That is not true. Statistics prove that good tires locked up, provide the most braking. However, it has to be done in a straight line whether on a bike or in a car with all tires locked at the same time.Maximum braking requires maximum traction, a skidding tire has gone beyond it's maximum traction. With one tire locked there may be a small amount of control left for the experienced rider (or lucky rider). With both locked, for the most part all control has been lost, in which case luck may not be your friend.