#### Treefrog

##### Book Wheeler

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

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

Here is a list of common terms found when talking about suspension.

1. Depends on suspension type

2. While reversing the front of the vehicle becomes the rear, and the rear becomes the front.

__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

__Terms and Definitions__Here is a list of common terms found when talking about suspension.

**Thank you. This list can be expanded or changed as needed.**__FOR CLARITY OF DISCUSION PLEASE USE THESE TERMS AND DEFINITIONS IN THIS THREAD.____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.

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