When we rode through Missouri and Kentucky we were chased by dogs a lot. I found that on that trip at least the dogs quickly backed off a bit to get out of range when they saw me reach for the can. It seemed to work just as well to brandish an empty can. We were chased at least 30 times in the 15 or so days there and didn't use the 1/4 or so can someone gave me when they were finishing their trip. That said it worked well the couple times I actually sprayed a dog.

As far as outrunning dogs... They are incredibly fast for a short burst. I doubt that Robbie Mc Ewen could drop most dogs in a 50 yards. On the other hand it is pretty easy to drop them over a moderate distance unless going uphill and most lose interest quickly once you leave their territory anyway.

I found racing them to be a fun pastime when we were crossing MO and KY. Probably not a good idea because it encourages them to chase, but it was fun.