Riding in a group: where the shelter is, and how to use it

The short answer: the best tactic for most gran fondo riders is simply to stay in a group, and in the right place in it. Right behind one rider you have about a quarter less drag. Deep inside a large group you can have as little as 5–10% of the drag of a rider alone. The front, and the edges near it, cost far more.

What one wheel is worth

Riding close behind one other rider, with almost no gap, cut drag by about 27% sitting upright, 23% on the drops and 14% on aero bars, in a wind tunnel. The gain shrinks as the gap grows. Even the rider in front gains 1–3% from the one behind ¹.

What a big group is worth

In computer simulations of two pelotons of 121 riders, checked in a wind tunnel, every rider had less drag than a rider alone at the same speed ²:

Where in the group	Drag compared with riding alone
The leading rider	86–94%
The front edges	59–67%
The middle and towards the back	5–10%

Deep inside, at 54 km/h, a rider had the drag of someone riding alone at 12–17 km/h. Older models assumed 50–70% for everyone in a peloton; that is closer to the back of a small line of riders than to the inside of a big group ².

In watts, worked out for a rider with a drag area of 0.25 m² at 40 km/h: about 200 W of air resistance alone, about 120–140 W on the front edge of a group, and only 10–20 W deep inside it.

Tactics that follow from this

• Get in a group and stay in it. Being dropped from a group on the flat costs more than almost anything you could gain elsewhere. It is often worth a hard minute to hold on over the top of a climb.
• Ride inside, not on the edge. The edges near the front are almost as exposed as the front itself. A little further back and inside, the shelter is huge.
• Take your turn short and steady. If you ride through and off in a small group, a smooth, short turn at the front costs less than a long hard one, and keeps the group together.
• Move up before it matters. Shelter at the back is cheap, but the back is where gaps open on a climb or after a corner. Move up before the road narrows or rises, along the inside where you can.
• Hold your line. Riding close only works if nobody swerves. Signal holes and obstacles, and don’t brake suddenly in a group.

Wind changes the picture

The simulations were done in still air ². In a crosswind the shelter moves to the side away from the wind, groups spread across the road in echelons, and riders at the end of a row that runs out of road get no shelter at all. Know where the exposed stretches are before you get there.

Check where the wind will be

Race weather shows headwind, crosswind and tailwind for every 200 m of your course, at the time you ride past, so you can see where the group will matter most and where an echelon may form.