Yesterday I saw a cyclist downtown hold onto a cab as he pedaled along, it looked like he was getting a pull. I've seen cyclists in foeign countries grab onto passing trucks. Are there any tricks to making this a safe practice? When a truck passes me going up hill at just slightly more than my speed I'm tempted to grab hold but I seem to remember "officer friendly" from my 3rd grade bike safety class give a stern warning against this particular move. Is it for adults only?