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Thread: A list of suspension setup actions and results.

  1. #1
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    Default A list of suspension setup actions and results.

    Found this at drifting.com when looking for camber numbers. A useful guide. Tell me if you want me to make this sticky (always shown in the list of posts)

    /Magnus F.


    Front spring rate increase:
    More under steer; increase in proportional weight transfer to the front when rear wheel rate is not increased; reduces front traction when rear rate is not changed.
    Usable adjustment: 150-600 lbs/in
    Symptoms of too much adjustment: terminal under steer; front of car hops in corners; excessive wheel spin on inside front tire on FF cars.

    Front spring rate decrease:
    Less under steer; decreases proportional weight transfer to the front when rear wheel rate is not increased; increases front traction when rear rate is not changed.
    Usable adjustment: 150-600 lbs/in
    Symptoms of to much adjustment: Too much over steer; over steer then under steer if spring is so soft that the car bottoms out on lean, car bottoms out excessively with a jolting ride.

    Rear spring rate increase:
    More over steer; increase in proportional weight transfer to the rear when front wheel rate is not increased; increases rear traction when front rate is not changed.
    Usable range: 100-600 lbs/in
    Symptoms of too much adjustment: too much over steer; sidestep hop in corners; twitchy; pretty scary.

    Rear spring rate decrease:
    Less over steer: decreases proportional weight transfer to the rear when front wheel rate is not changed; increases rear traction when front rate is not changed
    Usable range: 100-600 lbs/in
    Symptoms of too much adjustment: car under steers; if way to soft car under steers then over steers as car bottoms out on lean; car bottoms out excessively with a jolting ride.

    Front anti-roll bar stiffer: more under steer
    Usable range: none to 1.25 inches in diameter
    Symptoms of to much adjustment: terminal under steer; lifts inside front tire off the ground witch can cause massive wheel spin on FF cars; also not good for most effective tire usage as inside tire is now doing nothing.

    Front anti-roll bar softer: less under steer
    Usable range: none to 1.25 inches in diameter
    Symptoms of to much adjustment: overstate scary; more like fun

    Rear anti-roll bar stiffer: more over steer
    Usable range: none to 1 inch in diameter
    Symptoms of too much adjustment: Big-time over steer. Can cause inside rear tire to lift off the ground.

    Rear anti-roll bar softer: less over steer
    Usable range: none to 1 inch in diameter
    Symptoms of to much adjustment: under steer; slow and boring

    Front tire pressure higher: less under steer by reducing slip angels on most tires
    Usable adjustment: up to 55psi hot
    Symptoms of too much adjustment: no traction- tire crowned so more under steer; adds wheel spin in FF cars; jarring ride; center of tire wears out

    Front tire pressure lower: more under steer by increasing slip angles on most tires
    Usable adjustment: not less then 20psi
    Symptoms of too much adjustment: edges of tire wear quickly because tire is folding over; feels mushy; tires chunk because low pressure means heat build up.

    Rear tire pressure higher: less over steer by reducing slip angles on most tires
    Usable range: up to 45psi hot
    Symptoms of too much adjustment: no traction—tire is crowned so more over steer; bad wheel spin on FR cars; jarring ride; center of tire wears out.

    Rear tire pressure lower: more over steer by incresing slip angles on most tires.
    Usable range: not less then 20psi
    Symptoms of too much adjustment: edges of tire wear quickly because tire is folding over; feels mushy; tires chunk because low pressure means heat build up

    More negative camber front: less under steer because of better lateral traction as tread is flatter on the ground under side load.
    Usable range: up to 3.5 degrees negative
    Symptoms of too much adjustment: poor braking; car is road crown sensitive; twitchy; front tires wear on inside edge

    More negative camber rear
    : less over steer because of better lateral traction as tread is flatter on the ground under side load. More rear grip
    Usable range: up to 2.5 degrees negative
    Symptoms of too much adjustment: more over steer; car feels twitchy in back; tires wear out on inside edge; less breakaway warning when limit is exceeded.

    Ride height to low (typical beginner mistake): car is twitchy with unpredictable dynamics. Bump steer make you life miserable.
    Usable range: usually 1.5-2.0 inches lower then stock unless car has been modified to go lower.
    Symptoms of too much adjustment: everything that could possibly go wrong: sudden over/under steer; twitchy due to bump steer; very harsh ride; premature tire wear.

    Toe in – front: car is stable going straight. Turn in is average
    Usable range: 0-1/8th inch
    Symptoms of too much adjustment: car has slow twitchiness under braking; feels odd; kills outside edge of tires

    Toe out – front: Car turns in well; works pretty well on FF car as they tend to toe-in under load.
    Usable range: 0-1/4 inch
    Symptoms of too much adjustment: Car is really twitchy under braking; car wanders on straight road; kills inside edge of tire

    Toe in – rear:
    car is less likely to over steer when the throttle is lifted
    Usable range: 0-1/8th inch
    Symptoms of too much adjustment: weird, slow, rocking movement in back; feels slow but still unstable; wears outside edge of tires.

    Toe out – rear:
    Helps car rotate useful in low speed and slalom courses; very common on FF pro rally cars.
    Usable range: 0-1/8th inch
    Symptoms of too much adjustment: not to good for street driving; causes lift throttle over steer; makes violent side to side rocking motions in the rear; tie wears on inside more.

    Positive front caster:
    helps stability; suspension will get more negative camber when turning; reducing positive caster reduces steering effort. (Negative caster is not usable)
    Usable range: 4-9 degrees positive
    Symptoms of too much adjustment: can increase under steer especially in cars with wide low-profile tires. Can increase steering effort.

    Single adjustable shock stiffer
    : Better turn in; better transient response; causes slower onset of over/under steer by slowing weight transfer depending on what end of the car is adjusted.
    Symptoms of too much adjustment: suspension becomes unresponsive; ride gets harsh; car skips over bumps, loosing traction; Causes a big delay in weight transfer resulting in strange handling like under steer then late corner stage over steer.

    Single adjustable shock softer: slower transient response; quicker onset of over/under steer
    Symptoms of too much adjustment: car oscillates due to under dampened spring motion, like a boat. Car gets twitchy in turns. Feels unstable.

  2. #2
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    Thanks Magnus. If anyone is interested in this topic, Carroll Smith's book "tune to win" is a well known reference source and worth the investment.

  3. #3
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    Here's some more info which I learned in the context of open wheel. I follow the same approach for Caterham. If someone knows better please advise.

    Order of setting up car:
    1. Ride height. Rake for Caterhams should be about 15 mm (ie. rear 15 mm higher than front). Front lower a-arms should be parallel to ground.
    2. Camber. Aim for 3 degrees for track days.
    3. Toe. Zero to 1/8" toe in at front, zero toe at rear. (Also check rear wheels for alignment in chassis using string method.)
    4. Caster (front only) - recheck camber at each change. Caterham says 4.5 degrees give or take.
    5. Bump Steer (front only).
    6. Recheck toe.
    7. Corner weights. Be sure to set tires at operating pressure and disconnect sway bars. Driver, fuel and all other payloads must be in the car or you are wasting your time.
    Finally, tire pressures for slicks and sticky track tires should be in the 15 - 20 psi range when COLD. The reference to 45psi in your notes is obviously for street sedans and perhaps Fedex delivery trucks. A caterham would be like an ice skate with that much pressure.

  4. #4
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    Sep 2003
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    Lower A arms parallel to the ground only applies to those A arms that have the ball joint built in. For the earlier cars with trunnions, the steering arms should be parallel to the ground.

    Wayne

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