Leaf spring suspension is one of the oldest forms of vehicle suspension. You’ll find leaf springs on the first production of Jeeps, Land Cruisers and Scouts. Today, most trucks and many SUVs still use leaf spring technology.
Leaf Spring Shackle Length
It’s good to understand the basics of leaf springs when it comes time to modifying or lifting your truck for off road use. Replacement leaf spring shackles are an inexpensive method for increasing ground clearance.
One of the most commonly asked questions is: How much lift will longer shackles yield? Every 1″ increased shackle length will result in 1/2″ of lift. For example: if your truck has 3.5″ factory shackles and you installed 5.5″ long shackles, you’ll gain 1″ of lift (2″ longer shackle x 50% = 1″ lift). Why do you only gain 1/2″ lift for 1″ increase in shackle length? Simple, you’re only lifting 1 side of the spring (ie 50%).
The other common mistake when replacing leaf springs is proper shackle angle. Increasing or decreasing your shackle angle will have a dramatic effect on how your suspension functions including: spring flex, compression, handling and ride quality.
Leaf Spring Bad Shackle Angle
The above picture is an example of poor shackle angle. As you can see the shackle angle is very low which has several negative effects: 1. Springs bottom out easily over bumps. 2. Soft ride handling on corners. 3. Somewhat limited spring flex.
Leaf Spring Good Shackle Angle
The above picture is an example of proper shackle angle. Correcting the shackle angle drastically improved the ride handling.
Leaf Spring Shackle Angle
How do you know the correct shackle angle? This can be achieved by drawing an imaginary line through the middle of both spring eyes and making a 90 degree angle. The angle can be increased or decreased slightly to change spring rate.
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