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What is the essence of road cycling? Weightless, easy gliding? Going fast? And what do you need for that? Apart from a good posture and the associated good aerodynamics, above all: good tyres! Road bike tyres are the interface between road and bike. They are of paramount importance. Few parts of the bike have such a significant influence on the riding experience and performance. The ideal road bike tyre weighs nothing, rolls superbly, has excellent grip, steers precisely, is indestructible and absorbs bumps in the road. You guessed it, no tyre achieves this ideal, because the desired properties get in each other's way. Super-light and super-robust? Hard to reconcile. Super grip and minimal rolling resistance? Hard to reconcile. Great comfort and precise, agile steering behaviour? Hard to reconcile. But the best road bike tyres come very close to squaring the seemingly impossible circle. They combine these incompatible characteristics at an astonishingly high level.
The fact that road bike tyres have become better and more versatile is due not only to the continuous refinement of rubber compounds but also to tyre width. Vincenzo Nibali, who recently ended his professional career, named wide tubeless tyres as one of the top innovations during his career. Nibali's words carry weight, as the "Shark of Messina" was a world-class descender who could decide races downhill.
In the beginning there was the disc brake
The switch to disc brakes paved the way for the development of wider racing bike tyres. With the abolition of rim brakes, the restriction on tyre width also fell, and what was considered the norm began to falter. Where recently 25 millimetres was still considered "wide", 30 millimetres and more is now normal. The effective tyre width has increased significantly in racing. Today, 28 mm tyres are standard in the World Tour; however, the actual width can also be significantly greater, depending on the interaction between tyre and rim. This is because the effective width results from the shape of the tyre and the internal dimensions of the rim. What was once 15 or 17 millimetres internal width has become up to 25 millimetres for racing bike rims.
Take Tadej Pogačar, for example: The Slovenian rode the Tour de France this year with 28-millimetre tubeless tyres from Continental, which curved to 31.3 millimetres at the front and 32.2 millimetres at the rear on his Enve-SES 4.5 wheels with an inner rim width of 25 millimetres.
32 millimetres! That's almost cross format (the maximum permitted tyre width for cross is 33 millimetres). Why does Pogačar accept such wide tyres that are heavier than necessary? When the weight affects the climbing performance and the tyre width affects the aerodynamics of his racer - especially as it is well over the UCI limit of 6.8 kilograms when weighed by TOUR?
Rubber experiments on the mountain
We weren't able to talk to Tadej Pogačar about his tyre choice, but of course we also experimented and came to the conclusion - beyond pure performance considerations - that more is more. Conti's 5000 S TR tyres with a width of 32 millimetres, mounted on a wheel with an internal dimension of 25 millimetres, proved their worth in the mountains in summer. With a real width of 34 millimetres, this combination provides an extreme amount of confidence - even on cracked, wet mountain roads with changing surfaces. With the pressure adjusted accordingly (here: 3.6-3.8 bar), the wider tyre sits more firmly, absorbs bumps in the road much better and conveys more safety without sacrificing too much of the agility characteristic of a road bike tyre. This alone is reason enough for an amateur athlete to switch to wider tyres, provided the bike has the necessary tyre clearance. But where are the limits? What is the optimum width? What does excess width do to the ride feel, and what does the balance look like strictly in terms of performance criteria?
To find out the differences systematically, we ordered five sizes of the classic Pro One from Schwalbe - from 28 to 38 millimetres wide. The tyres have the same design, differing mainly in their dimensions. We also rode gravel tyres up to 45 millimetres on the same bike - not directly comparable because the tyres are constructed differently, but interesting for a comparison.
In addition to the road tests, we carried out numerous laboratory tests to determine the influence of the width of the tyres. We determined the rolling resistance on various surfaces and measured how well the tyres bounce. In addition to the comfort stiffness, we also determined the lateral stiffness as a measure of the handling characteristics of the tyres. We also tested the tyres in the wind tunnel for their interaction with the rim, wheel and rider and put the data obtained into riding simulations to find out where the sweet spot of the tyre width lies from a performance perspective.
Road bike tyres: Wider is safer
The riding impressions are clear: wider tyres feel safer and more comfortable - always provided that the air pressure is lowered accordingly with greater width. Only then can the benefits actually be experienced. Online calculators such as the one from Silca provide a very good guide to tyre pressure. If the pressure is too high, you are giving away the advantages of wide tyres and could just as easily fit slimmer tyres that weigh less.
Grip increases with width. This is because the contact area with the road increases. This increases the chances of getting over bumps or dirt on the piste without damage. However, the feedback from the road becomes weaker with increasing width and more rubber on the road; the riding feel is less direct. While the 28er still lets the grains of the tarmac through to the handlebars, the 34er largely filters them out. And the 38 is even smoother. Is that good or bad? That's a question of priorities, expectations and taste.
When is a road bike tyre too wide?
In our experience, Schwalbe's Pro One steers precisely enough for fast manoeuvres up to a width of 38 millimetres and feels like a racing bike; however, wider tyres roll a little slower than the narrower ones. The mass of the tyre on the outer circumference of the wheel can be felt as inertia in the steering and counts twice when accelerating: it has to be moved forwards and set in rotation. This is noticeable, but is only a small factor in the overall energy balance compared to the mass of the rider and wheel. This is more of an issue when frequently accelerating from a standstill - in city traffic, for example - than in sporty riding. The wider tyre is also higher, which also affects the steering geometry. The trail, the stabilising lever arm with which the front wheel is towed, increases with the tyre size. However, the jump from 28 to 38 millimetres does not have a huge impact. The trail of a typical road bike increases from 58.7 to 64.9 millimetres; this is noticeable, but acceptable.
If wider is better, why not fit even wider tyres? For comparison, we ride gravel tyres with different air pressures. From a width of 40 millimetres and more, the precision and direct steering feel on asphalt decreases and the inertia increases further - thus moving away from the typical road bike feeling. At the same time, however, the tyre's ability to absorb even rougher damage on tarmac increases - and of course on gravel and natural paths. The best gravel tyres are fast on the road - even at low pressure. They roll at the level of mid-range road bike tyres. With more pressure, thicker tyres can also be trimmed so that they turn in more directly; however, they do not achieve the feeling of riding a road bike and at the same time give away suspension travel. It therefore makes no sense to ride thick tyres with high pressure. The thick tyres also lose out in terms of air resistance. In the 3T Exploro, an aero gravel bike optimised for wide tyres, we measure with Schwalbe's 40 millimetre wide G One RS more than 20 watts higher drag than with the 38 Pro One in the Ridley Kanzo Fast. With coarser lugs, the resistance increases further and makes real top speed impossible. So, as expected, the light-footedness when accelerating suffers from a wide tyre width, as do the aerodynamics.
The ideal tyre width for road bike tyres?
From a performance point of view, the ideal width in our comparison of -
28 to 54 millimetre wide tyres is 28 millimetres. The slimmest Pro One is slightly ahead in our laboratory test in terms of both rolling resistance and aerodynamic drag. In the simulation, there is also the lower weight. This leads to the fastest riding times in all scenarios, whether uphill or downhill. However, the simulation does not take into account the different suspension capabilities of the tyres - and thus precisely the point that we felt most clearly during testing. This also affects the rolling resistance on real roads. If the road becomes rough, our tests on relatively smooth surfaces are only of limited use. Off-road, we know that tyres with less pressure roll faster. This also applies on poor roads.
Conclusion on the optimum tyre width for road bike tyres by Robert Kühnen, TOUR tester:
The bottom line is a mixed picture; wider is often better, but not always. An effective tyre width of 34 millimetres is a good compromise on asphaltWith the right rim, this combination is still aerodynamically good and proves itself in practice. As a tubeless set-up, this is our tip for marathon riders. If you want to ride as fast as possible, you can take Tadej Pogačar as an example and effectively mount 32 millimetre wide tyres on 33 millimetre wide aero rims, then there are no aerodynamic disadvantages to be expected. If you have perfect roads on your doorstep, you are sufficiently equipped with an effective width of 28 millimetres and slightly lighter on the road than with the wide tyres. If there are bumpy tracks or off-road trails in the area, you should not be afraid of even thicker tyres, as the suspension capacity increases with the width. Ultimately, the surface dictates what is necessary and what is good.
The great variability of the tyres is the inspiration for some to build a gravel racer as a one-wheel-fits-all. With an interchangeable wheelset, a sporty gravel bike covers a very wide field. From weightless gliding over roads of all kinds with 32 to 34 millimetre wide race tyres to gravel racing with 45 millimetre gravel tyres, everything is possible. Racing bikes have never offered more scope for unlimited riding fun.
The rolling resistance of road bike tyres
The construction of a tyre determines its rolling resistance more than its width. We measured five identical Schwalbe Pro One TLE tyres, each with adjusted pressures, on two different surfaces.
28 against 38 millimetres
The picture below shows 28 and 38 tyres rubber to rubber. With a high rim, the wider tyre is well concealed and is not particularly noticeable. In the rolling resistance test on two surfaces, we determined the values for a system weight of 85 kilograms (wheel plus rider) at 35 km/h. We adjusted the tyre pressure to the widths. As a result, the 28 mm tyre came out just ahead of the 32 mm and 38 mm tyres. In principle, however, the tyres are on a very similar level. The deviations can be explained by small differences in the construction. At the same pressure, the 38 would almost certainly roll more easily than the 28 - but only on an ideally flat surface, because its spring potential would diminish with more pressure.
The role of the rim for road bike tyres
Tyres and rims are partners. One can do nothing without the other. The relationship has developed rapidly: Rims have increased enormously in width. This also affects the shape of the tyres.
13 against 25 millimetres
The picture below shows rim cross-sections in the past (13 millimetres internal dimension) and now (Zipp 303 Hookless, 25 millimetres). The wider rim makes the tyre more voluminous and laterally stiffer; the wider tyre sidewalls support the tyre better. The effective width of the tyre on a rim depends on how wide the tyre is cut. Newer products are already adapted to the wider rims and reach their printed width at around 22 millimetres inside width. Problem: You can only see how wide the tyre really is after it has been fitted. There is a recommended minimum tyre width for each inner rim dimension - the specifications vary from manufacturer to manufacturer and from tyre to rim; if in doubt, choose the larger tyre dimension.
The suspension of road bike tyres
Tyres are part of the chassis. If the terrain becomes rough, the pressure must be reduced.
Paris-Roubaix
Every year, the pros test the limits of pain and material on the cobblestones in the north of France. The key to mastering the pavés: wide tyres and low pressure down to two bar. The spring stiffness (goal: as low as possible) depends heavily on the tyre pressure. The lateral stiffness - measured here with a rim width of 22 millimetres - is not quite as sensitive to pressure. It is a measure of steering precision and should be as high as possible. The ratio of control to comfort is best with the thickest tyre. The best usable pressure range for the 38 tyre is 2.5 to 3.0 bar.
The aerodynamics
Tyres and rims are the "sails" of the road bike and are important in the battle for seconds. Our wind tunnel test at 45 km/h shows how tyre width influences aerodynamics.
Wind tunnel test Ridley Kanzo Fast
We tested the Pro One on the DT Swiss ARC 1100 rims (20 mm inner width, 27 mm outer width) in the Ridley Kanzo Fast aero gravel racer. As expected, the 28 mm tyre is the fastest. The resistance increases linearly with the tyre width up to 38 millimetres. In absolute terms, the aero surcharge for the thickest tyres is surprisingly low.
Wind tunnel test 3T Exploro
We measured even wider tyres on the 3T Exploro, which have no place on the Ridley. The 34 Pro One, mounted on a Campagnolo Levante wheel, gains 19 watts compared to the Ridley. The 40 G-One RS on the DT Swiss GRC 1400 gravel rim is a further 8.5 watts slower, and with the profiled 54 mm wide MTB tyre, it's definitely difficult to keep up with the fast combos.
The optimum width
The TOUR guide to tyre width - suitable for the intended use.
To the lawn: 28 to 32 millimetres
The best possible aerodynamics, agility and lightness are the focus when racing. Modern rims, which are up to 33 millimetres wide, effectively allow tyres up to 32 millimetres wide to roll optimally. If the surface is rough, wider tyres are also acceptable.
Marathon & mountains: 34 millimetres
If riding fun and safety are the priority, more width is better. 34 tyres give you a lot of confidence downhill; grip and comfort increase. Riding down mountain passes on tyres of this size is a pleasure. We recommend a tubeless set-up in this size.
Rumble distances: 38 millimetres
Cobblestones, roads in danger of falling apart, occasional excursions on gravel - all this is the territory of the 38 plus class. A tyre pressure down to two bar takes the edge off even the worst tracks, which often lead to the most beautiful places.
