The Yorkshireman, who won the race for Bentley last year, has joined the Team Veloqx-run Audi UK squad in an attempt to retain his title and testing over the last week at Road Atlanta has convinced him he made the right decision.
Smith managed three days of testing as Audi UK prepare their two-car team for the Sebring 12 Hours next month and the Beverley-born driver was pleased with the results.
"I had a good feeling in the car immediately," he said.
"The Audi R8 is a very different car to drive than the Bentley that I have been used to in recent years and it requires a different driving style.
"It's a relatively easy car to drive which now features subtle aerodynamic changes compared to the R8 I drove in 2001.
"The team has made a massive leap forward," he said.
Ex-Formula One driver Johnny Herbert will be one of Smith's team-mates for Sebring along with Jamie Davies and the three-time grand prix winner was also impressed with his first taste of the Audi UK machine.
Herbert, from Essex, is familiar with the Audi R8 having driven successfully in the American Le Mans series in recent years, but even he was surprised by the car's consistency in testing.
"Both cars did a race simulation lasting almost three hours during yesterday which was run in cool, overcast and showery weather conditions," he said.
"I broke into the 1 minute 11 second lap times which was pleasing, but the more rewarding aspect was the consistency of pace throughout the race run by all three drivers, in changeable conditions.
"Both cars are evenly matched we started the race simulation nose to tail and finished together."
The team completed over 1,500 miles in total and another of their British contingent, Allan McNish was content to acclimatise to sports cars after his stint in Formula One.