## Thursday, November 08, 2007

### Mathefication

I wouldn't even bother reading this if I wuz you. Go away, come back another day.

Ok, then.

On to the calculization of the odometer!

But first, let us clear up one thing: The Measured Rollout Circumference Distance™, stated as 110.5 centimeters yesterday, was wrong. Because I fail at arithmetic.

MRCD™ at work: 82.9 inches (2106 millimeters (210.6 centimeters)/25.4)

MRCD™ at home: 83.25 inches Let us just say 83 inches, ok?

Jamis has 700 x 28c tires.

The Axiom odometer manual says should be 84.6 inches. And that is what the odometer was set to at the shop. But as you can plainly see, the circumference is closer to 83 inches than 84. That is a whole inch difference!! An inch and a half!!

In a mile (63,360 inches) of riding the error would be 14 inches, approximately. That's just over a foot (12 inches)! So in 3,710 miles (Last odometer reading recorded) that's an error of 309 miles!

And Axiom says a difference of two inches doesn't matter. And I quote:
"discrepancies of as much as 50mm (2") will not have a significant effect on the accuracy of the unit for most normal rides"
An inch here, an inch there, pretty soon you're talking about real mileage!

So the upshot is, just mentally subtract 309 miles from all my Jamis odometer readings.

And I'm just WAITING for everyone to tell me where I messed up the math.

I going to go watch My Name Is Earl now,

#### 1 comment:

steve said...

Don't forget that tyre inflation is going to make a difference over time as well, since the rubber will stretch slightly.

And if you try to get clever and use a GPS to measure distance travelled, you'll have problems with DOP - you just can't win! :-)