Basics of Handling

8/6/2019 Basics of Handling

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HANDLING CHARACTERISTICS

Two general terms are used to describe the handling of a car: understeer and oversteer.

Understeer (AKA tight or push) occurs when the front wheels of the car lose tractionbefore the rear wheels. The car is difficult to turn and ³pushes´ toward the outside of a

turn. Oversteer (AKA loose) is the opposite condition. The rear tires lose traction before

the front tires. Hence, the rear of the car is ³loose.´ It slides toward the outside of the

turn, and the car feels like it is going to spin out.

The goal of suspension tuning is to make the car ³neutral,´ not oversteering or

understeering. When the car is neutral, you should be able to control what it does in aturn by using the throttle. Giving a burst of throttle should make the back of the car

slide toward the outside of the turn and allow the car to turn better. Getting off the

throttle should make the back of the car step back in line.

When the car is neutral, it is easier to control, creates less wear on the tires, and usuallyallows for faster lap times. I say usually because a slightly oversteering car can also

yield fast laps. However, this is difficult to achieve because the driver must react

instantly to the car sliding by counter-steering. If the reaction is not quick enough, thecar will slide sideways achieving a large yaw angle (the angle between the direction the

car is pointing and the direction it is actually moving). This will scrub off speed and mayeven cause you to spin out. Therefore, an oversteering car can be fast but only with a

skilled driver. On the other hand, an understeering car is limited by the grip of its front

tires on the racetrack. Even a skilled driver will not be able to clock fast laps with aseverely understeering car. Nonetheless, you may want to set up your car for slight

understeer to make it more stable and forgiving.

Static Weight: Front Bias andLeft Bias

The most fundamental way of changing the handling of your car is by redistributing the weight. The weight distributionof a car is determined by literally placing a scale under each wheel. When making weight

distribution adjustments, you must consider the weight transitions that the carexperiences while you are driving. For example, when you accelerate, weight shifts

toward the back of the car onto the rear wheels. When you turn right, weight shifts tothe left side of the car. You can feel these weight transfers on your body while you are

driving.

The most useful weight adjustment for road racing is front bias, or the weight

distribution between the front and rear wheels. The purpose of adjusting front bias is tobalance the weight of the car evenly between the front and rear wheels while the car is

turning. If the front tires have more weight on them while turning, then they will have to

exert more force on the racetrack than the rear tires to keep from sliding. The samegoes for the rear tires. This can be seen from basic physics:

F = ma = (m * v^2) / R

F = Forcem = mass

a = acceleration

v = velocity

R = radius

It can be determined that the acceleration of an object of mass ³m´ traveling around acircle of radius ³R´ with a velocity ³v´ is v^2/R, and the force necessary to stay on the



circular path with this velocity is just the object¶s mass multiplied by that acceleration.Let¶s assume that your car has more weight on the front tires than on the rear tires.Looking at the formula above, we can see that mass is the only thing that changes theforce that the tires must exert since velocity and radius are essentially identical for the

front and rear of the car. Therefore, since the front has more mass, the front tires willhave to provide more force than the rear tires to keep from sliding. Eventually, the front

tires will begin to slip before the rear tires, which is the definition of understeer.

Making the weight on the front tires and the rear tires equal in a turn does notnecessarily mean that the weight distribution should be 50/50 (50% front, 50% rear)

while the car is standing still. The type of track you plan to drive on determines the ideal

weight distribution. If the track requires getting on the throttle early in the turns, thenweight will be transferred to the rear of the car while you are in the turn. Therefore, you

should add weight to the front of the car to offset the weight transfer when you get on

the throttle.

Instead of using a 50/50 distribution, you might want to try 55/45. The front of the carwill be heavier than the rear when the car is standing still, but when you accelerate in a

turn, weight will shift to the rear and balance the car. If you are driving on a track with

short, sharp turns, then you will probably be getting on the throttle late in the turn.

Therefore, you want a more even weight distribution to start out with (possibly 51/49)so that the weight will be evenly distributed as you drive through the turn.

Generally, if you are driving on a road coarse with approximately the same number of left and right turns, front bias should be the only weight adjustment that you work with.

However, there are two other adjustments that can improve handling if you will be

racing on an oval or a track with predominantly right or left turns: left weight bias andcross weight. Left bias is adding weight to the left side of the car so that it will be

balanced in left turns. The same can be done for right turns.

Cross Weight

Cross weight (AKA wedge) is slightly more complicated. Front bias and left bias

adjustments are made by actually moving components of the car around to try toachieve the desired weight distribution (e.g. moving the battery to the left side of the

car). Cross weight is adjusted by lowering or raising the upper spring perches on eachcorner of the car to raise or lower that corner.

To understand how cross weight works, imagine a car that is perfectly level with the

ground (equal ride height at each corner). If you raise the left rear corner (increase

cross weight), that corner now carries more weight because it is sticking up. In addition,the car is leaning towards the right front (trying to compress the right front spring) so

that corner is holding more weight than it did when the car was level. The left rear and

right front hold more of the weight of the car than the right rear and left front.

If you lower the left rear corner of the car, then the left front and right rear corners are

sticking up more than the left rear. Therefore, the left front and right rear hold more of the weight while there is less weight on the left rear. Since the left rear corner is

lowered, the car leans in that direction, which also takes weight off of the right front tire.In summary, by lowering the left rear (decreasing cross weight), the weight on the left

front and right rear increases, and the weight on the right front and left rear decreases.

Cross weight is usually measured as a percentage of the total weight of the car. Take thefollowing weight distribution as an example:



Left front: 750 lbs. Right front: 700 lbs.

Left rear: 700 lbs. Right rear: 750 lbs.

The cross weight is simply the left rear/right front (diagonal) weight divided by the total

weight of the car and multiplied by 100 to make it a percentage. In this case, the cross

weight is:

[ (2 * 700) / (2 * 700 + 2 * 750) ] * 100 = 48.3 %

Cross weight will not change left bias or front bias weight distribution. Using the example

above, you can see that front bias is 50% ((750+700)/(750+700)), and left bias is also50%. Assume you decrease cross weight to 46.6 % with the following settings:

Left front: 775 lbs. Right front: 675 lbs.

Left rear: 675 lbs. Right rear: 775 lbs.

The front bias and left bias are both still 50%.

Decreasing cross weight adds oversteer to the car in left turns. The front tires grip better

since the left front starts out with more weight than the right front. In the turn, weighttransfers from the left front to the right front, which balan ces the front of the car and

maximizes grip. On the other hand, the rear of the car is not balanced in a turn. The

right rear holds much more weight than the left rear. Therefore, the rear tires do notgrip as well as the front tires, which creates oversteer. With the same kind of reasoning,

you can see why increasing cross weight creates understeer.

Cross weight is usually difficult and time consuming to adjust on a street car even if youhave installed aftermarket suspension components such as coilovers. Unless you are

building a pure race car for oval tracks, you don¶t have to worry about cross weightadjustments. Remember that the weight distribution of your car, particularly front bias,

is the most fundamental characteristic that affects how your car handles. Keep in mindthat the weight of the driver affects weight bias. Placing parts on the right side of the car

will help balance the weight of the driver on the left side.

Tires

The tire you use is one of the most important suspension tuning choices you will make in

building and racing your car. Even a car with a professionally-tuned suspension will not

be able to clock fast laps or handle well on a poor quality or inappropriate set of tires.

The major performance factors to consider when choosing tires are compound, contact

patch, and sidewall height.

A softer compound tire will have more grip but will wear out quickly while a harder

compound tire will have less grip but will last for a relatively long time. Your choice of

compound is mainly affected by the type of racing you plan to do and your budget. For

serious racing, you will need a soft compound tire to be competitive. If you plan to do

mostly street driving and/or do not have the money to frequently replace tires, go with a

harder compound.



The second factor to consider is tire contact patch, or the area where the tire makes

contact with the ground. You want the biggest contact patch that you can get. When

more of the tire is in contact with the ground, the tire can exert more force and allow

your car to achieve higher cornering speeds.

The contact patch is determined by the width of the tire and the tread pattern that is on

the tire. (Usually the width provided in the tire specifications is the overall width of thetire, not the width of the actual part of the tire that touches the ground. However, some

manufacturers will provide the actual width of the contact patch, which should be slightly

smaller than the overall width of the tire.) If the tire has very little tread, the contact

patch will be larger (since there are fewer gaps on the tire surface for the tread), and the

tire will have more grip. A tire with no tread, used only for racing, is called a slick. Slicks

will maximize your car¶s cornering ability but are illegal and dangerous on the street. As

a rule of thumb, if you plan to drive on the street, use a tire with at least three vertical

treads.

You can use your choice of tire width to change the handling characteristics of your car.

For instance, if your car tends to understeer, you can increase the width of the front tires

to improve front grip. Also, if your engine produces substantial power, you should try tomaximize the width of the drive wheels to make sure you can get the power to the

ground.

The third factor to consider when choosing a tire is sidewall height. A tall sidewall flexes

more than a shorter one. Therefore, a short sidewall tire will provide a more precise

steering feel than a tire with a tall sidewall, but using a taller sidewall makes the car feel

more forgiving and less twitchy. Also, a short sidewall tire makes the ride harsh on the

street.

Tire pressure can be adjusted to change the handling

characteristics of your car. By increasing tire pressure,

you cause the tire profile to become more round, whichdecreases the size of the contact patch. You also cause

the spring rate at that corner of the car to increase since

you are making the tire harder and, therefore, ³bouncier´

by filling it with more air. Both of these results take away

grip from the tire. If you increase front tire pressure, the

car will become tighter, and if you increase rear tire

pressure, the car will be looser.

Lowering tire pressure causes the tire to sag, which

increases the size of the contact patch. In addition, it

decreases the effective spring rate at that corner of the

car and makes the tire rise in temperature. The additional rolling drag (or friction)produced by the sagging of the tire is responsible for the temperature change. These

factors provide the tire with more grip. If you decrease pressure in the front tires, the

car becomes looser, and if you decrease pressure in the rear tires, the car becomes

tighter. The temperature increase may be desired if it will allow the tire to heat up to

recommended operating temperature. However, overheating the tire can lead to loss of

grip, ³chunking´ (large pieces of rubber tearing off the tire), and generally faster tire

wear. Before making any tire pressure adjustments, find out the recommended minimum

and maximum pressures for your tire from the manufacturer.

Tire Profile with High Tire Pressure

(Left) and Low Tire Pressure (Right)

Enlarge



CamberCamber is probably the most useful and popular alignment adjustment that can be made

to a street car. The other alignment adjustments are toe and caster. Camber is the angle

of the wheel from the vertical as viewed from the front or the back of the car. Negative

camber means that the top of the wheel is leaned in towards the car, and positive

camber means that the top of the wheel is leaned out away from the car.

Maximum cornering force is achieved when the camber of the outside wheels relative to

the ground is about -0.5 degrees. A slight negative camber in a turn maximizes the tire

contact patch due to the way the tire deforms under lateral load. Hence, it is good to

have some negative camber to increase cornering force.

Another reason why it is helpful to align your suspension with a slight negative camber isthat camber will change with suspension travel and body roll. Most suspension systems

are designed so that camber increases with more suspension travel. However, camber

relative to the car's chassis is not the same thing as camber relative to the ground. It is

camber relative to the ground that affects handling. Therefore, even though camber

relative to the chassis is made to increase, camber relative to the ground may actually

decrease on the outside wheels if there is substantial body roll. To counter this tendency,

it is important to use negative camber and to control

body roll.

The only drawback to negative camber is increased wear

on the inside of each tire. Since the top of the wheel is

leaned in, the car is riding on the inside of the tire while itis on straightaways. In a corner, suspension travel and

lateral forces on the tire¶s rubber compound combine to

straighten the tire relative to the ground. Therefore, the

car rides evenly on the tire in turns, which improves

cornering ability. However, extra time spent driving on

the inside of the tire causes that part of the tire to heat

up and wear. This effect is small if you avoid adding too

much negative camber.

On most street cars, camber is not easily adjustable. However, if you choose to purchase

aftermarket camber plates, you can set camber to improve handling. More negative

camber tends to increase tire grip in corners. Therefore, if your car experiencesundersteer, you can decrease front camber (make it more negative) to improve front

grip or increase rear camber (make it more positive) to decrease rear grip. Remember

not to add too much negative or positive camber since it will decrease the life of your

tires and may cause a blowout. Even pure race cars rarely use more than about 3

degrees of camber.

Example of Negative Camber

(Front View)

Enlarge



Toe

Toe is an alignment parameter

that describes how the front

wheels are oriented with respect to each other and how the rear wheels are oriented

with respect to each other. With the steering wheel centered, if the front wheels are

pointing toward each other (from a top view), they have "toe-in" or are ³toed-in´. If they

are pointing away from each other, they are said to have "toe-out" or be ³toed-out´. Thesame definitions apply for the rear wheels. Toe can be measured as an angle between

the perfectly straight position of a wheel and its position after toe is adjusted. Toe can

also be determined by finding the difference between the distance separating the front

edges of the wheels and the distance separating the rear edges of the wheels. More

distance between the front edges than the rear edges is toe-out. More distance between

the rear edges than the front edges is toe-in.

Toe is used to change the way a car behaves on corner entry. The more toe-in you have

on a pair of wheels, the harder it is to make those wheels turn into a corner. The more

toe-out you use, the easier it is to get that pair of wheels to turn into a corner.

Why does this happen? Let's take an example where a car with toe-in on the frontwheels is about to enter a left turn. The driver begins to turn the wheel left. Now, the

left-front tire is pointing only slightly to the left while the right -front tire is pointing much

more to the left. The problem with this is that the left-front tire needs to turn with a

greater angle than the right-front tire because the left-front tire is on the inside of the

corner and, therefore, must trace an arc with a smaller radius than the outside tire.

However, with toe-in, the left-front tire is actually trying to trace a larger radius arc than

the right-front tire. It is difficult to make the car turn because the left-front tire is

fighting the right-front. When the car is already in the turn, weight transfers to the right-

front tire and diminishes the effect of the left-front tire. Because of this weight transfer,

toe mainly affects corner entry.

With toe-out, the inside tire in a corner turns with a greater angle than the outside tire(as it should). This improves the grip of the front tires on corner entry.

In addition to corner-entry handling, toe affects straight-line stability. Toe-in improves

stability while toe-out worsens stability. This can be explained through the same

reasoning as was used to describe corner-entry handling. Toe-out encourages turn-in

since the inside tire turns at a greater angle than the outside. Hence, the car is sensitive

to the slightest steering input. Toe-out will make the car wander on the straightaways

requiring corrective steering. The car will always be turning unless the steering is

perfectly centered. With toe-in, the inside tire fights the outside since the inside is trying

to trace a larger radius arc than the outside. As a result, toe-in discourages turn-in and

makes the car less sensitive to steering input. In other words, it is more stable.

Let's consider an example of the straight-line stability concept. Assume you have toe-out

on the rear wheels. You are traveling in a straight line when your right -rear tire hits a

small bump. It gets pushed back slightly by the impact, and it is now pointing more to

the right than the left-rear tire. Therefore, the back of the car turns to the right until the

right rear suspension comes back to its original position. The same thing can occur with

the front wheels. In fact, the effect on the front suspension is even worse because the

right-front wheel getting pushed back, for instance, will also turn the left -front wheel to

the right.



Rear toe is usually only adjusted on front-wheel drive cars or rear wheel drive cars with

independent rear suspensions. I wanted to include this example ju st to show that rear

toe can be adjusted just like front toe on many cars. With a front-wheel drive car, it is

sometimes helpful to add some rear toe-out to decrease the stability of the rear tires

and counter the understeer inherent in front-wheel drive cars. For a rear-wheel drive car

with independent rear suspension, the torque produced on the rear suspension when you

step on the throttle tends to pull the rear wheels forward on the suspension pivots. Thiscreates toe-in. To counter this effect, you can toe-out the rear wheels so they will

become straight when you step on the throttle. I do not recommend this since rear toe-

out in a rear-wheel drive car can cause severe oversteer. Instead of using toe-out, install

aftermarket bushings and suspension links to keep the suspension from getting pulled

forward under hard acceleration.

As you may have expected, toe increases tire wear because the tires are fighting each

other and, therefore, scrubbing along the ground. Toe-in tends to increase tire wear on

the outside edges of the tires. Toe-out tends to increase tire wear on the inside edges of

the tires. Make sure that you consider your camber setting when adding toe-out. If you

are using negative camber, you are already wearing the inside of the tires more than

normal. The combination of excessive negative camber and toe-out can quickly wear theinside of a tire and cause it to fail.

Springs

Springs, together with anti-roll bars, have a significant effect on the feel of a car and its

responsiveness to steering input. Increasing spring rate at a particular corner of the car

transfers more weight to that corner making it slide more. Hence, if your car is

understeering, you can either decrease front spring rate or increase rear spring rate to

correct the condition. You can increase front spring rate and decrease rear spring rate tocorrect oversteer.

Installing lowering springs on your car can provide a substantial improvement in

handling. The center of gravity of the car will be lower, which will allow the four tires to

stay more evenly planted to the ground. Lowering a car is more involved than just

installing shorter springs. It is usually necessary to readjust the camber on the front and

possible the rear suspension since it will change when the car is lowered. Generally, a

car should have a full alignment after lowering the suspension. Although lowering a car

will usually improve handling, lowering it too much will not allow for enough suspension

travel, or stroke. The car may bottom out on the suspension (suspension reaches full

travel) or the chassis may actually hit the ground, leading to loss of traction and possible

damage to the underside of your car.

When lowering a car, you must consider what type of driving conditions the car will see

and what spring rates are appropriate for you. If you significantly lower the car, you will

need stiff springs to limit the suspension travel and prevent bottoming out. Also, if you

plan to race on bumpy surfaces or do mostly street driving, I recommend avoiding a

suspension setup with very small travel. You need a fair amount of suspension travel to

absorb bumps. If you make your suspension too stiff because you have very little

suspension travel, then small bumps will tend to lift the wheels off the ground instead of



being absorbed by the suspension. If the car bottoms out, it will experience a sudden

loss in traction that can easily lead to a spinout or crash. Therefore, on bumpy tracks,

use softer springs and greater ride height to improve handling and avoid bottoming ou t.

Anti-Roll Bars

By providing a link between the left and right side suspension, an anti -roll bar (AKA sway

bar) keeps the left and right side of the suspension at nearly the same level vertically,

decreasing body roll. Larger diameter sway bars make the suspension stiffer and transfer

more weight to the end of the car where they are installed. If the car is understeering,

you can increase rear sway bar diameter or decrease front sway bar diameter to restore

balance. To correct oversteer with sway bars, it is necessary to install either a smaller

rear bar or a larger front bar. Most sway bars have adjustable links that can be used to

effectively increase or decrease the stiffness of the sway bar without buying a new one.

Anti-roll bars should be chosen to match your springs. If you are planning on installing

stiff springs, there is no need for a large diameter sway bar. The combination of stiff

springs and small sway bars is enough to control body roll. Large diameter sway bars are

necessary if you will be using relatively soft springs. This is a popular configuration since

the ride is not overly harsh, but the suspension is still stiff and body roll is reduced due

to the sway bars.

Soft springs with large sway bars and stiff springs with small sway bars accomplish

virtually the same goal of providing a stable suspension and reducing excessive weight

transfer. A stiff springs/small sway bars setup is generally better than soft springs/large

sway bars because stiff springs reduce front-to-back weight transfer. With soft springs,

side-to-side weight transfer is controlled by the sway bars, but there is a fair amount of

front-to-back weight transfer due to the soft springs. In other words, using soft springs

can result in brake dive and acceleration squat, which are detrimental to overall

handling.

Shocks

Shocks (AKA shock absorbers or dampers) are the most useful tool for adjusting corner

entry and corner exit handling characteristics of a street car. They are easily accessible

on most cars, and aftermarket shocks are usually adjustable in many ways. Shocks are

necessary to dampen, or gradually reduce, the bouncing of the springs on the car.

Without them, the suspension would oscillate up and down for an extended period of time after running over a bump or experiencing weight transfer.

There are two settings that determine the way a damper behaves: compression and

rebound. Compression is the shock¶s resistance to being pushed in, and rebound is the

shocks resistance to being extended. When the car accelerates, weight is transferred to

the rear, which results in the front wheels trying to lift off the ground and the rear

wheels pushing harder into the ground. The front shocks are being extended while the

rear shocks are getting compressed. Hence, during acceleration, the car is mainly



affected by front rebound and rear compression. The opposite is true for deceleration.

During deceleration, handling is affected by front compression and rear rebound.

So how do you use this information to adjust your car? First, you need to take note of

what your car is doing on corner entry and exit. Shocks can be used to change the way a

car handles going into a corner without noticeably affecting how it handles in the center

or coming off the corner. This ability to change a specific characteristic about a car¶shandling is what makes shocks so useful and important in suspension tuning. If your car

is understeering on corner entry, you need to decrease front compression or increase

rear rebound. If it is over steering on corner entry, increase front compression or

decrease rear rebound. The rest of the adjustments are shown in the Reference Chart.

Basics of Handling

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