Pattaya police detained 20 young motorcyclists early on Sunday and seized their bikes on suspicion they were planning illegal street races.
Muang Pattaya Police led by deputy superintendent Pol Lt Colonel Korn Somkanay began a sweep of Jomtien 2 Road at about 1.30am after receiving a tip-off about teenagers planning a race there.
No racing was going on when they arrived, but suspects were detained pending drug tests and their bikes confiscated to check if they were illegally modified.
If the suspects test free of drugs, their parents will be told to pick them up at the police station.
The owners of motorcycles found to have been illegally modified will be given directions for readjusting them.