The amount of energy a rider saves while drafting is usually quoted as 40%. It is scientifically proven that drafting in a paceline can save between 20 – 40% energy. This is substantial which is why you should notice that you need far less energy drafting. The energy savings will depend on the wind direction and speed, how far behind you are behind the rider in front and technique.
A group of road cyclists riding together are usually called a bunch. The lead riders break the wind with following riders reaping the benefits. When the riders start to regularly swap the position at the front it becomes a paceline. The objective of the paceline is to move faster so this allows each rider to have a turn at the front before returning to the back to recover.
Paul Doherty of The Exploratorium provides more details on the science of drafting.
In cycling races a group of breakaway riders from different teams are forced to work together and start a paceline. A single rider however can ‘leech’ off the paceline. If they refuse to take turns at the front this can cause the breakaway group to slow down so the peloton can catch up, or it is to save energy for the sprint finish.
Pacelines are an important part of the strategy in competitive cycling. At the sprint finish for example, a lead-out is where a cycling team will align its riders in line to provide as much drafting cover for their champion sprinter as the race towards the finish. Each exhausted rider will peel off, one-by-one and done well, the champion sprinter is only on their own for the last stretch to the finish line. Such is the advantage of the lead-out that riders from other teams will draft behind champion sprinters and compete for line honours.
Doubles and Singles
Depending on the size of the bunch, the road and traffic conditions and the wind, a bunch will typically ride in single file or two abreast, doubles. For competitive events, a bunch can be much wider as riders challenge for positions towards the front.
For cycling on open roads, a bunch may need to change from doubles to singles to allow traffic to pass or move from singles to doubles when there is more space.
A paceline means that the riders in the group rotate position, typically each rider has a go at the front. Commonly the rider or riders at the front will peel-off and slowly move to the back of the bunch, the next two riders move up and take the lead.
The time at the front can depend on many factors, riders may choose to stay at the front until they need a break, there may be an allocated time (by the ride captain) such as 2 minutes or 5 minutes at the front (or based on distance) or riders inside the bunch may call the lead riders to ROLL if they feel that the bunch is slowing. When the lead riders decide to peel-off they may call ROLLING to inform the riders following and also give hand signals to suggest the riders behind need to move up.
A faster paceline technique is a Rolling Paceline (or Circular Paceline). Rather than lead riders peeling off, instead riders from the rear race up to the front and position themself on the lead and this pattern continues. It require more energy by the riders but is also a means that much higher speeds can be achieved so this technique is popular in team time trials.
The following short video is headcam footage of a rolling paceline.
An echelon is a paceline which changes formation to accommodate a cross wind. Wind is a significant factor which can slow a paceline down and rarely can a bunch rely on a perfect head-wind, tail-wind or no wind.
In the echelon formation, riders position them self in the wind-shadow and it may mean that the bunch becomes further spread across the road. If it is a double-paceline, the riders in the wind-shadow will all be protected while the cyclists facing the wind all have to work harder. The bunch can protect a rider and help them to save energy by positioning them well inside the bunch.
For more on bunch riding and paceline formations, technique and etiquette, download the Free Bunch Riding guide.