UCI Aero Position Bans – The True Impact.

FD
posted by Fabienne Dirksen
February 13, 2021

So the UCI is banning the Super-Tuck and TT positions on the road bike. Regardless of your opinion as to whether you find this a good or bad decision, it will have an impact on racing and the ability for riders to break away from the peloton. But what is the true impact in concrete and tangible terms, such as in time, distance or speed? As we always say at Swiss Side, the data doesn’t lie and performance can be quantified. So this is what we have done. – Using our already available wind tunnel data on all of these riding positions, coupled with our powerful simulation tools for calculating the time a rider, or group of riders, need to cover a course, we’ve run the sims and got the numbers. This is what they say…

First of all the Super-Tuck in the descent.

UCI Aero Position Bans, Cycling Super Tuck, Swiss Side, Aerodynamics in Cycling

On a fast mountain descent, sitting on the top tube of your road bike can be a bit sketchy to ride but it is measurably faster. For a road cyclist who wants to use their bike handling skills to help break away from the bunch or a competitor, the Super-Tuck is a useful weapon. For this reason, it has become commonplace in modern day tactical cycle racing. But how much faster is it really? What advantage can be gained? In order to quantify this in a concrete way, we can demonstrate the advantage in terms of the following three metrics:

  1. Aerodynamic drag difference measured in the wind tunnel.
  2. Terminal speed difference between the positions on a straight 8% descent.
  3. Time difference between the positions, on a typical 10km segment of a grand tour descent.

 

Results - Aerodynamic Drag (CdA) and Drag Power (W):

UCI Aero Position Bans, Cycling Super Tuck, Swiss Side, Aerodynamics in Cycling

Speeds: 50 – 60 – 70 km/h

 As seen in the table above, at realistic descending speeds of around 70km/h, the aero drag difference is as high as 135W.

In terms of speed and time on the 8% descent, we calculate that the Super-Tuck position sitting on the top tube will bring a 5km/h higher top speed and save 30 seconds per 10km of descent. So this means a rider can potentially build a 30 second gap through the aerodynamic drag saving of this position, if they are riding in the Super-Tuck compared to a chasing rider or group who is not. If this position was banned, this tactic would no longer be possible.

 

Secondly, the TT position (no hands) on the flat.

UCI Aero Position Bans, Cycling Super Tuck, Swiss Side, Aerodynamics in Cycling

 

On the flat, many riders have discovered that they can save a lot of power by riding with the arms in a TT position, leaning with their forearms on the middle of the handlebar. Of course they do not have a TT bar on the bike as we did have for our wind tunnel measurement, but the result is the same. –A big aerodynamic drag saving can be achieved. For this reason, riders in a breakaway, or those in the leading position in the peloton commonly use this position. But how much benefit does it truly bring? What is the impact if it is banned? In order to quantify this in a concrete way, we can demonstrate the advantage in terms of the following three metrics:

  1. Aerodynamic drag difference measured in the wind tunnel.
  2. The difference in gap a rider could achieve in a breakaway, during a 10km effort, using drops (half bent arms) position or the TT position.
  3. The resultant time difference of the gap, a rider could achieve in a breakaway, during a 10km effort, using drops (half bent arms) position or the TT position.

 

Results - Aerodynamic Drag (CdA) and Drag Power (W):

UCI Aero Position Bans, Cycling Super Tuck, Swiss Side, Aerodynamics in Cycling

Speeds: 40 – 50 – 60 km/h

 As seen in the table above, at realistic breakaway speeds of 50 – 60km/h which would be possible in either a solo or multi-rider breakaway, the aero drag difference between the two most likely used positions, (drops with half bent arms, or the TT position), can be between 24W - 41W depending on the speed.

If we take our scenario of a 10km breakaway effort of a rider, if they can no longer use the TT-position, the gap that they will achieve to the peloton or chase group, will be 13 seconds or 180m smaller. This is purely due to the increased aerodynamic drag in the ‘hand on the drops position with half bent arms’. In tactical cycle racing, these are considerable amounts. However the assumption here is that the leader of chasing group / peloton is not riding in the TT position. Providing everyone is riding the same position, i.e. both the leader of the breakaway and the leader of the chase group, then there is no difference. However in reality, the chase group / peloton is never quite as disciplined as the breakaway rider(s) with the lead rider of the chase group not always using the best aero position.

 

Opinion:

In terms of aerodynamics, the impact is clear, quantifiable and undeniable. Banning the Super-Tuck position on descents will increase aerodynamic drag and decrease speed. On the flat, banning the TT-position on the road bike will have the similar effect and take the sting out of what is achievable by breakaway riders, by reducing the physical distance and time they can gap themselves to the peloton. Tactically, it simply reduces the tools the riders and teams have in their bag to plan and execute attacks. Certainly there is an element of risk involved in riding either position, because the level of control on the bicycle is reduced. However, it could be argued that professional cycle racing is not just about the physical abilities of the riders but their technical skill and abilities to ride their bike. This certainly is the case in mountain bike and cyclocross racing, so why should it be any different in road racing? Furthermore the excitement in road racing also inarguably comes in part from the tactics and the breakaways. Take this away and the racing will be less exciting and thereby less entertaining.

In any case, it is indeed true. With this rule change, the aero engineers are not amused!

 

Athlete: Emma Bilham // Photos: @nevisroad