v413nc3
03-28-2003, 12:06 PM
I figured I'd write some info for people who don't understand the mysterious thing we call suspension. Now I’d just like to state ahead of time that this is only going to lightly brush on suspension for drag racing. This article will be more geared towards road racing, although I suspect if you ask real real nice Amanda might put up some information on suspension for AutoX. Just a quick point on my experience so you can take for it what you will on how much I might or might not know about it… I started my racing career NHRA racing, from there I moved to the Amateur, semi-pro and pro class road racing and I was up until this season a driver on the GP1-I road race circuit, and plan on getting back in as an independent since I dropped my sponsor.
Sway bars, strut braces, pillow ball mounts, compression dampening, rebound dampening, spring rate, over-steer, under-steer, all kinds of things you hear mentioned about suspension, what do they mean, and how do they pertain to YOU?
Sway bars, or stabilizer bars are part of a car's suspension system. They are sometimes also called anti-sway bars or anti-roll bars. Their purpose in life is to try to keep the car's body from "rolling" in a sharp turn. Think about what happens to a car in a sharp turn. If you are inside the car, you know that your body gets pulled toward the outside of the turn. The same thing is happening to all the parts of the car. So the part of the car on the outside of the turn gets pushed down toward the road and the part of the car on the inside of the turn rises up. In other words, the body of the car "rolls" 10 or 20 or 30 degrees toward the outside of the turn. If you take a turn fast enough, the tires on the inside of the turn actually rise off the road and the car flips over. Roll is bad. It tends to put more weight on the outside tires and less weigh on the inside tires, reducing traction. It also messes up steering. What you would like is for the body of the car to remain flat through a turn so that the weight stays distributed evenly on all four tires. A stabilizer bar tries to keep the car's body flat by moving force from one side of the body to another. To picture how a stabilizer bar works, imagine a metal rod that is an inch or two (2 to 5 cm) in diameter. If your front tires are 5 feet (1.6 meters) apart, make the rod about 4 feet long. Attach the rod to the frame of the car in front of the front tires, but attach it with bushings in such a way that it can rotate. Now attach arms from the rod to the front suspension member on both sides. When you go into a turn now, the front suspension member of the outside of the turn gets pushed upward. The arm of the sway bar gets pushed upward, and this applies torsion to the rod. The torsion them moves the arm at the other end of the rod, and this causes the suspension on the other side of the car to compress as well. The car's body tends to stay flat in the turn. If you don't have a stabilizer bar, you tend to have a lot of trouble with body roll in a turn. If you have too much stabilizer bar, you tend to lose independence between the suspension members on both sides of the car. When one wheel hits a bump, the stabilizer bar transmits the bump to the other side of the car as well, which is not what you want. The ideal is to find a setting that reduces body roll but does not hurt the independence of the tires.
Strut braces work in the same way that a sway bar does. But they keep the top of the car from flexing, keeping the body flat through turns. The difference between them is that a strut brace is designed to so that the stiffer the better, since your strut towers do not need the functioning of independence. As a small side note, most people adjust their strut tower braces incorrectly. If it is adjustable the majority of people I have observed attempting to adjust it as short as possible, pulling the top of the tower towards each other, this is not the way they were designed, you should actually attempt to push them as far away from each other as possible, thus attaining rigidity of body.
Pillow ball mounts, or spherical mounts as they are also known attach to the top of the strut, just under where your strut brace connects. They allow the shock or strut to move under heavy load, attempting to keep correct alignment of the knuckle to the other. They help in keeping your suspension from moving at odd angles so that you can keep the same stroke distance with your piston, thus effectively helping you keep your compression and rebound settings the same throughout the turn.
Compression and rebound dampening, the first controls the downward movement of your vehicle (upward movement of the wheel). The second is rebound dampening. It controls the upward movement of your vehicle (extension of the suspension). Without these you basically feel like you’re on a trampoline bouncing like a bunny rabbit. With drag racing you want the wheels in the back to be able to come all the way up under acceleration and yet still be able to return quickly out of load back to their normal location, if you have moderate priced shocks like tokiko’s or KYB’s you’ll want to adjust them all the way soft, it’s better that you get less rebound with your less compression than more rebound and more compression. If you have a two or three way adjustable then start by turning compression down all the way and rebound up all the way, start to adjust them towards middle one click at a time until you get better traction results. For road racing I will only cover two-way adjustments since you really shouldn’t be racing on something that doesn’t have independent adjustments, if you do, take from this what you will…
The ultimate purpose of a shock is to work together with the spring to keep the tire on track, in compression to help control the movement of the wheel and in rebound to help absorb the stored energy of the compressed spring. When attempting to adjust compression dampening always start all the way soft, (0 clicks) and adjust harder. Rebound adjustments are usually indicated by the driver needing more stability, by increasing low speed dampening, stability will be enhanced; decreasing dampening will allow more movement in the car, but will result in a little better tire wear. Also, the amount of rebound dampening will great influences on weight transfer, less front rebound will allow weight transfer to the rear under acceleration. Less rebound in the rear allows greater transfer to the front under braking and turn in. When a car is over dampened in rebound it can pack down in a series of bumps and you will recognize this as too stiff and usually will think it’s compression dampening. Too much rebound can also cause lack of grip in cornering. When making a large spring change keep in mind where the rebound adjuster is and do you have enough range to compensate. Sometimes a spring change will bring a better balance to the dampening values after the spring change. If the spring/shock combination is balanced, the rule of thumb is a stiffer spring requires lower compression and higher rebound. A softer requires higher compression lower rebound.
Spring rate, a spring is a mechanical device that absorbs energy through deflection and then expels that energy by trying to get back to it's non-deflected state. As the suspension is compressed, the spring is compressed. The spring takes the energy of the compressing suspension, stores it, although it may only store it for a few milliseconds, and then releases this stored energy in the action of expanding the suspension back. A spring has a linear rate when they are wound in a constant spiral with each consecutive coil being spaced apart the same as the previous coil. If the distance between the coils gets smaller or larger depending on which way you go, then the spring is considered to be a progressive wind. What does "Linear Rate" mean? It's pretty simple. Let's say you have a 15-inch long 100-pound rated spring, and let's assume that it will coil bind, where the coils touch due to compression of the spring, at a compressed length of 5 inches. This means that it takes 100 pounds of force to compress the spring one inch. So, it will take another 100 pounds, for a total of 200 pounds, to compress the spring 2 inches. If you graph it out, it's a nice straight line. You can see that our spring can take 1000 pounds (or 10 inches of compression distance) to collapse it to the point of coil bind. What makes a spring progressive is a geometry where some of the coils bind up partway through the anticipated travel. For instance let's take our original spring and play with the coil spacing. Let's wind it so that the first two coils only have ¼ inch of air between them while the other two coils have substantially more. Put 100 pounds on the spring, it compresses 1 inch. But at that point, two of the coils can't compress any more. Add another 100 pounds and it only compresses ½ inch; i.e. the rate of the spring has doubled to 200 lb/in.
Over steer and under steer, two interesting terms in which the latter you hear about our cars all the time. Over-steer is the point in which entering a turn your rear tires break traction before your front ones do. Conversely under-steer is where your front tires break traction before your rear ones will. Most manufacturers will set a car suspension for under-steer because it warns the driver that you are reaching the limits of handling and you should back off. Over-steer is very prevalent in rear wheel drive vehicles, where power causes the back end to loose traction because of steering geometry. Companies such as RMDSM.com try to compensate for our bad under-steer by setting our suspension to “neutral” or basically neither over nor under steer. I believe that on courses with soft turns neutral works well, but on a course with sharp turns where a small amount of drift would be nice a solid over-steer capability can be very useful.
Sway bars, strut braces, pillow ball mounts, compression dampening, rebound dampening, spring rate, over-steer, under-steer, all kinds of things you hear mentioned about suspension, what do they mean, and how do they pertain to YOU?
Sway bars, or stabilizer bars are part of a car's suspension system. They are sometimes also called anti-sway bars or anti-roll bars. Their purpose in life is to try to keep the car's body from "rolling" in a sharp turn. Think about what happens to a car in a sharp turn. If you are inside the car, you know that your body gets pulled toward the outside of the turn. The same thing is happening to all the parts of the car. So the part of the car on the outside of the turn gets pushed down toward the road and the part of the car on the inside of the turn rises up. In other words, the body of the car "rolls" 10 or 20 or 30 degrees toward the outside of the turn. If you take a turn fast enough, the tires on the inside of the turn actually rise off the road and the car flips over. Roll is bad. It tends to put more weight on the outside tires and less weigh on the inside tires, reducing traction. It also messes up steering. What you would like is for the body of the car to remain flat through a turn so that the weight stays distributed evenly on all four tires. A stabilizer bar tries to keep the car's body flat by moving force from one side of the body to another. To picture how a stabilizer bar works, imagine a metal rod that is an inch or two (2 to 5 cm) in diameter. If your front tires are 5 feet (1.6 meters) apart, make the rod about 4 feet long. Attach the rod to the frame of the car in front of the front tires, but attach it with bushings in such a way that it can rotate. Now attach arms from the rod to the front suspension member on both sides. When you go into a turn now, the front suspension member of the outside of the turn gets pushed upward. The arm of the sway bar gets pushed upward, and this applies torsion to the rod. The torsion them moves the arm at the other end of the rod, and this causes the suspension on the other side of the car to compress as well. The car's body tends to stay flat in the turn. If you don't have a stabilizer bar, you tend to have a lot of trouble with body roll in a turn. If you have too much stabilizer bar, you tend to lose independence between the suspension members on both sides of the car. When one wheel hits a bump, the stabilizer bar transmits the bump to the other side of the car as well, which is not what you want. The ideal is to find a setting that reduces body roll but does not hurt the independence of the tires.
Strut braces work in the same way that a sway bar does. But they keep the top of the car from flexing, keeping the body flat through turns. The difference between them is that a strut brace is designed to so that the stiffer the better, since your strut towers do not need the functioning of independence. As a small side note, most people adjust their strut tower braces incorrectly. If it is adjustable the majority of people I have observed attempting to adjust it as short as possible, pulling the top of the tower towards each other, this is not the way they were designed, you should actually attempt to push them as far away from each other as possible, thus attaining rigidity of body.
Pillow ball mounts, or spherical mounts as they are also known attach to the top of the strut, just under where your strut brace connects. They allow the shock or strut to move under heavy load, attempting to keep correct alignment of the knuckle to the other. They help in keeping your suspension from moving at odd angles so that you can keep the same stroke distance with your piston, thus effectively helping you keep your compression and rebound settings the same throughout the turn.
Compression and rebound dampening, the first controls the downward movement of your vehicle (upward movement of the wheel). The second is rebound dampening. It controls the upward movement of your vehicle (extension of the suspension). Without these you basically feel like you’re on a trampoline bouncing like a bunny rabbit. With drag racing you want the wheels in the back to be able to come all the way up under acceleration and yet still be able to return quickly out of load back to their normal location, if you have moderate priced shocks like tokiko’s or KYB’s you’ll want to adjust them all the way soft, it’s better that you get less rebound with your less compression than more rebound and more compression. If you have a two or three way adjustable then start by turning compression down all the way and rebound up all the way, start to adjust them towards middle one click at a time until you get better traction results. For road racing I will only cover two-way adjustments since you really shouldn’t be racing on something that doesn’t have independent adjustments, if you do, take from this what you will…
The ultimate purpose of a shock is to work together with the spring to keep the tire on track, in compression to help control the movement of the wheel and in rebound to help absorb the stored energy of the compressed spring. When attempting to adjust compression dampening always start all the way soft, (0 clicks) and adjust harder. Rebound adjustments are usually indicated by the driver needing more stability, by increasing low speed dampening, stability will be enhanced; decreasing dampening will allow more movement in the car, but will result in a little better tire wear. Also, the amount of rebound dampening will great influences on weight transfer, less front rebound will allow weight transfer to the rear under acceleration. Less rebound in the rear allows greater transfer to the front under braking and turn in. When a car is over dampened in rebound it can pack down in a series of bumps and you will recognize this as too stiff and usually will think it’s compression dampening. Too much rebound can also cause lack of grip in cornering. When making a large spring change keep in mind where the rebound adjuster is and do you have enough range to compensate. Sometimes a spring change will bring a better balance to the dampening values after the spring change. If the spring/shock combination is balanced, the rule of thumb is a stiffer spring requires lower compression and higher rebound. A softer requires higher compression lower rebound.
Spring rate, a spring is a mechanical device that absorbs energy through deflection and then expels that energy by trying to get back to it's non-deflected state. As the suspension is compressed, the spring is compressed. The spring takes the energy of the compressing suspension, stores it, although it may only store it for a few milliseconds, and then releases this stored energy in the action of expanding the suspension back. A spring has a linear rate when they are wound in a constant spiral with each consecutive coil being spaced apart the same as the previous coil. If the distance between the coils gets smaller or larger depending on which way you go, then the spring is considered to be a progressive wind. What does "Linear Rate" mean? It's pretty simple. Let's say you have a 15-inch long 100-pound rated spring, and let's assume that it will coil bind, where the coils touch due to compression of the spring, at a compressed length of 5 inches. This means that it takes 100 pounds of force to compress the spring one inch. So, it will take another 100 pounds, for a total of 200 pounds, to compress the spring 2 inches. If you graph it out, it's a nice straight line. You can see that our spring can take 1000 pounds (or 10 inches of compression distance) to collapse it to the point of coil bind. What makes a spring progressive is a geometry where some of the coils bind up partway through the anticipated travel. For instance let's take our original spring and play with the coil spacing. Let's wind it so that the first two coils only have ¼ inch of air between them while the other two coils have substantially more. Put 100 pounds on the spring, it compresses 1 inch. But at that point, two of the coils can't compress any more. Add another 100 pounds and it only compresses ½ inch; i.e. the rate of the spring has doubled to 200 lb/in.
Over steer and under steer, two interesting terms in which the latter you hear about our cars all the time. Over-steer is the point in which entering a turn your rear tires break traction before your front ones do. Conversely under-steer is where your front tires break traction before your rear ones will. Most manufacturers will set a car suspension for under-steer because it warns the driver that you are reaching the limits of handling and you should back off. Over-steer is very prevalent in rear wheel drive vehicles, where power causes the back end to loose traction because of steering geometry. Companies such as RMDSM.com try to compensate for our bad under-steer by setting our suspension to “neutral” or basically neither over nor under steer. I believe that on courses with soft turns neutral works well, but on a course with sharp turns where a small amount of drift would be nice a solid over-steer capability can be very useful.