It's used to keep track of laps/lap times by computer. When you go through the scoring chute it will pick up your rider #. We zip tie ours to our chest protectors. Hope this helps!
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Liss
115g 00(lb)
Turtleosity!

Sponsor:
Week's Muffler Bearings and Powerbands

Mom of:
Kate 815 R
Buddy 15 lb
many many others I claim
Grandma of:
Josie..strider class #15
Brynn.... future racer