Phase 4 Report MEEG401: Team FSAE Suspension

December 10, 2010

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Introduction:

For Team FSAE Suspension, phase 4 was largely spent in the student machine shop. The final

design selected during phase 2, and developed in detail during phase 3, was manufactured and

installed. Many hours were spent in the manufacture of the components of the proposed

suspension system. The result of this semester’s work is the research, concept generation,

concept selection, and concept implementation of a successful unequal a-arm independent

suspension for the 2010 UD FSAE race car. The final touches are still being made to the

assemblies, but the components have been manufactured, and for the most part installed on

the new car’s chassis, and will shortly be subjected to testing and performance evaluation. The

completed design package includes Uprights, A-Arms, Push Rods, Tie Rods, Rockers, Shock

Absorbers, Sway Bars, and all of the clevises, mounting tabs and hardware needed to assemble

and test the suspension. During the final few days remaining before the deliverables are due to

the sponsor, the team intends to continue with the testing further defined in this report, and

will pursue ongoing work with the FSAE club during the winter session and spring semester to

continue to test and tune the car’s suspension.

Final Design Description:

Suspension Style: The unequal a-arm suspension was chosen by the suspension team as the design concept to be

pursued during phase two. The A-arm configuration meets the design requirements for

structural integrity and suspension travel, and benchmarking specific to FSAE indicated that the

Unequal A-arm design was by far the most common design in FSAE application. The chosen

design concept utilizes similar components for front, back, top and bottom control arms, which

will provide a high level of standardization of parts and components, and the similarity to the

prior car's design will enable easy use of components such as shocks and springs from previous

cars. Each control arm has been manufactured with a few simple welding and machining

operations, and the final dimensions of the upper and lower arms across all four corners of the

car have been standardized so that two configurations, top a-arm and bottom a-arm, are

similar. Other parts such as rockers, pushrods and clevises have been made as uniform as

possible to keep the number of discrete parts as low as possible.

The unequal a-arm suspension system is comprised of upper and lower V shaped frames

attached to the chassis in four specified suspension mounts with spherical bearings to provide

one degree of freedom. Each arm provides an attachment point for the wheel upright that is

fixed in two dimensions (laterally and longitudinally to the chassis) and free to move in the third

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dimension (vertically). The upper and lower arms are designed with different lengths and

mount points, with the shorter arm installed above the longer arm. This geometry provides a

change in camber as the suspension components move through the range of travel. The design

lengths have been optimized through the kinematic analysis to provide the desired cambering

behavior.

The suspension arms are supported by a push rod assembly that resists the motion associated

with the suspension travel, and supports the weight of the car in its neutral position. The push

rod attaches at the base of the wheel upright, and travels diagonally upward to an attachment

to a rocker. The rocker is affixed to the chassis, and transfers the force in the push rod to a

shock absorber and spring assembly that both dampens, and supports the travel of the

suspension system, and to a pushrod that actuates the sway bars during body roll.

Figure 1: Upper and Lower A-arms

Adjustability: One of the most important details that the sponsor emphasized for the design of the

suspension was adjustability. After careful consideration of the advantages and disadvantages

of each of the adjustability concepts discussed in the previous section of this report, three

stood out as the most promising: the threaded chassis mount, slotted chassis clevis, and upright

shims. These three ideas work in conjunction in the suspension system to achieve the desired

degree of adjustability. The merits of the three concepts are discussed below.

Threaded Rod End

This concept achieves adjustability in the a-arm length. The rod end is easily accessed by

removing a bolt and screwing it in or out to adjust the a-arm length. Additionally, the same

process can used to fine tune the caster angle. This concept did the best job of avoiding

weakness in the a-arm. It keeps the a-arm solid, with only a threaded insert at the end. This

design moves the weakness of the suspension to the bolts. If the bolts should fail, they are

easily replaced and we save the more important components like the a-arms. Team FSAE

suspension is confident that this will not become a problem. This concept is one of the easiest

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to adjust, requiring only the loosening of a bolt. The idea can also be standardized to be

compatible with all of the mount points, significantly reducing the number of drawings that will

have to be developed. Additionally, once the optimal geometry is determined through testing

on the car, the mount can easily be replaced with a rigid clevis mount, improving the strength

and reliability of the joint.

Figure 2: Threaded Rod End Chassis Pickup Point

Upright Shims

To achieve the desired camber adjustability, it was decided that the most effective way would

be to add shims in between the clevis and the upright. Each shim thickness corresponds to

specific degrees of camber change. It is very easy to implement by simply loosening the bolts

that attach the clevis to the upright and slipping a shim in between them. This concept is

commonly practiced and the most reliable, so it has been implemented in our design.

Figure 3: Upright Shims

Threaded A-arm

mounts to chassis spherical rod end

Locknut

upright a-arm clevis

shim

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Chassis Pickup Bushings

This design simply and efficiently achieves anti-squat and anti-dive through vertical adjustment

of the pickup points. This concept was chosen for its effectiveness and simplicity. It cut down

on the number of the required parts, and fully achieved the necessary purpose. This adjustable

mount will only be incorporated on the bottom pickup point nearest to the end of the car

lengthwise, on each of the four corners. Multiple sets of different length bushings have been

manufactured, and these sets will be switched in and out of the pickup points until the optimal

anti-squat and anti-dive characteristics are achieved. The method of adjustment can be

replaced by a non-adjustable mount on cars for future years once the optimal geometry is

determined through this year’s testing.

Figure 4: Adjustable Chassis Pickup Point

Hubs and Uprights: The front upright design has been reused as much as is possible for this project for both front

and rear upright applications. The front upright design from the past car was deemed

acceptable by the project sponsor and advisor, and upright design was determined to be

outside the scope of this project, however; the scope of the project does dictate some changes

with respect to the rear hub and breaking system. The former car used a different hub than the

one that the power train team has chosen, and utilized a single axle mounted rear brake

system. The new suspension design includes rear uprights that accept the hub from the drive

axle, as well as provide caliper mounts for a wheel mounted brake system. This accommodation

bushing

bushing

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has been made by modifying the front upright design (that already includes caliper mounts) to

receive the rear hub. The specific hub and bearing configuration has been chosen by the

drivetrain team, and the suspension team has accommodated by modifying the existing upright

design.

Figure 5: Front and Rear uprights

Shocks and Springs:

As per the customer and advisor recommendations, the Fox shocks already owned by the UD

FSAE club have been utilized in the design. Springs of varying stiffnesses are readily available for

these shocks, so the appropriate springs have been selected and purchased. Using vehicle

dynamics theory, as researched from an authoritative text on the topic, Race Car Vehicle

Dynamics, Milliken and Milliken, the desired ride and roll rates were found. Ride rate is defined

as the force required to make the wheel travel upwards per unit of distance. It defines not only

the travel of the suspension and the vertical movement of the chassis, but also the roll

characteristics of the car through the associated spring rate. As the car rolls, it causes the

outside wheel to travel upwards due to the centrifugal moment about the roll center. The

stiffness of the springs directly affects how much the car can roll.

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Roll rate is the torque required to rotate the car about the roll center per unit angle. Thus, the

roll rate is defined by the centrifugal moment about the roll center in cornering situations. Two

components define the roll rate: the spring stiffness and the sway bars. The spring stiffness

contributes to the roll stiffness as described above. The sway bars contribute to the roll rate by

utilizing a torsional spring. The spring links to the rockers on either side of the car, and resists

travel of the wheels in opposite directions. The desired ride rate defines the spring stiffness,

and the remaining roll stiffness desired is contributed by the sway bars.

Using vehicle dynamics theory, the optimal ride and roll rates were calculated. After this, the

geometry of the suspension was used to determine the necessary spring stiffness. From this,

the stiffness of the sway bars was calculated and translated into the design presented in this

report. The values are shown below.

Table 1: Ride, Roll, and Spring Rates

Front Ride Rate 148.4 lbs/in

Rear Ride Rate 146 lbs/in

Front Roll Rate 18750 lb ft/rad

Rear Roll Rate 20875 lb ft/rad

Front Spring Rate 250 lbs/in

Rear Spring Rate 250 lbs/in

Front Sway Bar Rate 50 lb ft/deg

Rear Sway Bar Rate 50 lb ft/deg

Performance Evaluation and Test Plan:

In order to gauge the success of the design at meeting the target values established, it was

necessary for a test plan to be developed. This plan needed to successfully measure all of the

metrics, so that the actual value for each metric could be compared to the target value, and

thus measure the success of the project solution. The methods of evaluating performance are

summarized in the Table 2, and discussed in detail in the following pages. Any actual values

that are not yet filled in will be measured by the final assembly of the car, and this document

duly updated.

Table 2: Metrics, Target Values, and Methods of Evaluation

Metric Target Value Actual Value Evaluation Method Wheelbase 61” Final Car Assembly

Front Track 50” Final Car Assembly Rear Track 48” Final Car Assembly Anti-Dive and Anti-Squat + 1" vertical movement of

bottom pickup points closest -1” vertical movement of bottom pickup points

Suspension Assembly and Measurement

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to CoG of car farthest from CoG of car Roll Center Stable, < 1" vertical

movement over 1.5” deflection in roll, ~3” height at neutral

---- Suspension Assembly and Measurement

Scrub Radius Minimize, <1” Suspension Assembly and Measurement

Camber -2: static, maintained over 0.5” deflection in roll

---- Suspension Assembly and Measurement

Kingpin Angle 0-5 degrees 0 degrees Suspension Assembly and Measurement

Caster Angle 0-5 degrees Suspension Assembly and Measurement

Center of Gravity Longitudinal: centered Lateral: centered Height: ≤ 10”

F/R Weight Distribution 50/50 Spring Stiffness TBD 250 lbs/in Damped Frequency TBD 3 – 3.5 Hz

# Tools to Adjust 3 3 (2 x 7/16 wrenches and 1 x 9/16 wrench)

Suspension Assembly and Measurement

Adjustments easy to access

Yes Yes (judged by all team members)

Suspension Assembly and Measurement

Camber and Toe adjustment without disconnection of parts

Yes Yes Suspension Assembly and Measurement

Material Strength Factor of safety >2 for range of normal operation

FOS >5 for range of normal operation

Material Machinability Maximize maximized

Material Cost Minimize Within budget Material Weight Minimize Minimized for material

Suspension Assembly and Measurement:

For the FSAE suspension, the most important metrics are related to the geometry. For this

reason, it is important that the suspension be fully assembled, so that these geometric metrics

can be measured. Since the suspension is still in the process of bei ng assembled on the chassis,

not all of the final values have been measured as of yet. One corner of the suspension can now

be fully assembled for testing. A poster board will be fixed to the front side of the suspension

box, so that instant centers and other geometric features can be marked. With the corner

assembled, the relevant metrics will be measured.

In order to meet the target value for anti-dive and anti-squat, the length of the switchable

bushings is all that must be known. This was measured, using the distance between the tabs of

the pickup point, the width of the rod end, and the variety of bushings that can be made.

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Measuring the roll center position will be slightly more difficult. The suspension will be set in

the neutral stance position, and the front-view instant center position constructed from the

geometry and marked on the poster board. The line from the instant center to the tire contact

patch will then be drawn, and assuming symmetry in the neutral stance, the roll center will be

marked on the board. The suspension will then be set at the 0.5” jounce position, and the

instant center reconstructed and marked. Since the roll center cannot be constructed from

only one corner when the suspension is not symmetrically deflected, the instant center position

of the one corner will be measured and compared the values calculated in the kinematic

analysis to confirm the predicted movement. If the values do not match, further steps will be

taken to assemble both sides of the suspension and physically measure the roll center

movement.

Measuring scrub radius will be a simple matter of measurement once the upright, clevis and

wheels are assembled. The steering axis will be measurable from the clevises, and the distance

between it and the wheel centerline at the contact patch will be easily constructed and

compared to the simulated values. Unfortunately, this metric could not be significantly

affected by any changes the team could make. The primary contributors to scrub radius are the

front hubs, which were outside the scope of the project. This is the reason for this target value

not meeting the goal value.

The Camber is a critical measurement of the jig assembly. With the suspension set in the

neutral stance, the camber angle will be measured by tracing the upright angle onto the poster

board, and drawing and intersecting vertical line using a plumb. The angle between the two

lines will then be measured. The suspension will next be set in the 0.5” jounce position, and

the previous angle construction repeated. This new angle will be subtracted from the

measured change in bottom a-arm angle to obtain the net camber change. The process will be

repeated in the 0.5” rebound position.

Kingpin angle was obtained by measuring the difference between the upright angle and the

line between the two clevis centers, which constructs the steering axis. Since the upright

clevises were all the same size, the kingpin angle as zero.

To obtain caster angle, the side-view line between the top and bottom upright spherical joints,

and then measuring the angle between this line and a vertical line constructed using a plumb.

The caster angle will then be adjusted as necessary by changing the lengths of each arm in the

a-arms until the desired angle is obtained.

The number of tools required to adjust the suspension was easily measured from the

suspension assembly, simply by noting how many tools were needed to adjust the key

adjustability components of the suspension as it is assembled on the chassis.

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The ease of adjustability metric will be a subjective measurement that is obtained by having

each of the team members adjust the suspension, and describe their experience as either easy

or not. This process will be repeated with members from the other FSAE teams, and receiving

their feedback on whether the suspension was easy to adjust or not.

Final Car Assembly: Some characteristics of the car simply cannot be measured before the suspension is assembled

on the chassis, and the car is run through testing. These metrics include wheelbase and track.

These values will have to be measured once the suspension and chassis are assembled and in

running condition, at the end of winter session.

Performance:

All of the metrics and target values discussed above were developed with the maximum

performance of the car as the goal. For the development of the project solution, it was

important that the performance be broken down into these physical target values. However,

once the car is assembled, it will be necessary to test whether the target values that were

chosen through research lead to the desired performance of the car. Since the car will not be

completed until the end of senior design, testing will take place over winter session and in the

spring. For this reason, a test plan has been developed for the measurement of key

performance characteristics. This plan will be left with the UD FSAE club, with instructions on

how to measure the performance of the car, and what steps to take to fine tune and improve

the performance. The key test procedures that will be developed are described below.

Tire Temperature Analysis: Measuring the tire temperatures after time on the track allows the camber, ride rates, and roll

rates, to be fine tuned. Using a tire pyrometer, the temperature of each tire will be measured

in three places, 1” from the inside shoulder, 1” from the outside shoulder, and in the center of

the tire. These three temperatures will be measured and recorded from each tire immediately

after 5-10 track laps. The temperatures will then be analyzed, and the necessary tuning steps

determined. A summarized diagnosis procedure is described in Table 3.

Table 3: Tire Temperature Diagnosis

Tire Temperatures Diagnosis Solution Individual Tire:

Inside hotter than outside Slight difference, good Optimal temperature distribution

Major difference, too much negative camber.

Add shims to top of upright.

Too much toe out Lessen toe out

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Outside hotter than inside Not enough negative camber Remove shims from top of upright.

Add shims to bottom of upright (only if absolutely necessary, toe will have to be readjusted.)

Too much toe in Lessen toe in

Sides hotter than middle Low Tire Pressure Increase Tire Pressure Middle hotter than sides High Tire Pressure Reduce Tire Pressure

Between Tires: Rear Tires Hotter than front (oversteer)

Front sway bar soft, rear stiff Stiffen front sway bar or loosen rear sway bar

Rear tire pressure low, front high Increase rear tire pressure or reduce front tire pressure

Front Tires Hotter than rear (understeer)

Front sway bar stiff, rear soft Stiffen rear sway bar or loosen front sway bar

Front tire pressure low, rear high Increase front tire pressure or reduce rear tire pressure

Jounce, Roll, and Anti-squat and Anti-dive: These performance characteristics will be measured directly during performance testing of the

car. Zip ties will be fit snugly around the shafts of the shocks, pressed up against the shock

body when the car is in the neutral stance. The car will then be run through a series of

maneuvers, and by measuring the distance that the zip tie has been pushed up the shaft, the

wheel movement in jounce can be directly measured. The use of car-mounted video cameras

has also been discussed for measurement of this and the other metrics described here.

To measure anti-squat and anti-dive, the car will be run through maximum breaking and

acceleration maneuvers. The car will be accelerated from a stop as fast as it is capable, and the

deflection of the rear suspension will be measured afterwards from the zip tie movement. The

accelerometer data from the data acquisition unit will be obtained, from which load transfer

will be calculated, and compared to the calculated % anti -squat. A maximum breaking

maneuver will be similarly performed to determine anti -dive.

Measurement of body roll will be achieved by using the same zip tie method and running the

car through maximum cornering maneuvers, replicating the skid pad event in competition. By

measuring the amount of wheel movement using the zip tie method, the effective roll rate will

be determined. Thus the contributions from the springs and sway bars to the roll stiffness can

be measured and compared to the theoretical values.

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The test plan outlined above will be submitted to the UD FSAE club as an independent

document, to be kept in the club and used during the testing of the car, both by other club

members and the members of the club in this senior design group.

Transition:

As our official responsibility for the project ends on the 17th when the deliverables are

presented to the sponsor, the importance of the transition to the UD FSAE club becomes very

important. The test plan given above, and attached separately, will be a primary way that the

team’s understanding of the suspension will be passed on to the club. Additionally,

participation of the team members within the club during the winter and spring will be

important. Our involvement in the club will foster the transfer of knowledge about the

suspension from the team to the club, preparing the junior club members for the potential

senior design project in 2011. During the spring semester, team involvement in the club will

help to test the durability of the suspension and tune it to its best performance. In the

summer, at least a few of the team members will be seeking to travel to California for

competition. This will be important for success in the static events, particularly the design

event. To assist with this transitional process, and at the suggestion of the advisor, a list of tasks

to be completed by the club is given here:

Complete manufacturing of bushings. All of the different types of bushings have been manufactured, but not as many of each as are needed. These simple bushing simply need to be manufactured on an as-needed basis to complete the assembly of the

suspension system. This includes primarily: o Bushing for the joints between the rockers and the pushrods, shocks, and sway

bar linkages.

o Bushings for the points where the shocks are mounted to the chassis.

One of the front uprights needs to have its center hole milled out to match the larger diameters of the other front upright.

The travel of the suspension needs to be confirmed (jounce and rebound), once the car

is fully assembled. Due to rounded weld joints that were not accounted for in the solid model, the bottom edges of the top a-arms may need to be ground down at the upright side.

Due to chassis/drivetrain complications over the location of the drive chain, the frame

member that the rear shocks are mounted to may need to be moved. The shock mounts and possibly the rear rocker mounts may need to be altered to fit the new frame members.

The full welding of all the tacked suspension/frame joints needs to be completed.

For suspension pickup points on chassis, C-shaped side gussets need to be cut and welded to the pickup tabs.

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All aluminum suspension components should be anodized and all steel components powder-coated.

Voids in the a-arms created by the parallel gusset plates need to be filled with foam or

capped to prevent debris filling the voids.

Nut faces should be added to the pushrods, tie rods, and sway bar linkages, to make adjustment easier. This can be achieved by drilling out the center of a nut, sliding it over the tube of the rod, and welding it in place.

When shims are manufactured for the uprights, they need to have tabs on the top or sides to make addition and removal of tabs easier.

For the adjustable anti-dive and anti-squat pickup points, multiple bushing sets should be made, to allow adjustment of the rod end up and down in ¼” increments.

Push/Pull testing should be performed on duplicate components of the adjustable anti pickup points, to validate the strength of the points.

Conclusion:

Team FSAE Suspension is glad to have reached completion of this project. At the beginning of

the semester, we knew close to nothing. Now, as we finish up the project, we are confident in

our knowledge of formula-style suspension, in theory and with some experience in practice.

The project began with an extensive amount of research, to educate the team and to develop

key metrics and target values. The sponsor and advisor were invaluable in this process,

providing a large amount of in-depth information on suspension and its workings. Moving

forward from metrics and target values, concepts were proposed and analyzed, until the top

ideas had been sorted out and developed. From there, the concepts were developed into

detailed designs, with the end result of component and assembly drawings in preparation for

manufacturing. Phase 4 was almost entirely consumed with manufacturing and fabrication,

transforming the CAD models and drawings into real parts. This required a lot of growth among

the team members in machining and welding ability. The team considers the project a success,

as all the parts have been manufactured, and by the 17th, it will all be finally attached to the

chassis. Testing and tuning in the winter and spring will confirm the performance

characteristics of the car, and the team is confident that the results will be positive and as

expected.

In conclusion, Team FSAE Suspension has enjoyed the opportunity to participate in the FSAE

sections of senior design. The project assigned us was very in-depth and involved, and possibly

too much to be realistic for one semester, especially considering the amount of manufacturing

involved. However the team was able to complete the project on schedule, with a design that

meets the target values and goals set forward at the beginning of the project, while also staying

within the constraints imposed on us. Many thanks are due to Dr. Steven Timmins, our advisor,

who provided oversight of the project, along with huge amounts of help through suggestions

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and discussions of concepts and theory. We are also indebted to Steve Beard and Al Lance,

who patiently helped us with manufacturing, and worked late to provide us with evening hours,

respectively. Moving forward, the team is confident in the future success of the suspension,

and looks forward to staying involved over the winter and spring, and proceeding to a

successful trip to competition at the beginning of the summer.

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APPENDIX

UD FSAE

Suspension Testing and Tuning

Instruction Manual

Senior Design Team FSAE Suspension

December 10, 2010

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Introduction:

Over the course of the senior design class of Fall 2010, the FSAE Suspension team developed

the suspension system used on the 2010 UDFSAE car. Due to the nature of the course, and the

depth of the project, fabrication of all of the car’s system was finished only days before the

deliverables deadline at the end of the semester. For this reason, the team was not able to

complete any kind of performance evaluation of the suspension system. This manual outlines a

set of test procedures intended to evaluated the performance characteristics of the suspension,

and provide guidelines for tuning the suspension to achieve maximum performance.

Purpose:

All of the geometry-related metrics and target values developed during senior design were

intended to maximize performance. Appropriate camber, ride and roll rates, and anti -dive and

anti-squat all serve to improve the performance of the car on the track. Theoretical target

values were developed during the semester, all with the goal of giving the car the best possible

performance. However, to actually achieve the best performance, it is necessary to tune the

adjustable parts of the car based on the results of testing and driving. The purpose of this

manual is to give some direction to the tuning of the car, making it easier to achieve optimal

performance.

Equipment:

1. Tire Pyrometer

2. Zip Ties

3. Video Camera – preferably car-mounted

4. 1 9/16 wrench

5. 2 7/16 wrenches

Procedures:

Ride Height:

To adjust the ride height of the car:

1. Using a 9/16” wrench, loosen the jam nuts on either end of the push rods.

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2. Turn the pushrods to either lengthen the pushrods to raise the ride height, or

shorten the pushrods to lower the ride height.

3. Retighten the jam nuts.

4. If the incorrect ride height is caused by the shocks being excessively

compressed, or not compressed enough, adjust the preload on the shocks as

necessary.

5. Make sure to keep the ride height the same from side to side. Front to back

can be different as desired.

Static Camber:

To adjust the static camber of the car at ride height:

1. Using the two 7/16” wrenches, loosen the two bolts on the top a-arm clevis at

the top of the upright.

2. Insert shims as necessary to add to the camber, or remove them to remove

positive camber.

3. If more negative camber is desired than be achieved by removing all the shims,

loosen the bolts at the bottom of the upright and add shims.

4. Retighten all the bolts.

Toe:

To adjust the toe of the wheels

1. Using the 9/16” wrench, loosen the jam nuts on either end of the tie rod.

2. Turn the tie rod as necessary to lengthen or shorten it, and toe out or in.

3. Retighten the jam nuts.

Tire Temperature Analysis: Measuring the tire temperatures after time on the track allows the camber, ride rates,

and roll rates, to be fine tuned. To perform a tire temperature analysis, complete the

following steps:

1. Bring the tires up to operating temperature by driving the car. Perform

several laps of the test course.

2. Immediately after performing the tire warm-up, use the tire pyrometer to

measure the tire temperature as shown in Figure 1. Measure in three places:

1” from the inside shoulder of the tire, 1” from the outside shoulder, and in the

center of the tire.

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3. Record the temperatures and repeat for all four tires.

4. Using Table 1, diagnose the tire temperatures and perform the solutions as

directed.

Table 1: Tire Temperature Diagnosis

Tire Temperatures Diagnosis Solution Individual Tire: Inside hotter than outside Slight difference, good Optimal temperature

distribution

Major difference, too much negative camber.

Add shims to top of upright.

Too much toe out Lessen toe out

Outside hotter than inside Not enough negative camber Remove shims from top of upright.

Add shims to bottom of upright (only if absolutely necessary, toe will have to be readjusted.)

Too much toe in Lessen toe in

Sides hotter than middle Low Tire Pressure Increase Tire Pressure Middle hotter than sides High Tire Pressure Reduce Tire Pressure Between Tires:

Rear Tires Hotter than front (oversteer)

Front sway bar soft, rear stiff Stiffen front sway bar or loosen rear sway bar

Rear tire pressure low, front high Increase rear tire pressure or reduce front tire pressure

Front Tires Hotter than rear (understeer)

Front sway bar stiff, rear soft Stiffen rear sway bar or loosen front sway bar

Front tire pressure low, rear high Increase front tire pressure or reduce rear tire pressure

Jounce, Anti-Dive, and Anti-Squat:

The stiffness of the suspension and its anti-dive and anti-squat performance are closely

linked. The amount of dive experienced during braking, and the squat during

acceleration, are direct results of both the spring stiffness and the geometry of anti -dive

and anti-squat. To adjust the jounce and anti features, follow the steps below:

1. Strap small zip ties tightly around the shafts of the shocks, and slide them up

the shock until they are sitting against the body of the shock.

2. Run the car through a straight line accelerating and braking test, accelerating

as fast as possible and locking up the wheels during braking. It is important to

not make any sharp turns with the car during this test.

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3. Measure how far the zip ties were pushed down the shaft on all four shocks

and record the values.

4. Generally, the stiffer the suspension, the better. If it is decided that the car is

diving excessively during braking or squatting during acceleration, replace the

bushings on the adjustable pickup points at each cornering, lowering the point.

5. Rerun the test, re-measuring the anti features and adjusting again as

necessary.

6. If the dive and squat are still excessive, or cornering performance is negatively

affected by increasing the anti features, stiffen the cars preload or replace the

springs with stiffer ones.

7. All of the solutions given in this section must be performed in conjunction with

other tests outlined in this manual. For example, stiffening the springs or

adding preload will also affect the roll of the car in corners, so the performance

of the car in this respect should be retested after any stiffness changes are

made to the car in anti-tuning.

Body Roll:

The body roll is one of the most important performance characteristics of the car. The

amount of roll the car undergoes during cornering significantly affects the camber

changes of the wheel, and cornering force the car can generate, and other features. A s

with other suspension characteristics, in general stiffer is better. Test the cars roll using

the following steps:

1. It is difficult to physically measure the roll of the car. It must be judged by the

driver’s feel, and visual evidence if video can be taken of the car in testing.

Run the car through a skidpad test as will be run in competition, a 30 ft radius

circle. Based on the driver’s input, observation, and video footage if possible,

determine if the car is rolling excessively. If so, unbolt the sway bar linkage

from the sway bar arm and re-bolt it to a hole closer to the base of the arm.

2. Rerun the test. If the roll is still excessive and the sway bar linkage is attached

to the shortest bolt hole, add pre-load to the shocks or replace the springs with

stiffer ones. However, make considerations of the affects this will have on

other performance characteristics before making changes to the spring

stiffness.

3. If the role is still excessive, and/or the springs cannot be changed due to other

performance factors, replace the sway bar with a stiffer one.

4. In the case that the roll is too stiff, perform the opposite of the steps above.

20

Notes:

All of the performance characteristics discussed in this manual are inter-related, and in

most cases adjusting one will affect the others. This must be kept in mind when

adjustments are made. No large changes should be made to any one feature without

then testing the car again to determine if other performance areas have been altered.

For questions regarding the 2010-2011 suspension, its design and tuning, contact:

o Seth Beckley – sethbeck@udel.edu