Tyres on more than 40 bikes have been slashed by nail traps set out on routes in Cannock Chase.
The traps were reported to the Forestry Commission over the weekend by cyclists who use the woodlands in Staffordshire.
The Commission says the traps were laid by hammering nails into wooden structures along horse riding routes, walking trails and cycling tracks.
Once in, the heads were snipped off leaving razor sharp half-inch points. Police are appealing for information.
The Forestry Commission says the snipped nail heads were almost impossible for people to see before it was too late.
Mark Swinnerton, who runs a cycle hire shop in Cannock Chase, said dozens of cyclists came into his shop on Sunday reporting slashed tyres.
He said: "There must have been many more besides. And with tyres costing anything up to £30 each, the damage must have run into hundreds of pounds.
"But the thing that terrified us was the danger of someone coming off a bike as their tyres burst and landing face down on some of these vicious spikes."
Volunteers from Chase Trail and staff from the Forestry Commission went out to find and remove the cut nails.
Police are appealing for anyone who may know those involved in setting up the traps to come forward.
The attack is thought to have been carried out between 1700 BST on Saturday and 0900 BST the following morning.