there are countless modifications that can be done to your suspension so ill do my best to explain some of the options.
the most popular modification to be made would have to be lowering springs.
Springs absorb and store road shock caused by bumps, dips, cracks, and so forth. They absorb this shock by either compressing or extending. When a car's wheel goes over a bump and gets pushed upward, the spring absorbs that additional load, keeps the road shock from reaching the chassis, and makes sure the tire maintains contact with the pavement.
How much a spring compresses or extends is determined by its "spring rate." Spring rate is measured in pounds per inch of deflection; for example, 100 pounds per inch. So, say a load of 200 pounds is applied, the spring will deflect 2 inches. Spring rate comes from various factors. For a coil spring, this includes the number of active coils, the diameter of the coils, and the diameter of the spring wire. The fewer coils a spring has, the higher the spring rate it will have.
The design of a spring affects how well the vehicle will ride and handle. A spring that absorbs lots of energy will generally offer a comfortable ride. After all, it can absorb most of the road shock (energy) that is being generated by the road surface. But there are always engineering trade-offs. This kind of spring generally requires a higher vehicle ride height, which will cause the vehicle to feel unstable during cornering. This instability is because the more distance a spring compresses or extends, the more the vehicle "rolls" around on its suspension. This rolling is called weight transfer, and it is caused by centrifugal force acting on the weight of the vehicle as it goes around a corner. Weight transfer can overload a tire's grip, which ultimately hurts traction, and therefore handling.
Shock Absorbers
The other main part of a car's suspension is the shock absorber. Contrary to its name, a shock absorber plays a minimal role in absorbing impacts taken by the suspension. That's the spring's job. A shock absorber dampens road impacts by converting the up and down oscillations of the spring into thermal energy.
People who live and breathe shock absorbers (like us 240sx owners) don't like the term shock absorbers; they prefer "dampers." The unwashed masses -- that's you and me -- just call them shock absorbers.
Without a shock absorber, a spring that has absorbed energy will release it by oscillating at an uncontrolled rate. The spring's inertia causes it to bounce and overextend itself. Then it recompresses, but again travels too far. The spring continues to bounce at its natural frequency until all the energy originally put into the spring is used up by friction. This effect can be quite detrimental to the stability of a vehicle.
Confused? OK, here's an analogy. If you have a Slinky lying around -- and who doesn't these days? -- you can use it as an example. Hold up a compressed Slinky in the air with your hand. Now hold just one end and let the other drop. The Slinky will absorb the potential energy caused by gravity (just like how a car's spring absorbs road shock) and then bounce up and down, up and down (aka: oscillate), for a long time. This what an automotive spring does if it doesn't have a shock absorber attached to it.
Perhaps you've heard the word "strut," or, more formally, MacPherson strut. Struts are simply shock absorbers used as major structural members. For struts, the shock absorber is placed inside the coil spring. In addition to saving space, it often costs less. Many cars use a strut design.
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Last edited by TwoFortySX; 12-03-2005 at 06:42 PM.
One of the parts that can have the most dramatic effect on a cars handling charectaristics and reaction to steering input is a sway bar. However, this part of the suspension is often overlooked when a driver seeks to improve the handling characteristics of their car.
A sway bar is a length of solid or hollow steel tubing that connects the right and left sides of the suspension together. Its purpose is to provide an increase in cornering stability by reducing body roll and maintaining proper suspension geometry throughout the radius of a turn. It does this by using the sub-frame of the car as a pivot between the right and left endpoints of the front or rear suspension. As pressure is applied to the suspension on one side of the car, an equal amount of energy is transferred via the pivot, to the opposite side of the car. The result is that both sides of the car remain relatively even through the turn. This allows both wheels to maintain proper camber and caster angles throughout the turn as well as use all of the tires contact patch to react to the drivers inputs. Because this has the effect of reducing body roll it is often referred to as an anti-roll bar.
More serious enthusiasts and races require a much wider range of adjustment in their suspensions to cope with the demanding driving situations that they are presented with. In order to satisfy these needs, adjustable coil over suspensions were created.
These suspensions allow for a broad range of adjustment in a suspensions ride height, spring rate and damper rate. It does this through a combination of height adjustable springs and a threaded and adjustable shock that they are attached to. This spring and shock are usually matched at the factory to provide the utmost suspension precision. These systems are very expensive and are usually beyond the budget of the average enthusiast
For this reason, threaded sleeves were created to allow for ride height adjustment, without the cost of the accompanying shocks. Although not ideal, these suspension systems have become very popular for enthusiasts on a budget.
Toe, simply put, is direction the wheels are pointing. Zero toe would be perfectly parallel wheels pointing straight forward. Toe-out means the front of the tires are farther apart than the rear of the tires. Toe-in means the front of the tires are closer together than the rear of the tires. Toe has different effects on tire wear in the front and in the rear. When the front wheels are toed out, the inside edge of the tire scuff and wear out early. When the front wheels are toed in, the outside edge will scuff and wear out early. However, on rear tires toe usually causes a diagonal cupping wear pattern whether the tires have too much toe in or too much toe out. The diagonal cups are caused by the tires hopping and skipping along the road. It's hard to explain why, but I'll give it a try. Draw an overview of a car with 4 wheels on a piece of paper, make the front wheels parallel, but toe the rear wheels in substantially (say 45 deg. in just to make the demo easier) Now draw lines parallel with the rear tires following their path of travel if they were to roll. You will notice that the lines you have drawn intersect. Since the tires are attached to the car they can not intersect. Instead they roll a bit, then skid outward, roll a bit, then skid outward again. This goes on and on until the tires have diagonal cups worn into the treads where they have been skidding outward.
Camber
Camber is the lean of the wheel. If the top of the wheel tilted away from the car, that is called positive camber. If the top of the wheel is tilted in towards the car, that is called negative camber. Camber can cause a pull to one side or the other depending on the direction of the lean. The car will pull in the direction of the wheel with the most positive camber. However, if both sides have the same amount of negative or positive camber, they will cancel each other out and the car will not pull. Camber can cause premature tire wear, but is not as hard on tires as toe is.
Caster
Caster is the hardest to explain of the three commonly used alignment angles. I like to use the motorcycle analogy. Lots of positive caster is like the forks on a chopper; the wheel is far in front of the support for the wheel. No car that I know of uses negative camber, so I'll describe less positive camber as like the forks on a regular street bike, the wheel is only slightly in front of the support for the wheel. Caster will not affect tire wear, but it can cause a slight drift if it's not equal on both sides. Caster is an angle that only applies to the front (steering) wheels of a car. The more positive caster is, the more stable the car feels, especially at higher speed. More positive caster also improves steering wheel return. To help understand what steering wheel return is, try this experiment: next time you turn a corner, let go of the steering wheel when you are done turning. You will notice that the steering wheel spins back to the centered position. Without positive caster, the steering wheel would stay turned until you manually turned it back to the center position. The only downside to lots of positive caster is it make the car hard/slow to steer. The reason positive caster adds stability, steering wheel return and increased steering effort is the weight of the car is trying to straighten the wheels. You may notice on some luxury cars with lot of positive caster (and powerful power steering) that the front of the car will rise when the wheel is turned to the side, and sinks as the wheel comes back to center.
The hub mounting surface is even with the centerline of the wheel.
Positive
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
Negative
The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.
In Europe, where selected highways do not have speed limits and high speed driving is permitted, speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tire manufacturer's ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits.
Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met.
It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired because the tire manufacturer can't control the quality of the repair.
Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:
225/50SR16 225/50SR16 89S or 225/50R16 89S
Each of these was an acceptable method of identifying speed ratings.
Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991.
225/50SR16 112 mph, 180 km/h
225/50HR16 130, 210 km/h
225/50VR16 in excess of 130 mph, 210 km/h
Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire's service description, such as 225/50R16 89S. The most common tire speed rating symbols, maximum speeds and typical applications are shown below:
M 81 mph 130 km/h
N 87 mph 140km/h Temporary Spare Tires
P 93 mph 150 km/h
Q 99 mph 160 km/h Studless & Studdable Winter Tires
R 106 mph 170 km/h H.D. Light Truck Tires
S 112 mph 180 km/h Family Sedans & Vans
T 118 mph 190 km/h Family Sedans & Vans
U 124 mph 200 km/h
H 130 mph 210 km/h Sport Sedans & Coupes
V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars
When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.
W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic Sports Cars
While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.
225/50ZR16 in excess of 149 mph, 240 km/h
205/45ZR17 88W 168 mph, 270 km/h
285/35ZR19 99Y 186 mph, 300 km/h
Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:
285/35ZR19 99Y 186 mph, 300 km/h
285/35ZR19 (99Y) in excess of 186 mph, 300 km/h
As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tires capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.
Bushings are flexible cylindrical cushions fitted between movable components to attenuate vibration and assist in alignment. Typically used between suspension components, bushings are constructed of synthetic rubber, polyurethane, special plastics or aluminum.
Bushings work by transferring the kinetic energy of moving parts into heat. Repeated heat cycles and oxidation eventually causes the bushings to shrink, harden and lose their elasticity. When this occurs, the bushings can no longer adequately attenuate vibration or assist in the alignment of components. The result is increased transmission of noise, vibration and harshness throughout the chassis.
When you get used to taking corners much, much faster than you ever thought possible in your car, with absolutely no perceivable body sway, tire squeal, or loss of control, you will find it difficult to drive a car with lower handling capabilities - it gets addictive! The right setup will give you this capability. Some weight & weight distribution, suspension, and handling basics before we get into details of modifications:
1.) Minimize overall vehicle weight as much as possible. With no other changes, the lower a car's weight, the less weight transfer there is in a corner, and the more cornering force a car will generate. A related issue is front/rear weight distribution - the closer to a 50%/50% distribution this is, the easier it will be to set up the car for maximum cornering. The handling will also be more balanced, predictable, and controllable. One easy way to help distribute weight more evenly is to relocate the battery to the trunk area. There are kits available to do this from a number of suppliers. Be sure you use the best quality, heaviest gauge battery cable possible to avoid increasing electrical resistance and be sure the battery is well-anchored.
2.) Minimize suspension unsprung weight for best handling. Unsprung weight is what is on the outboard end of the suspension - what is not being "sprung" by the suspension. This includes wheels, tires, brake components (rotors, calipers, drums) suspension arms, spindle, rear axle and associated brake components, and the leaf springs. By reducing unsprung weight you are reducing mass in motion in the suspension. Less weight moving up and down means the suspension can react more quickly to changing road surfaces and keep the tires planted on the ground better. This all equals higher acceleration traction, cornering traction, and overall better handling and road feel.
3.) Choosing spring rates, other suspension components. Generally, there are two "schools of thought" in setting up a car suspension for cornering / handling.
# -a) soft springs/stiff (thicker) anti-sway bars
# -b) stiff springs/soft (thinner) anti-sway bars
Both of the above have some (+) and (-) . The soft spring/stiff anti-sway bar setup, with matched shock absorbers, is, in my opinion, probably the best for an all-around (race and street) car as it gives you a very flat cornering car with a liveable ride on the street. Either approach will require a high performance shock absorber matched to the spring rates you are using. I ended up using the advice of some other SCCA members with 2nd generation camaros and generally went with the Guldstrand Engineering recommended spring rates, anti-sway bars, and shock absorbers on my car. The stiff spring/soft anti-sway bar approach also gives you a flat cornering car but I would recommend this more for a car that will see little if any street use as the ride is extremely harsh and best suited for the smooth surface of a race track. Cars I have seen set up this way have used 700 + lbs/in front springs, 190 to 200 + lbs/in rear springs, a 1" to 1 1/4" fr. anti-sway bar, and often a small or no rear anti-sway bar.
For those who have not heard of either Dick Guldstrand or Herb Adams, both of these have been involved with GM F bodies for many years. Dick Guldstrand has been involved with car racing (dirt track, oval track, road racing) and race car building since the late 50's. His area of specialty is GM car suspension, including the F body (camaro). He has an engineering degree and has also worked in the aerospace industry. His Guldstrand Engineering website is www.guldstrand.com - good source of parts/technical info for F body suspension and related hi-perf modifications. Also reachable at 11924 W. Jefferson Blvd., Culver City CA 90230 (310) 391-7108. Herb Adams is an engineer who also has many years of experience with GM cars, racing, and particularly the F body. He worked at GM early on with the Pontiac Trans-Am project (suspension in particular). I couldn't find a web site for his company, his high-performance auto parts business is: Herb Adams VSE, Monterey, CA 93940, (831) 649-8423.
Balancing handling by adjusting front vs. rear roll stiffness (This applies to the dynamics of really any front engine, rear wheel drive car. I have little experience with front wheel drive cars and hope to never see the day of a front wheel drive camaro!): Note: with the specs of the setup I describe further below (springs, anti-sway bars, shock absorbers, suspension alignment, etc) I ended up with very flat cornering and neutral handling car which needed little adjustment of front vs. rear roll stiffness. Varying tire pressure and changing front anti-sway bar bushing material is about the only change I have had to do to "dial-in" the suspension for different track conditions and for street use.
TIP: Before you do anything else, try adjusting front vs. rear tire pressure. This is easily done and you would be surprised at what a difference a 2 to 5 PSI change can make. Try adjusting in 2 PSI increments, and record the pressures that work (cold pressures, for repeatability) so you can duplicate them again in the future at different tracks, etc. - be aware that differing air temperature will have an effect on pressures.
The ideal end state is a neutral handling car which neither understeers or oversteers in a constant turn at a constant speed. A well set up car can be pushed into oversteer by more throttle, and back toward understeer by backing off the throttle - you can "steer" a well-balanced car by the throttle alone.
1.) If you car understeers too much (the front of the car wants to "push" out of the turn and it takes excess steering effort to keep it in the turn, you have too much front roll stiffness, and possibly the wrong tire pressure (too low). You need to reduce this front roll stiffness. What is happening is that the front tires are not able to maintain enough traction and are pushing (really sliding) out of the turn. The technical term for this lack of cornering traction is "slip angle". The more a tire loses cornering traction, the higher a "slip angle" it is said to have. In this case, the front tires have a higher slip angle than the rear tires. This causes the nose of the car to slide out of the turn and is commonly called "understeer". You are most likely not aware this is happening because there is not enough "slip" to feel, nor enough tire squeal to hear. If you have a good set of high-performance tires, and do not need to upgrade them, follow the advice below to balance handling (assuming all the other suspension parts are installed and chassis work is done). If not, I would recommend you invest in good tires before you do any further suspension tuning. Tires are the only point of contact where all the hard earned $ you invested in suspension and other hardware actually meet the road. Good high-performance will make the single biggest difference in overall car handling and especially cornering (see tire section for tire/wheel size/type recommendations). To adjust the suspension and reduce understeer:
a.) You can reduce front roll stiffness and adjust tire pressure by:
- increasing front tire pressure (for street use do not go above the maximum recommended safe pressure-usually posted on sidewall, ask tire manufacturer if you do not know what this is). By increasing tire pressure you are allowing the tire to work as intended, and the full tread width to stay firmly planted on the road for maximum cornering traction. Too low a tire pressure will cause the sidewall of the tire to deform, causing traction loss and understeer. At the extreme opposite end, excessively high tire pressure can distort (bow) the tire tread, causing only a small portion of the center of the tread to contact the road. This too can result in loss of traction and produce understeer.
- substituting softer anti-sway bar bushings (as discussed in the anti-sway bar part of the suspension section )
- reducing anti-sway bar stiffness - easier if you have an adjustable anti sway bar, but otherwise you will have to install a thinner bar.
- reducing front spring rate - install softer springs.
b.) If you feel the front setup is just about correct, or the above changes are not enough, or you want to experiment with changes and their effect on overall handling, you can also increase rear roll stiffness and adjust tire pressure by doing the opposite of the above to the rear suspension: - decreasing tire pressure (I wouldn't go below about 25 psi for a high-performance street radial or you will really speed up tire wear - ask the tire manufacturer for recommendations on min. safe tire pressure) - installing harder anti-sway bar bushing materials (see discussion under anti-sway bar section) - increasing anti-sway bar stiffness - increasing spring stiffness - can be done of course by swapping in stiffer springs, but you can also add an additional "helper" leaf. A number of auto parts suppliers carry these, to include J.C. Whitney, and they usually give specific info on how much these increase spring rate. This is a relatively easy modification and could provide you that extra measure of rear spring stiffness you need without spending a whole lot more time or money on your "project car".
Other suspension considerations in balancing handling and cornering:
- another consideration is the tire size, the tread width particularly. If you have smaller tires up front, your front tire/wheel combination may be too narrow, and you are losing traction in a turn, causing understeer. Consider going to a wider (and even a lower profile) tire. You may have to change to a wider wheel too, matched to the tire tread width. A good rule of is to select a wheel that is as close as possible to the tire's tread width-the width of the contact patch that touches the ground (don't confuse this with section width). The tire manufacturer can get you all these specs. This will allow the tire sidewall to remain vertical to allow the full width of the tread's contact patch to touch the road.
2.) If you car oversteers too much (the front of the car wants to steer into the turn too much, you have too much rear roll stiffness.and may also need to adjust tire pressure What is happening here is that the rear tires have a higher "slip angle" than the front tires, causing the tail of the car to slide out of the turn and aim the nose too much into the turn. Try increasing rear tire press / reducing front tire pressure, or some combination, and adjust roll stiffness as detailed below:
a.) To decrease rear roll stiffness: - installing softer anti-sway bar bushing materials (see discussion under anti-sway bar part of suspension section) - decrease anti-sway bar stiffness - decrease spring stiffness
b.) You can also increase front roll stiffness to further correct oversteer by: - substituting harder anti-sway bar bushings (as discussed in the anti-sway bar section ) - increasing front anti-sway bar stiffness (install new anti-sway bar) - increasing front spring rate - install stiffer springs.
Handling - Objectives
Handling comes down to one thing: Traction, and not just traction during cornering.A good handling car will be predictable and easy to control under cornering, braking, acceleration, on all sorts of roads, and in all sorts of conditions. As with anything, this means you need to compromise or balance the chassis for the majority of conditions the car will be operated under.....
Street vs. Racing - Ride vs. comfort.
Understeer vs. Oversteer
Most cars are designed to understeer, which is when the car approaches a corner it wants to keep going straight. If you enter a turn too fast the front end will slide and turning the steering wheel is useless, so you'll have to slow down and turn into the slide. This is also known as "push".
Oversteer is the opposite, where the rear end wants to slide out from under the car while the car continues to turn into the curve. This is known as "Loose".
Most cars are designed to understeer so a normal driver can instinctively control the car. In a race situation, oversteer is prefered because a good driver can control the car easier and corner faster.
To reduce understeer you add oversteer to the car by:
* Increasing front tire and wheel size
* stiffen the rear springs
* increase front tire pressure.
* increase rear stabilizer bar.
Summary: You want to set the car up to oversteer. I repeat this because if you run out and spend $$$$ on a larger front swaybar, you're actually adding more understeer to the car, which you are (supposed to be) trying to get rid of.
Wheels and Tires
The only thing attaching your car to the road surface is the tire. Therefore, the tires are the key to a good handling chassis. A poor driver with good tires can outrun a good driver with poor tires anyday.
Again, compromise is necessary due to the conditions the car will be driven under.
Shocks
Shocks dampen the actions of the springs.
For the ultimate in tunability, you want adjustable shocks. These are expensive and if you don't know what you're doing, a waste of money. Since you're reading this they may be beneficial. Street shocks are designed to provide most of the dampening force on the rebound, i.e. when the tire is going back down towards the road after it hits a bump. This makes for a smooth ride. Performance shocks usually dampen at a 50/50 rate, rebound vs. compression. This improves handling at the cost of a firmer ride. Nitrogen gas shocks are the prefered way to go. Adjustable shocks allow you to tune for compression or rebound, depending on the road conditions.
Swaybars and Springs
Swaybars or stabilizer bars twist when a car leans during a turn.
If your car doesn't have a rear swaybar, PUT ONE ON. This will be the most significant handling improvement you can make for little money.
By switching to polyurethane, you effectively make your bar think it's 20-25% larger in diameter due to reduced deflection which rubber mounts. This will also speed up the bars reaction time.
Springs hold the car up. They'll also rattle your teeth if they're too stiff. Use swaybars to TUNE your ride while maintaining softer springs if you need to drive on the road. Shortening springs lowers the car, which lowers the center of gravity. If you go too far, your car will bottom out either on the road or on the suspension, so pay attention.
Other Tips
Weight distribution - balance. Less weight = less effort to accelerate/decellerate.
Alignment & steering (deflection, scrubbing off speed).
when dealing with caster, picture a shopping cart. now i forget what it has exactly, i think more of a negative caster. because of this when you push a shopping cart the wheels have the propensity of turning towards each other thus you hear a lot of rattle and the wheel shakes violently. i do not feel like explain every little detail but you can figure out how this applies to automotives.
"A well set up car can be pushed into oversteer by more throttle, and back toward understeer by backing off the throttle - you can "steer" a well-balanced car by the throttle alone."
how is this possible...i sont quite understrood it...but i mean i heard about it in all Gran Turismo's...but never thought possible...yea im a newbie when it comes to real driving tech...well plz if any one knows hows this is done...let me know...thank!!
it makes total sense if you want to go in one direction around a turn. its not a drifting thing...
I just wanted to put in my 2 cents by posting my own writeup on camber, caster, and toe. I think these are some of the most misunderstood topics in suspension tuning, so I wanted to give you guys some info in addition to what TwoFortySX posted.
Camber
Camber is probably the most useful and popular alignment adjustment that can be made to a street car. The other alignment adjustments are toe and caster. Camber is the angle of the wheel from the vertical as viewed from the front or the back of the car. Negative camber means that the top of the wheel is leaned in towards the car, and positive camber means that the top of the wheel is leaned out away from the car.
Maximum cornering force is achieved when the camber of the outside wheels relative to the ground is about -0.5 degrees. A slight negative camber in a turn maximizes the tire contact patch due to the way the tire deforms under lateral load. Hence, it is good to have some negative camber to increase cornering force.
Another reason why it is helpful to align your suspension with a slight negative camber is that camber will change with suspension travel and body roll. Most suspension systems are designed so that camber increases with more suspension travel. However, camber relative to the car's chassis is not the same thing as camber relative to the ground. It is camber relative to the ground that affects handling. Therefore, even though camber relative to the chassis is made to increase, camber relative to the ground may actually decrease on the outside wheels if there is substantial body roll. To counter this tendency, it is important to use negative camber and to control body roll.
The only drawback to negative camber is increased wear on the inside of each tire. Since the top of the wheel is leaned in, the car is riding on the inside of the tire while it is on straightaways. In a corner, suspension travel and lateral forces on the tire’s rubber compound combine to straighten the tire relative to the ground. Therefore, the car rides evenly on the tire in turns, which improves cornering ability. However, extra time spent driving on the inside of the tire causes that part of the tire to heat up and wear. This effect is small if you avoid adding too much negative camber.
On most street cars, camber is not easily adjustable. However, if you choose to purchase aftermarket camber plates, you can set camber to improve handling. More negative camber tends to increase tire grip in corners. Therefore, if your car experiences understeer, you can decrease front camber (make it more negative) to improve front grip or increase rear camber (make it more positive) to decrease rear grip. Remember not to add too much negative or positive camber since it will decrease the life of your tires and may cause a blowout. Even pure race cars rarely use more than about 3 degrees of camber.
Caster
Caster is the angle between the steering axis and the vertical axis as viewed from the side of the car. Caster affects straight-line stability and "camber gain". Positive caster is when the top of the steering axis is tilted back (steering axis intersects the ground in front of the tire contact patch). Negative caster is when the top of the steering axis is tilted forward (steering axis intersects the ground behind the tire contact patch). I have never seen negative caster used, and I do not believe it is beneficial in automobile suspension geometry. Therefore, for the rest of this section, when I refer to caster, I am talking about positive caster.
To visualize caster, think about the wheels of a shopping cart. The steering axis of the wheel intersects the ground far ahead of where the wheel touches the ground. As a result, the wheel is essentially dragged behind the steering axis. This keeps the wheel moving straight. If the steering axis intersected the ground at the same spot that the wheel touched the ground, then there would be no caster effect. The wheel would be free to spin around the steering axis as long as it was not held in place by some other force.
Unlike in a shopping cart, the steering axis on a car is placed close to the hub of the wheel. Therefore, the only way to make the steering axis intersect the ground ahead of the tire contact patch is to tilt the steering axis. The more the axis is tilted (in the positive caster direction), the greater the caster effect.
Large caster settings increase the tendency of the front wheels to center themselves. This tendency is mainly due to the camber gain that occurs when the steering axis is tilted and the wheels are turned. Camber gain involved with caster is not easy to visualize. Think about the extreme case where the steering axis is tilted to the point where it is horizontal. When you turn the steering wheel, the front wheels would stand up on their edges. If you turn left, the left tire will stand on its outer edge, and the right tire will stand on its inner edge. If you turn right, the left tire will stand on its inner edge the right on its outer edge. The same type of camber gain, only on a smaller scale, takes place with less caster. This camber gain is exactly what you want in a corner. Read the previous section on camber to see what it is and why it’s beneficial.
When the tires stand up on their edges, the front of the car is actually raised up. This is why the wheels "center themselves" when you let go of the steering wheel. The weight of the car pushes the wheels flat on the ground, which resets the steering. This improves high-speed stability because it keeps the steering firmly in the center position. However, it is difficult to turn a car with a large caster setting because, while turning, you are actually lifting the front of the car with the steering. This effect is most visible in luxury sedans, where high-speed stability is important and sophisticated power steering makes up for the extra steering effort. If you watch one of these cars as the wheels turn to full lock (maximum steering angle), you will see the front end of the car rise slightly.
Increased caster is advantageous for racing and, in some cases, street driving. The only disadvantage is the added steering effort. While camber gain due to caster is generally good for increasing the grip of the front tires in a corner, too much camber gain will cause the tires to heat up, lose grip, and wear out prematurely. Therefore, do not use more than a few degrees of caster. If your car uses a MacPherson Strut suspension, it may be necessary to modify or install new strut tower mounts to be able to adjust caster.
Toe
Toe is an alignment parameter that describes how the front wheels are oriented with respect to each other and how the rear wheels are oriented with respect to each other. With the steering wheel centered, if the front wheels are pointing toward each other (from a top view), they have "toe-in" or are “toed-in”. If they are pointing away from each other, they are said to have "toe-out" or be “toed-out”. The same definitions apply for the rear wheels. Toe can be measured as an angle between the perfectly straight position of a wheel and its position after toe is adjusted. Toe can also be determined by finding the difference between the distance separating the front edges of the wheels and the distance separating the rear edges of the wheels. More distance between the front edges than the rear edges is toe-out. More distance between the rear edges than the front edges is toe-in.
Toe is used to change the way a car behaves on corner entry. The more toe-in you have on a pair of wheels, the harder it is to make those wheels turn into a corner. The more toe-out you use, the easier it is to get that pair of wheels to turn into a corner.
Why does this happen? Let's take an example where a car with toe-in on the front wheels is about to enter a left turn. The driver begins to turn the wheel left. Now, the left-front tire is pointing only slightly to the left while the right-front tire is pointing much more to the left. The problem with this is that the left-front tire needs to turn with a greater angle than the right-front tire because the left-front tire is on the inside of the corner and, therefore, must trace an arc with a smaller radius than the outside tire. However, with toe-in, the left-front tire is actually trying to trace a larger radius arc than the right-front tire. It is difficult to make the car turn because the left-front tire is fighting the right-front. When the car is already in the turn, weight transfers to the right-front tire and diminishes the effect of the left-front tire. Because of this weight transfer, toe mainly affects corner entry.
With toe-out, the inside tire in a corner turns with a greater angle than the outside tire (as it should). This improves the grip of the front tires on corner entry.
In addition to corner-entry handling, toe affects straight-line stability. Toe-in improves stability while toe-out worsens stability. This can be explained through the same reasoning as was used to describe corner-entry handling. Toe-out encourages turn-in since the inside tire turns at a greater angle than the outside. Hence, the car is sensitive to the slightest steering input. Toe-out will make the car wander on the straightaways requiring corrective steering. The car will always be turning unless the steering is perfectly centered. With toe-in, the inside tire fights the outside since the inside is trying to trace a larger radius arc than the outside. As a result, toe-in discourages turn-in and makes the car less sensitive to steering input. In other words, it is more stable.
Let's consider an example of the straight-line stability concept. Assume you have toe-out on the rear wheels. You are traveling in a straight line when your right-rear tire hits a small bump. It gets pushed back slightly by the impact, and it is now pointing more to the right than the left-rear tire. Therefore, the back of the car turns to the right until the right rear suspension comes back to its original position. The same thing can occur with the front wheels. In fact, the effect on the front suspension is even worse because the right-front wheel getting pushed back, for instance, will also turn the left-front wheel to the right.
Rear toe is usually only adjusted on front-wheel drive cars or rear wheel drive cars with independent rear suspensions. I wanted to include this example just to show that rear toe can be adjusted just like front toe on many cars. With a front-wheel drive car, it is sometimes helpful to add some rear toe-out to decrease the stability of the rear tires and counter the understeer inherent in front-wheel drive cars. For a rear-wheel drive car with independent rear suspension, the torque produced on the rear suspension when you step on the throttle tends to pull the rear wheels forward on the suspension pivots. This creates toe-in. To counter this effect, you can toe-out the rear wheels so they will become straight when you step on the throttle. I do not recommend this since rear toe-out in a rear-wheel drive car can cause severe oversteer. Instead of using toe-out, install aftermarket bushings and suspension links to keep the suspension from getting pulled forward under hard acceleration.
As you may have expected, toe increases tire wear because the tires are fighting each other and, therefore, scrubbing along the ground. Toe-in tends to increase tire wear on the outside edges of the tires. Toe-out tends to increase tire wear on the inside edges of the tires. Make sure that you consider your camber setting when adding toe-out. If you are using negative camber, you are already wearing the inside of the tires more than normal. The combination of excessive negative camber and toe-out can quickly wear the inside of a tire and cause it to fail.
I hope that helps you guys out. You can also get this writeup and some illustrations at my website, 240edge.com, but I posted it here for convenience.
Please let me know if you have any questions or if something is not clear.
Hey man, wonderful post. (but everyone's already said that) I was just wondering if you were going to be adding anything more to it like you mentioned on the last write-up post? I was also wondering what sort of monitoring devices could be used to measure whether the car is under/over steering?
definately good info.whats it called,or how do they have the rim wider than the tires? in drifting.ive seen a lot of cars,where their rims poke further out than their tires.almost as if they put skinny tires on a wide rim...what does this do for the handling?
its called stretching the tire. your exactly correct in saying that its a skinnier tire on a wider wheel. what it does for drifting is make the tire stiffer so its easier to break traction. Its absolutely pointless on a street driven car just like insane amounts of negative camber but they both have that wannabe JDM drifter look!
What about tire with? I'm trying to figure out whats going to be the best size tire for my 240. According to mathematics you would have the same contact patch on the ground for any size tire, if you have the same pressure in the tire. Is there other artifacts that would change this? I've always seemed to have assumed that tire size means more grip. Am i right or is this boggas?
what if i just want a lower stance with just the slightest ride stiffening over stock? i have a 600rr for twisties and speed. i want my car to have less autoX ability because it will be a daily driver and never see track time. what spring/shock combo would be good for this and would sway bars help roll even with soft springs? thanks
well if your not looking to slamma jamma your ride, a good strut/lowering spring combo will give you the lower stance and a decent ride. Theres many options out there as far as brands go, do some looking around theres lots of topics here and else where on what combos are the best.
Now get a good grip and start from the tip and dont stop till you're choking.
Bob up and down swirl you're tounge around suck it till the suckers smokin'
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when it comes to real driving tech...well plz if any one knows hows this is done...let me know...thank!!
my thread!!
