Rubber tires on the Montreal Metro transmit minimal vibration and help the cars go uphill more easily and negotiate turns at high speeds. However, the advantages of rubber tires are offset by noise levels generated by traction motors which are noisier than the typical North American subway car. Trains can climb grades of up to 6.5% and economize the most energy when following a humped-station profile (track profiles that descend to accelerate after leaving a station and climb before entering the station). Steel-wheel train technology has undergone significant advances and can better round tight curves, and climb and descend similar grades and slopes but despite these advances, steel-wheel trains still cannot operate at high speeds () on the same steep or tightly curved track profiles as a train equipped with rubber tires.