfaces, no significant improvements were detected. However, greater differences emerged on more rugged surfaces. Switching from a 26c to a 40c tyre on cobblestones revealed energy savings of up to 65.7 watts at higher speeds, questioning whether conventional wisdom about narrow tyres still holds.

Wind Tunnel Data

The wind tunnel results confirmed that while narrower tyres tend to perform better aerodynamically due to reduced frontal area, a structured development look at how wide tyres interact with air flow may present innovative optimizations for future designs.

Interestingly, tests indicated that at faster speeds, wider tyres start to yield better performance, especially on rougher surfaces.

Combined Conclusion

The results suggest that on smooth surfaces, wider tyres may not offer substantial benefits; however, the rugged terrain of cobblestones shifts the performance metric dramatically in favour of larger widths.

Real-world implications are significant; for those participating in events like gran fondos or on mixed surfaces, embracing wider tyres could provide critical performance advantages. The trade-off of a slight aerodynamics penalty could yield better comfort and handling on uneven roads.

The Future of Cycling Tyre Design

In short, while not all road bikes can accommodate 40mm tyres currently, the potential for future designs is expansive. Manufacturers will need to embrace wider tyres by engineering rims that are aerodynamic enough to negate the drawbacks.

So, should you consider switching to 40mm road tyres now? If your rides traverse a variety of terrains, the answer leans towards 'yes.' At the very least, riding with the widest compatible tyre, alongside proper inflation, can lead to a smoother experience on the road — and possibly save you energy for that final sprint to the finish line!

As cycling continues to evolve, wider tyres might soon become the standard, ushering in a new era of equipment that prioritizes rider efficiency without compromising speed.