What if you wanted to assemble a group ride from a larger group, such as church, school, office, etc., but you wanted to orient it toward more serious riders, or those interested in becoming more serious riders? What would be the best way to do it?

I've tried this in the past with limited success. I advertised a weekly ride in a bulletin, but I was hesitant to be too unfriendly by saying something like "serious riders only" or "only come out if you know what you're doing", or to post an average speed, because my whole idea was to encourage people who might be new to road biking or group riding. But it never failed, most of the riders who showed up came wearing sneakers, with ancient superstore MTBs with dry-rotted tires.

Is there some wording or phrasing that has worked for others to assemble groups in the past, sort of like code-speak for roadies or proto-roadies who don't necessarily want to kill it, but want to get a decent two-hour workout and fun group ride in?