Riders suffered in Friday’s heat as the peloton gave up its pursuit of an escape group.
The peloton had already been punished by the two days of monster mountain climbs, such as the Alpe D’Huez won by Tom Pidcock.
On Wednesday’s dramatic stage to Col du Granon, two-time defending champion Tadej Pogacar, known to dislike heat, wilted and lost his lead in temperatures well over 30 degrees.
“It was horrible, a furnace,” said French climber Thibaut Pinot.
His compatriot Romain Bardet said the following day had been worse.
“I was trembling and my pulse was racing,” he said.
But with sizzling air temperatures of 38-40 degrees forecast over the weekend, as the race moves towards the Pyrenees, the situation will be even worse.
As a result, special measures are being readied.
French departments road safety organiser Andre Bancala told AFP at the foot of the Alps on Friday that record road temperatures of 63 degrees could be beaten.
“During a heatwave, such as the one we are expecting of over 38 degrees, the road temperature gets much higher than that, around 60 degrees,” Bancala said.
“The absolute record for heat was in 2010 with a road temperature of 63 degrees when Sylvain Chavanel won in the Jura,” he added.
“But this weekend we may even break that, so we are mobilising between us and the fire brigade, to combat that.
“In certain places, the asphalt is going to start melting, not everywhere of course, but it is going to get much softer. So you can imagine how that might end?
“The solution will be to pour water on it,” he says explaining the Tour has a permanent truck for such demands.
The fire brigade will also be on hand to help execute the manoeuvres.
“We will have vehicles with 10,000 litres of water taken along the way, the regional departments are going to help us to cool the roads.”
But the logistical nightmare doesn’t end there.
“You have to do it at just the right moment, if you do it too early it just heats up again.
“If you do it too late the peloton rides onto wet surfaces. It has to be around 15 minutes before they get there,” he says.
“Think about it. If the road surface is 55 or 60 degrees, and the pedal is ony 20cm above that, then the rider is subject to exposure to extreme temperatures.”
Much has been made of how Jumbo team riders, including Tour de France leader Jonas Vingegaard, have been wearing cooling jackets ahead of the stages as the heatwave builds up.
They are the only team using such jackets for none time-trials.
After Friday’s stage Vingegaard said the heat hadn’t been a problem for him personally.
“Regular cold drinks and ice packs on the back as often as you can during the race to keep the body temperature down, that’s what you do,” said Vingegaard.