Originally Posted by mkadam68

Oh, it definitely gets annoying. You're right: it doesn't always need to be said, especially as you go up the ladder of rider experience. On the group training rides I do (with occasional world & olympic champions, and professionals--very experienced riders), I only ever let them know a car is back if it's a very narrow road and the car is passing very close by.

This would be where situational awareness comes in. What it comes down to: is the car's presence a credible threat to the safety of any riders in the group? Yes? Then the others need to know about it. Some considerations I run through before announcing, "Car back!":

• Is the group a bunch of new riders who might be startled by the presence of a motor vehicle?
• Is the group all over the place, swelling up and covering the whole road and then narrowing back down? Or consistently riding double file?
• Is the roadway narrow where the car passes the group so closely that it would run over someone if they were to swerve just a foot or two to their left?
• Is there one rider who currently is sitting out in the middle of the road away from the group?
• Is it an isolated road where traffic is minimal? A car suddenly appearing might not be expected.
• Is it a training ride where sudden movements out into traffic can be expected by someone?

Also, if it's a big group, I might say "Car back" much more loudly than if it's just 3-6 of my friends, where I say it at conversational volume.