Check out the 500mw Microgate Enc radio data transmitter if you want to use the most powerful and dependable system. We have used these units with great success for MTB Downhill at the US Open and other big events for 3 seasons.
http://www.sportstiminginterna...m/prod_linkgate.htmlContact a representative in your region
http://www.microgate.it/timing/contact.aspxWe know of a couple of customers using Summit timers but the range seems to be limited. You also need to use two timers one at the start and one at the finish.