Originally Posted by
bajajoaquin
Its moving at the same speed as the bike, by definition. The only way you would say "twice" is in relation to the ground. But you're not riding on the ground. You're riding on the bike.
Is is the bottom of the tire stationary from the perspective of the rider? Or, is the front edge of the tire more safe to rub against?
You are correct. It is going twice as fast as the bike in relation to the ground. I was as most people usually due implicitly assuming the stated speed is in relation to the ground. I should have stated it more clearly. If the bike is going 15 mph then the top of the tire is going 30 mph in relation to the ground and 15 mph in relation to you who like the bike are moving 15 mph forward in relation to the ground.
Details aside the point I was attempting to make is that it is potentially more dangerous than falling on something like the top tube.