How to Properly Measure Leaf Spring Size for Your Vehicle
On roads and highways across the United States, various types of vehicles carry heavy loads that often exceed the weight capacities of the cars, vans and trucks in question. Therefore, vehicles need all the gravity absorption they can muster.
In many types of vehicles and especially in today's larger ones, leaf springs are used to provide gravity absorption and prevent suspension sag. This is particularly vital in pickup trucks, where rear axles can often get weighed down with heavy items — such as furniture and moving boxes, for example.
Along the back end of a truck, van or SUV, leaf springs keep the tires round and the body evenly horizontal along all terrain. Sooner or later, however, the leaf springs that came with your vehicle will wear out. As you set about looking for replacements, it's best to know how to measure leaf spring length so you can better identify the needs of your vehicle.
What Size Leaf Springs Do I Need?
If you're looking to replace your leaf springs for the first time, it might be tough to determine exactly what size you need. The first step is checking what applications you need – the best place to go is General Spring to see if your application is one size fits all or if your application has multiple measurements. However, the easiest way to find out the right size of leaf spring is to measure the springs that are currently on your vehicle. Before you can measure, though, you'll need to understand the shape and structure of leaf springs. The following parts are what you must know about leaf springs to make an accurate size determination:
- The springs
The springs are the long metal strips that serve as the operative pieces of the whole component. The springs are stacked in an inverted pyramid with the longest on top. Collectively, the springs form an inverted arch that is held in place by a center bolt. Additionally, the springs are bound together at the quarter-lengths with clips. On some top springs, the ends curl upward to form enclosed circles, which are referred to as "eyes." Most leaf springs consist of three, four or five leaf springs, but they can go even higher than that depending on the capacity needed. In short, springs consist of the following pieces and characteristics:
- Metal strips (usually three, four or five)
- Inverted pyramid stack
- Inverted arch shape
Additionally, you'll need to check your applications because some leaf springs don't have multiple measurements, and it's one size fits all. Be sure to check on General Spring for your correct application.
- The bottom spring
Below the stacked set of arched springs is a horizontal strip known as the bottom spring, which is a shorter, thicker flat leaf that serves as a rebound spring for the other springs. The bottom spring is known as the overload spring, but since it doesn't add to the gravity absorption, it could be more accurately thought of as a rebound spring. On most leaf springs, there's only one bottom spring, though some models consist of two.
- The center bolt
At or near the center of the top spring is a vertical bolt that holds everything together. While the bolt is usually located directly at the center, some top springs will measure longer on one side than the other. The bolt connects all the springs in the stack that comprises the arch, as well as the one or more flat springs at the bottom. The bolt is used as the starting point for measuring the length of a given set of leaf springs.
However, since the bolt is usually not in the actual center, it's always important to measure each side separately, starting from the bolt. In short, the center bolt is known for the following characteristics:
- A vertical bolt near the center of the springs
- Holds the top and bottom springs together
- The starting point when measuring leaf springs
- The end tips
On most leaf springs, the end tips are also known as the eyes because of the enclosed, curled shape. On some leaf springs, the arch simply comes to an end with no curl at the tip — these are known as slipper springs. On most leaf springs, the tips are identical, whether it's an eye or slipper. However, some sets have both types of ends, such as an eye at the front tip and a slipper at the back.
How to Determine Leaf Spring Size
If you want to know how to determine leaf spring size, you need to think of leaf springs as multidimensional components. Basically, the size of a leaf spring can only be determined when measurements at all angles are taken into account. Therefore, you need to measure the width, height and thickness of the spring stacks, but most importantly, you need to measure the length of the top spring. The needed measurements can be broken into the following four categories:
- Leaf spring length. The length of a leaf spring is determined by the number of inches between the tip of the front eye or slipper, and the tip of the back eye or slipper. In all leaf spring sets, it's the long spring — the top spring — that is measured for its length, since the number of inches along this spring accounts for the greatest amount of length in a given set.
- Leaf spring width. A leaf spring's width is measured by the distance from one edge to the other along the top spring. On most leaf springs, the width is between 2.5 inches and 3.0 inches. Whereas the length of leaf springs correlates to the measurements of a vehicle's rear-axle suspension, the width is an indicator of the shock absorption needs of a given vehicle.
- Leaf spring height. The height of a leaf spring is determined by the thickness of the springs from top to bottom, as well as the space that fills the arch. Therefore, height is determined by more than just the measurements of the center bolt. To determine the height of your leaf springs, you need to place them upside down on a flat table and measure the vertical distance from the surface of the table to the bottom tip (upturned) of the center bolt.
- Leaf spring thickness. Once the length, width and height of a leaf spring are measured, the thickness of the springs should also be taken into account. This can be done by simply running a tape measure vertically down the edge of the top spring. A measurement of individual spring thickness won't add to what you already know about the overall height of a leaf spring set, but it will let you know the preferred thickness of springs for the gravity absorption of a given vehicle.
How to Measure Leaf Springs
A lot of vehicle owners are initially confused about how to measure leaf springs. The confusion stems from the common perception of length, which most people imagine would mean the distance between both eyes of a leaf spring set. As such, it's often assumed that leaf springs can easily be measured by turning them upside down on a surface and measuring the eye to eye distance with a ruler. However, this is an error when it comes to accurately determining the measurements in question.
For starters, leaf springs are not simply meant to be measured from one end to another because this won't give an accurate measure of the spring surface. For leaf spring measurements to be accurate, the following steps must be taken according to the spring type at hand:
- Eye to eye. To measure the length of a top spring with eyes at both ends, start your tape measure at the center bolt and extend the ruler tape against the surface until it reaches the center of the front eye. While measuring the leaf spring, follow the arch with the ruler. Take the measurement down, and then perform the same measurement in reverse, this time measuring the distance along the spring surface from the center bolt to the center of the back eye. Combine the two measurements into one, and you'll have the length of the longest leaf spring.
In some cases, the two half measurements are even, which confirms that the bolt is situated at the center of the set as a whole. With other leaf springs, however, there could be a disparity of as much as five inches between the two half measurements, which would indicate that the top spring extends further in one direction.
- Eye to slipper. On leaf springs with an eye at one end and a slipper at the other, the way to gain an accurate measurement of the overall length is much the same as with an eye-to-eye top spring. Start at the center bolt, extend the tape measure along the surface of the spring to the center of the eye, then take that measurement. Repeat that step in reverse, starting at the center bolt and extending along the other half to the tip of the slipper, with the ruler following the arch, then combine the two measurements.
It must be noted here that slippers come in several different shapes, including the following:
- Flat end, where the inverted arch turns flat and horizontal at the end.
- Radius end, where the inverted arch curves downward toward the end.
- Open eye, which curls up and over like an eye, but without shutting into a full circle.
- Hook end, a flat end that turns 45 degrees downward at the tip.
- Slipper to slipper. When measuring the length of a slipper-to-slipper top spring, the shape of the slipper determines whether the ruler must extend to the physical end of the tip. On regular, flat-end and radius slippers, the ruler ends from the center bolt to the physical tip of the slipper. On open-eye and hook-end slippers, the ruler extends to the outermost portion of the end, which would be the point at which the slipper turns downward or curls upward. As with eye-to-eye leaf springs, you combine measurements from the center bolt to both ends along the arch.
- Camel back. On Mack trucks, there's what's known as the camel-back leaf spring set, which consists of numerous leafs and is altogether very different from other leaf springs. The name is due to the shape of the design, which humps upward like a camel's back. As such, they feature an upright arch rather than the inverted arch of eye and slipper leaf springs.
Since the smallest leaf is at the top, there's no need for a flat leaf — every leaf is part of the camel. Another distinguishing characteristic is the placement of the longest leaf, which is second from the bottom and is therefore not the outermost leaf in the set. The longest leaf is sandwiched by two leaves of matching length. It's the length of those two second-longest leaves that you want to measure, starting from the center bolt and extending outward in both directions.
- Single point. Heavy-duty trailers are often equipped with single-point leaf springs, which — like the camel back — are designed in the shape of an upright arch, as opposed to an inverted arch. However, the arch is slight on a single point. Therefore, the smaller top leaves are mostly flat, while the bottom leaves form a small, shallow hill. The length to the end tips of the bottom leaf are measured in halves, starting from the center bolt in each direction.
How to Measure for Replacement Leaf Springs If you're wondering how to measure for replacement leaf springs, the easiest method is to take the measurements of the older leaf springs you intend to replace. Of course, you'll need to elevate the rear of your vehicle and crawl under the truck or SUV with a flashlight and measuring tape. Here are some other specifications you’ll want to consider:
- The type of vehicle. Even though leaf springs aren't as common in today's compact car, they are an essential addition to the rear-side chassis of vans, trucks and SUVs. The type of leaf spring used in a given vehicle can all depend on the weight capacity of the vehicle. For example, if the rear axle has a 6,000 lb. rating, the vehicle should be equipped with two 3000-lb. capacity leaf springs. As a general rule of thumb, the heavier the vehicle, the higher the load capacity.
- The make and model. The brand of your vehicle can also determine which type of leaf springs would be most suitable. Whether you drive a Ford, Chevy, Nissan or Toyota, it's best to look for replacement leaf springs that are tailor made for the vehicle in question. At General Spring, we have a vast inventory of leaf springs made especially for the vehicle subcategories of numerous automakers, including:
- The OEM part number. If you can locate the OEM part number on the leaf springs that came with your vehicle, you'll have an easier time finding replacement leaf springs that match. The OEM number — also known as the stamping number — is typically found in one of several places:
- The longest leaf, on the underside near the eye or slipper.
- The end of the eye wrap, at the place where the circle curls in.
- The leaf clips, on the bottom, top or sides of the clips that bound the leaf springs at quarter lengths.
- The bottom leaf, on the bottom side near the center bolt.
- The capacity of your springs. Another way to determine the best replacement leaf springs for your vehicle is to count the number of leaves stacked within the current leaf springs. Equally important here is the thickness of the springs in question, which has a huge bearing on gravity absorption. Simply put, you'll want to find new leaf springs with the same absorption capacity as the spring sets you're replacing because those old springs at one time were optimal for the vehicle.
How to Check Leaf Springs
Leaf springs protect the rear of large vehicles from gravity stress caused by heavy loads and vehicle components. Without leaf springs, a truck can easily sag in back whether loaded or not, but it can sag extensively when loaded with objects of considerable weight. Moreover, trucks are actually designed with a slight hike in back to compensate for the natural sag heavy loads can cause.
Therefore, when the back of your truck fails to absorb gravity, it's likely due to failing leaf springs that need to be inspected and possibly replaced. To determine this, you need to know how to check leaf springs for damage, and also monitor the balance of your vehicle. Keep an eye out for:
- Corrosion. The biggest enemy to nearly all forms of metal is rust, which can spread over the surfaces of metal objects and ultimately eat right through. Once rust has taken hold, it's generally difficult to clear away. Therefore, a rusted set of leaf springs should be replaced before the actual leaves begin to snap, break and fail on a given vehicle at dangerous moments.
- Cracks. The most tell-tale sign that leaf springs need to be replaced is when cracks appear on the leaves. Often times the end result of rust, cracks could cause the leaf springs to fail outright, which would leave your back-rear suspension in peril, especially if your vehicle carries a heavy load. Similarly, if parts of a leaf have chipped off, it's definitely time for new leaf springs.
- Leaning. If the truck seems to lean to one side, it's an indicator that a newly installed leaf spring on one side is ill-matched to the other or that one spring has given out. Leaf springs need to be compatible on both sides for even distribution of rear-end gravity suspension. Therefore, it's important that leaf springs of the same model be used on a given vehicle. On older vehicles, it's generally best to replace both leaf springs at once, even if only one of the leaf springs has shown noticeable signs of wear.
- Suspension sag. Monitor the performance of the rear suspension to your vehicle. Does your truck sag in back when loaded with heavy objects? If your headlights are pointing upward and your seat feels like a rocking chair, chances are your leaf springs are failing to provide sufficient gravity absorption. Does your vehicle sway heavily when you drive over speed bumps? This shouldn't be happening if your rear axles are equipped with optimal leaf springs.
Suspension sag is a dangerous symptom for your vehicle because it's hard on your back tires and axle. When your truck sags, it can also make driving uncomfortable because your seat is unable to offer sufficient back support. Furthermore, suspension sag causes your headlights to aim too high and shine straight through the windshields of oncoming motorists.
Some vehicles have low weight capacities that can barely handle a full load of passengers. That means no matter what you’re driving, it’s vital to have optimized leaf springs.
Get New Leaf Springs at General Spring
Now that you know how to measure leaf spring length as it applies to your vehicle, the time has come to swap your old, worn down springs for fresh new ones. Whether you drive a car, truck, van or SUV, at General Spring, we carry leaf springs of various sizes and thicknesses. The moment your new springs are installed, your Ford, Chevy, Nissan or Toyota will have optimal gravity absorption for the most challenging terrain. To see our inventory, visit our leaf spring pages today.