Descending faster and safer: position, corners and cold

The short answer: on a long descent the air is almost the only thing holding you back, so your position decides your speed. A low back with hands on the drops has a fifth less drag area than sitting up. But the time is won in the corners too, and a cold rider descends badly.

Position: lower and narrower

Fifteen descent positions of the same rider were measured in a wind tunnel and in computer simulations ¹. Drag area (CdA) of rider and bike, sitting on the saddle:

Position	CdA
Back up, sitting upright	0.277 m²
Elbows resting on the bar	0.258 m²
Back horizontal	0.236 m²
Back low, hands on the drops	0.222 m²
Back low, forearms on the bar	0.214 m²

The fastest positions in the study were on the top tube, the best at 0.201 m². The authors’ own choice for a descent where you also need to pedal and steer is the low back with hands on the drops, or a flat back: positions that keep your weight over both wheels and your hands on the brakes ¹. That is our advice for a fondo too. A few percent of drag is not worth giving up control on an open road.

What those numbers mean, worked out for an 85 kg rider and bike coasting down a 7% descent: about 65 km/h sitting up, about 73 km/h in the low tuck on the drops. Over 5 km that is half a minute, for no extra effort.

Pedal while it pays

At low speed on a descent, pedalling still adds speed. As you get faster, more and more of each extra watt goes into the air, and the tuck gives more than the pedals. Ease off and tuck once the descent runs away from you, and use the time to recover; see Race strategy.

The time is in the corners

Speed on the straights is only half of it. When eight World Tour riders were measured on the same descent, the fastest rider overall gained his time on the straights but lost time in the corners, and the corners kept changing the order. Through the tightest hairpin, the fastest braked 10–20 m later and took a tighter line on the inside ². How to take a corner is in Cornering.

Cold and wind

Descending at 60 km/h after a climb in a sweaty jersey is cold, and the top of a pass can be much colder than the valley. Cold hands brake badly and a shivering rider steers badly. Carry a jacket or a gilet over the top, and put it on before you start down.

Wind matters on descents too. A crosswind on an exposed stretch pushes a bike at speed sideways, and a headwind slows the whole descent.

Check the descent before race day

Race weather shows the temperature and the wind against the road along your whole course, at the time you get there, so you know whether the descent off the last pass will be cold, and where the wind will be across it.