If your gonna do it just get this. Its small and straps right onto a buggy or truggy wing perfectly. Super easy to capture top speeds, you dont need a second person to be the "radar man". and still pretty cheap. I have been using one for a few months now and its good. and pretty durable. its survived a few high speed crashes already.
http://cgi.ebay.com/Garmin-Forerunne...QQcmdZViewItem