Do Speedometers Lie?

Sep 06, 1997

RAY: A few weeks ago I was test driving a BMW with a 5-speed transmission. And my soon to be 12-year-old son Andrew and I were driving on one of our weekly pilgrimages to Toys R Us or some such place. And we're driving along the highway, and he says, as he always does when we drive a test car, he looks over at the speedometer, "Geez Daddy, will this thing really do 160?"

TOM: And indeed it does go up to 160.

RAY: The speedometer says 160.

TOM: 318 Convertible.

RAY: I wasn't about to divulge that piece of information.

TOM: Well, forget I said that.

RAY: I'll forget you said that. And I was driving along, I looked at the speedometer, looked at the dashboard, and I said, "No it won't."

TOM: Ooh. Just like that?

RAY: Now, I am going to give a hint.

TOM: Had you been reading any manuals? Car and Driver?

RAY: No.

TOM: Car and Drivel?

RAY: No, nothing like that.

TOM: None of the above.

RAY: I'll give a hint. A week later, he and I were again driving to Toys R Us and this time we were driving in a Mustang with a 5-speed manual transmission and again he looks over and says, "Geez Daddy, will this one do 160 because that's what its speedometer says?" And I look down to verify, I looked at the dashboard, and I turned to him and said, "Yes, it will."

TOM: Did he say, "How do you know Daddy?"

RAY: I said, I just know.

TOM: Trust me.

RAY: How did I know? That's the question.

RAY: Here's the answer: Because when I looked down at the dashboard, I not only looked at the speedometer, but also the tachometer. Both of these cars redline at about 6,000 rpms. Anything over 6,000, you're in danger of having the pistons become part of the environment. At 60 mph, the BMW was doing 3100 rpms. I knew that at 120 mph it would be beyond the redline and incapable of doing 160 mph. 6200 rpms only got me to 120. So I knew I was going to be well into the red zone and probably decorating the highway with pistons. The Mustang Cobra at 60 mph was doing less than 2000 rpms -- it was doing about 1750 rpms. It turns out that we called the Ford Special Vehicle Team and they said it wouldn't do 160 mph. I was able to get it to 155.

Get the Car Talk Newsletter