I think that you are stumbling upon the interesting phenomenon of physics and the limitations of your bicycle.

Let me first explain why your bike wheel turns (spins) while you are riding. The rubber part of your tire touching the ground actually sticks to the ground a little bit at the place that it is touching. When you push yourself and your bike forward, that part of the wheel wants to stay stuck to that part of the ground and thus gets pushed back, causing your wheel to start spinning.

When you lock your pedals or your wheel with your brakes and don't allow it to spin freely, it can 'skid' along the pavement or dirt when you are moving forward. What is happening when you are skidding on the pavement is that the outermost layer of the rubber on your tire is 'sticking' to the pavement and getting rubbed off of your tire. That is why you can leave a big dark mark in the road when you skid your bike.

Skidding can be dangerous if you are out of control. If you know what you are doing, it can help you come to a quicker stop or be a neat trick. One thing is for sure, however. Skidding wears out your tires and can one day cause you to get a FLAT tire!

Good luck!

Skidding can also make ruts in trails. Listen to Coach Keith and use skidding only if you know what you are doing. Do you have any questions about your training program? If you do email running questions to Coach Mick at coach.mick@rodale.com. Email other questions (such as cycling) to carol.kids@rodale.com