by Rich Savitt
This calculus is not something you want to do while you are at your anaerobic threshold, but it is good to keep a few ballpark numbers in your head.
6 ft/bike
15 bikes = 90 feet of single file paceline.
At 27 mph, the paceline takes 2.27 seconds to pass a stationary point.
Overtaking a slow rider going 15 mph takes 5.11 seconds
An oncoming rider going 15 mph closes 315 feet in the time it takes the paceline to overtake a rider going 15 mph in the same direction as the paceline.
Combined speed for a head on collision = 42 mph.
Unless you’ve spent time at both ends of the paceline, you probably don’t have a good feel for how long your tail is and how dramatically different a “bikes-both-ways” situation looks to the riders at the back.
This is not an argument for faster or slower pacelines. This is just an awareness thing. Other than the head on collision speed, it does not get automatically simpler or safer when you go relatively slower (in part because it takes longer to pass). For example, if you reduce the paceline speed to 20 mph (assuming we’re still single file), the head on collision speed reduces to 35 mph, but the oncoming rider moves 630 feet in the time it takes to overtake the slow rider.
Probably the reason slower feels safer is because it gives us more options and the adjustments don’t feel as chaotic.