Most of the older hire bikes don't have them and I've only seen a few unscrews, and that was people trying to hipster stop on the fence.
Riding in a group in a training session is about gradual movements, not hard stops and no sudden changes in pace (unless you are asked to sprint off the front). Crashes are usually caused by people not paying attention to instruction or losing concentration and touching a wheel.
Most of the older hire bikes don't have them and I've only seen a few unscrews, and that was people trying to hipster stop on the fence.
Riding in a group in a training session is about gradual movements, not hard stops and no sudden changes in pace (unless you are asked to sprint off the front). Crashes are usually caused by people not paying attention to instruction or losing concentration and touching a wheel.