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I dedicate this section of the website to those searching to expand their horizons. There are so few sources of information on off road suspension, Chassis design, and setup. I want to thank all those who have contributed and I would like to extend this knowledge to those willing to learn. Please read on.
Page still under construction
List of technical terms
Air craft grade materials: common materials used in the aircraft industry. Some common materials are 6061 aluminum 2024 aluminum 7075 aluminum, Chrome molly (4130, 4140, 4340, 300M) and Titanium to name a few.
Anti roll system: An apparatus used to limit the amount of body roll of a vehicle while traversing around a given arc. Body roll is induced by centripetal force acting at the center of gravity of the vehicle. This apparatus uses a spring, usually a torsion member that can be adjusted to increase or decrease the amount of roll for a given cornering force. An anti roll bar connects the moving suspension members from one side of the vehicle to the other. As the vehicle traverses around an arc the anti roll bar helps to distribute the weight of the vehicle to enhance vehicle handling. This bar does not stop a vehicle from rolling over.
Body roll: The tendency of the body or chassis of a vehicle to lean to the outside while traversing around a corner.
Bump steer: The amount of wheel steer due changes in suspension geometry as the vehicles suspension compresses.
Camber: is the angle between the vertical axis of the wheel and the vertical axis of the vehicle when viewed from the front or rear. When the top of the wheel is farther out than the bottom (that is, away from the axle), it is called positive camber; if the bottom of the wheel is farther out than the top, it is called negative camber.
Caster angle: The lay back angle of the upper and lower outer ball joints of a suspension system when viewed from the side. Suspension designers use this angle to adjust the high speed stability of a motor vehicle. This is also the reason your steering straitens out when you let go of your automobile steering wheel. The caster angle also effects the amount of feedback the driver will feel during one wheel bump.
Centripetal force: The external force required to make a body follow a curved path acting in the direction of the center of the arc being traversed.
CNC machine: A Computer Numeric Control machine is a computerized machine for cutting materials.
Coil-over: a spring and shock configuration ware the shock member is encompassed by the spring coils.
Coil Bind: Coil bind happens when a spring is completely compressed and successive coils actually make contact enabling any additional compression of the spring.
Cornering force: is the sum of the forces acting at the tire patch of a vehicle while traversing around an arc.
CV joint: also known as a constant velocity joint is used for transferring torque to unaligned rotated axis. CV joints are used in cars and trucks to transfer torque to from the transmission to the wheel. There are several types of CV joints each with their own purpose. Some CV joints plunge to allow compliance needed for changes in suspension camber, steer, and scrub during suspension compression and extension.
Dual rate springs: Having two springs acting on moving suspension members. A Smaller spring called the tender spring makes the spring rate of the vehicle seem soft until the suspension compressed far enough to bind the small spring (collapse completely) or cross over (mechanically force the main sprint to take over the spring curve) and the larger of the two springs takes over for the remainder of the suspension travel.
External reservoir: A component of a shock that houses oil displaced by the shock shaft as the shock compresses. External reservoirs are connected by a hose to the shock body.
High speed compression: The compression adjustment of the shock that dampens the large bumps and jumps of a suspension system. This adjustment can only be felt when riding the vehicle. It can not be adjusted by slowly compressing the vehicles suspension.
King pin axis: the angle of the steering axis of a vehicle. This angle can be seen by looking at a suspension system from the front or rear view and drawing a line between the pivot points of the upper and lower ball joint.
Knuckle: also known as an upright is the outer suspension member that connects the wheel and hub of a vehicle to the moving suspension members.
Lateral load transfer: the shifting of weight of a vehicle due acceleration around a corner.
Load transfer: The shifting of weight of a vehicle due to acceleration in any direction.
Longitudinal load transfer: the shifting of weight of a vehicle due to strait line acceleration or deceleration.
Low speed compression: the adjustment on a shock that changes the compression dampening of the shock when slow movements of the shock are made.
Motion ratio: is the ratio of shock travel versus wheel travel. It is equal to the Shock Travel (in inches) per 1 inch of Wheel Travel. Motion Ratio is used to account for the different suspension geometries and the resultant mechanical leverage on the spring. In almost all cases, the Motion Ratio is less than 1.
Over steer: Over steer is when the rear wheels do not track behind the front wheels but instead slide out toward the outside of the turn. Over steer is often the problem that occurs when a racer says the rear is too lose and wants to come around on me. Over steer is an unstable condition that can cause the vehicle to go into a spin and create a dangerous track condition.
Piggy back: A shock reservoir that is attached to the main body of the shock which house fluid displaced by the shaft of the shock.
Pre load: The amount of spring compression measured when a coil over shock is fully extended.
Pro dive suspension: a front suspension configuration that allows the deceleration forces applied at the center of the wheel add to the compression of the suspension. With independent a-arm suspension the rake of the a-arm mounting points on the front end dictates the magnitude of pro dive. This type of suspension is often used on the front of ATV’s and off road race buggies. Pro dive suspension transfers extra load to the front wheels and ads to the magnitude of longitudinal load transfer during deceleration. Pro dive suspension can help achieve more front end bite during corner entry. One con to pro dive suspension is the added time for the vehicle to transition from corner entry to corner exit. This is because your front suspension compresses further due to more load and compression so it takes longer for the front suspension to extend and the rear suspension to compress during corner exit. Pro dive suspension also helps slightly to absorb large bumps from the front because of the rake angle of the a-arms.
Pro squat suspension:A rear suspension configuration that allows the acceleration forces applied at the center of the wheel to add to the compression of the suspension. Pro squat suspension can add to rear traction due to added load transferred to the rear of the vehicle during acceleration. The cons to pro squat suspension are the added time it takes for the vehicle to react to deceleration and corner entry. On a-arm suspension the front inner a-arm pivots are positioned lower then the rear pivot points. For swing arm suspension the swing arm pivot point would originate lower then the axel creating an upward positive angle when looking from a side view and rear of the vehicle to the right.
Rebound: Extension of suspension due to reactions in load transfer or extension of suspension after the suspension has been compressed. Adjusting the rebound adjustment on your shocks will slow or speed up the rate at which your suspension rebounds. If your suspension rebounds too slow your suspension will compact and compress farther and farther until your suspension releases all the springs’ energy bouncing the rear of the vehicle up into the air. If your rebound is too fast your rear end will swap and bounce your rear end when you hit a bump or will send your rear end high off jumps. Rebound speed can also adjust the rate at which your suspension allows load transfer. Fast rebound will make for a fast acting twitchy unstable lateral and longitudinal load transfer. Slow rebound will make for a very sluggish safe feeling lateral and longitudinal load transfer.
Ride height: the resting height of the vehicle with the racer sitting in a neutral position.
Roll center- the center at which your suspension will roll from. A high roll center is closer to the center of gravity of the vehicle and makes for more stable vehicle less apt to unstable body roll. A low roll center will lengthen the distance CG and roll center making for a very unstable sloppy ride. A high roll center also allows for suspension jacking which lifts the vehicle up into the air while cornering.
Sag: The quantity of extending suspension travel when the suspension is at ride height.
Spring rate- The rate at which springs compress measured in pounds per inch of compression. If a spring is denoted as a 100lb spring it will resist compression with 100lbs of force when compressed 1 inch. That same 100lb spring will resist with 200lbs of force when compressed 2 inches. Constant wound metal springs compress linearly in this fashion. A stack of coil springs with the ability of lighter springs to coil bind will allow you to have a progressive spring curve that has a soft initial ride but gets stiffer at a faster rate when the suspension compresses
Suspension: an apparatus that allows a vehicles wheels to have compliance and react to changes in the track surface and load transfer.
Suspension jacking: Jacking occurs when forces applied at the contact patch feed back through the suspension members creating a lifting force of the suspension. Jacking of the vehicle raises the center of gravity leading to further body roll and lateral load transfer.
Tire scrub: Tire scrub is the change of track width due to compression or extension of the suspension system. Tire scrub is common with a-arm suspension systems. It is also apparent in swing arm suspension systems but the scrub is changes in wheel base of the vehicle.
Toe- The pitch of your front wheels pointing toward or away from each other. This distance is usually measured in inches. To find your toe you must measure from the center of the tires at the leading edge and subtract the distance between the centers of the tire at the rear of the same two tires. Toe adjustments can be use to add to high speed strait line stability. It can also be used to help steer in the front and the rear..
Torsion bar: is a linear spring that resists torsion. As a torsion bar is twisted it linearly reacts to changes in twist angle. Torsion bars can be used as the main spring supporting the suspension of a vehicle. A torsion bar can also be used as the spring component in an anti roll system.
Track width: is the width of the vehicle measured at the center of tire contact patch.
Under steer: Under steer is when the front wheels push in a corner causing the vehicle to track wide in a corner. Under steer is a stable condition, but reduces the ability to take corners at a high rate of speed.
Un-sprung mass: is the mass of all the moving components of a suspension system.
Upright: an upright is a member of a suspension system that supports the wheel, hub, and wheel bearings. The upright is also the outer connecting member of the a-arm pivots in independent a-arm suspension system.
UV joint: also known as a universal joint is used for transferring torque to unaligned rotated axis. UV joints are used in cars and trucks to transfer torque to from the transmission to the wheel. The down fall to universal joints is the acceleration and deceleration of the shafts as they rotate. This is why universal joints are used as offset pairs to make the rotation velocity constant.
Wheel base: the length of the vehicle measured at the center of the tires.
Wheel rate: is the effective spring rate at the wheel. It is also the amount of weight (lbs) it takes to lower the vehicle one inch (per corner). You can also see it as change in the load on wheel as the wheel travels vertically. In order to determine wheel rate, you must know the vehicles Sprung Weight, and the wheel travel.
Wheel travel: The quantity of suspension travel for a given corner of the vehicle
What is IRS and what are the benefits?
IRS stands for Independent Rear Suspension. Independent suspension is a type of vehicle suspension system where each wheel can react to differences in the road surface without influencing the other three. IRS is used by fastest high performance Racing Vehicle. From F1 to Baja 1000 the fastest vehicles in the world on or off road have independent suspension.
What is un-sprung mass and why does it matter?
Un-sprung mass is the mass of all moving parts of your suspension. This includes everything from the wheels, tires, hubs, axles, a-arms, and shocks. If it moves when you hit a bump it is un-sprung mass. It is very important to keep your un-sprung mass to a minimum. The faster your suspension can react to bumps the faster you can get your tires on the ground and accelerate.
What does an anti roll bar do and how can it benefit me?
An anti-roll bar is a combination of a torsional spring and linkages that connect the left moving suspension members to the right moving suspension members and effectively limits the body roll in a vehicle. Anti-roll bars are used in all street automobiles, road race cars, and off road race cars today. A correctly configured anti-roll bar will properly distribute the load on each corner of the vehicle in order to achieve the maximum traction and cornering speed. An anti-roll bar can also be used to adjust the steering characteristics of a vehicle.
What influences my vehicle's body roll and what can I do to fix it?
Body roll is a phenomenon that occurs when you’re cornering forces act at the center of gravity of the vehicle leaning the vehicle to the outside of the turn. The magnitude of body roll is governed by the distance from your suspension’s roll center to your CG. The distance between your vehicles roll center and the center of gravity is the length of the fulcrum. If your roll center is close to your center of gravity you will experience less body roll then if it is a long distance. To limit your body roll you can use stiff springs to counteract the body roll but this may offer a stiff ride. The best way to limit your body roll is by using an anti-roll bar.
What do my Shock adjustments do and how do I set my shocks up?
Most adjustable shocks have a compression adjuster at the top of the shock body and a rebound adjustment at the bottom. Some higher technology shocks also have a high speed compression adjustment.
The compression adjustments fine tunes the shock’s ability to resist compression. The low speed compression adjusts slow compression movements such as lateral and longitudinal load transfer, and the rate of body roll. High speed compression adjusts the resistance to big bumps woops and jumps.
The rebound adjustment resists the force of the spring as the suspension relaxes after being compressed.
What is the difference between using an anti roll bar to limit your body roll using shock crossovers and compression settings?
An anti roll bar uses the extended suspension member to add spring rate to the compressed suspension member effectively limiting roll and squatting the vehicle. The rider will feel more stability and a squat coming off the corner. Spring crossovers add spring rate at a certain ride height so the spring stack exerts more force to the compressed suspension members but no squat is seen and proper weight distribution to each of the four wheels isn’t seen. If you adjust your roll using the low speed compression adjustment on your shocks you can adjust the rate at which the vehicle will roll but ultimately in long corners the vehicle will roll to the same roll angle and roll isn’t limited.
What materials are good and what do they mean to the racer?
Most race products are made with materials that have a high strength to weight ratio. It is beneficial to keep the weight of your vehicle down as much as possible because mass opposes acceleration. Approved air craft grade materials are the best solution for the racer. For aluminum the grades most widely used are 6061 T6, 2024 T4, and 7075 T6. For steel components Chrome molly is used. Chrome molly comes in several grades such as 4140, 4130, 4340, and 4340 Modified 300 also known as 300M. For most aluminum components 6061 is used having a strength rating around 35000psi. Next is 2024 having a rating of about 45000 psi and the strongest is 7075 having a strength rating of about 75000 psi. Your extreme strength and wear components are made from 7075. High grade sprockets and some engine connecting rods are made from 7075.
The various grades of Chrome molly also have their own strength characteristics and properties. All of the grades listed are heat treatable and should be heat treated to gain the most benefit possible out of your material. The main differenced between the various grades of chrome molly are the carbon content, chromium content, and molybdenum content.
Why is my chrome molly frame TIG welded and what does this do for me?
Chrome molly tubing should only be TIG welded. This is because chrome molly is prone to stress cracking in the heat affected region right next to the weld. MIG welding or stick welding will over heat the welded joint and make for a weaker weld. TIG welding is also a much cleaner weld and it is easier to control the pitting and porosity of the weld. It is also very important to flame stress relieve your weld joints after welding to relax the metal and reduce the change of cracking.
How much power do I lose through my CV joints?
Power loss through CV joints varies slightly by the misalignment angle. If your CV joint and axle are aligned under power there is no loss at all. At max misalignment about 1% losses can be seen. Power loss with the CV joints is lost by friction. All CV’s have a break in period of about 300 miles. In the beginning of the life of the CV’s they will heat up and be hot to the touch. This is where your lost power goes. As the CV’s get broken in they heat up less and become more efficient.
