While a 5 post minimum is a fairly low hurdle to clear, I can kind of see the OP's point...
I have (and still do) participated in a number of online forums. I've been on some forums that limit your ability to start a thread until you've replied to a few posts (cuts down on SPAM), but this is the first and only forum I've ever participated in that limits access to certain parts of the forum (unless there are segments requiring paid access).
Honestly I'm not sure that the 5 post minimum has any real benefit to the Pedal-on community. What it tends to result in is people making "junk" posts to reach the 5-post minimum so they can see the private forums. Then when they get there and see there's not much action (let's face it - there aren't tons of new profiles being posted), they may not stick around... IMO, rather than increasing engagement for new forum members (which I THINK is the reason for the policy) - I believe it turns some people off and may even drive them away. Participation in this forum seems to be dwindling. I don't think throwing up road blocks to forum access helps that...
Bookmarks