Linked Suspensions Bible

[Treefrog]

Figured that with the talk of threads dedicated to specific tech topics, might as well get the ball rolling early.

THIS IS FOR SOLID AXLES ONLY, NOT INDEPENDENT SUSPENSIONS.

I will do my best to gather as much of this info below as possible. It should be noted that this is a collection of info from a variety of sources and observations from messing around with some of the design spreadsheets, not the recollections of someone who has been building suspensions for 20 years. Feel free to correct me if I am wrong at any point.

This starts with a general list of terms and what they mean, many of which are expanded upon later. After that, the most common types of solid axle suspension setups and some pros and cons. Followed by the math portions, CG and Geometry. Then its on to shock placement and a bit about springs. And to wrap up the initial info dump a little bit about what happens when one corner goes up.

Link to the Check my numbers thread: How's my numbers?

Link to the link calculator thread: New Version of the 4 Link Calculator

Link to link calculator download: https://irate4x4.com/resources

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Terms and Definitions

Here is a list of common terms found when talking about suspension. FOR CLARITY OF DISCUSION PLEASE USE THESE TERMS AND DEFINITIONS IN THIS THREAD. Thank you. This list can be expanded or changed as needed.

Lower links- Shown in Red. The lower members of the suspension. More importantly the line connecting the 2 points at the ends of the member. They are predominantly used to locate the axle fore and aft[SUP]1[/SUP].

Upper links- Shown in blue. The upper members of a suspension. More importantly the line connecting the 2 points at the ends of the member. They are predominantly used to locate the axle fore and aft[SUP]1[/SUP].

Panhard Bar- Shown in yellow. Also known as a trackbar. More importantly the line connecting the 2 points at the ends of the member. They are predominantly used to locate the axle side to side[SUP]1[/SUP].

Instant center- The point in space at about which a system moves. This is often shown in a side view. In a side view it is defined by the point at which an extension of the links would meet.

Roll Axis- The roll axis is the imaginary line about which something rolls. These are the solid lines in the picture below.

Front- This is the line about which the front suspension will roll relative to the body.​

Rear- This is the line about which the rear suspension will roll relative to the body.​

Vehicle- This is the line about which the vehicle will roll.​

Roll center- This is the point at which the front and rear roll axes pierce a vertical plane at the center of the wheel hub on their respective ends of the vehicle. These are the somewhat covered black dots in the picture below.

Pinion Angle- This is the angle of the pinion relative to horizontal. Its movement is best referred to as 3* of pinion up, not as 3* negative pinion rotation.

Up travel- Also known as bump. This is how much the suspension travels upwards. Describes both the motion of only one side or both sides of an axle. When the axle is said to droop, it means the axles moves such that it remains level.

Down travel- Also known as droop. This is how much the suspension travels down. Describes both the motion of only one side or both sides of an axle. When the axle is said to droop, it means the axles moves such that it remains level.

Flex- When the axle in question is not level side to side.

Flex Steer- Steering effect caused by the suspension as it flexes.

Link Separation- This is the vertical separation of the link mounts at one end, either the frame or axle.

Convergence Angle- This is the angle separating the upper links added to the angle separating the lower links. The angle separating the lower links is subtracted if the both the upper and lower links angle the same direction.

Sprung Mass- The weight carried by the springs of the vehicle. Often being the frame and body of the vehicle.

Unsprung Mass- The weight not carried by the springs of the vehicle. Often the axles, wheels, tire. ½ the weight of the suspension links is also considered to be part of this.

Vehicle CG- This refers to the location of the center of gravity (CG) of a body. A solid axle vehicle has 3 that are of interest.

Vehicle- This is the overall center of gravity for the vehicle. This included everything on the vehicle. It is best known including the driver, any passengers and gear. This one has the bigger effect on if the vehicle rolls over when climbing, descending, or off camber.​

Sprung- This is the center of gravity of the sprung mass. This is often the hardest to find and is usually fond through some calculation.​

Unsprung- This is the center of gravity of the unsprung mass. This is often assumed to be at the centerline of the axle for simplicity.​

Anti-squat- This is the tendency of the rear suspension to compress during acceleration.[SUP]2[/SUP]

Anti-dive- This is the tendency of the front of the vehicle to compress during deceleration.[SUP]2[/SUP]

Anti-lift- This is the tendency for the lifting of the rear of the body during deceleration and the front during acceleration.[SUP]2[/SUP]

Frequency- This is the undamped response rate of the suspension. Sometimes referred to as natural frequency.

1. Depends on suspension type
2. While reversing the front of the vehicle becomes the rear, and the rear becomes the front.

 

[Treefrog]

Common Linked Suspensions

Triangulated

What is commonly referred to as a four-link suspension. This consists of 2 upper links and 2 lower links. One or both pairs can be angle. If only one pair of links is angled and the other is parallel, then it is a Single Triangulated setup. If both are angled, it is a double triangulated setup. It is believed that the convergence angle must be at least 40* for the suspension to not move side to side. It is most common that the upper links to angle in at the axle and for the lower link to angle ion at the frame.

Pros: This type of suspension allows for all types of link ends to be used. It also offers high flexibility and ability to tune parameters during design.

Cons: When used in the front, steering is generally restricted to full hydro as the movement of the suspension will result in bump steer when used with a drag link. It can also be harder to package than other types. The other big downside is that the movement of the links towards the center of the vehicle during flex is not easily calculated by hand. And as of 11/27/2020, this inward movement is not accounted for in the 4-link calculator excel sheet.

Applications: Rear suspensions, front suspensions of dedicated of road rigs



Wishbone

A version of the Triangulated suspension in which the axle end of the upper links is at the same point in space, forming a “wishbone” for the upper link.

Pros: Offers known clearance as the suspension cycles since the upper link does not move towards the centerline of the vehicle. Also allows for lower link separation angle to be run, assuming the wishbone can be made to withstand the forces.

Cons: This has the same issues when used in the front suspension as the normal triangulated suspension. It tends to restrict the roll axis and roll center at that end of the vehicle.

Applications: Rear suspensions, front suspensions of dedicated of road rigs



4 Link with Panhard

Often incorrectly referred to as a four-link. It is a five-link suspension. It consists of 2 upper links, 2 lower links, and a panhard bar. This type of suspension does not require any link separation angle, and benefits from having very little.

Pros: Since a panhard bar is being used, a mechanically linked (has drag link) steering system can be used. Compared to a 3-link with track bar, the upper links see less force.

Cons: The suspension is over constrained and is in constant bind. This means the only ends that have some deformation (bushings) can be used.

Applications: Factory jeep TJs and newer, some factory Toyota Land Cruisers, some custom front suspensions



3 Link with Panhard

While this suspension does have 4 links, it is not called a 4 link normally to differentiate it from the triangulated four-links. It normally consists of 1 upper links, 2 lower links, and a panhard bar. This type of suspension does not require any link separation angle, and benefits from having very little.

Pros: Since a panhard bar is being used, a mechanically linked (has drag link) steering system can be used. This suspension is not in constant bind. It is possible to place the upper link such that the body does not roll from the engine torque.

Cons: The since there is only 1 upper link, it has to be able to withstand greater forces.

Applications: Front suspensions on trail and street rigs, only seen in rear for clearance purposes



Radius Arms

A version of the Four-Link with Panhard in which the frame side mount for the upper and lower links are at the same point in space.

Pros: Since a panhard bar is being used, a mechanically linked (has drag link) steering system can be used. It naturally resists roll. It takes up the least amount of space under the vehicle.

Cons: The suspension is over constrained and is in constant bind. This means the only ends that have some deformation (bushings) can be used.

Applications: Older Fords, some factory Toyota Land Cruisers, some aftermarket jeep suspensions.

 

[Treefrog]

Locating CG

Arguably the most important part of planning a suspension is knowing the location of the CG, both front to back as well as vertically.

Finding it is most easily done using car scales with one at each corner. It can be done with 2 scales, just takes a bit more time. If scales are not available, it can be done with a large balance.

First find the front to back location of the vehicle CG. If using scales, the is found by the following equation, with the 0% being all weight on the rear tires:

weight_on_front_tires /(total_vehicle_weight)*100%​

The distance from the rear tires is found by multiplying the wheelbase by this percentage.

If using a large balance, measure the distance from the rear tire to the balance pivot and divide by the wheelbase to get the weight balance ratio.

Put a piece of tape straight up and down on the vehicle at the end to end center of gravity.

Next raise the front of the vehicle by a foot or 2, how much does not matter, but more is better. If using scales this means putting blocks on the scales and putting the vehicle’s tires on the blocks. The same approach applies when using a balance.

Use the same approach as when the vehicle was flat, substituting the horizontal distance between the wheels for wheelbase. This gives you a temporary end to end center of gravity.

Once again put a piece of tape straight up and down (it will be at an angle to the first piece of tape) at the temporary center of gravity.

Return the vehicle to level on the ground.

Find and mark the point at which the two pieces of tape intersect.

Measure the height of this intersection. This is the height of the vehicle CG.

Finding the location of the CG of the sprung mass can be now be done with some math using the sum of the moments equal to 0. The equation for this is:

CG_Sprung=(Mass_Total*CG_Vehicle—Mass_Unsprung*Wheel_Rolling_Radius)/Mass_Sprung​

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Geometry 101 (Math)

This section goes over what some of the geometry does as well as how to calculate it. I recommend using the 4-link calculator, version 4.0 or newer, as it will do the math for you. The following is the coordinate system used for the calculations.

Antis

Anti-squat, anti-dive, and anti-lift are reported as a percentage. This percentage tells how much of the acceleration force is carried by the suspension links. 0% means that all of the force caused by weight transfer goes through the springs. 100% means that the links take all of the force. Below 0% means that the springs take more force than just the weight transfer. Over 100% means that the links will take more force than the weight transfer, pulling weight of the springs. This will cause the rear end to lift instead of squat under acceleration. Desired values change based on use. It seems dedicated competition vehicles tend to be lower, while trail rigs tend to be a bit higher. A higher value will ride stiffer when the force is applied, and a lower value will cause more pitching when the force is applied.

Anti values change throughout suspension travel. It is recommended to stay on one side of 100% during travel.

The following shows what anti is associated with what force when driving forward. Note that the following only applies to solid axles.

Anti-squat: The rear axle being powered.
Anti-dive: The front brakes being used.
Front anti-lift: The Front axle being powered.
Rear anti-lift: The rear brakes being used.

If one axle housing is not reacting to a force, then the anti associated with that force is 0% (the front has 0% anti-lift when the vehicle is in rwd.)

Before going into the mathematical way of finding the antis, let’s go through geometric way.

Plot the lines shown in the picture. The sprung center of gravity uses the Z coordinate found earlier. Its X location is the wheelbase*the bias for that force. Measure the distance of point A from the ground. Divide this distance by the distance of the center of gravity from the ground.

This picture also makes it easy to discuss the principle of how anti’s work. With solid axle suspensions, the links resist both force and torque. As such, the force is applied along the line from the center of the tire at the ground to the instant center. When this line crosses below the center of gravity the force creates a torque on the body causing it to rotate. The same thing happens when the line goes above the center of gravity.

To calculate an anti: Find the side view instant center of the end of suspension in question. This gives you X[SUB]IC[/SUB] and Z[SUB]IC[/SUB]. This is done by finding the point at which the upper and lower links would cross if extended in a side view projection.

You then need to determine the percent of the force, the bias, in question being done by this end. For example, a rwd vehicle would have 100% drive force in the rear suspension and 0% drive force in the front. In 4wd 50% is an okay assumption. For braking, unless known, 60% is an okay assumption.

To calculate the anti in question, use the following equation:

Anti = (wheelbase*bias*(Z_IC/X_IC))/Sprung_CG_height​

Roll Axis Inclination

Roll axis inclination plays a roll in the whether the vehicle will oversteer or understeer. Understeer is preferred if any sort of speed is present. Additionally, flatter axes seem to be recommended. A vehicle roll axis that is located closer to the center of gravity will feel more stable when of camber but provides less warning before tipping.

A brief on roll understeer and oversteer: The roll understeer and oversteer are not the only factors that can cause the behavior.

As with the antis the different roll axis result in different behaviors.

Rear Roll Axis: Slopes down towards front - understeer​

Front Roll Axis: Slopes down towards rear - understeer​

Vehicle Roll Axis: Slopes down towards front- oversteer​

First find the X_RL and Z_RL locations of where the rear lower links would intersect. Then find the X_RU and Z_RU locations of where the rear upper links would intersect. If a panhard is in use, use where the panhard crosses the center plane. The equation for this line is found using:

Z_R = ((X_RL-X_RU)/( Z_RL-Z_RU))*X_R+Z_RU​

The slope of this line is

tan^-1((X_RL-X_RU)/( Z_RL-Z_RU)).​

Find the Z_R location when X_R = 0.

Repeat for the front suspension to find Z_F when X_F=wheelbase. Stay in the same coordinate system as the rear suspension.

Then find the vehicle roll axis equation using:

Z = ((X_R-X_F)/( Z_R-Z_F))*X+Z_F​

The slope of this line is

tan^-1((X_R-X_F)/( Z_R-Z_F)).​

Link Length

For a variety of reasons, longer link length is better. Longer links reduce the change in geometry values throughout travel. They also reduce the change in wheelbase during travel.

Pinion Change

This calculation is possible, making use of the Pythagorean theorem, the law of cosines, and the law of sines. However, it involves calculating the movement of the axle through travel which I do not really feel like trying to walk the reader through. The calculations are performed in the 4-link calculator.

 

[Treefrog]

Shock Placement

Not much I can say when it comes to shock placement. Perhaps some more experienced members have something to say.

What I do know is that there is very small difference between mounting the shock at a 45* angle on the axle and vertically on the link. Additionally, it seems that you would want to locate you shock such that at full flex, it does not go past vertical when viewed from the end of the vehicle.

The more outboard a shock is located the more it helps to resist vehicle roll.

The more perpendicular to the lower mount the shock is the more 1:1 its effect is. When mounted on an axle, this means mounting straight up and down. When mounting to a suspension link, this means perpendicular to that link. Additionally, the shock becomes less effective as the suspension compresses due to the top being mounted more inboard of the bottom. The greater the difference between the mounts, the greater the reduction.
The picture below shows the change in install ratio as the suspension travels. The black line is the overall ratio, with the line just above it being the effect of the shock changing angle to its mount in a side view.

When placing the shocks on the trailing arm, placing the link side mount below the centerline of the link will eliminate the need for wobble stoppers. When mounting both coilovers and shocks on the link, mount the coilover below the centerline and the shock on the centerline. This is because the coilover always exerts a force pushing the link away, whereas the shock can both push and pull.

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Springs

Springs are talked about two ways, by their frequency and by the amount of preload they need. The values are comparable between rigs, that is X preload will have X frequency. It is recommended for the front to have between 1 and 2 inches preload and the rear to have 2 to 3 inches. The goal is to have as much force as possible on the shock when at full extension.

The needed spring rate is found by dividing half of the sprung weight on that end of the vehicle by the sum of the distance that you want the shock to compress and the desired preload.

K[SUB]Target[/SUB]=Mass[SUB]On Suspension[/SUB]/(Shock_Travel_Used+Desired_Preload)
​

It should be noted that this is a very general version of the equation. It does not account for install ratio. This equation is only accurate for a shock that is vertical and mounted on the axle.

On a general-purpose trail rig, it is best to account for the weight of passengers and gear, and just deal with the rougher ride when said passengers and gear are not present.

It is recommended that the lower spring be 2 inches longer than the shocks travel to help keep them seated.

The spring rate for dual spring coilovers is found using:

K[SUB]Combined=[/SUB](K[SUB]1[/SUB]*K[SUB]2[/SUB])/ (K[SUB]1[/SUB]+K[SUB]2[/SUB])​

Of note is that the effective rate of the spring depends on how it is installed and the travel of the suspension.

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Limit Straps and Bump Stops

When selecting limit straps, the total length of the strap is not extremely important. The strap length is most useful in creating a larger number of mounting locations. Account for the stretch of the strap when locating. Go fast cars are known to use an elastic band to pull the strap out of the way during travel.

Both limit straps and bump stop pads should be outboard of all coilovers and shocks. This will keep the coilovers and shocks from over compressing or overextending.

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Flex

The movement of the suspension during flex is difficult to calculate. The general effect with 4-link suspensions is that the upper mounts move towards the centerline of the vehicle. It will also cause the differential and driveshaft to move closer to the centerline of the vehicle.

Flex introduces the concept of flex steer. The amount of flex steer is difficult to calculate. Some say that the flatter the roll axis of that end of the suspension the lower the flex steer. A vehicle with a noticeable amount of flex steer is shown below.

More on flex steer in the future; it is taking me a while to create the data for this. I have reserved the next few posts for this.

 

[Treefrog]

Flex steer is a very difficult to calculate, by hand. Use some 3d sketches in CAD and let it solve? Easy, just takes a bit of time. I've been working on gathering the data as I can, but get borded every so often. Was planning to make a thread on this when I got the data, but this seems as good of a spot as ever. So, here is a more in depth look at flex steer.


To save a bunch of reading: Keep the roll axis flat.


So first off, some information about how the model used and how the data was found.

All measurements were taken on the passenger end of the axle, but value is identical on the driver side because solid axle. The angle was measured using a plane normal to the centerline of the axle located at the lower link point and the intercept with the ground. Positive values mean that this line of intersection crosses the centerline on the axle end, negative means it crosses on the frame side.

Unless noted, the driver side was held at maximum bump while the passenger side was cycled. Unless noted the links evenly split the convergence angle, with the upper frame spacing being the same as the lower axle spacing. Unless noted the links equal length and flat. Unless noted the side view length of the links was kept constant. Unless noted the horizontal line going from a driver side point to the passenger side of the same point is in the same vertical plane as the similar line of the other links, or put another way, all of the frame side or axle side mounts are in the same vertical plane.

The trends should be looked at not the actual data values. Since I was measuring in .1*, the data may seam odd in some places, apply smoothing with your mind.

The convergence angle was swept from 10* to 150*. Or viewed another way the roll axis was swept from shallow (10*) to steep (150*).

The side view link length was swept from 10” to 50”. Or viewed another way the roll axis was swept from steep (10”) to shallow (50”).

In this one, the links were kept parallel when view from the side, while the ride position of the axle was raised and lowered. It seems that at a static position of 3” droop, the roll axis was almost flat.

In this one, the upper links were moved towards the axle or away from it. The roll axis is flatter the further towards the axle the upper links are.

Here the vertical distance between the upper and lower frame mounts was changed, the axle spacing was held constant. 0 being flat. The higher the frame side, the flatter the roll center, at least in this setup.

 

[Treefrog]

And for part 2/2

Here the side to side distance between the center of the links was changed. Farther apart results in a flatter roll axis.

Here both the frame and axle side mounts of the upper links were moved up and down. Down results in a flatter roll axis.

Finally, we finally get to some interesting data. In this one the percent of the convergence angle held by the lower and upper links was changed. The labels are the percentage held by the upper links. So, .25 means that the upper links provide 25% of the combined angle, while the lowers provide 75%.

Here the side to side distance between the upper mounts was changed. The farther apart the flatter the roll axis.

Now for a look at a system that does not undergo any changes. In this test, the driver side was cycled as well. Of note is that the data is reflected along the line of pure travel with no flex. This means that we only need to look at half of the data, providing a clearer view of what happened.

 

[Treefrog]

Something I did not address in the section about flex is the change in the antis. To look at this I am going to consider a triangulated 4 link with the upper links converging at the axle and the lower converging at the frame. This will not transfer directly to the other types, but the theory should be accurate.

in flex with the driver wheel going up and the passenger side going down, the line connecting the driver upper axle mount to the driver lower axle mount will lay become more horizontal. Whereas the line connecting the passenger axle mount will become more vertical. When the links on each side are projected to the side view and the anti is calculated the driver side will have decreased while the passenger side has increased. Of note, it is possible that the values will be more extreme than any of the pure travel values. What I do not know or have immediate info on, is the effect of each side on the other.

The model used is at equal flex on both sides and at ride has flat, parallel links for an anti of 0%.

The driver side:

And the passenger side:

But what about the roll centers and axes? Well, those aren't doable from a geometry standpoint as far as I can tell, so solving these would require a force and moment based approach.

 

[vetteboy79]

Link Separation- This is the angle separating the upper links added to the angle separating the lower links. The angle separating the lower links is subtracted if the both the upper and lower links angle the same direction.

I'd clarify this one - typically when people talk about 'separation' on a link suspension, they're referring to the vertical distance between the upper and lower links - for example, "a general rule might be to have 75% of the vertical separation at the frame side, compared to the axle side". Yes you can differentiate vertical vs. angular separation, but as far as angular, I've always heard that referred to as 'included angle'. Example: "a general rule might be to incorporate 45 degrees of included angle in your design" - meaning the angle of the uppers + angle of lowers is 45 or greater.

Just some thoughts - thanks for getting this thing rolling

 

[gt1guy]

Yes you can differentiate vertical vs. angular separation, but as far as angular, I've always heard that referred to as 'included angle'. Example: "a general rule might be to incorporate 45 degrees of included angle in your design" - meaning the angle of the uppers + angle of lowers is 45 or greater.

Just some thoughts - thanks for getting this thing rolling

The term I've heard most used for angular separation is "convergence angle".

 

[Treefrog]

I'd clarify this one - typically when people talk about 'separation' on a link suspension, they're referring to the vertical distance between the upper and lower links - for example, "a general rule might be to have 75% of the vertical separation at the frame side, compared to the axle side". Yes you can differentiate vertical vs. angular separation, but as far as angular, I've always heard that referred to as 'included angle'. Example: "a general rule might be to incorporate 45 degrees of included angle in your design" - meaning the angle of the uppers + angle of lowers is 45 or greater.

Just some thoughts - thanks for getting this thing rolling

The term I've heard most used for angular separation is "convergence angle".

It has been updated. Not sure how I messed up separation, oops. I decided to go with "convergence angle" since it had more results in a Google search and it seems more straight forward.

 

[Austin]

Awesome Start!, just want to make sure this is all original content .... not copied from some other place

 

[Treefrog]

Awesome Start!, just want to make sure this is all original content .... not copied from some other place

The side view shot of the JKU, anti squat diagram, and flexing Jeep are from google images with a bit of editing. Cord. system image is from the four link calc. If these need changed, just say so and give me a day or so to make some from scratch.

Typed out everything myself, and made the rest of the images/gifs.

 

[AgitatedPancake]

This is great, and will be nice to have a suspension bible 5-10 years refreshed from the previous era's thought processes. I'm going to have to read through it a few times to refresh some of my thought processes, but looking forward to the discussions to come!

 

[Lil'John]

Will this bible cover just geometry? Or will there be any coil spring tech?

 

[Treefrog]

This is great, and will be nice to have a suspension bible 5-10 years refreshed from the previous era's thought processes. I'm going to have to read through it a few times to refresh some of my thought processes, but looking forward to the discussions to come!

As far as I can tell from looking at pictures of rigs, especially race and comp crawler rigs, the thought processes haven't changed a ton, just a bit of rpolishing that all of the race teams don't want to post online about.

 

[SLOWPOKE693]

This is great, and will be nice to have a suspension bible 5-10 years refreshed from the previous era's thought processes. I'm going to have to read through it a few times to refresh some of my thought processes, but looking forward to the discussions to come!

Long time no see....... You still building that U4 car? I miss that thread alot!

 

[Treefrog]

Will this bible cover just geometry? Or will there be any coil spring tech?

I don't have anything against covering coil springs here, they tend to go hand in hand with linked suspensions. The only problem is how to go over them. Billavista was a fan of the frequency approach to determining spring rate, but his target recommendations have since been considered wrong. The people who consider them wrong use the preload approach to determining spring rate. I guess the theory and math behind it can be discussed. Other than that the only thing I can really think of is discussion over step up ratio in dual spring setups.

 

[Lil'John]

I don't have anything against covering coil springs here, they tend to go hand in hand with linked suspensions. The only problem is how to go over them. Billavista was a fan of the frequency approach to determining spring rate, but his target recommendations have since been considered wrong. The people who consider them wrong use the preload approach to determining spring rate. I guess the theory and math behind it can be discussed. Other than that the only thing I can really think of is discussion over step up ratio in dual spring setups.

While I'd love a good deep dive on springs, I'd hate to derail this topic too badly.

My curiosity stems from one of my projects getting two different recommendations: one from the shock seller and one from my fab shop that is a "model" expert(FJ55). I forget who was heavier.

 

[AgitatedPancake]

As far as I can tell from looking at pictures of rigs, especially race and comp crawler rigs, the thought processes haven't changed a ton, just a bit of rpolishing that all of the race teams don't want to post online about.

I'd agree for the most part, nothing has completely changed the game too hard, and bummer that it's gotten so secretive (but understandable). I have a few topics I'd like to offer up for discussion here, but I want to spend the time to address them appropriately.

Slowpoke, Yeah I finally caved and made an account over here hah. Unfortunately I sold my U4 chassis to a buddy earlier this year, it was just slipping further and further onto the backburner. But he'll do it right, and may even have me do some work on it which would be cool

 

[snivilous]

Tree frog this is awesome! The part about flex steer is great, I've never seen data for it and (like most suspension things) just rough ideas with no data explaining it. Those graphs are awesome, thank you for compiling this.

 

[Austin]

While I'd love a good deep dive on springs, I'd hate to derail this topic too badly.

Tree frog this is awesome! The part about flex steer is great, I've never seen data for it and (like most suspension things) just rough ideas with no data explaining it. Those graphs are awesome, thank you for compiling this.

Both of these x10

Just a friendly reminder to keep chit-chat to a minimum, all of these posts, questions and answers will be used to generate an article, aka Bible, then this topic will just be used to discuss that article.

Treefrog do you have a page 7/7 you're working on or was that just to save space?

Is there more to build on? Can the diffrent types discussed be dove into?

 

[Treefrog]

do you have a page 7/7 you're working on or was that just to save space?

I do have some stuff to put there, plan to get it up tonight, just been forgetting to do it when I have time.

 

[Treefrog]

To prompt some discussion:

When determining antis at some point other than ride height, you should account for the change in the wheelbase and the change in cg height relative to the bottom of the tire, correct?

 

[Treefrog]

One thing that is worth mentioning regarding antisquat is that the numbers people throw around, especially with older builds, is that they almost always have a bias of 1, since that was the bias built into the version of the 4 link calculator that was around at the time (3.0). This means that most of the time the numbers are greater than what they actually are. So when you see people say 100%, they more likely have 50% or so when in 4x4 on a level part of a trail. When they begin to climb, a portion of the weight shift to the back and takes the drive balance with it. This results in the bias going back towards 1 and the antisquat value increasing.

 

[bdkw1]

I don't have anything against covering coil springs here, they tend to go hand in hand with linked suspensions. The only problem is how to go over them. Billavista was a fan of the frequency approach to determining spring rate, but his target recommendations have since been considered wrong. The people who consider them wrong use the preload approach to determining spring rate. I guess the theory and math behind it can be discussed. Other than that the only thing I can really think of is discussion over step up ratio in dual spring setups.

Frequency matters in valve springs, not suspension. Tuning for a certain frequency in something that is completely random and variable is more of an academic exercise than something useful.

Pre-load is also a can of worms. The majority of TT's run tenders and mains with the tenders being fully compressed at ride height. This is technically less than zero pre-load as without the tender there would be slack in the spring. The tender also has no effect on the ride.


Rock crawlers need more compliance and will always have a lower rate thus more pre-load. Driving style also has a lot to do with it, what one driver feels comfortable with may make another nervous.

 

[bdkw1]

One thing I don't see discussed on the link geometry or accounted for in the calculator is the effect the angle of the links has on chassis lift under acceleration. Keeping those numbers down will keep the height of the instant center down also. This also has an effect on the squat numbers.

 

[Austin]

I've been reading as you post Treefrog but this AM I broke out my old professor red pen ( never had a red pen) and started going through it as an newb ... here are some parts that could be clarified


Is “linked suspension” just solid axel vehicles or do these work with independent suspensions?

For definitions in general, I don’t think we should use the name of the term we are defining in the definition of that term. The upper and lower link definitions for example:
“Lower links- Shown in Red. The lower link of a suspension. More importantly the bar connecting the 2 points at the ends of the link. They are predominantly used to locate the axle fore and aft.”

For the up and down travel … if that does not account for flex does that mean just for level axels? If you are flexed and it moves up or down evenly is that travel?

Flex – since we're talking about axel suspensions, would it be the "wheels" at the end of an axel?

Anti-Lift – “extension of rear suspension” … extend how? Get longer?

Frequency – “undamped frequency”. Term used in definition

Different steering systems are discussed in the Common Linked Suspensions sections, they should probably have a definition

Shock Placement - Not much I can say when it comes to shock placement. Perhaps some more experienced members have something to say.

Bueler? Bueler? Bueler? Anybody?


I'll put my dunce hat back on and keep reading this afternoon.....

 

[Treefrog]

I've been reading as you post Treefrog but this AM I broke out my old professor red pen ( never had a red pen) and started going through it as an newb ... here are some parts that could be clarified


Is “linked suspension” just solid axel vehicles or do these work with independent suspensions?

For definitions in general, I don’t think we should use the name of the term we are defining in the definition of that term. The upper and lower link definitions for example:
“Lower links- Shown in Red. The lower link of a suspension. More importantly the bar connecting the 2 points at the ends of the link. They are predominantly used to locate the axle fore and aft.”

For the up and down travel … if that does not account for flex does that mean just for level axels? If you are flexed and it moves up or down evenly is that travel?

Flex – since we're talking about axel suspensions, would it be the "wheels" at the end of an axel?

Anti-Lift – “extension of rear suspension” … extend how? Get longer?

Frequency – “undamped frequency”. Term used in definition

Different steering systems are discussed in the Common Linked Suspensions sections, they should probably have a definition



Bueler? Bueler? Bueler? Anybody?


I'll put my dunce hat back on and keep reading this afternoon.....

And here I thought I was done with being graded.

Linked suspension is just solid axles. Technically some of the stuff does apply to independent, but that's a can of worms not worth opening here. I'm open to discussing it, but not in this thread.

From a textbook standpoint, travel is any up down movement of a wheel. But, for up and down travel as I used it, it does mean a level axle. I use flex as any condition in which that is not true. So, going from flex and moving equally, is still flex. I split flex and travel because it provides a separation between level, which is easy to make calculations for and look at and understand, and not level, which is not nearly as easy to look at in such a way.

It would be wheels at the end. I'm not really sure what you are saying here.

I will update the definitions as best as I can.

The problem I am having is figuring out the level at which things are being discussed. For example, I assume that if you are looking at linking a rig you already have some idea about different steering setups, and that you have some idea of what a linked suspension is.

 

[Austin]

And here I thought I was done with being graded.

just constructive criticism ... thats what I told my students

The problem I am having is figuring out the level at which things are being discussed. For example, I assume that if you are looking at linking a rig you already have some idea about different steering setups, and that you have some idea of what a linked suspension is.

I hear ya. Nobody should be building a suspension if they don't know PS box and full hydro.

When I think "Bible" ... I think it has it all.

What we may need, is to start a definitions page and add to them as we bible along. Then you can just link assumed words to there.

 

[Treefrog]

just constructive criticism ... thats what I told my students




I hear ya. Nobody should be building a suspension if they don't know PS box and full hydro.

When I think "Bible" ... I think it has it all.

What we may need, is to start a definitions page and add to them as we bible along. Then you can just link assumed words to there.

A collective definitions page is a good idea.

Next time at least use red. :rolleyes: