I've been asked to help out with timing the finish line of a bike event. The race is 240km long and it's done in a team/relay format. The finish line is quite manageable with finishers normally coming across in singles or pairs. Occasionally there are packs of 8 or 10 riders.

I can either use a thumb-button plunger to trigger finish impluses, or I could set up a photo-cell. My question is, if I use a photo-cell at the finish, should it be set up to catch the leading edge of the front wheel of the bikes? Will a front wheel trigger a cell or is it too narrow? Alternately I could set the cell at a height above the handle-bars and catch the riders at torso-height?

Also any suggestions on settting the lock-out time for the cells? (So that the cells are not triggered by multiple wheels and tubes on the bikes.)

This isn't exactly a top-level competition, so we don't care about precision to 1/100th of a second. (It's typically been timed manually in the past.) No photo-finish equipment is available.

Any advice would be great.

Thanks!

I would use a plunger to trigger the impulses. A person can easily distinguish between two or more close finishes whereas a photo cell is essentially "dumb". We have been using a plunger for years with Mt Bike events with no significant problems. We usually have a video camera running at the finish (usually with the display clock in the picture) and if any confusion arises, it isn't a big deal to review the tape and see what really happened. After doing hundreds of MTB events, I think we have had to go back and look at the film only twice, and in both cases it confirmed the result from the guy on the plunger.

Havn't visited for a while.
Let me tell you about bike race timing rules, Riders must have a full second gap before a new time is given From the rear of the last rider in a bunch to the front of the wheel of the next rider must be a full second or they both get the same time,
the 1/10 ths are dropped so the timing resolotion is 1 second. In a really big field it is possible to have 60 riders together with the same credited time and have a 1 second gap giving the 1st person after a gap 10 or more seconds later than a guy that was only 1 second in front.
Time trials are timed to the 1/100 and the parts of a second are only used to break ties and to create rankings.