i never really thought about it before but i am putting twin elliptical rear springs on a car i am building and was wondering what degree to put the rear shackle at. i know when putting a straight or dropped axle on the front they should be at a 37 degree angle. i have looked at a few cars and trucks and the rears seem to be straight up and down. does this have to do with the front axle ones are on the front of the spring and the rears are at the rear of the spring? now that i think about that, do you put the shackle straight up or on an angle when they are on the rear of the front spring? my head is starting to hurt thinking about this.