Drafting, Group Rides and Fair Segment Times
Riding in a draft saves 25 to 40 percent of power. That explains a large share of the top times on flat segments.
The magnitude
Directly behind one rider, drag falls by roughly a third; in a group of eight it can be half. On a flat segment that is more than any equipment optimisation can deliver.
What that means for leaderboards
Strava does not distinguish solo from group efforts. A time from a race or a fast group ride is practically unreachable solo. If the top times all come from the same date, it was very likely a group.
Comparing sensibly
Decide which category you are chasing: a solo best or a leaderboard position. For your own development the solo best is the more honest measure — and it is exactly the anchor prediction models use.
In short
Compare solo with solo. For your own prediction, your solo best is the right reference.
Frequently asked questions
Is a group KOM legitimate?
It breaks no rules. It is not comparable to a solo time though, and that belongs in your goal setting.
How do I spot group efforts on a leaderboard?
Several very similar times on the same date are a strong hint.