Tasmanian Porte was a narrow runner-up in each of the past two years as the South African ace became the first man to win back-to-back titles in and around Adelaide.

The near misses came immediately after Porte - who has been second four times in total - broke through for his only overall Tour success to date in 2017.

McEwen said the sheer number of competitors in contention for stage wins this year made the 22nd edition of the Tour an intriguing and unpredictable prospect.

But he tipped Trek-Segafredo's Porte would use his climbing ability to turn the tables on Impey and rip the balance of power away from the strong Mitchelton-Scott outfit.

"Porte is my overall favourite because we've got both Paracombe and Willunga Hill," McEwen said ahead of Tuesday's first stage at Tanunda.

"Last time we had both of those in the race and Richie got it right, he won both of them.

"The time before, Richie and Cadel (Evans) and (Domenico) Pozzovivo were all looking at each other and Rohan Dennis managed to come back and go over the top and win the stage, and it won him the race.

"But I think Richie's found the right recipe with those two stages, as long as he doesn't lose time somewhere else."

McEwen noted Mitchelton-Scott's Simon Yates had the ability to take on Porte in the climbs, with the undisputed 'King of Willunga' to chase a seventh consecutive win in the signature stage on Australia Day.

However, McEwen said there were question marks over what sort of preparation Yates had been through leading into his Tour Down Under debut, which doubles as his first race of the year.

Yates will form part of a strong Mitchelton-Scott unit alongside Impey, who is aiming to become the second man behind four-time winner Simon Gerrans to win overall Tour honours on at least three separate occasions.

The team includes recently crowned Australian road race champion Cameron Meyer, runner-up Lucas Hamilton and national time trial title holder Luke Durbridge.

Meyer was the overall Tour winner in 2011.

"(Impey) will be up against it because of the two hill-climb finishes, but he's got other opportunities to get time bonuses in intermediate sprints," McEwen said.

"(Then there's) the finish in Stirling and if we have a windy day to Victor Harbour or Murray Bridge, Mitchelton-Scott can do some real damage and force Richie to lose some real time, which they've done before."

McEwen, a record three-time winner of the Tour Down Under sprinter's jersey, will provide expert comments for the Seven Network during the January 21-26 event.

Australian Associated Press