Forget 28mm tyres: The rise of wider road bike tyres is here, and if you ride your gravel or all-road bike on the road, pay attention

It is no secret that tyres are getting wider across the cycling spectrum. WorldTour road racers have left the 25mm rubber in the dust in favour of 28mm or even 30mm options. Gravel professionals, meanwhile, are riding tyres well beyond the 50mm threshold. Even on the UCI Mountain Bike World Cup, some of the top riders habitually race 2.5 inches rather than the lightweight 2.2-inch tyres of old.

All of this is trickling down to consumers as the market adjusts to the new standard set by the sport's cutting-edge athletes. This momentum has led to new and novel ways for cyclists to think about products and find the right options to make their riding experience as enjoyable as possible. Tyres are, after all, where the rubber meets the road.

A notable shift in this sea change is the rise of supersized road tyres, with an increasing amount of options now available in the 35mm-40mm range – all promising little to no speed loss from the former standard of 25mm-28mm tyres. But how do these beefy tyres really compare to the race-tested “skinies”? And who are these tyres made for?

I’ve been putting the market’s leading big-volume road tyres to the test to find out.

The making of a convert

The seed of this story started a year ago at the launch of the Enve Fray, an all-road bike built around 35mm tyres. While I only rode the Fray a few times, I was able to bring the 35mm Enve SES tyres home with me. Over the next few weeks, I grew to really like the wide 35mm slick tread, which improved the road riding performance on my gravel bike.

As a roadie at heart, I was initially surprised by how much I liked them, especially considering that 28-31mm tyres are still the race standard at WorldTour events. This piqued my curiosity about other wide tyre options on the market – a small but growing sector.

I was keen to explore a few key questions:

• Who are these tyres for?
• At what width do tyres lose their benefits?
• In the superwide category, does puncture-resistance come before speed?
• And do the benefits of width win in the long run?

For the past year, I have exclusively ridden on various thick, slick tyres to answer some of these questions. My test pool consisted of eight different tyres from seven different brands at five different widths. Each model was ridden hundreds of miles over a variety of tarmac and light gravel surfaces. Additionally, every tyre was mounted on the same set of Enve 4.5 rims, incidentally, the same wheelset that UAE Team Emirates have been riding this past season.

While there was a great deal of variance between the different models and widths, this test was not about the specific tyre, but rather to find a use case for these (super) wide road tyres in general riding as well as adapting gravel bikes to the road in a more effective manner. It wasn’t long into the testing before I knew I was onto something.

28mm tyres are not optimal for all-road and gravel bikes

The primary market for these wide slicks has historically been commuters and bike tourers. Yet, thanks to a booming gravel and all-road market, an increasing number of riders are using their off-road bikes as versatile, all-purpose machines. It's now just as common to see them on paved roads as it is on gravel.

However, when treating a gravel bike like a road bike, there are parameters to consider, especially when it comes to speed and efficiency. Simply throwing on what would be the fastest tyre option for a road bike is not going to be optimal on a gravel bike. Here’s why:

Geometry

Gravel bikes, without exception, have a longer wheelbase, which allows for bigger tyre clearance and a more stable ride feel. There are other geometric changes, too, but the wheelbase is the big shift between road and gravel bikes.

The frame was designed around high-volume tyres. When using smaller, lower-volume tyres –standard road tyres, in short– on a gravel bike, the longer wheelbase effectively drops the centre of gravity of that bike. The even lower bottom bracket height increases the risk of pedal strike. It may also make the bike’s handling feel even slower.

Aerodynamics

In most cases, narrower is better for aerodynamics. Yet, when it comes to the tyre-frame interface, the benefits of narrower tyres are less clear-cut. Gravel bikes often have robust downtubes designed for stiffness and durability and were not aerodynamically shaped to match the profile of 25-30mm tyres, as seen on road bikes.

Speaking broadly, pairing a slick 35-45mm tyre with a gravel frame will not be a significant aerodynamic penalty. Quite the opposite, it may even be an aerodynamic gain. Throughout discussions with several engineers and aerodynamic experts, it all comes down to the importance of system aerodynamics – the way the frame, the wheels and the tyres all work together. Wind tunnel testing is the only way to draw specific conclusions between frame, wheels and tyres but if there is a rule to follow, matching the width of the tyres and rims to tube shape is likely to yield a better aerodynamic system rather than a narrower tyre.

Wider does not necessarily mean slower

After many months of testing wider tyres for road riding, the overwhelming benefit was a smoother ride without the sacrifices one expects from compliance – primarily speed.

Compliance is the most anecdotal of all testing data points, as it comes down to ‘feel.’ For me, the benefit of a larger volume tyre was compounded by where I do most of my road riding, which is in and around Phoenix, Arizona. With some of the most intense summer temperatures in the United States, Phoenix is uniquely challenged in its ability to maintain roads to the same standard as other states. Pair that with relatively low taxes, and you are left with poorly maintained pavement that is anything but smooth. That environment showed that a major efficiency gain can actually be felt when using larger-volume road tyres. The gain here is comfort, which in turn translates into less body fatigue and a more consistent speed across bumpy terrain.

We’ve all heard it said before: smooth is fast. And this is because of the under-discussed enemy of speed: suspension drag.

Suspension drag is the loss of speed, or efficiency to be precise, of an object in forward motion due to vibrations, bumps or other vertical movement. Or, to put it differently, any vertical movement will cause the object to have less energy propelling it forward. In cycling, the greatest cause for that vertical movement is the road surface.

These suspension losses, as they are most frequently called, factor into a bike tyre's overall rolling resistance. Thus, rolling resistance in a lab test is very different from rolling resistance on the actual road. Regardless of what the lab test says is most efficient, that test is only accounting for the hysteretic losses of a tyre – the energy lost as heat due to the continuous deformation and flexing of the tyre as it makes contact with the road while rolling. Accurately assessing the suspension losses, which are the counterparts to hysteretic losses, is virtually impossible on a drum because road surfaces are inconsistent.

“If you test tyres in the lab, you're only measuring the hysteretic losses in the tyre casing, and so generally the harder you pump up the tyre, the less losses you have,” Jan Heine told Cycling Weekly. Heine is the CEO of the tyre company Rene Herse and is an expert on the matter.

“But when we started testing on real roads, we found that that's not true at all. Lower pressures roll just as fast. From that point, we realised we don't need narrow tyres, because at lower pressures, we can make wider tyres with supple casings. But the big question we still had was, why do we see such different behavior on the road compared to in the lab?”

Heine credits Jim Papadopoulos, a former tech expert, for uncovering a key insight to this question in his book Cycling Science. Papadopoulos referenced a United States Army study on tank vibrations, where the drivers absorbed 2000 watts from vibrations. This led to the realisation that energy loss from vibrations was slowing down the vehicle. Heine notes that lab tests, which didn’t account for the rider or uneven surfaces, missed this important factor in measuring energy loss on bikes.

In cycling, we’re dealing with much smaller forces and, at least on tarmac, fewer vibrations, yet the physics are the same – vibration is an enemy of forward movement and one that’s undervalued in cycling at large.

“[Tyre size] almost doesn't matter, because the suspension losses and the hysteretic losses balance each other out,” Heine said about what he finds to be the right width on smooth tarmac.

“I'm just as happy on a smooth road on a 32 millimeter tyre running 55-60 psi, or a 54 millimeter slick tyre, with the same tyre construction that I'm running at 25 mm.”

Yet, whenever the road has any kind of imperfections, the width must go up to balance the equation.

How wide is too wide?

A fundamental question heading into the testing was at what width do tyres lose their benefits?

Ultimately, there are very few slick options above 700c x 44mm, so that is where I topped out in size. On that end of the spectrum, I looked to Rene Herse because the brand has long championed wide tyres for road riding and has several options.

I tested the 700c x 44mm Snoqualmie Pass model in both the sturdy Endurance casing and the supple Extralight casing. I found that the two casings offer two completely different ride feels. The Endurance Casing offers a ride quality that is in line with a semi-slick gravel tyre, minus the knobs. With a heavy rubber compound, the tyre is better protected against thorns, sharp rocks or other impacts that could ruin your ride. Yet, as is always the case when discussing tyres, there is always a trade-off. The thicker casing is heavier and less malleable, with higher suspension losses relative to a more supple tyre construction.

The Extralight Casing is at the opposite end of that spectrum, with a very lightweight construction and a thin, malleable sidewall. It is, however, more susceptible to pinch flats and sidewall cuts. With that said, the Extralight Casing performs great on smooth gravel, and on tarmac, the 44mm tyre rolls as well as anything else on the market.

For riding on paved roads exclusively, I found the 44mm width too wide for handling and aerodynamics.

Even if wider tyres cause less of an aero penalty with the wider tubes of a gravel bike, there are limits to that equation. With the frame I tested –a Rodeo Labs Trail Donkey 4.0- the 44mm exceeded that threshold. Across different terrain, the tyre climbed well, without much of a speed penalty relative to other, smaller tyres. Yet, the tyre was consistently slower on the downhills and flat roads.

The added volume created handling challenges on the tarmac as well. The added height that comes with the increase in volume raises the height of the bike relative to the bottom bracket, which creates a less stable ride. For riders who typically ride smaller frames, those challenges can present at an even lower volume of 44mm. Off-road, that volume is less challenging because the handling demands differ, but when the surface is fast and predictable, the larger volume makes the handling suboptimal.

The sidewall's malleability also exemplifies that unease at speed. Once again, this is where the difference between off-road priorities and road performance diverges. When the surface is hard, smooth, and predictable, a thin sidewall that reduces the all-important suspension losses is less important than a sidewall construction that fortifies enough to retain its shape while under a load through higher-speed corners. When the sidewall is light and malleable, the confidence the tyre inspires is sacrificed.

How the industry is adjusting to the new normal

Of all the tyres I tested over the past year, the 40mm Pirelli P Zero TLR came out on top. While it might have been conceived as a fast gravel tyre, the result is a product that feels to be a future-proofed all-road tyre that provides speed at a width well-suited for a wide range of riders.

“We decided to work on the bigger P Zero TLR to create the fastest gravel tyre possible,” said Samuele Bressa, Global Marketing Manager at Pirelli.

“The two people we were trying to serve were pros and amateur riders who ride on light gravel. For the pros, the idea is that the slick is ok because they have the skill to navigate the loose turns without the tread. For the amateurs, the turns are slower, but they can have the advantage of speed on the straights. Much more speed.”

The TLR is a cousin of the heralded P Zero RS tyre, which is their top-of-the-line road racing option. While the RS is the fastest road compound Pirelli has in its stable, the RS was too light of a construction to have the durability needed in the all-around 40mm version of the P Zero line. Yet, the TLR has properties similar to its faster counterpart and tests similar in rolling resistance to the brand’s collection of road tyres.

With high-volume tyres, simply making a tyre bigger isn’t as easy as it sounds. The way the tyre interacts with the width of the rim, for instance, changes the tread height. This, in turn, determines how steep the crown of the tyre is. The crown and height can dramatically impact how the tyre handles on all surfaces, especially over uneven or slick areas.

All of this has resulted in a robust tyre for the road that performs incredibly well. This is because the tyre’s durability does not come from a thicker rubber construction or a lower TPI count, which can lead to a sluggish-feeling tyre. Instead, the P Zero has the quality of a higher-performance road tyre with some increased durability afforded by the much bigger margin for error that comes with 40mm of volume.

“The 35 was born from the road and our partnership with LIDL-Trek,” Samuela said. “Last year, the team did lots of testing with the 35mm tyre before Paris-Roubaix. They didn’t race on it this year, but it did help the development. The 40 was the primary option for the gravel riders and gravel bikes.”

Pirelli’s team partnerships recently expanded when the brand replaced Vittoria as the tyre sponsor for Alpecin-Deceuninck. The partnership means the reigning UCI Gravel World Champion and Paris-Roubaix victor will now ride the full line of Pirelli tyres at the biggest races across four disciplines, which can only push development forward.

Yet, despite the speed and strength of the 40mm P Zero TLR, we're unlikely to see it raced at Paris-Roubaix.

“A 40mm could be good for Paris-Roubaix, but the aerodynamics is the big unknown,” Samuela said. “It could be faster but it would have to exist in a new bike system. The frame, wheels, and tyres would all have to be considered, which means you would have a special frame for one race because if you make a bike aero optimised for a 40mm, a 30mm tyre is no longer aerodynamic.”

But since I’m not racing the Paris-Roubaix, I’ll happily take the marginal aerodynamic penalties in favour of compliance that gives me more power and less soreness at the end of long rides.

Conclusion

The tricky thing about a topic like wide road tyres, speeding up gravel bikes or the balance between road and gravel demands is just how complicated the confounding variables are. Aerodynamics are highly variable, handling is vastly different with the same size tyres on different size frames, and vibrations are never the same twice, even on the same route.

However, after consistently riding this category of tyre across many different brands and different widths, all those variables coalesce into a key shift in understanding that I have had in adopting wider road tyres for the vast majority of my riding. Bigger volume tyres are smoother, they are more efficient when the pavement has any consistent imperfection, they are better at managing fatigue, and they make handling better on bikes with gravel geometry.

“It used to be that we’d say, ‘well, you need to tough it out, because you want to go fast.’” Jan Heine said. “So, you know, the bike was vibrating like crazy at 130 psi, which was ridiculous, but we thought the vibrations were the cost of speed. And now we realise it's the opposite. The more you have to tough it out, the slower you go.

“If somebody had told me 10 years ago that the Tour de France winner would be on 30 or 31 mm of tyres, I would have laughed and said,’ You're kidding me.’ And I can tell you our most popular gravel tyres. Used to be the Bon Jon Pass 35 mm that's now our most popular road tyre.”

Tyres tested