I am living in Sai Gon, Viet Nam. I join a small group of cyclists. We have pretty fun ride together, but one day i felt really shock when some of my cycling mates trying to follow trucks or motorbike for a light pedalling. I got more confusion as everybody take it as normal but myself. I just decided to ride alone rather inhaling truck exhaust air. What do you think my friends? what is your riding habit out there? Is that cheating riding? Or it is just a very dangerous way of riding. Thank you very much for your comments.