Thanks, but I've got a more immediate issue. Just been checking my wifes Gazelle Innergy bike - no magnet on the wheel - I am now worried that the speed sensor is internal in the front wheel motor. May need to do some investigative dismantling!
Just found this thread - definitely going to build this for my wife's Gazelle. I'm guessing from your reference to code that you are going the Arduino route. Can you post your updated code? Also love to see a pic of your magnet.