tyoneal
03-14-2009, 08:41 PM
Steve:
I thought this would be to long a post to send the normal way so I decided to just post it up here. It might be Helpful for some, or, illicit some additional information from others. Hopefully Both.
Regarding a 3-Link Rear Suspension:
I added what you told me that you knew, and sent off for some additional information from a Engineer who has a pretty fair amount of knowledge in Racing.
==========================================
Here are the results: They are general as there are many different components, that also affect the specific performance of each adjustment hole, however, I think it is enough to get us on the right path.
==========================================
How the 3-Link adjustments work (Generally)
Adjustments at the Watts Link: Raise the anchor point for the rear end (watts or panhard) then you raise the roll center. This effects the oversteer/understeer. Mostly matters in a car cornering, not so much in a straight line.
Adjustments to the 3rd/Center Link: Track bar height (third link, four bar, etc) effects the instant center in acceleration and braking. This can have an effect on how the rear tires hook up, and in lift of the front end. Low connections for hard acceleration but can lead to tire hop. Higher slows the reaction of the torque to the tire, can be more stable, but not 'lift' as hard for weight transfer. In all of this though, spring rates, bushing hardness, slop, weight distribution, static roll center, polar moment of inertia center, and alignment all interconnect for the ultimate outcome. No absolutes but general directive effects.
==========================================
Ok, now for a Glossary of Terms. (I'm putting these in, so people who are not familiar to the terms won't have their eyes glaze over when they read it)
Watt's Linkage and Panhard Bar
http://en.wikipedia.org/wiki/Watt%27s_linkage
(Scroll down to, "Car Suspension")
Watts Linkage in motion
http://www.youtube.com/watch?v=blDJ-bu3NLo&feature=related
The Watt's linkage is used in the rear axle of some car suspensions as an improvement over the Panhard rod, which was designed in the early twentieth century. Both methods intend to prevent relative sideway motion between the axle and body of the car. The Watt’s linkage however approximates a vertical straight line motion more closely.
It consists of two horizontal rods of equal length mounted at each side of the chassis. In between these two rods, a short vertical bar is connected. The center of this short vertical rod – the point which is constrained in a straight line motion - is mounted to the center of the axle. All pivoting points are free to rotate in a vertical plane.
In a way, the Watt’s linkage can be seen as two Panhard rods mounted opposite of each other. In Watt’s arrangement however, the opposing curved movements introduced by the pivoting Panhard rods are compensated by the short vertical rotating bar.
The Watt's linkage can also be used to prevent axle movement in the longitudinal direction of the car, this is however more common in racing suspension systems. This application usually involves two Watt's linkages on each side of the axle, mounted parallel to the driving direction.
Roll Center:
http://en.wikipedia.org/wiki/Roll_center
Oversteer and Understeer:
http://en.wikipedia.org/wiki/Oversteer
http://en.wikipedia.org/wiki/Understeer
Track Bar Height: "Type of Panhard Bar", Here is a link for a "Track Bar", install. It's not the Best, but it's the best I could find.
http://offroad.automotive.com/87630/0809or-off-road-unlimted-crossover-steering-kit-install/index.html
Instant Center: It was explained at LS1tech. http://www.ls1tech.com/forums/ls1-domestic-forums/t-396309.html
Tire Hop: An undesirable suspension characteristic in which a wheel (or several) moves up and down so violently that it actually leaves the ground. Wheel hop can be caused by many problems, including excessive unsprung weight, insufficient shock damping, or poor torsional axle control.
This is Stupid but it was the only thing I could find.
http://www.youtube.com/watch?v=HothKxgULF8
Weight Transfer: A fundamental topic in any discussion about handling is weight transfer. If you do not fully understand weight transfer, you will not be effective in understanding how to adjust the car for maximum handling performance.
http://www.turnfast.com/tech_handling/handling_weightxfr
Spring Rates: The springs and related parts intermediate between the wheels and frame of an automotive vehicle that support the frame on the wheels and absorb road shock caused by passage of the wheels over irregularities.
http://www.answers.com/topic/automotive-suspension
Bushing Hardness: A bit self explanatory but, this puts it into some context
http://74.125.47.132/search?q=cache:1mIX98BrbsoJ:www.bmcforums.com/showthread.php%3Fp%3D1321692+Define+%22Bushing+Har dness%22,+Car&cd=9&hl=en&ct=clnk&gl=us
Weight Distribution: Scroll Down to next item
Static Roll Center: Read below
+++++++++++++++++++++++++++++++++++++++++
While searching, "Static Roll Center", I came across this page. By Reading down the page it give a lot of definitions, formulas, and examples of things to thing about when setting up your car. "Static Roll Center", as well as many other suspension and Handling aspects are addressed. It's really a pretty neat site that after a while might make your head explode, but if you take it slowly, it can put many things into perspective and show how they are used together.
http://74.125.47.132/search?q=cache:8H5dXAY1xqkJ:www.engr.uconn.edu/ece/SeniorDesign/projects/ecesd01/sp01_reports/sae_final_sp01.doc+Define+%22Static+Roll+Center%22 ,+Car&cd=3&hl=en&ct=clnk&gl=us
http://74.125.47.132/search?q=cache:8H5dXAY1xqkJ:www.engr.uconn.edu/ece/SeniorDesign/projects/ecesd01/sp01_reports/sae_final_sp01.doc+Define+%22Static+Roll+Center%22 ,+Car&cd=3&hl=en&ct=clnk&gl=us
Polar Movement of Inertia Center:
INERTIA
Inertia is the resistance to change the direction or velocity of a body, either at rest or in motion. In this case, it is related to changing the heading, or direction, of a vehicle; that is, changing from straight ahead driving to a turn.
The importance of inertia and weight distribution as they relate to driving is that they affect the amount of time required to make a transition from straight to turning or vice versa. Although these changes with the usual loading of a vehicle are not large, a driver should recognize the unusual loading of a vehicle, such as the placing of a large load on the tailgate of a station wagon (or the addition of a heavy load on the vehicle roof) will cause changes in the way the vehicle drives and adjustments should be made in driving accordingly.
Since inertia dictates that a body in motion will continue to move in a straight line, a force must be applied to cause a vehicle to turn. This force is called Centripetal force, and is a result of tires stretching to pull the car from a straight path. Centripetal force must exceed centrifugal force for the vehicle to turn.
MOMENTS OF INERTIA:
A. Pitch – the force felt in acceleration or braking movement around (Horizontal axis) of vehicle
B. Roll – the force felt in cornering, side to side movement (Lateral axis) of the vehicle
C. Yaw – the force felt in a spin movement around (Vertical axis) of the vehicle
POLAR MOMENT OF INERTIA
A very important handling concept, which dictates the willingness of a car to change directional position if called Polar Moment of Inertia. “Poles of inertia” are just another way of saying “center of weight concentration”. The “moment” in this concept is determined by the front-to-rear location of the center of gravity. The car turns (changes direction) about its center of gravity in a corner so the further away the centers of weight concentration are located from the center of gravity (which is their common center), the bigger the “moment”.
A high polar moment of inertia is present when the weight concentrations are heavy and are far apart. The low polar moment of inertia is found when weight concentrations are light and are close together. In other words, it is easier to steer a vehicle with a low polar moment of inertia.
A vehicle with a low polar moment of inertia gives a quick response to steering commands. A vehicle with a high polar moment has high directional stability (meaning it resists changing its direction).
=====================================
That concludes this post.
Let me know if this is helpful for you in any way. For other, please feel free to make any remarks with regards to this post, and let me know if:
a) It's at lest somewhat helpful
b) It's ok, but it would be improved by adding __________________. (Please feel free to add things, as I am in a position to trying to get my arms wrapped around this Concept as well.
Thanks,
Ty
I thought this would be to long a post to send the normal way so I decided to just post it up here. It might be Helpful for some, or, illicit some additional information from others. Hopefully Both.
Regarding a 3-Link Rear Suspension:
I added what you told me that you knew, and sent off for some additional information from a Engineer who has a pretty fair amount of knowledge in Racing.
==========================================
Here are the results: They are general as there are many different components, that also affect the specific performance of each adjustment hole, however, I think it is enough to get us on the right path.
==========================================
How the 3-Link adjustments work (Generally)
Adjustments at the Watts Link: Raise the anchor point for the rear end (watts or panhard) then you raise the roll center. This effects the oversteer/understeer. Mostly matters in a car cornering, not so much in a straight line.
Adjustments to the 3rd/Center Link: Track bar height (third link, four bar, etc) effects the instant center in acceleration and braking. This can have an effect on how the rear tires hook up, and in lift of the front end. Low connections for hard acceleration but can lead to tire hop. Higher slows the reaction of the torque to the tire, can be more stable, but not 'lift' as hard for weight transfer. In all of this though, spring rates, bushing hardness, slop, weight distribution, static roll center, polar moment of inertia center, and alignment all interconnect for the ultimate outcome. No absolutes but general directive effects.
==========================================
Ok, now for a Glossary of Terms. (I'm putting these in, so people who are not familiar to the terms won't have their eyes glaze over when they read it)
Watt's Linkage and Panhard Bar
http://en.wikipedia.org/wiki/Watt%27s_linkage
(Scroll down to, "Car Suspension")
Watts Linkage in motion
http://www.youtube.com/watch?v=blDJ-bu3NLo&feature=related
The Watt's linkage is used in the rear axle of some car suspensions as an improvement over the Panhard rod, which was designed in the early twentieth century. Both methods intend to prevent relative sideway motion between the axle and body of the car. The Watt’s linkage however approximates a vertical straight line motion more closely.
It consists of two horizontal rods of equal length mounted at each side of the chassis. In between these two rods, a short vertical bar is connected. The center of this short vertical rod – the point which is constrained in a straight line motion - is mounted to the center of the axle. All pivoting points are free to rotate in a vertical plane.
In a way, the Watt’s linkage can be seen as two Panhard rods mounted opposite of each other. In Watt’s arrangement however, the opposing curved movements introduced by the pivoting Panhard rods are compensated by the short vertical rotating bar.
The Watt's linkage can also be used to prevent axle movement in the longitudinal direction of the car, this is however more common in racing suspension systems. This application usually involves two Watt's linkages on each side of the axle, mounted parallel to the driving direction.
Roll Center:
http://en.wikipedia.org/wiki/Roll_center
Oversteer and Understeer:
http://en.wikipedia.org/wiki/Oversteer
http://en.wikipedia.org/wiki/Understeer
Track Bar Height: "Type of Panhard Bar", Here is a link for a "Track Bar", install. It's not the Best, but it's the best I could find.
http://offroad.automotive.com/87630/0809or-off-road-unlimted-crossover-steering-kit-install/index.html
Instant Center: It was explained at LS1tech. http://www.ls1tech.com/forums/ls1-domestic-forums/t-396309.html
Tire Hop: An undesirable suspension characteristic in which a wheel (or several) moves up and down so violently that it actually leaves the ground. Wheel hop can be caused by many problems, including excessive unsprung weight, insufficient shock damping, or poor torsional axle control.
This is Stupid but it was the only thing I could find.
http://www.youtube.com/watch?v=HothKxgULF8
Weight Transfer: A fundamental topic in any discussion about handling is weight transfer. If you do not fully understand weight transfer, you will not be effective in understanding how to adjust the car for maximum handling performance.
http://www.turnfast.com/tech_handling/handling_weightxfr
Spring Rates: The springs and related parts intermediate between the wheels and frame of an automotive vehicle that support the frame on the wheels and absorb road shock caused by passage of the wheels over irregularities.
http://www.answers.com/topic/automotive-suspension
Bushing Hardness: A bit self explanatory but, this puts it into some context
http://74.125.47.132/search?q=cache:1mIX98BrbsoJ:www.bmcforums.com/showthread.php%3Fp%3D1321692+Define+%22Bushing+Har dness%22,+Car&cd=9&hl=en&ct=clnk&gl=us
Weight Distribution: Scroll Down to next item
Static Roll Center: Read below
+++++++++++++++++++++++++++++++++++++++++
While searching, "Static Roll Center", I came across this page. By Reading down the page it give a lot of definitions, formulas, and examples of things to thing about when setting up your car. "Static Roll Center", as well as many other suspension and Handling aspects are addressed. It's really a pretty neat site that after a while might make your head explode, but if you take it slowly, it can put many things into perspective and show how they are used together.
http://74.125.47.132/search?q=cache:8H5dXAY1xqkJ:www.engr.uconn.edu/ece/SeniorDesign/projects/ecesd01/sp01_reports/sae_final_sp01.doc+Define+%22Static+Roll+Center%22 ,+Car&cd=3&hl=en&ct=clnk&gl=us
http://74.125.47.132/search?q=cache:8H5dXAY1xqkJ:www.engr.uconn.edu/ece/SeniorDesign/projects/ecesd01/sp01_reports/sae_final_sp01.doc+Define+%22Static+Roll+Center%22 ,+Car&cd=3&hl=en&ct=clnk&gl=us
Polar Movement of Inertia Center:
INERTIA
Inertia is the resistance to change the direction or velocity of a body, either at rest or in motion. In this case, it is related to changing the heading, or direction, of a vehicle; that is, changing from straight ahead driving to a turn.
The importance of inertia and weight distribution as they relate to driving is that they affect the amount of time required to make a transition from straight to turning or vice versa. Although these changes with the usual loading of a vehicle are not large, a driver should recognize the unusual loading of a vehicle, such as the placing of a large load on the tailgate of a station wagon (or the addition of a heavy load on the vehicle roof) will cause changes in the way the vehicle drives and adjustments should be made in driving accordingly.
Since inertia dictates that a body in motion will continue to move in a straight line, a force must be applied to cause a vehicle to turn. This force is called Centripetal force, and is a result of tires stretching to pull the car from a straight path. Centripetal force must exceed centrifugal force for the vehicle to turn.
MOMENTS OF INERTIA:
A. Pitch – the force felt in acceleration or braking movement around (Horizontal axis) of vehicle
B. Roll – the force felt in cornering, side to side movement (Lateral axis) of the vehicle
C. Yaw – the force felt in a spin movement around (Vertical axis) of the vehicle
POLAR MOMENT OF INERTIA
A very important handling concept, which dictates the willingness of a car to change directional position if called Polar Moment of Inertia. “Poles of inertia” are just another way of saying “center of weight concentration”. The “moment” in this concept is determined by the front-to-rear location of the center of gravity. The car turns (changes direction) about its center of gravity in a corner so the further away the centers of weight concentration are located from the center of gravity (which is their common center), the bigger the “moment”.
A high polar moment of inertia is present when the weight concentrations are heavy and are far apart. The low polar moment of inertia is found when weight concentrations are light and are close together. In other words, it is easier to steer a vehicle with a low polar moment of inertia.
A vehicle with a low polar moment of inertia gives a quick response to steering commands. A vehicle with a high polar moment has high directional stability (meaning it resists changing its direction).
=====================================
That concludes this post.
Let me know if this is helpful for you in any way. For other, please feel free to make any remarks with regards to this post, and let me know if:
a) It's at lest somewhat helpful
b) It's ok, but it would be improved by adding __________________. (Please feel free to add things, as I am in a position to trying to get my arms wrapped around this Concept as well.
Thanks,
Ty