I assume the box is over 62" W+L+H so regardless of what is in it - if they want - they have a fee for that. Some times when they know what's in it they charge less. I always get stuck paying for bikes, but sometimes reduced rate (last trip payed $150 on Delta to LAX to DUS) and not all airlines are the same. Some are free. But the wheels I told the story, showed them how cool the container was and no charge although it was a bit over the 62.
I researched about every airline I could for the team last year and found the free bikes also had higher ticket prices. So we paid for the team.