Mending punctures is big business in the Indonesian capital, Jakarta.
But competition is intense. And police believe some tyre repairmen are paying criminal gangs to throw nails onto the roads, to drum up more business.
Now, a community group is trying to clear the roads using home-made magnets.
They've collected more than two tonnes of nails in the last three years.
Police say they'll work with these volunteers to tackle the problem.
drum up 鼓動