"Wade Hasbrouck" wrote:
"The general rule I was taught for the 172 is, provided you haven't 'creeped
in on your downwind', once the landing traffice passes your wing tip, you
can begin your turn to BASE, and it works out just about right..."

That's a pretty good rule of thumb when the two aircraft are flying at
similar speeds. It doesn't work when (for example), you're a 172 and the
guy on final is a Cub going 10 or 20 kts slower than you.

On the other hand, if you're a spam can mixing it up with jet traffic,
there's no reason you can't turn base long before your traffic has crossed
your wingtip. If you're doing 80 kts on base, and he's doing 130 on final,
there's no way you're going to catch him.