The bonus sprinter perk or unlocked sprinter perk for "Biker" and "Dragon" does not seem to work. The Sprinter perk said your character will gain +10% movement speed.
I have noticed that my character (without Sprinter perk) have the same movement speed with regular infected. If I unlocked the Sprinter perk, I can see the change between my and regular infected's movement speed (I am faster than regular infected).
That is the working effect part. Here is the problem. I've unlocked Biker and Dragon with bonus unlocked perk (Sprinter). When I use them, they SHOULD BE faster than regular zombies (not crawlers). I noticed that I still have the same movement speed with reg and bio infecteds when I'm running away from them in a straight line one direction.
HOW is that possible? I should have 10% more movement speed but it appears I don't, even I've already unlocked Sprinter perk as a bonus.
Devs, thank you for reading this and I hope you're concern about this issue and please test it yourself and see if its true.