Suspension Primer by Ingalls Engineering
#1
04-03-2008, 10:55 PM
Join Date: Aug 2007
Location: Wayne, NJ
Posts: 6,213
Suspension Primer by Ingalls Engineering
I thought that this was an awesome article. I have to admit, some of this is over my head, but great info if you can follow it!
Disclaimer: This is copied from the link below.
http://www.ingallseng.com/performance/primer.html
************************************************** ****************************************
TUNING PERFORMANCE SUSPENSION
--A PRIMER--
By Tom O’Rourke
INTRODUCTION
Designing and tuning the automotive suspension for performance involves fact and science, as well as a good measure of experience and art. In the following monographs I will emphasize the former, but will occasionally use a first person presentation to acknowledge the intertwining of my opinions. Keep in mind that cats can be skinned numerous ways. One man’s stay bar adjustment is an other’s sway bar change. Often differing approaches do not mix well. Accordingly, for the most part, my comments will be more qualitative than quantitative.
And particularly keep in mind that "performance" comprises quite a range of cats. Completely opposite objectives and expedients are appropriate for various specialties. My bias tends towards road and circle racing on pavement. Organization of the various subjects under set-up or dial-in reflects the above-mentioned bias. Under set-up I address those items more readily sorted out in the shop or during testing. Set-up items typically alter other settings, or are difficult to set and/or measure. Dial-in items tune the suspension to a particular track or changing conditions. Each topic is developed further in a more focused paragraph.
SET-UP
The first concern is basic housekeeping. Chassis rigidity, particularly resistance to twist in torsion, is a necessity. Chassis flex will render the other tunable suspension control mechanisms insensitive or inoperative. The chassis should be square --check the wheelbase and wheel diagonal measurements. And place as much weight as feasible low and toward the center of the vehicle, except high for drag racing, somewhat higher for dirt, and towards the left (driver’s side) and maybe a bit more rearward for circle racing.
Ride height is the primary suspension setting. Most of the other suspension settings change when ride height is altered. Set ride height first and check it regularly. Static wheel weight should also be set during this process. I prefer to treat wedge as a fixed parameter, though this is a minority view in many circles.
Locate and, if necessary, adjust the various pivot axes between the sprung weight and the unsprung weight. These include the roll centers and dive and squat characteristics. The front and rear roll centers define the roll axis which, in conjunction with the Cg, in turn define the roll moment, i.e. the tendency of the vehicle to lean when turned. Dive and squat suspension geometry influence the vehicle pitch attitude, i.e., nose down under braking and tail down during acceleration.
While springs and dampers, though often varied somewhat during dial-in, are initially chosen to keep the vehicle from bottoming and oscillation, respectively. Calculating the wheel-rate during set-up aids understand of the effect spring and damper changes will have on handling.
Steering geometry is also an early consideration. The front spindle determines the steering inclination angle to produce a reasonable scrub radius. Caster, Ackerman geometry, and bump steer are important parameters which should at least be recorded and tracked.
With these items under control, we can proceed to dial-in.
DIAL-IN
My preference in "dialing-in" is to first optimize the absolute total adhesion of the tires at speed, and then work on balancing the vehicle. Of course if the vehicle balance is vicious, it is only prudent to kill the biggest and closest snake first.
Tire temperatures are an excellent measure of tire adhesion. Tire pressure and camber are adjusted to produce a flat temperature profile across the tire. Roll stiffness at one or the other end of the vehicle is then adjusted to balance the handling in terms of understeer (push) or oversteer (loose). Springs may also be varied in small increments to tune pitch stiffness as well as roll stiffness.
At this stage the tires will be flat on the ground and working. The vehicle will have a reasonably balanced response. If a locked rearend is involved in a circle track setting, stagger is provided at the rear tires to facilitate power-on turning. Front to rear brake bias is adjusted to optimize braking effectiveness and stability, and /or enhance corner turn-in. Dampers can be tuned to adjust the rate of weight transfer, either fore and aft or in roll -but usually roll- as well as to control small, rapid wheel movements.
Though not one of my favorite expedients, wedge is sometimes fine tuned to balance the vehicle. While wedge changes ride height somewhat, it is often effective as a quick pit stop adjustment to correct an unbalance roll stiffness resulting from tires fading unequally during a race.
Of course the trick is to make the best compromises and get all of the above to work together to approach (but never reach) the optimum.
AckermanThe Ackerman concept deals with the differing radii followed by the inner and outer steered wheels when turning. By varying the angle between the steering arm (an imaginary line from the tie rod attachment point to the actual steering axis) and the tie rod, the amount of turning of the inner wheel relative to the outer wheel can be varied. For parking lots and wagons, each steered wheel follow its actual turning radius to minimize tire wear. For racing there is a theory for any possibility.
My view is that we want to gain as much cornering power as possible from the inside tire. Tire slip angles under maximum turning allow the actual radii traveled by the tires to differ from each other as well as to deviate from the direction in which each tire points! The more heavily loaded outer tire pretty much determines the actual cornering line. Provided the inside tire is not turned so far as to induce it to lose its slip angle and slide (wash), there is worthwhile cornering power to be gained by turning the inside tire even beyond the theoretical Ackerman angle –though the reasons for this are beyond the scope of this discussion.
Optimum Ackerman geometry is best determined by testing. With rear steer (the st
Disclaimer: This is copied from the link below.
http://www.ingallseng.com/performance/primer.html
************************************************** ****************************************
TUNING PERFORMANCE SUSPENSION
--A PRIMER--
By Tom O’Rourke
INTRODUCTION
Designing and tuning the automotive suspension for performance involves fact and science, as well as a good measure of experience and art. In the following monographs I will emphasize the former, but will occasionally use a first person presentation to acknowledge the intertwining of my opinions. Keep in mind that cats can be skinned numerous ways. One man’s stay bar adjustment is an other’s sway bar change. Often differing approaches do not mix well. Accordingly, for the most part, my comments will be more qualitative than quantitative.
And particularly keep in mind that "performance" comprises quite a range of cats. Completely opposite objectives and expedients are appropriate for various specialties. My bias tends towards road and circle racing on pavement. Organization of the various subjects under set-up or dial-in reflects the above-mentioned bias. Under set-up I address those items more readily sorted out in the shop or during testing. Set-up items typically alter other settings, or are difficult to set and/or measure. Dial-in items tune the suspension to a particular track or changing conditions. Each topic is developed further in a more focused paragraph.
SET-UP
The first concern is basic housekeeping. Chassis rigidity, particularly resistance to twist in torsion, is a necessity. Chassis flex will render the other tunable suspension control mechanisms insensitive or inoperative. The chassis should be square --check the wheelbase and wheel diagonal measurements. And place as much weight as feasible low and toward the center of the vehicle, except high for drag racing, somewhat higher for dirt, and towards the left (driver’s side) and maybe a bit more rearward for circle racing.
Ride height is the primary suspension setting. Most of the other suspension settings change when ride height is altered. Set ride height first and check it regularly. Static wheel weight should also be set during this process. I prefer to treat wedge as a fixed parameter, though this is a minority view in many circles.
Locate and, if necessary, adjust the various pivot axes between the sprung weight and the unsprung weight. These include the roll centers and dive and squat characteristics. The front and rear roll centers define the roll axis which, in conjunction with the Cg, in turn define the roll moment, i.e. the tendency of the vehicle to lean when turned. Dive and squat suspension geometry influence the vehicle pitch attitude, i.e., nose down under braking and tail down during acceleration.
While springs and dampers, though often varied somewhat during dial-in, are initially chosen to keep the vehicle from bottoming and oscillation, respectively. Calculating the wheel-rate during set-up aids understand of the effect spring and damper changes will have on handling.
Steering geometry is also an early consideration. The front spindle determines the steering inclination angle to produce a reasonable scrub radius. Caster, Ackerman geometry, and bump steer are important parameters which should at least be recorded and tracked.
With these items under control, we can proceed to dial-in.
DIAL-IN
My preference in "dialing-in" is to first optimize the absolute total adhesion of the tires at speed, and then work on balancing the vehicle. Of course if the vehicle balance is vicious, it is only prudent to kill the biggest and closest snake first.
Tire temperatures are an excellent measure of tire adhesion. Tire pressure and camber are adjusted to produce a flat temperature profile across the tire. Roll stiffness at one or the other end of the vehicle is then adjusted to balance the handling in terms of understeer (push) or oversteer (loose). Springs may also be varied in small increments to tune pitch stiffness as well as roll stiffness.
At this stage the tires will be flat on the ground and working. The vehicle will have a reasonably balanced response. If a locked rearend is involved in a circle track setting, stagger is provided at the rear tires to facilitate power-on turning. Front to rear brake bias is adjusted to optimize braking effectiveness and stability, and /or enhance corner turn-in. Dampers can be tuned to adjust the rate of weight transfer, either fore and aft or in roll -but usually roll- as well as to control small, rapid wheel movements.
Though not one of my favorite expedients, wedge is sometimes fine tuned to balance the vehicle. While wedge changes ride height somewhat, it is often effective as a quick pit stop adjustment to correct an unbalance roll stiffness resulting from tires fading unequally during a race.
Of course the trick is to make the best compromises and get all of the above to work together to approach (but never reach) the optimum.
AckermanThe Ackerman concept deals with the differing radii followed by the inner and outer steered wheels when turning. By varying the angle between the steering arm (an imaginary line from the tie rod attachment point to the actual steering axis) and the tie rod, the amount of turning of the inner wheel relative to the outer wheel can be varied. For parking lots and wagons, each steered wheel follow its actual turning radius to minimize tire wear. For racing there is a theory for any possibility.
My view is that we want to gain as much cornering power as possible from the inside tire. Tire slip angles under maximum turning allow the actual radii traveled by the tires to differ from each other as well as to deviate from the direction in which each tire points! The more heavily loaded outer tire pretty much determines the actual cornering line. Provided the inside tire is not turned so far as to induce it to lose its slip angle and slide (wash), there is worthwhile cornering power to be gained by turning the inside tire even beyond the theoretical Ackerman angle –though the reasons for this are beyond the scope of this discussion.
Optimum Ackerman geometry is best determined by testing. With rear steer (the st
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