Communityinterview

DYLAN JOHNSON'S 13-WATT WIND TUNNEL TEST | ROADMAN CYCLING PODCAST

with Sam Calder — Founder of Rule 28, aero testing and cycling apparel company specializing in wind tunnel optimization

39:34·9 June 2025

LISTEN NOW

Listen on

Spotify Apple Podcasts YouTube

SAM CALDER

Founder of Rule 28, aero testing and cycling apparel company specializing in wind tunnel optimization

PROFILE →

KEY TAKEAWAYS

A 4-hour Silverstone wind-tunnel session with Dylan Johnson produced ~13W of total savings — projecting to roughly 13 minutes off his Unbound finish time without a single change to the bike.
Sock fabric matters. Upgrading to a new woven construction saved ~3W at Dylan's 35 km/h race pace. Dual-layer Neo fabrics only deliver gains above ~50 km/h, which is why gravel needs different fabric choices than road TT.
Hydration-pack volume and head position drive a surprising share of total drag at gravel speed. The bike isn't where most of the watts are hiding; the rider and kit are.
Helmet sizing matters. Testing the same helmet model in medium vs large produced a 4–5W difference (medium faster via smaller frontal area). Buying the right size beats buying the next-tier helmet.
The aero / time-spent equation: at Unbound (a ~10-hour race at gravel pace), 1W ≈ 1 minute. Adding 13W to your average by training takes far longer than the 4 hours of testing that produced the same result.

TOPICS

Sam Calder, founder of aero testing and apparel company Rule 28, took Dylan Johnson into Silverstone's wind tunnel for four hours and saved him 13 watts. At one watt per minute for sharp-end racers, that's 13 minutes off his Unbound finish time. The biggest single gains didn't come from the bike.

Key Takeaways

The sock result alone is worth understanding. At 45 km/h, Rule 28's new One socks saved 10.5 watts versus their previous generation on their test rider. At Dylan's Unbound race speed of 35 km/h, the gain was 3 watts versus the older Aero sock. The fabric change is the reason: woven construction instead of knitted, finer fibres packed tighter, and a rib structure that steps up rather than down, which turbulates airflow differently. If you are completely unoptimized and move to a dialled gravel setup, Sam puts the total potential saving at around 20 watts.

Helmet size matters more than helmet shape in gravel. Because your head sits above your shoulders in a gravel position, there is no meaningful interaction between the helmet and your torso airflow. The aero shape gains you one or two watts. Going from a Metander large to a Metander medium gained four to five watts just from reduced frontal area. On the hydration pack, the counterintuitive finding was that a 3L reservoir is faster than a 1.5L because it fills the void behind the helmet rather than leaving a low-pressure gap. Bare hands are still faster than aero mitts. These are the calls worth making before you spend money anywhere else.

In a four-hour Silverstone wind tunnel session conducted by Rule 28 founder Sam Calder, professional cyclist Dylan Johnson achieved a 13-watt total drag reduction, equivalent to approximately 13 minutes off his projected Unbound Gravel finish time based on the one-watt-per-minute rule of thumb applicable to sharp-end racers. Rule 28's new One socks, constructed from woven rather than knitted fabric, saved 10.5 watts at 45 km/h and 3 watts at 35 km/h versus the previous generation on test riders. Wind tunnel data showed a 4-5 watt difference between Metander helmet sizes (large versus medium) in gravel riding position due to frontal area, with helmet aerodynamic shape producing only 1-2 watts of variation. A 3L hydration reservoir tested faster than a 1.5L reservoir in gravel position because it fills the low-pressure void behind the helmet rather than leaving a gap. GCN presenter Alex Patton recorded a 16.5-watt saving by switching from standard kit to a Rule 28 gravel suit optimised for his speed range. Matt McGrath from CORE has documented the performance impact of rising core temperature as it relates to fabric air permeability at lower speeds.

If this kind of marginal gains thinking interests you, the Team Sky episode goes deep on where the original marginal gains philosophy came from and what it actually delivered. The European gravel champion episode covers how the sport's top gravel teams are thinking about race-day performance at the elite level.

CLAIMS FROM THIS EPISODE

Each tagged with the strength of evidence behind it.

STUDY
A four-hour wind-tunnel session with Dylan Johnson at the Silverstone facility produced approximately 13 watts of total measured savings without any changes to his bike, projecting to roughly a 13-minute reduction in his Unbound finish time.
Source: Sam Calder, founder of Rule 28, describing the wind-tunnel session on the Roadman Cycling podcast
STUDY
Upgraded woven sock fabrics produced ~3W of saving at Dylan's 35 km/h race pace versus the previous generation of aero socks.
Source: Sam Calder, Roadman Cycling podcast
STUDY
Dual-layer Neo aero fabrics only produce a measurable drag reduction above approximately 50 km/h, which is why gravel racers averaging 35 km/h need different fabric construction (smoother weaves) to capture aero gain.
Source: Sam Calder, Roadman Cycling podcast
STUDY
Testing identical helmets in different sizes produced a 4–5W difference between a Met Manta in medium vs large, with the smaller size being faster owing to reduced frontal area.
Source: Sam Calder, Roadman Cycling podcast
EXPERT
At gravel race pace, kit and fabric choices, helmet selection, eyewear placement and hydration-pack setup consistently deliver larger aero gains than wheel or frame upgrades.
Source: Sam Calder, Roadman Cycling podcast

KEY QUOTES

“For for Dylan when we took him the main thing we were looking at was validation of some of the work we'd done before and then a few different optimizations for him for the 2025 season. So his race speed of 35k an hour, I think we had about a 3 watt performance gain versus our previous generation of Aeros.”
Sam Calder — Founder of Rule 28, aero testing and cycling apparel company

“We tested a Metanter in large and a Metant in medium and that was like a four or five W difference between the two. I think less medium faster. Just because it's smaller frontal area wise.”
Sam Calder — Founder of Rule 28, aero testing and cycling apparel company

“I think it was about 13 watts that we saved in all. For a 4-hour session that we had with them, like for anybody that's considering it is a very good use of time. It's fairly expensive. But if you're thinking about, hey, for Unbound, it's a 10-hour race. How long would it take me to add 13 watts to my average power output across that race? It's a hell of a lot more than four hours, and it's going to be a lot more effort.”
Sam Calder — Founder of Rule 28, aero testing and cycling apparel company

EPISODE TRANSCRIPT8 SECTIONS

Dylan Johnson's Wind Tunnel Session

In just 4 hours, Sam Calder, the founder of Rule 28, chopped 13 minutes off Dylan Johnson's Unbound estimated finish time. 13 minutes. But the craziest part, the biggest gain didn't come from a new frame or a $3,000 wheel set. It came from something that cost less than your morning coffee. When Sam took Dylan into the tunnel, they discovered something that flips the script on what we thought we knew about going fast in gravel racing. Because if you're leaving even five watts on the table, you're handing your rivals a fiveminute head start at your next race. Today I'm sitting down with Sam to unpack the most surprising findings from that test. Aero tradeoffs, hidden mistakes, and the gear choices that make the biggest difference. Welcome to the Roadman podcast. Sam Calder. Sam, welcome to the Roadman podcast. Thanks for having me. You had Dylan Johnson in the wind tunnel and we're all very curious as to exactly what happened, what the gains were, what the testing protocols were, and I think importantly for a lot of listeners, where's the easy gains that they can apply into their own racing or possibly training if you're looking to half wheel and smash one of your training partners. Maybe to start out, when Dylan came into the wind tunnel, did you have a testing protocol in mind? Yeah. So for for Dylan, he's been to wind tunnels not with us but separately um quite a few times before. So he does know what he's doing there. I think he was quite impressed with Silverstone just sort of the extra features that it has that none of the tunnels he's been in before did have. Um things like uh cameras on the side, top and front and then they will project your images in front of you. So you can see exactly the position that you're holding and compare that to a previous one. Seems pretty um common sense to have something like that so that you can make sure you're keeping a constant position, but none of the tunnels in the US had that. Um so yeah, it's it's a very good tunnel uh to go to and use and it allows us to to get really accurate precise data. So for for Dylan when we took him the main thing we were looking at was validation of some of the work we' done before and then a few different optimizations for him for the 2025 season. So main thing we were excited to show him was the the different fabrics that we've been working on uh where we could upgrade his suit and then really helping him with some other things like helmet choice as well. Um, yeah, just to make him an all round fast athlete. Kit is one part, but yeah, we're we're here to help him with everything. When I'm getting packed for a bike race, when I'm packing my bag, I always think about in my head, okay, I'm getting dressed. I'm getting dressed from the ground up. So, let me think about that in terms of the wind tunnel testing. So, if we're getting dressed from the ground up, first thing Dylan's likely putting on is socks. I know you have the new one sock. Did you test old socks versus new socks? If so, what were the results? Yeah, we tested with him old versus new. We also tested our Neo socks, which is a dual layer sock like our skin suits. Um, that one didn't actually work on him, which wasn't really a surprise because it's aimed at sort of 50k an hour plus as a speed range. Um, more of a track. Yeah. Uh, so different way it works. Um, different demands for 50k an hour versus 35. So, wasn't really a surprise, but we figured we'd give it a go, too. Uh, we tested him with the new one socks, our older version of socks, and our aero-ish socks. Um, which are more of a training sock with a bit of added flare. They'll save you a little bit, but um they actually do still perform quite well at low speeds just because it's a a different way it works um versus what you need at mid and high speed. But yeah, it was a a good gain on Dylan. So his his race speed of 35k an hour, I think we had about a 3 watt performance gain versus our previous generation of Aeros. That's amazing. Yeah. And did you test that at various speed ranges? So say 25k an hour, 30k an hour, 35, 40k an hour. Yeah. So for Dylan, we weren't really interested in anything above 35k an hour. So we did 25 through 35. 35 being pretty spot on for what the the front of the pack will be at for Unbound. Um so it's a really good option to optimize him around. And as you say, you tested your newer 50k an hour track socks. What are they called? Uh Neo. So Neo needed the the previous uh season, the error base layer that we had needs to be worn with a a smooth skin suit.

Woven Fabrics and the Neo Sock

So we called that one the Neo suit being it's our new suit. Um so as it was a standalone product, it was called that. We then expanded it into a range of products. So we had a road version, a tri version, and then the socks and over shoes as well. Got that sort of dual layer upgrade. So it went into calling the whole thing Neo, which then matrix wise also helps name the single layer suits uh and socks. We called them the one. Uh so yeah, it's I'm looking forward to the full Morpheus launch in four years from now. In terms of the in terms of the fabrics, what's the different how do the different fabric choices from your old sock to the new one to the neo sock, how do they influence speed, airflow, like what's the considerations when you're thinking of these new fabrics on what new fabrics to test? Yeah. So, the the biggest difference we made between these two is we swapped from a a knitted fabric that we' used previously, we're now using woven fabrics. Um, it gives you much more precision in terms of the construction of the fabric. We won't go into it too nerdly because I don't think anybody will care particularly that much, but the uh the fibers you can use are much finer. You can pack them much closer together, so you can get much better performance out of them. Um, for the the textured fabrics that you're seeing on the one socks as well, the the way they work is kind of inverted too. So older generations, the ribbing was actually a a thinner part of the fabric. So you had the small lines would be actually a step down in the fabric. The newer fabric, that area of the thin rib is actually thicker, so it steps up. Um, small won't really mean anything to people, but it's a different way that it then works to turbulate the air flow. Um, and we found a a good gain from doing that. And when you go to the dual layer, you're saying that works at speeds over 50k an hour. Why is that? Why is that not working at lower speeds? It's it's a tricky one on the legs because it works on arms of suits higher than that. So, it's it's a bit of a weird one that we don't have a good answer to on the socks as to why it doesn't work at a lower speed. On the the suits, the way it performs is kind of like a smart material. Um, so you've got fabric draped over a structure underneath. Um, then in areas of high pressure like the front of the arm, that top layer of fabric is pushed down more into the under structure. So you get more texture in those areas effectively. And then in areas of low pressure where you don't want any structure, that fabric is pulled away from the ribbing underneath slightly. So it ends up being smoother overall. So with changes in your and things like that, you actually get to control effectively where texture is on the arm. So yeah, it's it's quite a clever way of doing things. I found your whole testing session just really interesting because you tested kind of quirky stuff that I typically I've been in the wind tunnel once a good few years back and it was for a track and we didn't get to play around with all the cool stuff you were testing for gravel. Like you tested the reservoir down the back, you tested sunglasses on the helmet, no sunglasses, and sunglasses down the front. And unsurprisingly for anyone who's, you know, slightly follows the arrow scene, if you can close that gap in between your two pecs by putting the sunglasses or a bottle or anything in there, even stuffing your gile down the front of it, as I did for my TT last night, it seems to be faster. when you went to testing the reservoir, why not build the reservoir into the front to close that gap off? Um, it's a tricky one. It's it's mainly comes down to comfort there. Um, having something on your front is a lot more obvious uh in terms of feeling and comfort uh than on your back. Um, there we do have an option to do that. So, we make a cargo base layer if you want to put a bottle down your front, but as it's designed for for gravel races, having a a three kilo pack of water on your back is quite a bit more comfortable than having it pulling on your front. Um, in terms of space as well, it's it's just about making a rider comfortable. Like the the whole thing people usually think about is um what's per kilo. The thing we think about here is what's per CDA. So if you can get your drag down for the same power, great. But if you're then doing something that's going to impact your power, that's going to throw off the numbers.

Hydration Pack Size and Aero Gains

So we could put something down the front that's going to be quite heavy and uncomfortable. Is that going to have an impact on the actual total power you're going to be able to put out from mechanical restrictions or comfort? Yeah, it it might be faster in theory, but in reality, does it make you quicker? Maybe not. And that's why I'm quite surprised. And I was chatting to a friend who works in a wind tunnel last night and we're talking about one of the easiest wins world tour teams can make is putting their radio in the front. Uh I know Uno X slightly offset the radio so it's not bang in the front in case they crash. You just don't want that impact. but having it in the front somewhat and then you see UAE or still have the radio in the back and it just makes no sense aerodynamically why they wouldn't move that across. But that's just a random thought more than a question cuz I want to go a little bit deeper on the reservoirs cuz I thought that was really interesting because I'm getting ready for a bunch of races later in the summer. I'm going to kick off my gravel calendar in Rift and we're going to finish out in Badlands towards the end of the year. Probably won't race with a reservoir in Rift, but I definitely will be in Badlands. How does the size of the reservoir seem to impact speed? Did you test different reservoir sizes? Yeah, we have. It's It's an interesting one because sort of counterintuitively what we found is the the bigger ones actually do help. um when you look at it side on it starts to make a bit more sense because you in a gravel position probably have your head a little bit higher slightly higher riding position than you would in like a really aggressive road position. So head is typically above shoulders which means that it's creating a bit of a low pressure area behind it. So the bigger pack actually helps to fill in some of that space and you can draw like a nice clean curve from the back of the helmet down over the pack and onto the hips. A smaller reservoir like a one and a half liter versus a three sits a bit lower on the back. So you have air coming off the helmet big void still and then the pack. So yeah, you have a low pressure area then generated in between helmet and pack which isn't going to be as good for drag than just filling that whole space in. I guess this is something you probably didn't test. But the bigger pack you're saying seems to be slightly faster, but as you get through the race you're going to be drinking that pack and that three liter is going to be emptying. Does that start to change the consideration whether you go with a hydration typical hydration vest as opposed to an integrated like bladder? Yeah. Um the the con misconception with the gravel suit was like it's designed with that pocket on the back to be insanely quick and much faster than a pack. The the main thing we actually built it for was for comfort. Um, so wearing a backpack for 10 hours as you're moving and it's rubbing and you've got the straps into your shoulders is going to affect your comfort. And then going back to that what's per year equation, you being uncomfortable is going to have a material impact on your performance. So making a rider as comfortable as possible without impacting CDA. Great. the the suit is marginally quicker than the pack itself just because it's getting rid of a lot of messy things like straps, zips, things like this. Um, but yeah, it it's not something we tested in the tunnel. Um, but yeah, I'm sure it will have a performance impact going from 3 L full to drinking all of it and depleting it. But the the problem then again is coming back to kind of a so what question like we tested it and put it on like reals and things and you get some answers going like oh so to stay fastest you just shouldn't drink then it's like you always have to drink like the point is to reduce the amount of damage that we're doing aerodynamically but it's all still going to be about performance. So yeah, we could test what it's like with a half drink and half drunk reservoir, but the answer is kind of like, so what then at the end of it? Like you it's not going to affect what you're going to have to do come race day. Yeah. And it's unlikely you're going to choose to use a hydration pack in a race where you don't need a hydration pack just for the aerodynamic benefits because races go uphill as well as flat and downhill. So at different times the equation changes from what's per CDA to what's per kilogram.

Head Position and Visibility Tradeoffs

Yeah. And again like the would I choose to ride with three liters of water on my back if I didn't have to? Like it's obviously not going to be as comfortable as not having it there. So yeah, don't don't wear it if you don't need it. Some of our pros still choose to wear the gravel suit even though they have access to the road race suit because they just have got really used to it. So yeah, it doesn't need the pack to be uh sorry, it doesn't need a reservoir in there to be a fast suit. Uh it's still very good standalone and it's not loose and baggy as a pocket. It's still tight to your back. I thought your comment about the pack and your head position was actually quite insightful because my experience with the wind tunnel, the one time I've been there, I optimized for an individual pursuit position, but visibility on that was horrible. Like I could see maybe two feet in front of me in the individual pursuit. So when I took that position and tried to use the same position for a time trial, then it's just not a safe position to only be able to see two feet in front of you for a time trial. The demands of gravel are obviously totally different again where if you only have a twoft field of vision, you're going to hammer into craters, you're going to get caught the wrong side of little fault lines and end up crashing and a crash is going to more than offset any aerrow benefits. So, you've decided to give away a little bit of pure aerodynamics to create a functional head position. Yeah, it's it works out quite well with the the gravel suit as well. We tested it with a ar a sort of tucked head position and then a more upright, more sustainable position. And it's actually quicker with the upright head position, which like makes sense, but it was still interesting to see that dropping your head actually didn't really help at all because you have the pack behind you or the reservoir. Um, so it's it's about optimizing the the air flow onto the pack, which would be head slightly higher. Um, so yeah, it's it's a happy win-win situation there of it's a more sustainable position that also happens to be three or four watts more efficient. And how did helmet choice factor into this? You've tested a range of helmets as well. Was there a fastest to slowest that you can remember off hand? Um the the biggest takeaway really for gravel is helmet size. Um with a a more upright position, helmet being above shoulders and torso. There's two set like different parts to aerodynamics. So we said CDA which is coefficient of drag and frontal area. So coefficient of drag would be the rough shape and it's independent of size. You could be really slippery and massive and really slippery or and tiny. With time draw helmets, when you see them getting really big, that's because they're having an effect on coefficient of drag. They're trying to shroud the shoulders because the head is in line with it. So the helmet itself can be bigger, but it can still be faster. So that's the trend we've seen in time travels for the last couple of years of people sizing up. Yeah. And I say this like the the frontal area if their head is in line with their torso isn't going to change that much either. Um but yeah, you you rewind a few years ago before the wild TT helmets came out and people were finding larger helmets worked better. That's because it was shrouding the shoulders. A lot of energy has now gone into taking that idea and running with it and designing something specifically to shroud the shoulders. So like that new Jirro is is fully designed around that. You wouldn't wear that in a road race. Obviously it would test horrifically poorly once that helmet comes above uh the torso because then frontal areas coming into play and it's not helping shroud anything. It's just massive. Yeah. The opposite kind of holds true in gravel where there's not really any interaction in air flow going over your head and helmet onto your torso. your head's above all of that. So, we saw a tiny difference in how error helmets performed, like a what or two. Um, but the big difference was in helmet size. So, we tested a Metanter in large and a Metant in medium and that was like a four or five W difference between the two. I think less medium faster. Yeah. Just because it's smaller frontal area wise. But the the best helmet still was the Metant. Um I think it it makes sense like they've got a wind tunnel of their own. They're obviously putting in a lot of work there into making fast helmets. Um I'm going to go out on a bit of a limb and say like because of that it's a fairly universal rule.

Helmet Choice and Total Watts Saved

I would say if your head is above your shoulders that that met is quite a good option as a helmet just because the interaction between helmet and body isn't really happening for roads. And you do often see this. I remember a few years ago like the cask TT helmet was just testing pretty well on almost everyone. Yeah. Yeah. There are there are a few things that if you're not able to go and test it yourself, there are the ones that are more likely to be fast on you. The problem with aerodynamics is it's always couch with like it depends and it changes from person to person with different variables. So the gravel position, fewer variables in the helmet choice once you're going into roads where your head is probably if you're really into it like more of a TT position like in line with your torso or at least getting that way then helmet choice can vary from person to person just because it's interacting with other things. Then you get into a TT where helmet heads are really low then it can vary even more. Did helmet choice affect the air flow onto the integrated hydration pack? We we didn't test it that way. Um it's the problem with going to the wind tunnel like you always end up with more questions than you came in with just because there's a a matrix of options you get there. So you can go we've tested 13 helmets. Okay, we'll test 13 helmets with the different packs. will test it head up, head down and you you have to call it quits at some point. Um it is a a technical sort of they're basically technical drug dealers sort of thing. Like you go in with a few questions and then they'll be like you'll be back. Um and yeah, you you come back with more questions, things improve, you come back with even more questions, hopefully things improve again, but yeah, you can never answer everything that you want. So, how many watts did Dylan save from walking in the door to walking out the door? I think it was about 13 watts that we saved in all. There's a a couple of things you can add in in addition to that um that would make it more that we tested, but if we're talking strictly what's he most likely to race come Unbound or Seotter or something like that, it was 13. So for a 4hour session that we had with them, like for anybody that's considering it is a very good use of time. It's fairly expensive. But if you're thinking about, hey, for Unbound, it's a 10-hour race. How long would it take me to add 13 watts to my average power output across that race? It's a hell of a lot more than four hours, and it's going to be a lot more effort. Um, so yeah, I wonder what my math isn't good enough to figure out. I wonder what that breaks down as as a time saving on something as long as Unbound. Uh rule of thumb, it's a watt per minute. It can be a little bit less than that. Um but yeah, it it varies. If you're It's a nice way to think about it. The slower you are, the greater the time saving one watt makes. Um but for the people at the very sharp end of the spear, it's basically one watt equals 1 minute if you were to time char it. Like obviously, and this is the wildest thing that I've heard around it. You'll have the actual data because I don't know it off hand, but for somebody listening who's not into arrow at all, the difference from going from your traditional I bought a pair of cotton socks to moving across to something like your one sock. What's the savings there? Um, so the ones are designed for sort of road racing speeds, 40 45k an hour. Um, obviously they're going to vary in performance between people, like how big you are. Um, but on our test rider, uh, when we were putting the final touches together, 45k an hour, they saved 10 and a half watts versus our previous edition of socks, which is like insane. Hey everybody, let's take a quick break to talk about the bike I'll be riding this season, Reap. I've been lucky enough to ride all the top brands in the world over the past few years, but these Reap bikes, they're not the same. And I'll tell you why. Reap is the first company I've seen that isn't chasing sales targets and the mass market. They're chasing something very rare, perfection. Every bike they make, it's crafted in the UK factory. And it's not about slapping a made in Britain label on a bike from a Chinese factory. It's about control. From the first sketch to the final build, they're hands-on, ensuring that every detail is dialed in. That's very rare in an outsourced world of mass production.

Rule 28 Sponsor Break

What sets them apart is innovation. While others pump out the same old designs, reaps pushing boundaries. They're not following trends, they're setting trends. Think precision and performance like an F1 car for the road. Absolutely no compromises. And it shows and you can feel it when you ride the bikes. These bikes are built for riders who demand the best. Whether they're chasing podiums or just want a machine that feels like an extension of your body, a piece of art, it's not hype, it's substance. Ride a Reap for yourself and you're riding something crafted with intent. So, if you're serious about cycling, check them out. It's reapikes.com. I absolutely love my one and I couldn't recommend it highly enough. Back to the show. But, and even your previous edition was still quite a fast set of socks. back to like a cotton set of socks that I would have wore, you know, on my club race three nights ago. Yeah, it's it's wild what it can do. Like you could be looking at sort of again varies from person to person. You could be looking at 15 watts potentially, which is insane um to do that at the high speeds. Um, but it it comes into it again when like you look at the pros and they go like the average speeds now versus 10 years ago have got so much higher and people look at the sort of they put their skeptical glasses on and go if the dopers were doing this doesn't that mean they're doping now? I was like, "No, like the knowledge base in terms of kit selection and like training and fueling has come on so far that like head-to-head you could put the best guys today with all the knowledge we have against the the most doped up riders from 20 years ago. And I don't think it would be close. I wonder what that set of socks change is going to translate to time savings if I were a set of them for Badlands. Like it's a 780 kilometer race. You're out there for I I don't even know what the winning time was last year, but it's like it's two days or something. Two and a half days. You're out there for It's massive. It's so It doesn't With with aerodynamics, if you were to treat it in its simplest form, to double your speed requires eight times more power to overcome the aerodynamic drag. There are different things like rolling resistance and drivetrain efficiency that don't work the same way. But it so it doesn't scale as sort of directly as you would think. Yeah. On top of that again you have fabrics performing differently at different Reynolds numbers. So it it kind of factors in all the characteristics of the air speed air. So you would have layman's terms basically consider it speed. Um, there's other things in there, but not really important for most people to think about. Um, different fabrics perform differently at different speeds. So, in our other testing at the lower speeds on some riders, the Aero-ish socks have tested slightly better than the one. Um, so if you're doing 20 25k an hour, different socks are probably a better option. So, the air is would probably be the way to go for sort of ultra endurance. We're not talking about sort of hitting 35 40k an hour. Um, but it's 25. That's probably the way to go. Um, benefit is they're they're a cheaper sock as well and probably comfier to to wear for ultra long distance. But, yeah, it's it still all adds up. Like how many easy watts are on the table for me if I to start thinking about this from totally unoptimized thrown on you know my my club kit with a pair of cotton socks with no thought to aerodynamics to starting to get dialed in on a event like rifts which your speeds are probably closer to 35k an hour versus a bad lands where your speeds are probably closer to 25k an hour. 30. Uh, error is quite a tricky one at 25. Um, it's I'd say it's probably the lowest limit to where you should actually start potentially considering it. Um, it's probably much more of a thing to stay comfortable there. So, our top-of-the-line TT suits and things like that aren't particularly breathable. Um, there is a a correlation between air permeability of fabrics and air performance. So unless you've got a lot of air flow going over you as well, you might find that you're overheating. Um so breathability would be something to think about there. But Matt McGra on from core as well and he'll he'll give quite good data on as core temperature rises how performance goes down as well. But so your example of 35k an hour like completely unoptimized to sort of absolutely everything that you've got. I'm gonna sort of base it off, I don't know, like a a reasonably big person. Um, not absolutely tiny because obviously it will scale, but you you could be looking at sort of 20 watts in total.

Aero Mitts, Tubeless and MTB Tires

Like we had Alex Patton from GCN in uh the wind tunnel to to optimize him for unbound. And yeah, the the difference between his aero jersey and Bib Schwarz from GCN's standard kit provider to one of our gravel suits um optimized for his speed. That just by itself is about 16 and a half watts. So then you add in socks, you add in like maybe mits if you want them as well. Um quite error mits make a difference versus non-eromits. Um, some other companies have said they found three or four watt savings with air emits versus somebody else's. Everything we found is that bare hands are still faster than air mits. Looks cooler as well. Yeah. The the reason we make them is because if you're racing something like unbound or a race where you think like there's a possibility that you might crash or you just want the padding, an error mit's better than a non-erommit. Um, but bare hands is still the fastest there. We do make some TT gloves which are actually a little bit quicker than bare hands, but it's it's a small saving then uh still. So cost per watt saved, it's not the most effective place to look. That's my favorite metric. Dollar per CDA change. Oh yeah. Given that question, like what's the most effective way to deploy like a small budget like hundred euro $100? You looking at socks? Socks? Yeah. Um if I'm not limited to clothing, everybody's heard this now, but tubeless. Um minus the faf of setting it up. It does have really good um advantages to rolling resistance. So yeah, if if you don't mind changing it every few months, um it is worth doing. And I know tires and tire wit has got really invogue. You guys did test that. Didn't you need a tire wit in Silverstone's rolling resistance rig? Since then, Dylan seems to be exclusively mountain bike tires and gravel races 2.2 most of the time. What was the data on that to support that decision? Yeah, so it's it's obviously going to if you're riding on really nice smooth tarmac, we're not saying 2.2 two mountain bike tires are going to be the fastest. So, it it's horses for courses. Um really rough gravel. Um those those Quant Race Kings did perform really well. Um softer gravel or like finer onto something where maybe the race is like 80% tarmac and then has 20% gravel. That's obviously going to affect your decision. Um but yeah, they interestingly I think there was a a a kind of an aerodynamic performance from that tread on the Contis. Um they've got textured down the sides like quite a long way. Um so there will be something going on there rather than just having a tread sort of in the center part of the tire. Um but yeah, it's it's a trade-off between rolling resistance and uh aerodynamics. So obviously the if you're going very very wide with a tire, you are going to start impacting performance. Um if we're limiting ourselves to road, there's not really that much of an impact difference between like those super skinny now whatever you would call them 25s up to 28s and 30s. Um especially as frames are getting designed with those in mind. So the forks getting a bit wider. Um the the advantage overall lies with the wider tires uh for rolling resistance there. Road men, are you leaving free speed on the table every single ride? Because most riders are. Why? Because they have a simple strategy when it comes to tire pressure, and it's called pump and prey. They hope it feels right, but too much air, you head out the door and you're skidding through corners. Too little air and you're slogging up every single climb. Either way, you're wasting watts and you're toasting your legs. At Roadman Cycling, we have built a tool that takes out the guesswork. It calculates your perfect tire pressure in under 30 seconds based on your weight, tire size, terrain, and even the weather. It works for road, gravel, tubeless, tubler, clincher. It's built with insights from World Tour pros and engineers. And yes, it adapts for race day wet roads and gravel terrain. It isn't fluff. It's free speed. It's better grip. It's more comfort for extra watts at no extra effort. It's totally free. All you have to do to get it is head on over to roadmycling.com/tire pressure. Now, I'm going to leave that in the description down below, plug in your details, and get yourself the perfect pressure every single time. Takes 30 seconds. Check it out. It's below. And again, the thing with the rolling resistance on the wider tires is we got to think about it being adapted to the environment you're racing in. Because if you're in a gravel race, especially if you're competitive in a gravel race, you're trying to qualify for UCI gravel worlds and trying to hit that qualification time, you're going to be spending a lot of time in the wheels.

Puncture Risk vs Aero Fabric Breakthrough

And it anyone who's ridden a gravel race and you're in the wheel at 35k an hour, your visibility on hitting a paw hole is practically zero. You're reacting in milliseconds. So you are absolutely nailing these holes and having that 2.2 I don't know statistically how much it reduces your puncture chance but it definitely helps. Yeah. And I think there's there's different levels to puncture protection and things like this that you then have to factor into it. So are you are you willing to save a watt or two for having much less puncture protection and then kick yourself if you do flat and that's the end of the race. Um, so it's it's not as simple as just going this is the fastest on paper. I'm going to erase that every time. Um, yeah, it you can go down the rabbit hole of trying to figure out all the different inputs that you need to figure out your decision. Since you started rule 28, you've spent a lot of time in the wind tunnel chest testing fabrics, optimizing this clothing to be some of the fastest in the world. Did you have a moment where you looked at a test run data and you just thought, "Whoa, this changes everything." Probably like, yeah, this this upgrade in fabrics that we just made. Um, you you can't tell by looking at a fabric how it's going to perform. Um, but you can over the years get a a rough idea of sort of what you think's going to work and what's not going to work. So once we had these made, you're going like, okay, there's a there's a good chance this is going to perform quite nicely, but it's it comes down to seeing in the tunnel and yeah, seeing that readout and just going like, okay, this this is a massive improvement on what we could do before cost a lot to do in terms of to produce these fabrics, but the fact that we don't care about anything else besides performance as a brand, like it's not it's not cafe kit basically. Um, so once we we found the performance, we couldn't really say like, yeah, but it's going to it's going to make quite expensive kit, it's like, yeah, for good reason. Um, yeah. So, yeah, that that does change quite a lot, I think, in just what we can offer to people. What's coming down the pipeline? Have you anything in the secret vaults that you're working on that's not quite ready or even where the aero industry is going? really think have we you know obviously that parto principle uh 8020 it seems like we've made a lot of the easy gains already is it now a case where we start chasing marginal within marginal gains um I think I think the main thing to look at is customization um as everything is really specific to fit and like your body proportions Um, we don't offer custom fit at the moment, but I get quite a lot of people getting into contact saying, "Hey, look, I'm quite tall, but quite skinny. What's the best size for me?" And typically, people in the past would have gone like, "Go for the tightest thing you can get into because it will look good." Um, and tight is right unless you have a good Yeah. I tend to lean the other way and go like, "Hey, look, if you're if you're 190 cmters, get the XL and take the suit to a Taylor's really stand there in it and get them to take out any of the excess material." Um, because yeah, we could customize kit, but it's going to cost you a lot more than just getting something off the shelf from us and getting it made to measure on you. It's going to be much more accurate you doing it yourself because you'll be there in person. But yeah, I I would push people that way if they're looking for the next step. It's it's fitting things to you personally. Brilliant. I love it, Sam. There's some brilliant insights. Thank you for being so open with sharing all your wind tunnel data and really appreciate you taking the time to chat. Oh, thanks for having me. Great to talk. Thanks for watching Roadman. Take one second. Click up here to subscribe to the channel and click down here where there's another video I know you'll love. See you next day.

FREQUENTLY ASKED QUESTIONS

how much time can wind tunnel testing save in a gravel race?+

Sam Calder's four-hour wind tunnel session with Dylan Johnson at Silverstone produced a 13-watt saving, which projects to roughly 13 minutes off Dylan's Unbound finish time. At the sharp end of gravel racing, one watt equates to approximately one minute, making aerodynamic optimisation one of the highest-return investments a competitive racer can make.

do cycling socks actually make a difference to aerodynamics?+

Yes, and the gains are larger than most riders expect. Sam Calder measured approximately three watts of saving from upgrading to woven sock fabrics at Dylan Johnson's 35kph race pace. Fabric texture and weave construction have a measurable effect on drag at gravel racing speeds, making socks one of the most cost-effective aero upgrades available.

at what speed do aero cycling fabrics like Neo start working?+

Dual-layer Neo fabrics only produce aerodynamic benefit above roughly 50kph. Below that threshold the fabric's surface properties do not interact with airflow in a way that reduces drag, so gravel racers averaging 35kph will see no gain from Neo and should prioritise woven fabrics optimised for lower speeds.

what are the biggest aero gains in gravel cycling beyond the bike?+

Sam Calder's testing with Dylan Johnson showed that kit and fabric choices, helmet selection, eyewear placement, and hydration system setup consistently produce larger gains than wheel or frame upgrades at gravel racing speeds. None of the 13 watts saved during the Silverstone session required any change to Dylan's bike, which highlights how much performance is left on the table through unoptimised clothing and equipment positioning.

NEVER MISS AN EPISODE

Weekly insights from the podcast. The stuff that actually makes you faster.

READ THE GUIDE

The written companion to this episode.

Gravel Cycling for Beginners: Everything You Need to Know in 2026

Gravel is the fastest-growing discipline in cycling. Here's everything you need to know to get started — from bike choice to tyre pressure t…

Best Cycling Podcasts 2026 — 15 Shows Worth Your Ears

Over 200 English-language cycling podcasts are active in 2026. Most aren't worth your time. Here are the 15 that are, ranked across training…

Best Gravel Riding in Ireland: 12 Routes Worth the Effort

Ireland is quietly one of the best gravel riding destinations in Europe. Forestry roads, mountain tracks, abandoned boreens, and greenways —…

FREE TRAINING PLANS

BADLANDS →UNBOUND →

USE THESE TOOLS

RELATED EPISODES

More episodes you might enjoy

Episode

Community14:05

WHY CYCLISTS SHAVE THEIR LEGS: THE REAL SCIENCE | ROADMAN CYCLING PODCAST

Specialized's wind tunnel data says shaved legs save 79 seconds over 40 km. That's more time than a deep section wheelset. But Mike Burroughs, the man who designed Chris Boardman's Olympic gold medal-winning Lotus 108 bike, says rough surfaces can actually reduce drag. So which is it, and does it

Episode

Community22:25

THE PANTANI TEST, THE MAFIA, AND THE DEATH ITALY WON'T CLOSE | ROADMAN CYCLING PODCAST

In 1999 Marco Pantani was leading the Giro d'Italia by five minutes and thirty-eight seconds. By lunchtime that day, his career was effectively over. Five years later he was dead. This solo episode walks through what the Italian Parliament's anti-mafia commission found in 2022, why an Italian prosecutor reopened the file in July 2024, and why, twenty-seven years later, the case is still officially open.

Episode

Community15:36

WIND TUNNEL SECRETS FOR AERO GAINS ON YOUR BIKE | ROADMAN PODCAST

Josh Poertner joins Anthony for another Roadman Cycling Podcast.

with Roadman Podcast

LIKED THIS EPISODE?

Join the Clubhouse to discuss this episode, ask Anthony your questions, and connect with serious cyclists.

Join the Clubhouse — Free More Episodes

Key Takeaways

DYLAN JOHNSON'S 13-WATT WIND TUNNEL TEST | ROADMAN CYCLING PODCAST

Key Takeaways

You Might Also Like

CLAIMS FROM THIS EPISODE

KEY QUOTES

FREQUENTLY ASKED QUESTIONS

NEVER MISS AN EPISODE

READ THE GUIDE

RELATED EPISODES

WHY CYCLISTS SHAVE THEIR LEGS: THE REAL SCIENCE | ROADMAN CYCLING PODCAST

THE PANTANI TEST, THE MAFIA, AND THE DEATH ITALY WON'T CLOSE | ROADMAN CYCLING PODCAST

WIND TUNNEL SECRETS FOR AERO GAINS ON YOUR BIKE | ROADMAN PODCAST

RELATED CONTENT

WHY CYCLISTS SHAVE THEIR LEGS: THE REAL SCIENCE | ROADMAN CYCLING PODCAST

LACHLAN MORTON: WHY HE QUIT WORLDTOUR | ROADMAN CYCLING

PAS NORMAL STUDIOS: CYCLING BRAND TO FASHION LABEL | ROADMAN CYCLING PODCAST

LIKED THIS EPISODE?

DYLAN JOHNSON'S 13-WATT WIND TUNNEL TEST | ROADMAN CYCLING PODCAST

Key Takeaways

You Might Also Like

CLAIMS FROM THIS EPISODE

KEY QUOTES

FREQUENTLY ASKED QUESTIONS

NEVER MISS AN EPISODE

READ THE GUIDE

RELATED EPISODES

WHY CYCLISTS SHAVE THEIR LEGS: THE REAL SCIENCE | ROADMAN CYCLING PODCAST

THE PANTANI TEST, THE MAFIA, AND THE DEATH ITALY WON'T CLOSE | ROADMAN CYCLING PODCAST

WIND TUNNEL SECRETS FOR AERO GAINS ON YOUR BIKE | ROADMAN PODCAST

RELATED CONTENT

WHY CYCLISTS SHAVE THEIR LEGS: THE REAL SCIENCE | ROADMAN CYCLING PODCAST

LACHLAN MORTON: WHY HE QUIT WORLDTOUR | ROADMAN CYCLING

PAS NORMAL STUDIOS: CYCLING BRAND TO FASHION LABEL | ROADMAN CYCLING PODCAST

LIKED THIS EPISODE?