1 1/2" is the difference between spring perch centering hole and the center of the axle tube on the torque tube rear, the other 1 1/2" is because the factory didn't center the wheel in the fender. If you turn the spring around you'll be 7/8" off to the rear. A stock spring is 54 1/8" long with the front eye centerline to centerline on the locating pin is 25 1/2" now from centerline of the pin to the center of the rear spring eye is 29". I have been told by two very knowledgeable spring people that making the front half of the spring longer than the back half will have an effect on stability.