Police said today they are keeping on eye on cyclists on the route of the cancelled event, from Norwood to Uraidla in the Adelaide Hills.

Tour Down Under organisers announced yesterday that the ride had been cancelled due to today’s extreme heat. That decision means that all support facilities – including food, mechanical support and medical services – had been withdrawn.

“As the event was due to be held on public roads, there is nothing to prevent riders being on roads used by the course, but organisers strongly recommended that cyclists not ride the route for their own safety,” SA Police said in a statement.

Police revealed they had received a traffic complaint about 100 cyclists on North East Rd, including children, spanning the road.

They urged motorists to be patient in the area, which was being monitored by Police and ambulance officers.

“Given the extreme heat, I would urge all riders to make sensible choices today – don’t put yourself or others at risk,” said Assistant Commissioner Scott Duval.

“There is some water available at the planned refreshment stations, but these are not staffed.”

Meanwhile on the professional Tour, today’s fourth stage from Norwood to Uraidla gives the overall contenders a chance to assess their chances.

The 128.2km stage is the day before the crucial Queen stage at Willunga, where the race winner will be confirmed.

Porte, who is well-positioned at 20 seconds behind race leader Caleb Ewan, wants to be the first champion to successfully defend his title in the Tour’s 20-year history.

The stage started an hour early because of the blast furnace conditions and a mass-participation ride scheduled for earlier in the morning was cancelled.

The Uraidla finish is new to the Tour and it comes after the Norton Summit climb, an Adelaide cycling landmark.

“Obviously it’s a tricky one … I think it’s going to be fireworks on Norton Summit, especially in this heat,” Porte said.

“It’s not the hardest climb, (but) the wind might be a factor also.

“Everybody is suffering, we’re all in the same boat.

“There’s nowhere to hide when it’s so hot.”

Fellow Australian Nathan Haas is one of Porte’s key rivals for overall honours.

Haas said if riders want to attack, they will have to be careful when they make their move.

“It will be a brief visit to our friend Mr Pain today,” he said.

“You will only get one bullet today with the heat, so you have to time it just right.”

– with AAP