Police arrested 83 motorcyclists and seized 79 motorcycles on Friday that were found to have been illegally modified for road racing.
Pol Maj Gen Nithitorn Jintakanon, traffic police chief of the Metropolitan Police, said the arrests were made throughout Friday night by police manning checkpoints on roads in Metropolitan Police Division 5.
He said 34 of the arrested are under 18.
He added that one suspect under 18 and a suspect above 18 were found to have abused drug.
On Friday, police also checked 28 motorcycle repair shops in the same jurisdiction and seized two illegal exhaust pipes that could emit noise louder than the legal limit.
Nithithorn said police also suspended the use of 28 big-bike motorcycles for 30 days after they were found to make noise louder than the legal limit.