Tyre widths have quietly become one of the most interesting battlegrounds in professional road racing.A decade ago, a 23mm tyre was still commonplace in the Tour de France, with 25mm considered progressive and 28mm reserved for the roughest cobbled stages. Fast forward to 2025, and the picture has changed dramatically.Looking across a sample of 13 bikes we got hands-on with from this year's Tour de France spanning both road and time trial machines the data suggests the pelotons trend towards the use of wider tyres shows no sign of abating. That said, nominal tyre widths are misleading. While tyre sidewalls still read 28mm or 30mm, the tyres teams are racing on are frequently much larger once mounted to modern rims.Plus, the tyre widths observed on time trial bikes continue to lag behind those for road racing.Heres what we can say about tyre sizes from our sample. Read more: 7 Tour de France 2026 tech trends and why there's "no fastest tyre size" The era of the true 30mm race tyre has arrived Jonas Vingegaard has chosen to run a 30mm nominal front tyre and a 29mm nominal rear tyre the only rider of our sample to do so. Simon von Bromley / Our Media For years, wider tyres have been creeping steadily into the professional peloton.While nominal tyre sizes still range from 25mm to 30mm, the tyres riders are racing on average just over 30mm wide once mounted to their wheels.The data paints a fascinating picture of how modern race bikes are being optimised, and why the number printed on the tyre sidewall no longer tells the full story.Across 26 individual tyres, the mean measured width comes out at 30.29mm, despite the median nominal size being only 28.5mm.In other words, the average WorldTour race tyre, from our sample, measures 1.79mm wider than the size printed on its sidewall.That growth is likely the product of two trends working together. The first is the widespread adoption of wider rims, with internal widths of 22mm to 25.4mm now common among the biggest wheel manufacturers. Remco Evenepoel's setup features 30mm tyres, which inflate narrower than advertised a clear outlier. Simon von Bromley / Our Media Remember, a rim measuring 21mm across internally, bearing a nominally 28mm-wide tyre, should measure 28mm wide, according to the ETRTO.The second factor is tyre construction itself, with modern casings designed to spread wider once installed.The result is a nominal 30mm tyre frequently measures 3133mm in real-world use on these wider rims, while nominally 28mm tyres often end up close to 30mm.Perhaps the biggest surprise, though, is that 30mm has overtaken 28mm as the most common nominal tyre size in this sample, appearing on 12 of the 26 tyres measured. 28mm tyres made up 11 of the 26 sampled, though, so it remains close.Only a single sampled bike still used nominal 25mm tyres for racing: Tadej Pogaar's Colnago TT2 time trial bike, although we also know that the rest of his UAE Emirates-XRG team were sporting the same setup.TT bikes remain more conservative The Colnago TT2 of Tadej Pogaar (and the rest of his UAE Emirates-XRG team) ran 25mm Continental Grand Prix 5000 TT TR tyres, which inflated over 3mm wider than advertised. Simon von Bromley / Our Media Accordingly, the distinction between road and time trial bikes has become increasingly clear.Road bikes in our sample averaged a measured tyre width of 30.82mm, compared with 29.68mm for TT bikes.1.14mm may sound insignificant, but in elite racing it's a meaningful difference, with multiple potential causes.Another notable trend is front tyres averaged 30.72mm, compared with 29.87mm at the rear. That reflects the increasing prevalence of wider front-tyre setups in the modern peloton. Teams are seemingly placing a greater emphasis on front-end grip, comfort and rolling efficiency, while maintaining slightly narrower rear tyres for aerodynamic integration and frame clearance.Vingegaards use of a 30mm nominal front tyre and a 29mm rear tyre is the clearest example of this in action.The demands of modern road racing also generally places increased value on reduced rolling resistance, rider comfort and grip on imperfect road surfaces, with rim and bike frame designs changing to accommodate wider tyres in an aerodynamically optimised package. The recently updated Orbea Orca Aero has 37mm-wide tyre clearance a sign of aero bike design moving towards optimisation around wider tyres. A great example of this is the Orbea Orca Aero, which can sport 37mm tyres (measured), while its been common for a while to see race bikes with capacity for upwards of 32mm.The efficacy of time trial bikes, by contrast, remains defined by aerodynamic priorities to the exclusion of almost everything else. Broadly speaking, designers are still trying to minimise frontal area while carefully managing airflow around the fork, frame and wheels.The regulations governing the design and use of time trial bikes arent a million miles away from those controlling road bikes but there are differences, including the ability to use specific handlebars, while riders can adopt a more aerodynamic tuck position.While many modern TT bikes now accept significantly wider tyres than their predecessors, aerodynamic integration still encourages teams to use slightly narrower tyre packages than on their road bikes. That means narrower tyres continue to have a place against the clock, even as road racing moves decisively towards larger volumes.Of course, narrow remains a relative term when race bikes commonly used nominal 23 or 25mm tyres, it wasnt unheard of to find 19 or 21mm tyres fitted to TT bikes.The biggest tyres are now remarkably big Matej Mohori's rear tyre measured a whopping 33.65mm wide. Simon von Bromley / Our Media If there's one bike that encapsulates the wider-is-better trend for road bikes at the Tour de France, it's Matej Mohori's Bianchi Specialissima.His nominally 30mm tyres measured a startling 33.31mm at the front and 33.65mm at the rear. These were the largest tyres we measured.They're closely followed by the front tyre on Jonas Vingegaard's Cervlo S5, which measured 33.2mm. Vingegaards was the only bike we measured running a nominally wider tyre at the front, which we speculated could be to help his bike make the UCIs 6.8kg weight limit. That said, its fair to say these widths would have looked at home on an endurance bike, rather than a Tour de France race machine.At the other end of the scale sits Pogaar's TT bike, with its 25mm-labelled tyres measuring 28.2mm at the front and 27.94mm at the rear the narrowest tyres we recorded.But even these are substantially wider than what many professionals raced a decade ago.Rim width matters, but it's only part of the story The Reserve wheels used by Visma-Lease a Bike are 25.4mm wide. Simon von Bromley / Our Media The data reinforces the general takeaway that wider internal rims produce wider measured tyres.The widest rims in the sample the 25.4mm internal width of the Reserve wheels on Vingegaards Cervlo S5, and teammate Per Strand Hagenes' Cervlo P5 also unsuprisingly produced some of the widest measured tyres.The relationship between internal rim width and measured tyre width is broadly consistent, though. Rims measuring around 22-23mm internally typically produce tyres (which are most often 28mm or 30mm nominally) around 1-2mm larger than their nominal size, while the widest rims in the sample (25.4mm internal) consistently produce some of the largest measured tyres. Reserve uses the same greater internal width on its TT wheels an anomaly in our data set. Simon von Bromley / Our Media The biggest exception remains Mohori's Specialissima, with tyres measuring more than 33mm on relatively conventional 23mm rims, suggesting tyre construction can be just as influential as rim width.The clearest illustration is Lenny Martinez's Continental Grand Prix 5000 TT TR-equipped Bianchi Aquila RC. Despite using nominally 28mm tyres on 23mm hooked rims, its front tyre measured 31mm wider than the nominally 30mm Vittoria Corsa Pro Speed fitted to Luke Plapp's Giant Propel on 22.4mm hookless rims.Hooked, hookless or mini-hook? The bead profile isn't driving tyre width There still isn't compelling evidence that hookless rims result in a tyre inflating wider than it would with a hookless rim in fact, the opposite is indicated by our data. Simon von Bromley / Our Media One of the more interesting questions raised by the data is whether rim design influences measured tyre size.Hookless wheels produced the smallest average increase over nominal tyre size in our sample, at 0.61mm, compared with 1.70mm for conventional hooked rims and 1.90mm for so-called mini-hook designs.However, those figures shouldn't be interpreted as evidence that bead design itself determines tyre width. The hooked and mini-hook rims in our sample also tended to sport wider internal rim profiles and different tyre models, both of which are likely to have a much greater influence on the final measured width than the presence or absence of a bead hook. Measuring 0.54mm wider than advertised here, inflated width is more likely down to tyre construction. Simon von Bromley / Our Media For example, consider Plapps Giant Advanced SL with hookless Cadex wheels and Mohoris Specialissima with hooked Vision wheels. These featured the same nominal tyre sizes (30mm), but the different tyre constructions from Cadex and Continental, respectively, and rim designs from Cadex (hookless) and Vision (hooked) resulted in different measured widths.Mini-hook rims, as their name suggests, retain a very small bead hook to help with tyre retention while, its claimed, enabling the rim to benefit from the traits of what is officially a hookless design (according to the ETRTO).However, the data doesnt clearly suggest that any of these rim design solutions are specifically impacting width.The sidewall number is becoming meaningless Rider Bike Nominal tyre size (front) (mm) Nominal tyre size (rear) (mm) Measured tyre size (front) (mm) Measured tyre size (rear) (mm) Internal rim width (front) (mm) External rim width (rear) (mm) Hooked/Hookless Road / TT Jonas Vingegaard Cervlo S5 30 29 33.2 29.92 25.4 24.8 Mini-hook Road Luke Plapp Giant Propel Advanced SL 30 30 30.54 31.04 22.4 22.4 Hookless Road Matej Mohori Bianchi Specialissima 30 30 33.31 33.65 23 23 Hooked Road Milan Fretin Look 795 Blade RS 3 28 28 29.63 29.32 23 23 Hooked Road Remco Evenepoel Specialized S-Works Tarmac SL9 30 30 29.42 28.89 21 21 Hooked Road Tadej Pogaar Colnago Y1Rs 28 28 31.6 30.84 23.5 23.5 Hooked Road Tobias Halland Johannessen Prototype Ridley 28 28 29.43 29.32 22 22 Hooked Road Lenny Martinez Bianchi Aquila RC 28 28 31 28.5 23 19.5 Hooked TT Mauro Schmid Giant Trinity Advanced SL 28 28 28.78 28.13 22.4 22.4 Hookless TT Per Strand Hagenes Cervlo P5 30 30 32.32 31.17 25.4 24.5 Mini-hook TT Soren Wrenskjold Ridley Dean 30 30 31.32 30.36 20 20 Hooked TT Tadej Pogaar Colnago TT2 25 25 28.2 27.94 22 22 Hooked TT Tom Pidcock Pinarello Bollide 28 28 28.66 28.49 23 23 Hookless TT Edit Table Perhaps the most striking conclusion isn't that Tour riders are using 30mm tyres it's that they're often not.They're using tyres that say 28mm or 30mm on the sidewall but measure anything from around 28mm to nearly 34mm, once mounted.As rims continue to widen and tyre constructions evolve, nominal sizing is becoming less useful as a point of comparison.For consumers, it's a reminder to pay attention not just to the printed size, but also to measured width, rim compatibility and frame clearance. 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