aerodynamic benefit of drafting, whereby a rider can significantly reduce the required pedal effort by closely following in the slipstream of the rider in front. Riding in the main field, or peloton, can save as much as 40% of the energy employed in forward motion when compared to riding alone. Some teams designate a leader, whom the rest of the team is charged with keeping out of the wind and in good position until a critical section of the race. This can be used as a strength or a weakness by competitors; riders can cooperate and draft each other to ride at high speed (a paceline or echelon), or one rider can sit on a competitor's wheel, forcing the other person to do a greater share of the work in maintaining the pace and to potentially tire earlier. Drafting is not permitted in individual time trials. Breaks A group of riders that "breaks away" (a "break") from the peloton has more space and freedom, and can therefore be at an advantage in certain situations. Working together smoothly and efficiently, a small group can potentially maintain a higher speed than the peloton, in which the remaining riders may not be as motivated or organized to chase effectively. Usually a rider or group of riders will try to break from the peloton by attacking and riding ahead to reduce the number of contenders for the win. If the break does not succeed and the body of cyclists comes back together, a sprinter will often win by overpowering competitors in the final stretch. Teamwork between riders, both pre-arranged and ad hoc, is important in many aspects: in preventing or helping a successful break, and sometimes in delivering a sprinter to the front of the field. Terrain and conditions To make the course more selective, races often feature difficult sections such as tough climbs, fast descents, and sometimes technical surfaces (such as the cobbled pavé used in the Paris–Roubaix race). The effects of drafting are reduced in these difficult sections, allowing the strongest riders in the conditions to drop weaker riders, reducing the number of direct competitors able to take the win. Weather, particularly wind, is also an important discriminating factor. Climbs Climbs are excellent places for a single rider to try to break away from a bunch, as the lower riding speeds in a climb seriously reduce the drafting advantage of the bunch.