Leaf spring U bolts torque spec

The service manual specs out 45 ft lbs for the leaf spring U bolts. This sounds low concidering they are 1/2-20 threads. Everyone I have talked to says they need to be alot tighter 70-100 ft lbs. Does anyone know what is correct? Also do you torque them while the weight of the car is down on the ground or up on jacks?