"We're concerned with the credibility of the comparison . . . really the factual nature of the ad itself," said Baba Shetty, manager of marketing communications at BMW.
BMW protested the ad in a letter to GM General Counsel Tom Gottschalk this month.
The controversy stems from the tires used on the two cars, not the headline, which reads: "Ultimately this is the driving machine in slalom." That's a play on words of BMW's "The ultimate driving machine" ad tagline.
The small print in the Cadillac ad reveals that the Seville was tested with optional Z-rated tires, while the 540i ran the course with standard H-rated tires.
"They put performance equipment on the Cadillac, but elected not to do that on the BMW," Mr. Shetty said. "That's not an apples-to-apples comparison."
Z-rated tires are certified for a top speed of 150 mph; H-rated, up to 118 mph, said a Cadillac spokesman. He said Cadillac had not heard anything about the flap from GM's legal department or from BMW, and has no plans to pull or change the ad.
Mr. Gottschalk was unavailable for comment. And Terry Rhadigan, manager of safety and legal affairs at GM, said he could find no one on the legal staff who knew of BMW's letter.
'THAT'S WHERE WE'RE AT'
Seville Brand Manager Steve Rosenblum said Seville advertising, both TV and print, "is all comparative of sorts. That's where we're at."
Agency D'Arcy Masius Benton & Bowles in Troy, Mich., declined to comment.