It's Bike slang for Bikes. N = the number of bikes you have now. N + 1 is the correct number of bikes to own.

What's the default bike?

When you join, a default bike is created. You can click on it and turn it into your first bike.

How do I take a component off my bike?

Enter a date for "date removed from bike". This will change the status. Removing this date will put the compnent back on your bike.

How do I change my display units from miles to kilometers?

Log off and back on, you'll have the opportunity to change the display units.

I've got multiple bikes but all my miles/kms are under one, how can I split my rides up ?

You can enter a negative number, -200 for example, for the bike with all the miles/kms. Then enter 200 for the new, to Trackie, bike.