The front spring of a car's suspension system has a spring constant of 7.11 x 106 N/m and supports a mass of 291 kg. The wheel has a radius of 0.360 m. The car is traveling on a bumpy road, on which the distance between the bumps is equal to the circumference of the wheel. Due to resonance, the wheel starts to vibrate strongly when the car is traveling at a certain minimum linear speed. What is this speed?