When it comes to truck suspension, many four wheelers see it only as an instrument to fit the desired tire size they want under their truck. Once you factor in the limits of the hard parts you are using, the laws of physics will dictate what the final design becomes. The specialized off-road racing vehicles that Craig Hall creates may not look like your truck but they use the same basic suspensions designs found on production vehicles.

In its most simple role, your suspension needs to hold your truck up and keep your tires planted on the ground. There are several ways to get that done but each has strengths and weaknesses. You cannot compare factory suspension designs without talking a little about caster and camber.

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Caster angle is built into the front suspension so the steering is more stable and will return to center. Camber is the angle of the tire to the road — negative camber is when the tire leans in at the top and in contrast, positive camber is when the tire to leans out at the top, seen below.

Old Faithful, The Solid Axle. A solid axle is just that, an axle that runs from one side of the vehicle to the other. The entire axle moves as the suspension cycles. It is still coveted by hardcore four wheelers. The reason this design has survived for so long is because it does double duty as leaf springs suspend the vehicle and locate the axle. Attached solidly to the axle with U-bolts, the leaf springs run parallel to the frame.

The springs are mounted to a solid perch on one end and a shackle that pivots on the other end. When the axle hits an obstacle, the leaf spring compresses getting flatter and longer, the shackle allows the spring to move without binding. The more they compress, the higher the spring rate rises. By varying their width, length, arch, thickness and number of leaves, they can suspend anything from a Suzuki Samurai to a cement truck.

They work best with a shock that has the necessary damping to control the springs in rebound. Leaf springs are large and they need space to work. Some solid axle designs use coil springs instead of leaf springs.

The suspension members need to locate the axle while also allowing it to move. The radius arm design uses two arms that run parallel to the frame. A track bar runs from the frame to the axle perpendicular to the radius arms to keep the axle centered on the frame. Since the radius arms are fixed at the axle end, the caster angle changes when the suspension cycles up and down, shown in the figure above.

Radius arm designs have been used by Ford and Dodge among others. A variation on the radius arm suspension is the parallel four-link, shown in the figure above. Instead of a radius arm with a fixed mount on the axle, it uses an upper and lower link on each side with pivots on both ends.

As the axle cycles up and down, the links allow it to maintain the same relationship with the ground and the caster angle remains constant. Anytime you add a pivot, you add a wear item and the potential for deflection. What the parallel four-link gives up in strength compared to the radius arm, it makes up for in better ride quality and handling. Another four-link design is the triangulated four-link. The parallel four-link needs a track bar to locate the axle side to side.When we talk about suspension settings and setups, you often hear spring rates and damping levels thrown around without context or proper validation.

Much like spouting peak horsepower without talking about peak torque or better yet the torque curve, spring rates and damping are rather meaningless without taking your suspension frequency into account.

Before we can examine suspension frequency, we need to introduce the concept of natural frequencies. Every [elastic] object, material, etc has a certain speed of oscillation that will occur naturally when there are zero outside forces or damping applied.

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This natural vibration occurs only at a certain frequency, known as the natural frequency. Derived straight from Natural Frequency, is the suspension frequency found in cars. This is how fast the suspension travels up and then back down to the same point when you drive over a bump.

suspension frequency calculator

To calculate suspension frequency for an individual corner, you need Mass and Spring rate:. When using these formulas, it is important to take Mass as the total sprung mass for the corner being calculated.

That is, the axle weight divided by two, minus an estimated or measured unsprung mass for that corner things like wheels, tires, brakes, control arms, suspension components etc. Anything that is not supported by the springs.

Suspension Spring Rate & Wheel Rate Calculator

So now we have a calculable frequency, which has next to no science behind what frequency to use on your car beyond proven empirical findings from decades of racing. Choosing a specific frequency for your application is still a little beyond my current knowledge base, however the following is a good guideline for choosing your starting point for calculations:. One of TopGear's many tests showcases some of the differences between various race cars that are likely to have completely different suspension frequencies.

The Touring car in the middle likely has a 3. The bike will run off the same principles as a car's suspension. While much of this may seem rather arbitrary, there is some reason behind selecting frequencies.

The higher grip levels that are available to you, the higher frequencies you will be able to and be forced to use. For OEM passenger cars and rally cars, the available grip levels are extremely low, and therefore the suspension frequency has to remain low to provide as much mechanical grip as possible. On race cars with wide, race compound tires, solid bushings, and high levels of downforce, the frequency is significantly increased to take advantage and work with the available traction.

Like adjusting any suspension component: increasing the stiffness on one corner, axle, or side of the car, will reduce the available mechanical grip for that corner, axle, or side. It is for that reason that you will want to run as low a suspension frequency as possible for the current vehicle setup. Any higher and you are sacrificing mechanical grip, but too low and the car will respond too slowly for the grip available in the tires.

Front downforce will consist of a large front splitter and diffuser, ducted hood venting, and vented wheel wells. Rear downforce will be the new BMSPEC rear wing, and a moderately sized diffuser with a full flat floor and side skirt extensions.

The first thing to notice is that the mass is vastly different from the front and rear of the car. This is why frequency is much more valuable than spring rate: it provides a relatively similar 'feel' for different corner masses. If we want the front and rear to behave the same, we will run similar frequencies in the front and rear, and for this reason we will run the same frequency from one side to the other on the same axle.

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Without any downforce, we run near identical frequencies in the front and rear of the car to keep the car balanced.Use tire scales, as used by racing teams, or weight the vehicle on axle scales used by trucking companies.

Make sure to weigh the vehicle in the configuration of its most frequent use. Add weight to compensate for the driver, passengers, and cargo in proper locations. If the suggested scales are unavailable, you may use the table below for approximations. Unsprung weight is the vehicle weight that is not supported by the springs. Unsprung corner weight is usually around lbs.

Dimension A - Measure the distance from the control arm pivot point on the subframe centerline of the bushing to the point on the control arm directly under the center of the spring or coil-over assembly.

Dimension B - Measure the distance from the control arm pivot point on the subframe to the centerline of the ball joint. Using a protractor or similar measuring device, find the angle of the centerline of the spring or coil-over assembly from the horizontal of the control arm.

In most cases, this will be somewhere between 75 and 90 degrees, and 90 degrees can be used for the angle. This measurement helps determine the "force angle" and resultant spring force applied to the control arm. Determine the total travel of the shock absorber using the shock manufacturer's catalog; or by pulling the shock shaft to the full extension position and measuring the length of the chrome shaft.

For example, if a shock has 4. It is the weight of the vehicle that is supported by the spring and is the only weight used when calculating spring rates. The static load is the load that the spring sees from the sprung weight acting through the motion ratio.

You should always find the closest spring rate available for your application. When in doubt, choose a lower spring rate. It is easier to achieve handling and performance with a lower spring rate and a "stiff" stabilizer bar or shock. Spring Rate Calculator jwinkler T Required Measurements Corner Weight lbs :.

Unsprung Weight lbs :. Dimension A in :. Dimension B in :. Spring Angle deg :. Shock Ride Height from Extended Height in :.

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Unsprung Weight Unsprung weight is the vehicle weight that is not supported by the springs. Dimension A Dimension A - Measure the distance from the control arm pivot point on the subframe centerline of the bushing to the point on the control arm directly under the center of the spring or coil-over assembly.

Dimension B Dimension B - Measure the distance from the control arm pivot point on the subframe to the centerline of the ball joint. Spring Angle Using a protractor or similar measuring device, find the angle of the centerline of the spring or coil-over assembly from the horizontal of the control arm. Shock Ride Height From Extended Height Determine the total travel of the shock absorber using the shock manufacturer's catalog; or by pulling the shock shaft to the full extension position and measuring the length of the chrome shaft.Cyclic Loads: Res.

Design Home. Spring Designer Eqns. Fatigue Equations. Search Member. Resonance is an issue for springs used in a dynamic cyclic loading environmentwhere the compressive force varies between two values.

For example, the valve springs used in a car engine are subject to dynamic loads. By design intent, a spring is a static mechanism. However, a spring will no longer behave as a static mechanism if the frequency of operation approaches the spring's first resonant frequency.

Worse, the force the spring exerts on its boundaries will tend to decrease, which could have disastrous implications for the spring assembly.

In light of this, a rule of thumb for spring design is to make sure the frequency of operation is 15 to 20 times less than the first resonant frequency of the spring in question. Use this calculator to find the first resonant frequency of a compression spring when you know its spring constant and its mass.

The spring mass can be found by weighing the spring. Spring constant, k :. Mass of spring, M :. Lowest spring resonant frequency, f res :. Hz kHz cpm. Equations Behind the Calculator. The frequency of the lowest spring resonance in Hz is found from the equation, where k is the spring constant and M is the spring mass see derivation. The spring mass M can be found by weighing the spring.

If you do not know the mass of the spring, you can calculate it by multiplying the density of the spring material times the volume of the spring. Inserting this product into the above equation for the resonant frequency gives, which may be a familiar sight from reference books. This equation is implemented in the Compression Spring Designer calculator, which includes a definition of all its terms.So the suspension geometry up front is completely different than a standardand the rear is converted to a coilover setup from the factory spring on the rear semi-trailing arm.

Suspension Frequency, measured in cycles per minute cpm and expressed in Hertz Hzis defined as the undamped natural frequency of the body in ride. Imagine a car with no shock absorbers and how the suspension would oscillate on its springs as you drive it down the road. A car with stiffer springs will oscillate more rapidly higher Hz and have a harsher ride, while a car with softer springs will oscillate more slowly lower Hz but have a more comfortable ride.

According to OptimumGa vehicle dynamics consultant group that trains race engineers and offers sophisticated software packages that help race teams dial in their racecars, these are good ballpark Suspension Frequency ranges to work from:.

Wheel Frequency Calculator

The ride frequency split should be chosen based on which is more important on the car you are racing, the track surface, the speed, pitch sensitivity, etc. Furthermore, in my experience too high a suspension frequency will produce a very unforgiving car when driven at the limit and one that may struggle to put heat into its tires. That being said, high suspension frequencies do create less suspension travel for a given track, allowing lower ride heights, lower center of gravity, and improved aerodynamics, so at a smooth and fast track like CTMP Mosporthigher frequencies work very well.

We measured the front suspension, which is a MacPherson strut design and thus going to be close to Having read an awful lot of opinions on the subject of spring angle correction factor, the consensus of opinion is that it should also be squared in the calculation, just like the motion ratio is.

Any thoughts? When you think about it, you have already accounted for the spring angle on the front suspension with your empirical measurements because you measured the actual displacement of the strut in situ, ie at its installed angle.

This measurement takes full account of the impact of both lever arm ratios and installed spring angle, on the motion ratio. If you wanted to apply the spring angle correction factor separately you should have measured only purely vertical displacement of ball joint on the suspension arm.

suspension frequency calculator

This would have given only the lever arm motion ratio. I plan to do a follow…. Source: Eibach. Most reacted comment. Hottest comment thread. Recent comment authors. Notify of. Sorry, your blog cannot share posts by email.Understanding the handling characteristics of a car is kind of like putting together a puzzle.

At the beginning, there are just a bunch of pieces and it is impossible to see the picture. As the pieces of the puzzle are assembled it starts to become apparent what the picture might be and it becomes easier to see how the rest of the pieces fit together. The picture is not revealed completely until the last piece has been put into place. Unlike the store bought puzzle where all the pieces are included, with vehicle handling, we have to find all the pieces first and then attempt to fit them together if we have any hopes of figuring out what the picture looks like.

Understanding how to find the roll centers at the front and rear of the car and how they affect its handling is one piece of the puzzle. It takes some time and effort but it is important to try to understand how it fits with the rest of the handling puzzle. The roll axis is a line that connects the front roll center to the rear roll center.

The body of the car sprung weight rotates about this axis when it leans during cornering. The roll center, as its name implies, is the center of rotation for a suspension system. There is a roll center for the front suspension and rear suspension. The front roll center is rarely at the same height as the rear roll center. If you draw an imaginary line between the front and rear roll center, this line is the roll axis of the car.

When the body of a car leans in a corner it pivots about its roll axis. Why would one want to find the roll center of their car?

It is one of many puzzle pieces that influence the handling characteristics of the car: spring and wheel rates, shock dampening, CG location, track width, wheel base, and many others. Knowing where the roll center is in the front of the car gives an idea of what the wheels will be doing as the nose of the car dives under braking or leans in a corner.

Without roll center information, one cannot estimate how much the camber angle of the front wheels will change during suspension travel or how much body roll will be present while cornering. The roll center for a leaf spring suspension is found by drawing a line between the center of the forward attachment point A and the center of the upper shackle attachment point B. Where that line crosses the vertical center line of the axle is the roll center.

The roll center height is the vertical distance from the ground to roll center. Each suspension configuration has a roll center. The location of the roll center is determined by the position and attachment points of the suspension arms. Leaf spring rear suspensions are found on many older American cars, including Novas and older Camaros. It is a suspension found commonly in Street Stock and Bomber classes.

The roll center for this type of suspension is found by creating a line that connects the center of the front attachment point to the center of the rear attachment point looking from the side of the car. The roll center is located where this line crosses the vertical center line of the axle and is centered between the rear wheels.

The roll center for a GM metric chassis shown left is found by drawing a line between the theoretical intersection of the upper links A and the theoretical intersection of the lower links B. The roll center is located where the line crosses the vertical center line of the axle. The roll center for a GM A-Body shown right is found by drawing a line parallel to the lower links through the theoretical intersection of the upper links A. The four link suspensions found on the GM A-Body and Metric chassis are also common among the ranks of Saturday night racers.

The roll center for these styles of suspension can be found by drawing a line between the theoretical intersection of the upper and lower links. The roll center is located where this line crosses the vertical center line of the axle.And I am going to replace my springs. I can't wait to put them in. I guess, they will be very good. Spring Rates Calculator. In the right margin of this blog I have posted a spring rate calculator. It looks like a small excel spreadsheet and it will help you determine what spring rates will work best for your application.

They may be basing their decision on opinions or reviews they read online and they may not be getting the best setup for their application. So for them, the spring rate is inconsequential because they are looking for either a good brand they can brag about or something that is inexpensive.

If, on the other hand, you are interested in actually participating in some sort of motor sport like AutoX, track days, or racing, then a properly tuned suspension will give you an advantage over your competitors who may have only bought a recommended coilover package. But understanding spring rates and how they can be used to custom tune your suspension to very specific tracks or your own driving style can give you an edge on the competition.

At the very least it will give you a better understanding of how the suspension works. Usually the rates will be available in 50lb increments.

This gives you much better suspension tuning options than an aftermarket spring kit that is designed to fit the stock spring locations. The standard spring rate measurement I will be using is lbs per inch which represents the amount of force in pounds it takes to compress a spring one inch.

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For example a lb spring will compress one inch when lbs of force is applied. The same spring will compress two inches when lbs are applied and four inches when lbs are applied. To give you some perspective a Ford Focus might have lb springs, a mildly built Miata might have lb springs and a full track car may have lb springs. Obviously the higher the spring rate the harder the ride. Bigger cars will also have stiffer springs since the springs will have to carry the weight of a heavier vehicle.

It seems obvious to many why stiffer springs would be more desirable, but it may not be obvious to everyone. The compromise is that the ride quality will be much harsher and that means less comfortable for daily driving. This will be covered in more detail in future articles. Suspension frequency SF describes the natural frequency of the spring in relation to wheel motion and can be used to estimate the appropriate spring rate for various applications.

Ride rate, Roll rate calculation : Part 1

You can also use this to evaluate spring rates of various coilover kits and stock spring packages. Most passenger cars will have a rate of approximately 1 Hz.

suspension frequency calculator

A fairly aggressive suspension setup will be around 2. So you can use this information to figure out where on this spectrum of suspension frequencies will fit your application. If you drive your car to the track or AutoX event you might want to try a SF a little over 2. It is important to note that you want your rear SF to be slightly higher than your front otherwise the car might start to porpoise; rock forward and backward.

The spring rate calculator on the right is fairly simple to use. Figure out what suspension frequency you want, update the vehicle data for your car in the white cells and the ideal spring rate will update in the yellow. Everything in gray should be left alone and the calculated spring rates will be yellow. For now none of the cells are protected so you could go in and modify any of them but none of the changes will be permanent. If you make any mistakes, refresh the page and it will reset the calculator.

The spring rates are calculated for individual corner of the car but since the left and right side should be essentially the same the calculator will only calculate front and rear.

suspension frequency calculator

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