"Karen, do you realise that the circumference of our tyres is a fraction over two metres?"
"Yes. I remember measuring it and entering it into our cycle computers before we left Sydney."
"Right. So that means that every time we cycle a kilometre, our wheels revolve about five hundred times?"
"That makes sense," Karen said, after a short delay as she worked out the maths.
"Okay. Do you also realise that we have cycled almost ten thousand kilometres now?"
"Yes, and it sure feels like it too."
"Yeah, me too. So if we've travelled ten thousand kilometres, and our wheels turn around five hundred times a kilometre, it means that our wheels have turned around five million times. Agreed?"
"Okay, but what are you driving at?"
"You'll see. Now if we assume that our wheels have gone around five million times, would it be correct to assume that our legs have gone around five million times too?"
"No, because sometimes we don't pedal, like when we are going down a hill."
"Alright. Let's assume we are only pedalling fifty percent of the time."
"Okay, let's." Sometimes when I carry on like this, Karen's comments become a bit sarcastic.
"So our legs have been around two and a half million times, right?"
"Wrong. You fell right into my trap. We haven't taken the gearing of the bike into account."
"No, we haven't, have we? Why didn't I think of that? What a silly bugger I am!" Despite Karen's facetiousness I carry on unperturbed.
"The top gear on the bike had a ratio of about four to one, hasn't it?"
"If you say so." Karen is starting to become resigned to her fate by this stage.
"And the lowest gear is a bit less than one to one, right?"
I have to keep asking questions otherwise Karen stops concentrating on what I am talking about.
"I'll take your word for it," she says.
"But when we are riding along normally, we're in the big gear on the front and the middle gear on the back, aren't we?"
Karen nods. She is beginning to get upset now, so I will have to be quick.
"Okay. The big front cog is a forty four, the middle at the back is a seventeen, so the ratio is about two and a half to one. Which means that every time our legs push the pedals around once, the back wheel goes around two and a half times. So if the wheels have been around two and a half million times, then our legs have been around one million times!!"
Karen gives a sexy little pout, sidles up to me, rubs her thigh against mine and changes the course of the conversation completely when she whispers in my ear, "My legs have been around a lot more than that ..."