Buying the right leaf springs for your specific truck involves a mix of measurement, math, and knowing what your vehicle needs to carry. Here is a practical, step-by-step checklist to guide you through the process.
Before You Start: Safety First
Never rely on measurements taken from a spring that is still installed on a sagging or broken vehicle. You must remove the spring and place it on a level surface to get accurate numbers.
Step 1: Get Your Truck’s “Vitals”
Write these down first:
Make, Model, and Year: (e.g., 2018 Ram 2500)
Cab Style: Regular, Quad, or Crew Cab?
Engine: Gas or Diesel? (Diesel engines are heavier and require different front springs).
GVWR: Look on the sticker inside the driver’s door jamb. This is the maximum weight your truck is designed to handle.
Step 2: Measure the Physical Dimensions (The 5 Numbers)
You need to match these five specifications exactly, or the new spring won’t fit.
Overall Length: Measure from the center of one eye to the center of the opposite eye while the spring is lying flat.
Width: Measure the width of the steel leaf. Common sizes are 2.5″ or 3.0″.
Free Arch: Measure the height of the arc from the flat surface up to the center bolt. This determines your ride height.
Bushing Size: Measure the inner diameter (ID) of the hole where the bolt goes through. Common sizes are 5/8″, 3/4″, or 7/8″.
Number of Leaves: Count them, but note that this is less important than the spring rate.
Step 3: Identify the End Type
Look at how the spring mounts to the frame. There are three common configurations:
Double-Eye: Both ends have a full eye. (Most common on rear axles).
Slipper End: One end has an eye, the other is flat and slides in a bracket. (Common on front axles or trailers).
Military Wrap: Look at the front eye. Does the second leaf wrap around the main eye? This is a safety feature you should keep.
Step 4: Locate the Axle Position (The Center Pin)
Look at the center bolt that holds the leaves together. Is it perfectly centered between the two eyes, or is it closer to one end?
Centered: The axle sits in the middle.
Offset: The axle is shifted forward or backward to help with weight distribution and driveline angles.
Crucial: You must buy a spring with the exact same offset. If you install a centered spring where an offset one belonged, your wheel will be out of alignment in the wheel well.
Step 5: Determine Your Load Needs (Spring Rate)
This is the “strength” of the spring. You cannot measure this; you must calculate or look it up.
Option A: OEM Part Number: Look for a stamped number on the main leaf. Search this number online. This guarantees you get the factory-spec spring.
Option B: Lookup by VIN: Go to a dealer or reputable parts website and enter your VIN. They can tell you which spring package left the factory.
Option C: The “Heavy-Duty” Trap: If you buy generic “heavy-duty” springs, be aware they often raise the ride height of your truck. If you want to keep the stock height, you must specifically search for “Stock Height Replacement” springs.
Step 6: Check the Little Things
Shackles: Are the ends of the spring bolted to a moving “shackle” or a fixed hanger? Make sure your new springs match the mounting style.
Auxiliary Springs: Does your truck have a small secondary spring pack on top of the main one? If so, you need to buy a “spring pack” that includes this, or buy the helper separately.
Step 7: The “Must-Buy” Extras
Never reuse old hardware on new springs. Always buy these separately:
New U-Bolts: Old U-bolts are stretched and fatigued. They will not clamp the new spring to the axle properly and can snap.
New Bushings: If your new springs don’t come with bushings pre-installed, buy them. Worn bushings will ruin the handling of a brand-new spring.
Summary Checklist for Ordering
Before you hit “purchase,” ensure you have confirmed:
Length: _ inches (eye-to-eye)
Width: _ inches
Arch: _ inches (Free arch)
Capacity: Matches my GVWR (e.g., 2,500 lbs)
Ends: Double Eye / Slipper / Military Wrap
Center Pin: Centered or Offset? _
Hardware: New U-bolts and bushings in the cart?