We all know the quickest and cheapest way to change the ride height of a leaf spring equipped vehicle is by using blocks between the axle and a spring. Heck, it can’t get any simpler.
Remove the U-bolt, slip a block in, bolt her back up, and, wa-la, a new stance. But there’s a price for this simple method, and that cost can be excessive Axle Wind-Up.
Simply put, Axle Wind-Up is, when you hit the gas, the axle twists one way while the tires are twisting the opposite way. Now, physics makes this a normal occurrence, but too tall of a block can cause normal wind-up to become abnormal wind-up.
And your question is why? And the answer is easy.
Right through the center of the axle would be the perfect place for a leaf spring to mount. But that ain’t going to happen. Something called the axle shaft gets in the way. So the second best place for the spring to mount is as close to the centerline of the axle as possible like right on top or right below it.
So why are too tall of blocks bad? If we apply to springs, blocks, and axles what that dude Archimedes said way back around 225 B.C, or about 2245 years ago: “If you give me a lever and a place to stand, I can move the world.”
Now think of the distance between the center of the axle and where the spring is mounted to the axle. Let’s call that distance our lever.
The further away we move the spring’s seat from the center of the axle, the longer our lever becomes. So applying what good old Archimedes said, the taller the block, the more the axle will wind up. The more the axle winds up, the worse the handling can become.
So when lifting or lowering a vehicle, the change of ride height should be built right into the springs whenever possible.