As we’ve alluded to before, tire sizes - they are a’changin’. Most intermediate to advanced triathletes who have been around the block know that the recommended and acceptable tire sizes have increased over time. If you’re new, consider this your official notification. Wider tires generally bring advantages in grip, comfort, and rolling resistance (with some caveats) – but they also bring an aerodynamic penalty if they’re too much wider than the rim on which they’re mounted. To help combat this, rims have also gotten wider. BUT WAIT – widening the rim also makes the tire wider, at least with clincher-style wheels and tires (for more on that topic, check out THIS article from last week).
It’s at least a little bit tricky. Before everyone gets overwhelmed, let me state the goal for this article: To find out what tire size you should be using, given all of the current technology in 2018.
A Brief History
Only a mere 20 years ago, everyone knew that you used 18-20mm-wide tires for going fast (which is to say, for time trials and triathlons). Back then, the wheels were narrow – and so the tires were narrow. Aerodynamic performance, in general, was all about reducing frontal area. If you’re going really fast, this tends to work pretty well.
Over time, things evolved. By the mid-2000’s, some pro cycling teams started using wider tires. At first they weren’t much wider – 21 or 22mm – but the cycling world moves in baby steps.
Above image © ENVE
By my best recollection, the standard tire size for road racing, time trials, and triathlons hovered between 21 and 23mm up through about 2012 (give or take). By about 2010, rims with a 17mm internal width started to become fairly common, which add 1-2 millimeters to the labeled tire width. This mostly got ignored, and we all still went by what the label said.
Then, things started to get strange. Rims began to get really wide, with Hed’s introduction of the “Plus” rim series in 2013, featuring a 21mm internal, and 25mm external width (previously unheard of for road cycling – and adding even more width to the inflated tire size). Over time, other manufacturers started to make road rims in the range of 18-21mm for internal width. We even saw pro cycling teams using 25mm tubular tires for road stages, and even for some time trials (something thought to be blasphemy in the 1990’s).
Given all this history and hub-bub, I decided to poll some of the major wheel manufacturers and industry experts, to see where we stand today. I wanted to know a couple things:
1. In 2018, what is the current best or fastest tire size for top-level amateurs and professionals? This is asked with an understanding that the complete package of aerodynamics and rolling resistance trump comfort or user-friendliness. This is the top 5% of the food chain, and they want speed over anything.
2. Is there a different choice that’s recommended for your average athlete? The person that does triathlon or cycling for fun, personal development, competition, and socialization? They want to go as fast as reasonably possible, but they have realistic constraints on their time and athletic ability. Also, they want to be comfortable. What should they choose?
NOTE: I asked for this information with the caveat that not all bike frames can fit wide tires, even today. I wanted the “perfect world” answer. I wanted to know what tires we should use assuming that all of our bikes have ZERO trouble with fit and compatibility.
NOTE: I asked them to note, whenever possible, if there was a clear difference between the labeled tire size, and the actual inflated tire size.
Here are the responses I received.
"We’ve been studying this topic like crazy. We have hundreds of very accurate tire measurements for a variety of pressures on all of our wheels. For our current wheel line, we recommend 23mm-28mm [labeled] tires. I would imagine things will be wider in the near future. We have published a study that shows the fastest overall tires on our wheels taking both aerodynamics and rolling resistance into consideration. You can find that study HERE.
With respect to an overall recommendation, I would say the 25mm Continental GP 4000s II would be a good choice. That tires’ measured width on both the FLO 60 CC and FLO 90 CC at 95 psi is 27.49mm.
In the study above you’ll see the the Continental Force was the fastest tire we studied. It’s measured width on the FLO 60 and 90 CC is 26.88mm at 95psi. The Continental Supersonic is in second place. I don’t have that tire width at 95psi… but at 100psi it measures 24.14mm. "
Above image © FLO Cycling
"For road triathlon specific applications, a 23mm tire is going to be the fastest tire option we offer for any of our wheels when considering aero and rolling resistance. This applies especially for the front wheel. For larger or heavier riders, opting for a 25mm tire in the rear will have only a very minimal impact on aerodynamics."
Above image © Zipp / Joe Vondersaar
"For other applications requiring pack riding, poor road conditions, or hard maneuvering, other tire sizes might be preferable. For the solo, sustained effort of a road triathlon, all of our deep aero rims are between 23-27mm wide and benefit aerodynamically from a 23mm tire (rather than a 25mm+ tire). The aero improvement of the 23mm tire over a 25mm+ tire outweigh any relative losses in rolling resistance. Our shallower rims (303, 202) are wide and shallow, which helps delay stall in crosswinds when paired with wider tires. The handling characteristics of these shallow rims with a wider tire are significantly improved over the narrower, deeper rims (404, 808). Still, if you are running a pair of 303s in a triathlon, 23mm tires are going to be faster than 25mm tires.
23mm tire – optimal for TT/tri
25mm tire – almost as good, especially in rear. Using in front will increase drag and worsen crosswind handling characteristics on our narrow/deep rims
28mm tire – tangibly worse aero performance, especially for drag and handling in crosswinds"
"Tire/rim widths and volume have been our focus for a few years now, but we’ve admittedly done a poor job of telling the story related to the why for a variety of reasons. But to answer your questions:
Gen 1 SES – 3.4, 6.7, 8.9 (These are the first generation of SES wheels, we don’t make these anymore…)
-Developed and optimized around LABELED 23mm tires
-Continental GP4000 in 23mm will measure closer to 25mm
-Inner rim widths in the 17mm range
Gen 2 SES – 3.4, 4.5, 5.6, 7.8 Rim and Disc Brake Models (Current Generation)
-Developed and optimized around LABELED 25mm tires
-Continental GP4000 in 25mm will measure upwards of 27mm
-Inner rim widths between 18.5-20mm
SES 4.5 AR (All-Road)
-This is where we believe the future of road cycling is headed
-Wheel was ahead of its time as we launched this in the summer of 2016
-Developed and aerodynamically optimized for LABELED 28mm tires
-An inflated Schwalbe Pro One Tubeless 28mm will measure just shy of 32mm on this rim
-Rim is Tubeless ONLY! It features a hookless design
-Inner rim width is 25mm
-Disc brake only (This is what’s possible when you don’t have to work inside the limitations of a rim brake caliper)
-I’m unaware of any disc brake tri bikes that can accommodate these wheels.
It’s my belief that 28mm will make its way into triathlon and a couple years from now it will be the primary size being run by performance oriented triathletes. I also don’t see 25mm tires going away in the same way that 23mm tires have. I think what we may begin seeing are tires labeled by their inflated sizes.
From a performance standpoint, larger volume equates to lower rolling resistance especially on any imperfect surface. In our research, and this is reflected in our latest SES lineup, we’ve sacrificed some aero efficiency in rim shape with some models to achieve a wheel that is more stable in crosswinds and higher volume for lower rolling resistance. While we give up a watt or two in absolute rim efficiency, we pick up 5-10 watts in rolling resistance and even more by enabling the rider to stay calm and relaxed in their aero position."
Above image © ENVE
"For all of our 25mm-wide Plus and Black rims, we recommend 23-28mm [labeled] tires. When inflated to normal pressure, the sizes go up 2-4mm depending on the tire model and pressure.
For the really fast people, a 23mm tire (inflated to 26mm) is the best option. For everyone else, a 25mm tire (inflated to 28-29mm) is the best choice. When used with the proper tire pressure, it will have better grip and comfort… which can make a normal person faster than the narrower tire, when you take everything in to account – rough roads, riding confidence, and so on.
The big news for us is our new Vanquish, which is the first wheel we’ve ever tested that is very accepting of different tire widths. With a 28mm tire (measuring almost 32mm), it is nearly as fast as a 23mm tire. We think this is the future. "
Above image © Hed Cyling
"From what I've seen and people I've talked to the rule of 105 still stands, but the key now is to figure the measured width on that particular rim. For some rims the wider bead seat works against them in aero [performance] as it allows the tire to equal or surpass the rim width. [It seems] that Continental is still winning the aero tire game with GP4000, and there is lots of talk about how awesome the Grand PrixTT 25mm tire is in both Crr and aero, but I don't have the data myself.
Lastly, narrower tires are still generally faster at lower yaw, so for pure TT you probably can't beat the Vittoria Corsa Speed TLR. It's aero, it's narrowish, and it's the lowest Crr we've ever seen by like 2 Watts per tire. Downside is that it's definitely a bit fragile compared to the Continental stuff."
Above image © Vittoria
To expand on what Silca representatives said regarding the Rule of 105 – this states that the widest part of the rim must be at least 105% of the inflated tire width. In other words – the rim must be at least a little bit wider than the tire for everything to work aerodynamically. You can read more in their excellent blog post HERE .
Conclusions for the TL/DR Crowd (Too Long, Didn’t Read)
I’m going to cut through the clutter, and offer my own conclusions – call it an amalgamation of everyone’s responses.
The new standard / minimum tire size is 25-26mm. The old standard of 23mm is dead. NOTE: When I say 25mm, I mean the INFLATED size on a modern clincher rim (so the tire label probably says 23mm). Anything under a measured 23mm, on a modern wide rim is DEFINITELY dead, short of some rare special cases.
The ‘What Should I Use’ Cheat Sheet
-If you’re a pro, aspiring pro, or just super-duper fast, use a tire that’s labeled 23mm (inflating to 25-26mm).
-If you’re an average, middle-of-the-pack person, trying to be competitive and have fun, use a tire that’s labeled 25mm (inflating to 28-29mm).
-If you’re a fat-tire-lover like me, and want to feel like you’re riding a magic carpet, use a tire that’s labeled 28mm (inflating to 31-32mm). With any luck, more new wheels will emerge, making this a legitimate aerodynamic choice.
Of course – your bike frame is the trump card, and will dictate how big you can go.
It’s funny, but I have a feeling that we’re going to see more rims with a sorta-wide internal width, but VERY wide external width. This is what the Hed Vanquish does with its 21mm internal, 30mm external rim, to help the tire stay narrower than the rim’s widest point (to not violate the Rule of 105, discussed above). I tested a pair of Profile-Design carbon clinchers in 2013, which in hindsight, were ahead of their time with a 17mm internal and 24.4mm external width. I don’t know if this type of design is really possible with aluminum rims, at least without making them very heavy – so it may be a feature that’s exclusive to the pricey carbon stuff. I also expect that cat-and-mouse game between frame manufacturers and wheel/tire manufacturers will continue, as the industry tries to decide what tire sizes should be allowed in our bikes.