Developing a FAQ page for Suspension
12-13-2003, 07:04 AM
#1
Developing a FAQ page for Suspension
I'd like to develop a FAQ page for suspension. Please help me create this page by asking the question and answering it if possible. Only relevent questions please....
Here's my first question to start off......
Q: What's the differance between linear rate and pregressive rate springs?
A:??????
Thanks,
Victor
Here's my first question to start off......
Q: What's the differance between linear rate and pregressive rate springs?
A:??????
Thanks,
Victor
12-14-2003, 12:05 AM
#2
The spring rate is the rate at which a spring will compress a specified distance with an applied force acting against it. Typically this is expressed in lbs-in. A spring with a 350 lbs/in. rate will depress 1 in. for every 350 lbs. applied to the spring. A linear rate designates the spring has uniform measure in regard to the springs dimensions from top to bottom. A linear spring's rate can be measured:
spring rate = 11,250,000 x ( d to the 4th power) / 8 x N x ( D to the 3rd power)
d = outside wire diameter in inches
N = number of active, or complete, coils
D = mean, or center, wire diameter
The other two numbers are constants for steel springs.
A variable rate spring is a coil spring that is not uniform in measure in regard to the spring's dimensions from top to bottom. The diameter of the wire may vary, or the overall diameter of the spring may taper, or a combination of both to alter the spring's rate of compression at some point. A progressive rate will require progressively more weight to compress the spring one inch the further it travels. If our before mentioned 350lb-in. spring was progressive, it might have a 375lb-in rate the next inch, and a 400lb-in rate the following inch. Variable, or progressive, rate springs cannot be measured easily.
In both spring types, the rate of compression is different than the load. The spring load is the amount of weight necessary to compress the spring a given measure. Our linear spring will compress 3 inches with a load of 1050 lbs acting on it, at a rate of 350lb-in. Our progresive rate spring will compress 3 inches with a load of 1125 lbs acting on it, at a varible rate of 350lb-in to 400 lb-in. Load is important only in designing springs to ensure proper support of the vehicle's weight, and will not affect handling performance. The rate of a spring is important in regards to handling, as it is the measure of force necessary to compress the spring. A progressive rate has the advantage of a softer rate to absorb small irregularities in the road surface, and then as it compresses, a higher rate to absorb larger irregularities. The problem with progressive springs is that in practice, a car's springs only operate in a limited range of their total travel, and therefore the amount of progression in spring rate must be kept small. A linear rate spring with the assistance of good jounce bumpers or stops like Koni's uerathane design have often proven the better route.
spring rate = 11,250,000 x ( d to the 4th power) / 8 x N x ( D to the 3rd power)
d = outside wire diameter in inches
N = number of active, or complete, coils
D = mean, or center, wire diameter
The other two numbers are constants for steel springs.
A variable rate spring is a coil spring that is not uniform in measure in regard to the spring's dimensions from top to bottom. The diameter of the wire may vary, or the overall diameter of the spring may taper, or a combination of both to alter the spring's rate of compression at some point. A progressive rate will require progressively more weight to compress the spring one inch the further it travels. If our before mentioned 350lb-in. spring was progressive, it might have a 375lb-in rate the next inch, and a 400lb-in rate the following inch. Variable, or progressive, rate springs cannot be measured easily.
In both spring types, the rate of compression is different than the load. The spring load is the amount of weight necessary to compress the spring a given measure. Our linear spring will compress 3 inches with a load of 1050 lbs acting on it, at a rate of 350lb-in. Our progresive rate spring will compress 3 inches with a load of 1125 lbs acting on it, at a varible rate of 350lb-in to 400 lb-in. Load is important only in designing springs to ensure proper support of the vehicle's weight, and will not affect handling performance. The rate of a spring is important in regards to handling, as it is the measure of force necessary to compress the spring. A progressive rate has the advantage of a softer rate to absorb small irregularities in the road surface, and then as it compresses, a higher rate to absorb larger irregularities. The problem with progressive springs is that in practice, a car's springs only operate in a limited range of their total travel, and therefore the amount of progression in spring rate must be kept small. A linear rate spring with the assistance of good jounce bumpers or stops like Koni's uerathane design have often proven the better route.
12-14-2003, 07:34 PM
#4
On a coil-over the spring rests on a perch that is threaded around the damper casing. The threads allow the perch to be rotated either right or left, which in turn moves the perch up or down relative to the damper. Since the spring load has already been carefully chosen by the coil-over manufacturer to support the weight of the vehicle, the spring will not compress as the perch moves upward. Therefore, the body of the car will raise as the perch is rotated up the damper body and conversly drop in height as the perch is rotated down the damper body.
Now the damper is attached to the top perch that retains the top of the spring, and the bottom of the spring is compressed onto the bottom perch that is able to rotate up or down the damper. Since the spring does not compress or expand as the bottom perch is rotated, the damper must accomodate the difference in length by expanding or compressing as ride height changes. As can be imagined, the damper then must sacrifice some travel as the spring is moved down in relation to the casing, and gain some travel as the spring is moved up the casing. With this in mind, a coil-over can be adjusted the full length of the threaded damper body by turning the bottom perch, but must be done with consideration to the amount of travel offered by the damper either in full extension or compression.
A coil-over for strut type suspensions may have a threaded body with two perches isolating the knuckle mount. This allows the ride height to be raised up or down in regards to the mounting position on the knuckle rather than sacrificing damper travel.
Now the damper is attached to the top perch that retains the top of the spring, and the bottom of the spring is compressed onto the bottom perch that is able to rotate up or down the damper. Since the spring does not compress or expand as the bottom perch is rotated, the damper must accomodate the difference in length by expanding or compressing as ride height changes. As can be imagined, the damper then must sacrifice some travel as the spring is moved down in relation to the casing, and gain some travel as the spring is moved up the casing. With this in mind, a coil-over can be adjusted the full length of the threaded damper body by turning the bottom perch, but must be done with consideration to the amount of travel offered by the damper either in full extension or compression.
A coil-over for strut type suspensions may have a threaded body with two perches isolating the knuckle mount. This allows the ride height to be raised up or down in regards to the mounting position on the knuckle rather than sacrificing damper travel.
12-16-2003, 09:35 AM
#6
Registered User
Sway bars tie the front front wheels together and the rear wheels together. They are torsion springs, which means that as you twist one end of the sway bar, a force will be generated on the other end. That force will be dependent on the spring rate of the sway bar, which is determined by the bar's size and shape. In general, sway bars are shaped like a flattened U, with the wheels at the vertical sides and with the bottom stretching across the car to connect the left and right sides.
In practice, when you corner and compress the outside suspension of the car, the movement of the outside suspension will wind up the sway bar which will then exert a compressive force on the inside suspension. This helps keep the car flatter in the corners. The higher the stiffness of the sway bar, the more force generated on the inside suspension, and the flatter the car will be.
As far as whether bigger is better or solid is better, I don't believe that is necessarily the case. What is important is determining a torsional stiffness that is best for your specific application. When you go to a larger diameter or a solid bar, the stiffness increases, which may be good or bad depending on your application. The adjustable sways typically work by changing the length of the vertical sections of the U. A long section will be less stiff than a short section, so by providing a series of optional connection points the user can adjust the effective length of the vertical U sections, the therefore change the springrate.
-D'oh!
In practice, when you corner and compress the outside suspension of the car, the movement of the outside suspension will wind up the sway bar which will then exert a compressive force on the inside suspension. This helps keep the car flatter in the corners. The higher the stiffness of the sway bar, the more force generated on the inside suspension, and the flatter the car will be.
As far as whether bigger is better or solid is better, I don't believe that is necessarily the case. What is important is determining a torsional stiffness that is best for your specific application. When you go to a larger diameter or a solid bar, the stiffness increases, which may be good or bad depending on your application. The adjustable sways typically work by changing the length of the vertical sections of the U. A long section will be less stiff than a short section, so by providing a series of optional connection points the user can adjust the effective length of the vertical U sections, the therefore change the springrate.
-D'oh!
Last edited by D'oh; 12-16-2003 at 09:44 AM.
12-16-2003, 12:49 PM
#7
D'oh made some great points about anti-roll bars, but to add, an anti-roll bar will unload the inside tires very quickly compared to running springs alone, and the stiffness of a bar is dependent on the diameter of the bar.
A vehicle's body roll is caused by weight transfer, and weight tansfer cannot be changed except by changing vehicle design like wheelbase, track width, Cg height, etc. Body roll in and of itself is not a bad thing except for aerodynamics at high speed and camber change on the tires. By limiting it though we not only help alleviate these two problems, but can also manipulate the weight transfer on the car.
The bars work to limit body roll, like D'oh said, as torsion bars - they resist the twisting motion created when the inside tire extends and the outside tire compresses in a turn. The bar is connected to the suspension by a lever arm on each end. If you were to hold one arm and turn it, the other end would follow suit. The same happens with your car in a turn. The outside suspension compresses, raising one of the arms from its neutral position. The inside arm wants to raise as well, but has the weight of the car and the extension of the spring working against it. The stiffer the anti-roll bar, the more resistance it has to the differences in lever arm height, and the more "push" the inside lever arm will have against the inside suspension and the forces against it. This resistance is what limits the body roll, but increases the wt transfer to the outside tire, and is why too stiff an anti-roll bar cannot be used. The wt transfer can compress the outside suspension and raise the outside lever arm of the bar, so that too stiff an anti-roll bar will in turn compress the inside suspension with equal force on the inside lever arm- raising the tire. This is not what you want on the driven end of the vehicle, where the tire contact patches must be kept as large as possible. This is the trade-off of using bars. They are wonderful to control the roll angle of the car without resorting to stiffer springs, but can cause unwanted contact loss at either end of the vehicle.
Since the forces that roll the car are fed into the bar and the suspension as described above, the compression the bar exerts on the suspension components as it is twisted can be controlled by the length of the lever arms. Without the arms, the pure tension force of the bar would act on the suspension, but with the lever arms, the suspension has some leverage over the bar's stiffness to reduce compression from the bar. This allows the amount of stiffness, and therefore the rate of compression, exerted by the bar to be adjusted by varying the length of the lever arms, which some manufacturers incorporate into their design. However, unlike springs, a bar's compression rate will apply against the inside tire's extension as much as towards the outside tire's compression, which is why and how they can alter the amount of wt transfer so easily. The compression rate the bar has on the suspension is linear and can be easily measured and incorporated into suspension design. The equation is fairly simple and can be found in about any auto math book. This allows a bar to be selected that not only limits roll to a desired effect, but also assists spring compression and weight transfer into corners as desired.
The arm lengths on an ant-roll bar do not affect the stiffness of the bar, but are the means by which to determine how much of the bar's stiffness will be transmitted to the car's suspension. Bar stiffness is a measure of diameter to the 4th power. Increase the diameter of an anti-roll bar from 1 inch to 1 1/4 inch and you just increased the bar's stiffness 144 percent. Where a solid bar adds weight but not stiffness, it is marginally stronger against fatigue from compressive and tension forces, all else being equal, as the stress will be distributed through more mass. It has also come to my attention that solid bars are more common in the aftermarket for this reason alone, as the extra mass provides a safe buffer against yield that would otherwise be more sudden on a lighter hollow bar.
edit: tried to help clarify some things
A vehicle's body roll is caused by weight transfer, and weight tansfer cannot be changed except by changing vehicle design like wheelbase, track width, Cg height, etc. Body roll in and of itself is not a bad thing except for aerodynamics at high speed and camber change on the tires. By limiting it though we not only help alleviate these two problems, but can also manipulate the weight transfer on the car.
The bars work to limit body roll, like D'oh said, as torsion bars - they resist the twisting motion created when the inside tire extends and the outside tire compresses in a turn. The bar is connected to the suspension by a lever arm on each end. If you were to hold one arm and turn it, the other end would follow suit. The same happens with your car in a turn. The outside suspension compresses, raising one of the arms from its neutral position. The inside arm wants to raise as well, but has the weight of the car and the extension of the spring working against it. The stiffer the anti-roll bar, the more resistance it has to the differences in lever arm height, and the more "push" the inside lever arm will have against the inside suspension and the forces against it. This resistance is what limits the body roll, but increases the wt transfer to the outside tire, and is why too stiff an anti-roll bar cannot be used. The wt transfer can compress the outside suspension and raise the outside lever arm of the bar, so that too stiff an anti-roll bar will in turn compress the inside suspension with equal force on the inside lever arm- raising the tire. This is not what you want on the driven end of the vehicle, where the tire contact patches must be kept as large as possible. This is the trade-off of using bars. They are wonderful to control the roll angle of the car without resorting to stiffer springs, but can cause unwanted contact loss at either end of the vehicle.
Since the forces that roll the car are fed into the bar and the suspension as described above, the compression the bar exerts on the suspension components as it is twisted can be controlled by the length of the lever arms. Without the arms, the pure tension force of the bar would act on the suspension, but with the lever arms, the suspension has some leverage over the bar's stiffness to reduce compression from the bar. This allows the amount of stiffness, and therefore the rate of compression, exerted by the bar to be adjusted by varying the length of the lever arms, which some manufacturers incorporate into their design. However, unlike springs, a bar's compression rate will apply against the inside tire's extension as much as towards the outside tire's compression, which is why and how they can alter the amount of wt transfer so easily. The compression rate the bar has on the suspension is linear and can be easily measured and incorporated into suspension design. The equation is fairly simple and can be found in about any auto math book. This allows a bar to be selected that not only limits roll to a desired effect, but also assists spring compression and weight transfer into corners as desired.
The arm lengths on an ant-roll bar do not affect the stiffness of the bar, but are the means by which to determine how much of the bar's stiffness will be transmitted to the car's suspension. Bar stiffness is a measure of diameter to the 4th power. Increase the diameter of an anti-roll bar from 1 inch to 1 1/4 inch and you just increased the bar's stiffness 144 percent. Where a solid bar adds weight but not stiffness, it is marginally stronger against fatigue from compressive and tension forces, all else being equal, as the stress will be distributed through more mass. It has also come to my attention that solid bars are more common in the aftermarket for this reason alone, as the extra mass provides a safe buffer against yield that would otherwise be more sudden on a lighter hollow bar.
edit: tried to help clarify some things
Last edited by Resolute; 12-18-2003 at 11:59 PM.
Trending Topics
12-17-2003, 12:37 AM
#8
Q: How do anti-roll bars change the handling balance of the car?
A:
The anti-roll bars can be used to affect wt transfer front vs. rear by changing the front bar diameter or arm length, relative to the rear bar diameter or arm length.
If the car is understeering, there is either too much wt transfer on the front outside tire or too little on the rear outside tire. A less stiff bar on the front will relieve some of the wt transfered to the outside tire, and a stiffer bar out back will increase the wt transfered to the rear outside tire.
If the car is oversteering, too much wt transfer is on the rear outside tire, or not enough wt transfer is on the front outside tire. A less stiff rear bar will lessen the wt transfer to the outside tire, and a stiffer front bar will increase the wt transfer to the outside tire.
In both instances, anti-roll bars can be used to keep the front and rear outside tires equally loaded, thereby keeping the car's balance in a turn neutral. However, considerations should be made to the driven end of the vehicle, so that as light an anti-roll bar as posible is used to maintain as much traction as possible on the inside tire.
A:
The anti-roll bars can be used to affect wt transfer front vs. rear by changing the front bar diameter or arm length, relative to the rear bar diameter or arm length.
If the car is understeering, there is either too much wt transfer on the front outside tire or too little on the rear outside tire. A less stiff bar on the front will relieve some of the wt transfered to the outside tire, and a stiffer bar out back will increase the wt transfered to the rear outside tire.
If the car is oversteering, too much wt transfer is on the rear outside tire, or not enough wt transfer is on the front outside tire. A less stiff rear bar will lessen the wt transfer to the outside tire, and a stiffer front bar will increase the wt transfer to the outside tire.
In both instances, anti-roll bars can be used to keep the front and rear outside tires equally loaded, thereby keeping the car's balance in a turn neutral. However, considerations should be made to the driven end of the vehicle, so that as light an anti-roll bar as posible is used to maintain as much traction as possible on the inside tire.
12-17-2003, 04:18 PM
#10
Strut bars are rigid bars bolted to the top spring mounts on a car. They are designed to stiffen the body where it will benefit handling and weight transfer the most. When a car turns and wt is transfered to the outside of the car, the body can flex and absorb some of the forces that cause body roll. This is not desirable because the body can unload these forces quickly, like releasing a spring, and upset the handling balance of the car with sudden wt distribution. The chassis can also deteriorate feedback from steering and suspension systems by absorbing some of their forces generated as well. Finally, since the wt is ultimately carried to each of the four tires, the suspension is the most vulnerable area to be affected by chassis flex, as they will have to bear any additional torsion load created by the twisting body. By connecting the top of the suspension together, a more efficient means of wt transfer is created through a stiffer structure than the open body alone - just as ant-roll bars are more efficient. The stiffer chassis is not only more adept to properly transfer wt to the tires, which assists in proper tuning, but will provide better feedback and response from all the suspension and steering components as their forces will not be dampened by the body.
12-17-2003, 06:43 PM
#12
Good idea, Mike.
Though I occassionly put the metal all the way down & enjoy the twisty-turneys as much as others, my primary use of the Zzzz is as a cruisor. Add that I want my wife & I to take more/longer trips in the Zzz which means encountering more roads causing a bumpy ride......a condition wifey does not like.
Question: What can I do to give the Zzzz a more luxury car style ride? (Besides trading the wife in on a "sportier" model who will not fuss......LOL!).
I'm not going to be taking the Brick to the outer edge of performance limits so I don't mind giving up preformance for a more comfortable ride.
Though I occassionly put the metal all the way down & enjoy the twisty-turneys as much as others, my primary use of the Zzzz is as a cruisor. Add that I want my wife & I to take more/longer trips in the Zzz which means encountering more roads causing a bumpy ride......a condition wifey does not like.
Question: What can I do to give the Zzzz a more luxury car style ride? (Besides trading the wife in on a "sportier" model who will not fuss......LOL!).
I'm not going to be taking the Brick to the outer edge of performance limits so I don't mind giving up preformance for a more comfortable ride.
Last edited by The Brickyard Rat; 12-17-2003 at 06:55 PM.
12-18-2003, 10:26 PM
#13
Originally posted by Yielar
How do traction rods work? Do they also adjust camber?
How do traction rods work? Do they also adjust camber?
12-19-2003, 09:56 PM
#14
Originally posted by The Rat's Z
Question: What can I do to give the Zzzz a more luxury car style ride?
Question: What can I do to give the Zzzz a more luxury car style ride?
In order to change the ride feel of a vehicle, the optimum factor for tuning to a person's preference begins with the car's suspension frequency. The suspension frequency is the rate at which the spring will travel it's full cycle- compression to extension and back to neutral - in a given amount of time. This rate is measured in CPS, or cycles per second. The higher the frequency, the stiffer the ride, and ultimately the better handling potential of the vehicle. Several factors affect a suspension's frequency but, since luxury is what we're after over ultimate performance, it is the spring rate that is most important. A lighter spring will lower the CPS of the suspension. For the 350Z, a 400 in-lbs or less spring should be desirable. This will, with a good damper, better absorb the impacts of road irregularities and lessen the force transmitted to the chassis. This will unfortunately also allow more body roll. To help keep a sporty feel and good handling characteristics, a lighter spring should be accompanied by a well-matched anti-roll bar and damper assembly. It is an option to match the stock damper with an aftermarket spring alone, however, the simple fact is that it is harder to match a spring to a damper than it is to design a damper for the spring. In other words, 9 out of 10 times, a reputable system that includes a damper will give a more comfortable ride and better performance than just a spring that was designed for the stock damper. There are, undoubtably, springs alone that would perform better than the stock set-up for a softer ride, but would be hard pressed to beat a softer coil-over design that has been properly tuned. If the design also includes ant-roll bars to match, then a complete package would be the odds favorite for the ultimate in a comfortable yet well handling design. Finally, for a smoother, less disturbing ride, pay attention to the mounts and bushings offered with the kit. Hard materials like polyurethane or nylon will transmit more force to the chassis than stock rubber mounts, and pillow-ball mounts should be avoided at all cost. A well-designed coil-over like the Tein CS might be a good place for you to start looking. I believe Tein posts their spring rates and ride height information, along with pictures, for this unit. www.tein.com
12-20-2003, 10:43 AM
#15
Registered User
Join Date: Sep 2003
Location: British Columbia, Canada
Posts: 217
Likes: 0
Received 0 Likes
on
0 Posts
Several people have been adding traction rods to their Z's. Do a search and you'll know what I'm talking about. From what I've read they reduce wheel hop providing more traction off the line. I was just hoping someone with some expertise in this area could explain their job.
Yielar
Yielar
12-23-2003, 03:18 PM
#18
Registered User
Join Date: Feb 2003
Location: los angeles
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Corner Weigthing is ussually done in Cars that have Coilover suspensions with height adjustability. What they do is place each of the four corners(wheels) of the car on weighing scales. They then take the measurements regarding weight on each corner. They also take the the weight of the driver and put a similar weigth on the driver side and they adjust the ride height until the can get the right weights on each corner of the vehicle. The reason this is done is to be ablt to achieve a specific weight ratio depending what the person wants to achieve. A 50/50 wieght split front/rear or even 25% on each corner. The ratio really depends on the preference of the driver. Raising and lowering of ride hegth affects the weigth applied in each corner. The end result might not be all four corners perfectly matched height wise. BUt the car will be very well blanced. I had it done to my Audi S4 and it made a really big difference in how the car handled without any other mods added after. Most Companies that sell coilovers recommend that this is done when switching to coilovers. The overall process is basically fine tuning more than anything else.
12-23-2003, 05:25 PM
#19
Professional
iTrader: (17)
Join Date: Aug 2003
Location: San Diego
Posts: 1,045
Likes: 0
Received 0 Likes
on
0 Posts
Softer Ride
For a nicer ride, you may want to switch to a 17" rim because the larger tire side walls will help smooth up the bumps. The performance model has 18s. Maybe buy someones G35 coupe springs and swap.
Originally posted by The Rat's Z
Good idea, Mike.
Though I occassionly put the metal all the way down & enjoy the twisty-turneys as much as others, my primary use of the Zzzz is as a cruisor. Add that I want my wife & I to take more/longer trips in the Zzz which means encountering more roads causing a bumpy ride......a condition wifey does not like.
Question: What can I do to give the Zzzz a more luxury car style ride? (Besides trading the wife in on a "sportier" model who will not fuss......LOL!).
I'm not going to be taking the Brick to the outer edge of performance limits so I don't mind giving up preformance for a more comfortable ride.
Good idea, Mike.
Though I occassionly put the metal all the way down & enjoy the twisty-turneys as much as others, my primary use of the Zzzz is as a cruisor. Add that I want my wife & I to take more/longer trips in the Zzz which means encountering more roads causing a bumpy ride......a condition wifey does not like.
Question: What can I do to give the Zzzz a more luxury car style ride? (Besides trading the wife in on a "sportier" model who will not fuss......LOL!).
I'm not going to be taking the Brick to the outer edge of performance limits so I don't mind giving up preformance for a more comfortable ride.
