Handling Characteristics

Handling Characteristics

1. Road Isolation – ability of vehicle to absorb rough ride effects before transferred to passenger

compartment

· Solid axle – not good

· Independent – SLA good

· McPherson – modified good

· Tires = size, type, wear, damage, inflation

· Steering = relay rod – with non independent – not good

· Parallelogram linkage – good

· Rack and pinion - rubber bushings help

· Correct alignment angles

2. Directional stability – tendency of vehicle to maintain a straight path – little

· Uniform tire construction, especially same axle

3. Overall weight affects alignment

4. Proper alignment involves – caster, camber, SA1, Toe

5. Vehicle load – uneven distribution

6. Return ability – tendency of vehicle to go back to straight ahead

7. + Caster, SAI; tire pressure, overall

8. Tracking – independent path take by front and rear wheel

· Dog tracking – front/rear when not parallel to chassis

9. Cornering – how easily follows a curved path

· Alignment geometry

· Tire size, construction in

· Feedback – feel of load to drive for a sense of control

10. Tire tread life affected by – camber and toe

11. Centerline steering – straight or level steering wheel while traveling straight

12. Predictability – driver’s expectations of handling

· Sound suspension

CAMBER

· Inward/outward tilt at wheel top

· Preferred positive in front

Why? Weight will be placed inboard on spindle, will require more force to move weight.

Alterations to specs:

· Wide set tires will vary from manufacturers specs:

· More sensitive to camber – choice between ride comfort ability and tire wear

· Unusual tire wear at spec…

Side-to-side Camber – vehicle will pull to more positive side

· Vehicle load effects this

· More than .5 degrees difference in _____ will pull to most positive sides

· Add shims – move out, increase camber; other vehicles are opposite

· Upper control bushings – offset shaft will give 1 degree camber additional

Specifications			Actual Reading		Shim
Caster	Camber		Caster	Camber	A	B
3°	1/2°	¯	3°	0°	Add	Add
3°	1/2° ®	¯	2°	0°	Add	Same

More examples…

Specifications		Actual			Shim
Caster	Camber	Caster	Camber		A	B
3°	1/2°	3°	0°	¯	Add	Add
3°	1/2°	4°	0°	¬ ¯	---	Add
3°	1/2°	4°	1/2°	¬	Delete	Add

CANNOT TELL DIFFERENCE FROM DRIVER’S SEAT:

Shimmy – rapid toe change – shakes; caused by a dynamic imbalance (both halves of tire)

Wheel tramp – vertical movement of spindle (up + down) while driving

· Due to static imbalance

· Will try to “hop” on you

On a new car static balance is fine, needs dynamic after it has miles on it.

CAMBER

A car will tend to lead to the side with the most camber and least castor.

· Moderate tire wearing angle

- the wider the tire, more tire wear due to camber

- the more extreme camber, the more tire wear

· 2 reasons to have positive camber on SLA suspension

1. Loads up inner wheel bearing which is bigger

2. Road isolation – decreases leverage on spindle

· Side-to-side camber needs to be with 1/2 degree within each other

· SLA – will increase camber when you sit in driver’s side

· Tire wear – smooth – on outside shoulder

Why? Dissipates weight across the contact area so its not because of the weight

· Cone effect of Camber

1. Whichever way it leans, is the way it will go

2. Smaller diameter will take the most wear, because of a variety of diameters

CASTOR

· Must be within 1/2 degree of each other, side-to-side

· Non – tire wearing angle – “in the straight ahead position”

· PRO - Usually want to have a little positive castor, this gives stability and directional control

· Has capability of making a car lead one way or another

· With 9 degree castor – no stability – will never have 0 castor

· Positive castor – when turning left, the left side of body will raise up (this is an inside turn)

· Positive castor – tends to toe in the tires

· PRO - Positive castor – provides steering wheel return ability

- When you let go of steering wheel it will go back to straight

· Castor – will tend to pick up one side of car and lower the other when turning

· Car will lead to side with least castor

· Positive castor is normally around 2-3 degrees

· CON - Positive castor makes it harder to steer away from straight ahead position – not an issue in most cases because of power assist steering

· CON - High or extreme castor tends to promote high speed shimmy (rapid toe change)

· Steering dampener – absorbs shock of this effect

- If vehicle has a shimmy, check this

- Take 1 bolt off and push in, needs to have good resistance going in and out

Negative castor tends to wander – “chase cracks”

- PRO –Ease of low speed steering

Camber roll – caused by extreme castor, tilting of the tire during turning

· This wears tires on either side, same kind of wear caused by under inflation

· CON - Promotes camber roll

· When you turn right, leans to right – visa versa

TOE

· Extreme tire wearing angle

· Rub your hand one way, you will be smooth; other way, will feel sharp or rough edge

· When you feel sharp edge: SMOOTH IN, TOE IN

SMOOTH OUT, TOE OUT

Example: Technician rubs hand from outside, in and feels rough edge

- Too much, toe in

- The opposite tire should show similar wear

· Toe is critical on a newer tire

· Set to with an adjustable sleeve

· 2 things to be careful of when adjusting:

1. Don’t line up slot in clamp and the slot in sleeve

- Having offset makes a nice round clamping action

2. When done, must be able to rotate the whole unit

- Even to the tie rod ends

- Must have flexibility

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