Unfortunately this does come up a lot, and I usually avoid posting - because I'm somewhat on the dog's side.
If you use pepper spray - please only as a last resort (unless it's on the owner, they probably deserve it ).
Fear Aggression is the #1 non medical reason dogs are put to sleep in this country. Pepper spraying a fear aggressive dog re-enforces the behavior, likewise it can initiate the behavior in a non-fear aggressive dog. Dogs think differently, they just associate the pain with the thing they think caused the pain and attack it the next time.
This isn’t to say that you can’t defend yourself - you definitely should, but be aware that dogs don’t think the way humans do, and won’t associate their bad behavior with the cause of the corrective action, instead, they’ll associate the corrective action with cyclists and become fearful and aggressive toward them.
I’ve heard good things about airzounds and loud whistles - I carry a coach’s whistle, but I’ve never been quick enough to use it.


The reason I worry about all this:
My dog (see my avatar) was on his way to be euthanized - he would have been the first dog in over a year put to sleep at my no-kill Humane Society. Even the no-kill shelters euthanize vicious dogs, and my little guy fit the bill perfectly. He had been terribly abused by his former owners, and had become extremely fear aggressive toward people, dogs, and inanimate objects.
I have been working with him for 3 years trying to socialize him, to keep him from having to be put to sleep. Twice he’s attacked strangers, one was a cyclist, who got off his bike and put the bike between himself and Murphy and talked sweetly to him. If he’d done anything else, I never would have been able to teach Murphy not to be afraid of cyclists! (This event, obviously, was totally my fault, twice he’s gotten away from me while I’ve had him in public parks trying to socialize him - the other time he backed a pedestrian into a tree). After 3 years, I took him to Petsmart this weekend and he fearfully rode around in a shopping cart, He growled at one Great Dane, and didn’t threaten anyone/anything else - a huge breakthrough!