Collegiate Design SeriesSuspension Tuning & DevelopmentSteve LymanFormula SAE Lead Design JudgeDaimlerChrysler Corporation

Suspension Tuning and DevelopmentPart art, part science, and a little luck (but not much)Successful organizations take methodical approachThoughtful development saves time and moneyDevelopment is the means for discovery of all of the stuff we didnt think about when we designed the vehicle Development is only required to correct the ignorance of the designers. the late Keith Duckworth, the worth in Cosworth

Before We Leave For The Track ..We need a plan..testing or racing is more than just driving aroundKnow your partsKnow your car(s)Line up support

We Need A PlanProgram objectivesRealistic,aggressive team goal (1st year team- no DNF, 2nd year-top 20, 3rd year-top 10, 4th year-top 5, 5th year-drink the milk)Timeline w/ key milestones (the race will be run whether or not youre ready)Winning programs front load development activityTesting is expensive- every test should take a step toward the goalWe wear out tires, brakes, diffs, engines. Make it count.Agree on priorities, test procedures before you go test

Know Your Parts

Every part should be inspected, labeled, measured and/or performance checked Component testing may seem boring, but it is the foundation for a winning carHistory- how much running time, design level of part?Quantity- do we have enough to cover us for stuff wearing out, an accident, or race prep rebuild?Organize stuff so you can find it quicklyCreate Inventory or Bill of Laden You really need this to run internationally

Know Your CarVisual, functional inspection of all systemsBrakes, Fuel, Steering, Suspension, Structure, SafetyRecord static corner weights Physically measure center of gravity location (x,y,z) You dont know how much antis you have otherwisePhysically measure bending and torsional stiffness of chassis Measure and plot wheel alignment and bump steer front and rear through full suspension travelKeep a logbook, record all changes to car

Line Up SupportLine up and delegate supportHero DriverData acquisition whizHelpers/spotters/timersRadiosTiming equipmentVehicle measurement equipmentWeather stationTow vehicle/trailerPermission to use track or lot RestroomsRefreshmentsEnough fuel? Tires?

Care and Feeding of TiresKeep a 3 X 5 card on each tireRecord popping pressures to seat beadsCheck durometer at each test along with ambient temperatureMonitor inflation pressures before and after each runMonitor tread temps (O/C/I)Monitor treadwear (chunking, blisters, rubber flow, color change, fast wearout, uneven wear)When adjusting pressures more than 3 psi, recheck after one minuteRecord tire temps right after each testScrape junk of tread w/ hacksaw blade, not your hands

Take Some Of The Opinion Out of TestingStop watches, 2-3, digitalQuality tire pressure gauge, 0-60 psi (2)Tire pyrometer- probe type (infrared not accurate)Durometer-Shore hardness A4 bathroom scalesSteel tape measure 12 ft, English/MetricDigital inclinometerSimple g-g measurement box (g-Tech,Escort, part of data acquisition system)

How to TestWarm up vehicle at part throttle to get fluids, tires, brakes up to operating temps The engine should be performing well to make meaningful chassis adjustmentsDriver must be prepared to push limits, stretch the envelope (maybe not terrified, but a little scared)Stay out just long enough to feel the change (or not), 1-2 hot lapsMake one change at a time, dont be afraid to make big changes initiallyBracket in on what seems to workRecord every lap time (segments if you have more helpers) and any notes/driver comments (if radio)Create a track map/ driver debrief sheet for each session and use them

More Advice for Productive TestingDont make more than one change at a time-at least in related areasDont evaluate chassis performance on cold or worn out tiresDont evaluate chassis performance until you have established good throttle responseDont make miniscule changes until you are close to optimum performance- 1 click on dampers, for exampleDont be afraid to try big changesyou can always go back to the previous iterationDont trust subjective judgments or lap times. Take corner and straight segment times to find out where you are gaining and losing timeDont make or accept excuseswere a half second slower, but we have our weak motor in the car or if we had new tires or if the sun wasnt in the drivers eyes.Dont work with a physically or mentally exhausted driverTesting is expensive. Be prepared, have a test plan in advance

Driver Feedback

What to Do with FeedbackBreak down the course in segmentsCorner entry- turn in response, weight transfer under braking, brake pull, transient roll balance, understeer/oversteerMid-corner- understeer/oversteer , steer corrections, throttle applications, path firmnessCorner exit- understeer/oversteer, progressiveness applying the power off of the corner (diff torque distribution, weight transfer under accelerationThe straights : straight line tracking, pitch attitude (stiction leaving the corner)-can affect steering and aero lift/drag

Chassis SetupOverall ride frequency range 1.5-2.0 Hz (FSAE), 1.2-1.7 Hz (Mini-Baja)Remember Maurice Olley shoot for 20% delta front to rear to achieve flat rideTuning hierarchy: springs,anti-roll bars, and dampersMy philosophy: the springs contribute 60-75% of roll stiffness, use anti-roll bars to trim out the roll couple distributionDampers: Start at 3:1 rebound to bump ratio, bracket damping, charge dampers to about 200 psi (monotube), 100 psi (twin tube)Tires: Use old tires for training, new tires/scuffs for testing/racing, use tire maker inflation recommendation to startWheel alignment hierarchy: toe, camber, caster

Where Can We Find Time?Consider every optionWere looking for tenths, not seconds (hopefully)There is no magic bullet

Damper AdjustmentsIf you have adjustable dampers, start at settings that provide about 3:1 rebound to bumpWe need less bump since it damps the movement of the unsprung mass and doesnt vary much due to dynamic loading, the rebound side damps the sprung mass reaction after the bumpDampers control rate of weight transfer, not the amountOverdamped- tire chatters over bumps, body control will be choppy, car will have nervous, darty feel, may lack progressivity in cornering with road camber, surface changesUnderdamped- body floats, steering response is sluggish, bouncing off bump stops

Adjustable Dampers

Chart1

-1731.07-1472.28-1095.49

-1684.14-1242.99-713.34

-1556.75-937.27-353.99

-1224.22-545.73-108.61

-927.88-142.13-36.2

-698.59-44.25-17.43

000

206.4995.232.18

244.04175.6561.68

308.4246.72158.22

384.83312.42235.99

514.89391.53315.1

750.89598.03455.9

Cold R0C0

Cold R12C6

Cold R24C12

Velocity (in/sec)

Peak Force (lbs)

Production ACR Dampers - Front - DSI

PROD ACR FRT

Prod ACR Rt FRTProd ACR Rt FRTProd ACR Rt FRT

Cold R0C0Cold R12C6Cold R24C12

Velocity (in/sec)PK Force (lbs)Velocity (in/sec)PK Force (lbs)Velocity (in/sec)PK Force (lbs)

10.542-1731.0715.942-1472.2819.884-1095.49

9.985-1684.1413.113-1242.9914.399-713.34

8.614-1556.759.728-937.2710.028-353.99

5.785-1224.226-545.736.085-108.61

3-927.883-142.133.043-36.2

1.5-698.591.543-44.251.543-17.43

000000

1.543206.491.54395.21.54332.18

3.043244.043.085175.653.12861.68

6.128308.46.214246.726.214158.22

10.199384.8310.199312.4210.242235.99

14.999514.8915.085391.5315.342315.1

22.841750.8923.398598.0323.741455.9

Dyno Date:9/5/00Dyno Date:9/5/00Dyno Date:9/5/00

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PROD ACR FRT

Cold R0C0

Cold R12C6

Cold R24C12

Velocity (in/sec)

Peak Force (lbs)

Production ACR Dampers - Front - DSI

PROD ACR RR

Prod ACR Rt RRProd ACR Rt RRProd ACR Rt RR

Cold R0C0Cold R12C6Cold R24C12

Velocity (in/sec)PK Force (lbs)Velocity (in/sec)PK Force (lbs)Velocity (in/sec)PK Force (lbs)

18.984-1268.4620.698-1016.3822.284-766.98

13.97-1044.5414.442-734.814.827-457.24

9.814-827.3210.028-512.2110.028-258.79

6-606.076-312.426.042-107.27

3-421.033-127.383.043-32.18

1.543-324.491.543-36.21.5-13.41

000000

1.543144.811.54391.181.54336.2

3.085178.343.085135.433.08565.7

6.214227.956.214185.046.171130.06

10.242282.9210.199238.6810.199185.04

15.299352.6515.042299.0115.042242.7

23.527535.0123.655438.4723.87340.58

Dyno Date:9/5/00Dyno Date:9/5/00Dyno Date:9/5/00

&C&"Arial,Bold Italic"&14&A

PROD ACR RR

Cold R0C0

Cold R12C6

Cold R24C12

Velocity (in/sec)

Peak Force (lbs)

Production ACR Dampers - Rear - DSI

Time for a Pit StopThanks for your attentionQuestions?