Chris Froome took another huge stride towards overall victory at the Tour de France by claiming his third win of the race with a superbly measured display on stage 17’s individual time trial.The Team Sky leader trailed rival Alberto Contador at all three intermediate splits on the 32km course from Embrun to Chorges, but then swapped his road bike for a time trial bike at the top of the second of two categorised climbs and comfortably overturned the deficit on the descent to the finish line.Contador (Saxo-Tinkoff) paid the penalty for choosing to stay on his road bike and had to be content with second place, nine seconds behind Froome’s time of 51min 33sec, and one second ahead of third-placed Joaquim Rodriguez (Katusha).The result means Froome extends his overall lead to 4min 34sec with four stages to go and remains firmly on course to become Britain’s second successive Tour winner.It was another flawless performance from the 28-year-old, who adopted a risk-free approach on a day marred by rain but nevertheless emerged as the stage’s superior rider.Starting six minutes behind Contador, he was two seconds behind the Spaniard at the first split, 20 seconds down at the second and still 11 adrift at the third.But despite the pressure, he remained calm and stopped to change bikes for the downhill drag to the finish line and duly negotiated the final 12km 20 seconds faster than his adversary.Contador himself rode superbly, eclipsing outstanding efforts from Rodriguez, team-mate Roman Kreuziger and compatriot Alejandro Valverde (Movistar), but he was ultimately unable to make inroads into Froome’s overall lead and now needs a near-miraculous reversal in fortunes in the Alps to claim a third Tour win.Course drenched by rainAll of the general classification rivals were spared the heavy rain that fell during the middle part of the day, but still had to take caution on the damp and twisting descents off the two climbs.Tejay van Garderen (BMC) took the lead just before the deluge in 53min 24sec and as the roads became increasingly treacherous and other riders’ times soared, it appeared the American was on course for victory.But when the downpour ceased, the roads quickly began to dry and Valverde surged to the top of the standings in a blistering 52min 3sec.He was quickly overhauled by Rodriguez, Kreuziger and Contador, but then Froome surged down the final descent to trump them all and tighten his grip on yellow.Contador was elevated to second overall after Bauke Mollema (Belkin) endured a tough day and fell to fourth, while Jean-Christophe Peraud (Ag2r-La Mondiale), who had been ninth in the general classification, was forced to abandon the race after falling twice and breaking his collarbone.