FRIDAY OCT 7 / 2016 / by Andrew Talati

Benefits through the Bunch

A bunch rolling along the countrysidePhoto courtesy of Nathan Chan "The Flash"

From the leading rider  back through the bunch, all riders can benefit by where they position themselves and following some tips.Single paceline formation

Generally the second rider will receive a 25-30% benefit, with the third and forth riders getting in excess of 30% reduction in power output while a large pack can experience up to 40% reduction while sitting mid-pack.

See the Faria paper (Faria et al. - 2005 - The science of cycling factors affecting performa)
Also the Lukes Paper (Lukes et all., 2005 - The understanding and development of cycling 

 

Smooth is fast

Eric Haakonseen found that some riders were expending more energy getting back onto the last wheel that compromised their ability to pull the turn when they returned to the front.

When the rider goes from second wheel to the leading rider, the amount of wind increases significantly, the power demand goes up but the ideal is for the athlete not to accelerate, otherwise the other riders must therefore accelerate and more gaps are created by the trailing riders’ wheels and their aerodynamic benefit is diminished.

Repeat this dozens of times and eventually it will take its toll on a bunch ride. Some riders may fatigue a lot earlier. so the ultimate goal  is being smoother and creating a steady speed and pace.

Transitioning within the bunch

The transition from finishing a turn up the front and moving across too quickly means a rapid acceleration to get back onto the wheels and therefore a spike in power output which adds up when being repeated dozens of time over a ride.

Rolling turns social keeping it smooth

Also remember to accelerate slightly so you are moving diagonally across rather than swinging directly across and potentially clipping the wheel of the rider behind.

Use your speedo

An easy way to keep a steady pace is to quickly glance down at your speedo but often this is easier said than done if you going fast and trying not to clip the wheel in front, especially if you’re like me and do your riding early in the morning.

Not being twitchy 

Ideal distance to other riders in the bunchPhoto courtesy of Ben McIntyre www.bjmdesign.com.au

There are some unfavorable rider rider interactions in drag when you are immediately next to a rider. You need to be at least 1.5m apart (distance between sholders) as you move backwards in the train. This was based on findings by Nathan Barry, Monash "For two riders drafting directly inline there was a maximum drag reduction of 49% for the trailing rider and over 5% for the lead rider. During overtaking a drag increase of over 6% was recorded with riders positioned side-by-side." who showed that you can be too close side-by-side.

The proximity to riders in front, behind and beside you will increase the potential twitchiness, i.e. riders going onto the breaks or constantly accelerating or decelerating to avoid other riders.

Ultimately, this will amplify to the riders in the back of the group and conversely place greater demands on energy consumption with gaps being formed or getting back on the gas to get closer to the wheel in front, in bunches we call this the ‘rubber band’ effect.

So, keep it safe by not being too close, i.e. 10cm may be ok for a well oiled machine but any closer and the risk of crashing increases.

Communication is supreme

Proximity to other riders in the bunchPhoto courtesy of Ben McIntyre www.bjmdesign.com.au

Maintain good communication during and after is important for improving a rider’s awareness while transitioning from the back to the front.

And while some may find it deflating to their ego, be open to advice and positive feedback whether on the ride itself or back at the coffee shop. It's difficult to have that awareness of where you are relative to other riders, i.e. if you have gapped a rider from getting close to clipping another wheel.

Those riders around you have the front row seat and you can gain valuable insights, ‘Hi John, when you hit the front, this is what happened.”

Remember nobody is out to embarrass you, rather than help to improve your bunch riding skills and make the ride more enjoyable for all.

Enjoying the bunch ridingPhoto courtesy of Brendan Edwards @thedandenongranges

However, to complicate matters it can come down to an individual’s physiological makeup - where a sprinter may find the rapid acceleration more efficient being  anaerobic (conversion of energy without oxygen) whereas an endurance athlete may find the slower motion means that they are staying aerobic. This may be an area for further research of strategies based around the individual.

Best sequence of riders

Even the combination of riders has an effect where you have the taller rider sitting behind the smaller rider means they are less shielded from the wind and expending more energy. Whereas a smaller rider can gain an aerodynamic benefit by drafting behind the taller rider before their turn.

But consideration must be given to allowing riders to sit behind those wheels they feel comfortable with.

One complete system moving through the air

Bunch forming one complete system moving through the airPhoto courtesy of Ben McIntyre www.bjmdesign.com.au

Overall the whole bunch becomes one huge system with all the individual parts forming one complete system. While it is widely shown that the second wheel can get a 30% reduction in wind resistance, the leading rider can also get a slight reduction of 1.5 -2%. There is a collective benefit for all the members of the bunch. Therefore the  trailing cyclists fill in the low pressure area behind the leading cyclist which is similar to a tear drop helmet where the tear drop is filling in the space behind the head so it improves the shape and reduces the drag.

The Blocken paper (Blocken et al., 2013 - CFD simulations of the aerodynamic drag of two drafting cyclists) discusses the interaction between two riders and how the leading rider gets a small advantage by having someone on their wheel. It also shows that the trailing rider can be more aerodynamic by being in the drops or TT position vs upright

The more the merrier

The more the merrier in the bunchPhoto courtesy of Ben McIntyre www.bjmdesign.com.au

When trying to move your bunch quickly, the more the better. If you only have 3 riders doing the work up the front then you need to be more strategic in choosing how long each rider completes their turn. Each rider will need to spend 15 -20 seconds up the front.

So, try to balance the time spent up the front to ensure the other riders get a rest and recover sufficiently before doing another turn; more riders equals less time up the front and more time to recover.

Having 4 riders enables you to have a true pace line, by adding one more rider you can have the riders rolling through and have an efficient rotation while allowing for recovery.

In the Pro ranks, a team trail of 8 riders can really motor along and are exceptionally fast for quite a long period of time.

Practice makes perfect

Like anything you do, practice makes perfect, especially getting familiar with the regular riders and their individual nuances when transitioning.

The ultimate goal is that awareness becomes second nature so they are always strategically in the correct position relative to other riders.

Being bigger can be better

While you may think that a bigger riders would be creating more aerodynamic drag, some studies have shown their shape is more aerodynamic and more favourable. Their body surface area relative to their power output can produce a slightly lower aerodynamic drag. For example the difference between a small climber like Nairo Quintana versus Fabian Cancellara, where Quintana will not have the additional power output that he needs to overcome the additional surface area to cut through the air, so having a net surplus of energy from your frontal area.

This is why you don't see climbers out the front driving the bunches, it’s not the power they can produce but they have a relatively larger surface area they need to punch through the wind. However, climbers like Richie Porte can get into an exceptional efficient are dynamic position.

The Padilla paper (Padilla et al., 1999 - Level ground and uphill cycling ability in professional road cycling) discusses the aero advantage or bigger cyclists:

Body surface area and frontal area increase aerodynamic drag. Both of this are high in larger cyclists. However, bigger cyclists have lower Body surface area relative to their total body mass ratio; and a lower frontal area to body mass ratio. Assuming body mass correlates with power output (roughly a pound for pound increase in power output with increased mass), than relative to their body mass, bigger cyclists have an aerodynamic advantage. This is why we rarely see small time trialists or breakaway specialists, however on climbs where the speeds are lower, aerodynamics are less important and their low mass becomes an advantage.

Tips when riding in a bunch

Tips when riding in a  bunchPhoto courtesy of Ben McIntyre www.bjmdesign.com.au

Some key coaching cues while Eric Haakonssen was working with the TTT (Team Time Trial):

  • Hold a stable line on the front: by riding like you’re on a rail, you keep things smooth and stable and avoid small movements which get amplified for the trailing riders.
  • Important that the lead rider looks ahead to the line they are intending to take. Also important for following riders to be looking up and ahead, and almost looking through the bike.
  • Being in line with the rider in front is far superior aerodynamically, even over a longer distance.
  • Lateral deviation can cause big increases in drag, ie stay directly behind the rider though safety first
  • When feeling strong, pull longer not harder turns.
  • When fatigued, pull shorter turns at the consistent pace.
  • If the pace has fallen and needs to increase, this should be done gradually.
  • Stay in the aerobars/drops until you are at the back.
  • Shrugging is aerodynamically more efficient to reduce the frontal area
  • Make sure it is clear when you are done on the front and maintain pace or slightly accelerate as you swing off. Don't drop the gas too much as you go backwards or you will decelerate too much. In a bunch ride, a flick of the elbow can be a useful indicator.
  • Select the gear for your turn on the front while you are in second wheel so you don't jerk around when you hit the front.
  • The lead rider should not accelerate too much our of turns as there will be a concertina effect for the trailing riders. Accelerate gradually.

Article kindly contributed by Eric Haakonssen PhD
Senior Physiologist | Australian Institute of Sport

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