The Socrates Wheel

The not so well considered statement of the day was made by my boss. Sorry. Here's the conversation:

G: "Last weekend I put the snow tires on my car."
M: "Sounds like fun..."
G: "It was pretty tricky, because they are larger."
M: "Huh?"
G: "Yeah, the circumference is slightly larger and I almost couldn't fit them in the wheelhouse."
M: "Did you have to adjust your speedometer?"
B: "Oh, you don't have to adjust them, because the velocity is measured on the axis, not on the outside."

Usually, my boss (person B, as you might have guessed) is a smart guy. But this time, he got himself into hot water and I could hardly keep myself from pulling a Socrates on him.
(Okay, actually I don't know if you can really say "to pull a Socrates". What I mean is that I wanted to ask him stupid questions about the things his overhasty statement implied in order to make him realize that what he said does not make sense. Socrates used to do that a lot when he hung around at the market place.)
Since I'm not exactly good at dealing with human beings (back on Mars, etiquette was completely different!), things might easily become embarrassing for at least one of us, so I let it slide.

But seriously, consider two cars: on with tiny wheels, and one with huge wheels. Now let them both drive as far as one rotation of the axis will get them. If both axes rotate with at same speed (which is what a speedometer measures), the car with the bigger wheels will drive a longer distance at the same time. Hence, it will be faster. This means that when you put on larger wheels, your speedometer will underestimate your actual speed. Duh!
Luckily, speedometers usually overestimate the car's actual speed by about 5 %, so larger wheel's won't do any real harm.

And yes, I'm a smart ass. I know. ;-)