Avid watchers of professional bike racing will undoubtedly have spotted it: the black and white striped sleeves poking out of heavily branded team skinsuits and jerseys, or riders sporting tight-fitting crop tops as they warm up on turbo trainers. There’s no doubt that Rule28’s aerodynamic base layer stands out, and it’s becoming more and more common for it to be seen on the shoulders of the world’s very best riders. But what’s the science behind such a small section of material having an impact when it comes to aero gains?
“It kind of works like a smart material,” Sam Calder, founder of Rule28 explains. “If you think of a suspension bridge, the ribs on the base layer push into the fabric of the skinsuit so you get this draping of the fabric between two raised points. The surface profile changes depending on the pressure of air. In the low pressure behind the arm, it won’t have so much of a raised structure as on the front of the arm where the area is high pressure. It works a smart material in that way so you get the benefit of increased texture in the areas where you need it and less where you don’t need it, which you wouldn’t get from a traditional sleeve where the texture is constant.”
The striped fabric ridges on the sleeves of the baselayer bulge through the fabric of your skinsuit or jersey and ‘trip’ the airflow from laminar to turbulent. This creates what is called a boundary layer of airflow around a rider’s arm, reducing the size of the low pressure wake behind the arm and hence aerodynamic drag. Rule28 has also recently introduced a new aero base layer designed for speeds of over 50kph that are regularly hit in track sprinting. In the High Speed Aero Base Layer, the ribs on the sleeves are closer together than in the regular option – Rule28 has found this to be more effective at high speeds.
“The rule of thumb is that the higher the speed, a slightly narrower spacing works. There are some people that it doesn't work on but in the testing on a test rider who is a South African track sprinter, we found a really good increase in performance above 50kph. The new baselayer is aimed at track riding and road sprinting,” Calder explains. “There's the trade off to say, is it worth it being slightly less optimal throughout the majority of the stage in order to then when you launch your sprint be saving that little bit extra energy? Or do you go with the traditional base layer and save slightly more throughout the day, but be less efficient when it really counts?”
The Rule28 base layers embody the same concept that has been used in garments like aero socks, which is the area of cycling clothing in which Rule28 was founded back in 2017.
“The first products were aero socks,” Calder says. “The thinking behind those was that there's a lot of thought and effort put into skinsuits to make sure they're as fast as possible and the majority of the advantage you get in a skinsuit is by adding texture to the arm. When you think about the shape of an arm, really, it's just a smaller, lower leg in terms of the angle it moves through the air and the rough shape of it. So anything that works on the upper arm should, in theory, work on the lower leg.”
Four prototypes of Rule28 socks were used by the Derby-based track team, Team KGF (latterly called HUUB-Wattbike and then including current Team Ineos Grenadiers aerodynamicist Dan Bigham), and they were worn to a British national title in the team pursuit on the track.
“It was never really supposed to be a business but there were quite a few people that saw the socks, were interested and said, ‘I'd like to get some of these’,” Calder explains. “We initially had no funding at all. We started doing pre-orders for socks and that went into buying more stock and it just snowballed from there. For the first year and a half, we were out of stock more than we were in stock for socks, then we brought out overshoes and skinsuits and really have just been expanding the business from there, now offering a full range of kit.”
Calder’s idea for an aero base layer sparked in 2019 and it was released soon after the Covid-19 pandemic when professional racing began to kick off again in earnest. The recently released high-speed version of the base layer for speeds of over 50kph took five to six months of testing to perfect, the majority of which was done in the Silverstone Wind Tunnel Facility. Despite the complexities of the garments Rule28 is creating, it is still only Calder who works full-time on developing products.“It’s me full-time and then we will test in the wind tunnel. We have quite a big collection of test riders that we can draw in. I work specifically with factories that I've worked with now for four years on our custom fabrics. It's quite a long process to get right, but it's my brain child,” he explains.
Rule28’s progression from Calder's idea to a product coveted by many WorldTour teams is an impressive one. Calder explains that Rule28 skinsuits and base layers are on offer in Silverstone Sports Engineering Hub’s equipment room, which means they are often used when riders are undergoing aerodynamic testing, something he sees as key to getting the products used in the professional ranks.
“It's a very, very good place to go and test and it's where we developed all of our kit and it's where a lot of teams go to test as well. We've had teams test the base layers there that we've provided for the equipment room and then get in contact immediately,” Calder says.
“This was the case with UAE Team Emirates this year. They said, we want to order a whole range, can you deliver them to our hotel in Silverstone? Even though for client confidentiality, Silverstone doesn't tell you who's training there, the fact that they're being delivered to the hotel right next to Silverstone kind of gives it away that they've tried it, they’ve got good gains and they want it as quickly as possible.”
Teams wanting to use Rule28 products even when the company isn’t an official kit supplier is certainly a positive affirmation for Calder that the products really do work.
“It reminds me of when SRM used to have that claim to fame where they didn't sponsor any rider or team, yet the majority of riders were still using SRM power meters, because they just were the best,” Calder says. “I think if we were to sponsor a team, you'd probably get more visibility. But to those in the know, I think it means even more knowing that these riders have gone outside of their sponsorship agreements to wear our kit. We've had some teams buy them directly. We've had some kit suppliers buy them from us, and then cover the labels over which is quite funny to see. We have some teams that we are providing kit for white labelled so that it doesn't annoy their sponsors.”While Rule28 has risen to fame at the highest level of professional cycling, Calder notes that the base layers are not only for professional riders. Though he adds that they are most likely to be worn by those looking to add every incremental gain to their riding, the products are designed to be versatile enough to be used with a range of skinsuit types from various brands.
“The reason we went for quite a pronounced rib structure on our base layer is so that it is quite versatile. It will work under a lot of different jerseys and skin suits whereas other ones like HUUB, when we've tried them out and what we've heard from people testing the wind tunnel is that it is specifically one of their skinsuits that is required for it to work,” Calder says.
The product will work better when worn alongside a smooth armed skinsuit, however, as using a ribbed arm skinsuit can interfere with base layer stripes and could even be more draggy as a result. Rule28 found that at 60kph, when paired with the smooth armed Rule28 Neo TT Suit and compared to the Rule28 2021 TT Skinsuit, the aero base layer yields a power saving of 22.1 watts.
So, with their products being used in the WorldTour and widely regarded as the fastest in the game, what’s next for Calder and his pioneering business?
“There are a few different products we have in the pipeline. We've got some winter stuff coming up. We're going to try and create a range of winter aero kit, because that is pretty lacking at the moment,” Calder says. “It's a bit trickier to do, you're never going to get as fast as full-on summer kits because you're limited as you have to keep riders warm. But it's a market that's not really served at the moment and the technical know-how to be able to do it now is quite good, so we can offer thermal fabrics that are water repellent, whereas a few years ago, those just weren't on the market. We want to create an aero long sleeve jersey and potentially even a winter skinsuit which will be both thermal and water repellent.”
In an era where the level in cycling is only getting higher and higher, Calder’s creativity and innovative products likely will only become more popular as riders search for every marginal gain. Rule28 is not a company you might have heard of, but it feels like a name to watch and remember for years to come.