The aero engineers are not amused.
Jean-Paul Ballard spent 14 years as lead engineer for Formula 1 racing teams before co-founding Swiss Side, which provides aerodynamic analysis to the likes of Ineos Grenadiers, Canyon Bicycles, and other teams and companies. Ingmar Jungnickel is the principle investigator in Specialized’s Futures Group, where he helps lead the bike brand’s aero research with athletes and product. Both men are flummoxed at the UCI’s recent announcements to ban both the super tuck and the forearms-on-bars positions, saying the move will make racing slower and less exciting.
“I’ve counted on the super tuck as one of my special weapons and am sad to see this go,” Jungnickel said. “We have tunnel tested that a couple times. The difference is massive — around 20 percent! In fact, it is comparable to the drafting advantage the person behind you has if they are in their drops.”
Ballard, who has advised Ineos for four years, said it’s a weird time with the UCI.
“On one hand, the UCI has recently become fairly progressive about how you can build the bike — an aero bike can now basically be a time trial design. But on the other hand, the UCI is way too conservative in how you can ride the bike,” Ballard said. “You want cycling to be exciting, tactical. It’s like in motor racing: it’s about handling, being able to control your device across the entire course, and also on the descents. If you can super tuck on a descent, why not?”
While the UCI would argue that the ‘why not’ reason is safety, Ballard and Jungnickel have each spent years quantifying the ‘why’ in terms of aerodynamic drag reduction for various positions inside wind tunnels, outside on the road, and within modeling software.
Speed losses, in ballpark terms
“We can talk in terms of coefficient of drag, which is independent of speed, or we can talk in terms of watts at certain speeds,” Ballard said of comparing positions.
Ballard helpfully assembled the following chart for VeloNews, which does both. For each position, the baseline drag figures are averages of pro riders Ballard’s team has tested over the years. (CdA is coefficient of drag times frontal surface area. All other things being equal, less drag means higher speed.)
|Aero Power Component (W) @various speeds (km/h)|
|CdA||Deltas to Ref||40||50||60||70|
|Flat Course Positions:||Absolute||Delta to ref||Absolute||Delta to ref||Absolute||Delta to ref||Absolute||Delta to ref|
|Hands in drops, straight arms||0.260||0||211||0||412||0||713||0||1132||0|
|Hands in drops, half bent arms (1)||0.246||-0.014||200||-11||390||-22||674||-38||1071||-61|
|Hands on hoods, horizontal forearms (2)||0.244||-0.016||198||-13||387||-25||669||-44||1062||-70|
|No hands ‘invisible aerobars,’ horizontal forearms (3)||0.231||-0.029||188||-24||366||-46||633||-79||1005||-126|
|“Aerodynamic suicide” (4) not measured|
|Hands in drops, full bent arms (not pedaling)||0.225||0||183||0||357||0||617||0||979||0|
|Super tuck (not pedaling)||0.194||-0.031||158||-25||308||-49||532||-85||844||-135|
“The difference between a super tuck and a bent-arms-in-drops position, at 60kph, you are looking at a 85-watt difference,” Ballard said. “At 70kph, which is reasonable on a WorldTour descent, that’s 135 watts. It’s a big difference!”
These drag differences can be calculated out for time differences on a given course. Ballard has the profiles of many Tour de France stages, for instance, that he uses in modeling.
As for the forearms-on-bars breakaway or praying mantis position, Ballard and Jungnickel have studied that versus a flat forearms position with the hands on the hoods, and also compared it to a bent-arms-in-the-drops position.
“Riding on the flats in that praying mantis position, compared to the bent-arms-in-the-drops position, you can save 15 watts at 40kph, or 24 watts at 50kph. That’s significant,” Ballard said. “At a 450-watt effort, say for 10 minutes to get a breakaway going, you’re looking at a 24- to 25- savings, or five or six percent.”
Compared to riding with flat forearms with the hands on the hoods instead of just dangling in front of the stem, the differences aren’t huge, Jungnickel said.
“Many riders now have learned that bending your arms is the trick to going faster,” Jungnickel said. “If you can get your forearms horizontal, that saves you roughly 5 percent power. This is compared to a normal hoods position and is faster than your hands in the drops. That being said, for most athletes there is no difference between their hands grabbing the hoods and the ‘invisible aerobars’ — and the hoods position is certainly safer.”
Cylinders are slow
For both the super tuck and the praying mantis/invisible aerobars positions, a common principle applies — cylinders are slow shapes in the wind.
“Your legs make up for 50 percent of your total drag, and your arms for up to 25 percent,” Jungnickel said. “Considering your head is around 15 percent, this leaves 10 percent for the torso. A flat back that is considered so synonymous with a slippery position is actually relatively unimportant compared to getting all your cylindrical appendages out of the way. The super tuck position effectively shortens your legs to the wind.”
While the praying mantis isn’t as big an advantage as the super tuck, Ballard does see its elimination as a detriment to race tactics.
“On flat courses for a breakaway, the lowest aero drag is given by the [praying mantis] position. So banning this position will result in higher drag, and thereby limit the sting of a breakaway and the distance achievable,” he said. “If we use the direct comparison with the second best position, which is on the hoods with horizontal forearms, there is about a 5 percent difference in CdA.”
In all cases, Ballard and Jungnickel emphasize, the faster riders go, the bigger the impact, as drag power increases exponentially with speed.
“Regarding the race outcomes, I think [the UCI bans] remove one technical element and pushes the selection more to pure fitness,” Jungnickel said. “Personally, I am drawn to cycling for the ‘Formula 1 with a human engine’ vibe of it: I love the carbon, the high-end bikes, the wind tunnel testing. I enjoy the tactical finesse and the skill of breaking at the last moment, picking the perfect line through a turn and sprinting out of it. The drafting games and the attacks. Peter Sagan in Richmond super tucking his way to a rainbow jersey. Unfortunately, this display of skill comes with some crash risk. Some people like pure endurance events like running races but you won’t find me watching one on TV.”