Suspension Tuning (Forza Motorsports Style) –
I found this when reading up on how to tune my cars in Forza Motorsport 2. The game is extremely realistic so all of the information applies in real life as well. Its a great read and does a very good job of explaining things in a way that is easy to understand...
Welcome to the LAB.
The intent of the article is give you the knowledge to set about tuning within Forza motorsport 2.
Therefore I will be writing the articles in the same manner as the tuning options in the game.
1. Tires
2. Gearbox
3. Alignments
4. Suspension A
5. Suspension B
6. Aero
7. Brakes
8. Differentials
I will be trying to make the explanations simple enough for a novice to follow but detailed enough to give some relatively experienced people a better understanding.
1. TIRES
Race Tire Pressures
Race tire air pressures are often viewed as confusing and contradictory information. The truth is that air pressures and the measurement of the same is a simple, safe and sane science. The disinformation is usually the culprit here as there is no chicanery or track-side voo-doo involved. The air pressures used in most roadrace paddocks are usually the result of what works on what track, where and why.
How does tire pressure affect my tires?
Tire pressure affects the contact patch; it also affects the way the tire corners. Together, these affect the manner in which the tire grips.
How will this afftect my traction?
Sure, the bigger your contact patch is, the better the tire will grip on a dry day. but too low of a pressure could result in the car being unstable, or “squirrelly” in a corner. Going to high with our air pressure will give a smaller contact patch. You must maintain the delicate balance between all these factors working in harmony; contact patch, stability, ride and grip. Get all those right then you are ready for your next topic.
Tire temperature
Tire temperature is affected by:
1. The construction and compound of the tire
2. Your car and suspension set-up
3. Your style of driving
4. Your top speed and lap time
5. Your cold pre-race starting pressures
6. Your attitude and expertise
How should I set my tire pressure?
Start with the recommended pressure. If you feel like you need to alter the setting from what was recommended, use a plus or minus setting of only 1-2 pounds. Avoid any major setting increases or decreases as that will only muddle your original setting reference point. Any major setting change (anything above or below five pounds of air) would indicate a failure to have dialed in your suspension. Grip is more finite while all your chassis components can be adjusted more easily.
Speedways
Speedway air pressures are higher than other tracks to counter heat-related decomposition of the tires and the tremendous centrifugal forces slamming the same tire.
Road courses
Road courses are where you can more fully utilize all of the tire; however, the tire is less likely to heat to proper consistency of adhesion quickly. Road courses with their wide expansive sweepers and slow corners will allow more frequent adjustment of the pressures.
To put things into a nutshell though. Follow this simple guide.
2. Gearbox (Transmission)
Gearbox settings ….. WOW. So your looking to set your gearboxes up for racing generally or for a specific circuit.
Ok well for this section lets forget all the techi mumbo jumbo as most people will get lost thinking out aerodynamic drag, driveline loss, ratio this, ratio that, weight, RPM limits, BHP, Torque, engine map characteristics, wheel diameter, wheel width……. etc.
So I am going to try and make this as simple as possible.
First we need to talk about long and short. Long and Short. WHAT!
Long and short are generally the terms we us to describe a gearbox’s characteristics, and no I don’t mean the physical size.
A Long Gearbox. (wide ratio)
A wide-ratio transmission requires the engine to operate over a greater speed range, but requires less shifting and allows a wider range of output speeds.
A Short Gearbox (close ratio)
A close-ratio type of transmission is designed to allow an engine to remain in a relatively narrow operating speed
Final Drive.
So what is the final drive ratio! The Final Drive Ratio shows you how many times the engine turns for one complete turn of the tires. This Final Drive number is also your torque multiplier when in that gear. The final drive can have a significant effect on how your gearbox works Long or Short!
Drag it left. The gearbox becomes longer i.e. the space between gears gets wider. SO what does that mean. That’s right the operational speed of the gear becomes longer increasing the maximum speed both in gear and top speed. That said it also reduces the cars acceleration.
Drag it right. The gearbox becomes shorter i.e. the space between gears gets closer. SO what does that mean. That’s right the operational speed of the gear becomes shorter decreasing the maximum speed both in gear and top speed. That said it will increases the cars acceleration.
Individual gears.
Now we are getting really technical.
Essentially the same principles to the individual gears as they do to the final drive.
So to repeat
Drag it left. The gear becomes longer i.e. the gear is lengthened meaning operational speed of the gear becomes longer increasing the maximum speed both in gear and top speed. That said it also reduces the cars acceleration.
Drag it right. The gear becomes shorter i.e. the gear is shortened meaning operational speed of the gear becomes shorter decreasing the maximum speed both in gear and top speed. That said it would increase the cars acceleration.
Now this adjusting the individual gears of a transmission can make or brake a car so be very careful
3. Alignments
Camber, Caster and Toe by john hagerman
The three major alignment parameters on a car are toe, camber, and caster. Most enthusiasts have a good understanding of what these settings are and what they involve, but many may not know why a particular setting is called for, or how it affects performance. Let's take a quick look at this basic aspect of suspension tuning.
UNDERSTANDING TOE
When a pair of wheels is set so that their leading edges are pointed slightly towards each other, the wheel pair is said to have toe-in. If the leading edges point away from each other, the pair is said to have toe-out. The amount of toe can be expressed in degrees as the angle to which the wheels are out of parallel, or more commonly, as the difference between the track widths as measured at the leading and trailing edges of the tires or wheels. Toe settings affect three major areas of performance: tire wear, straight-line stability and corner entry handling characteristics.
For minimum tire wear and power loss, the wheels on a given axle of a car should point directly ahead when the car is running in a straight line. Excessive toe-in or toe-out causes the tires to scrub, since they are always turned relative to the direction of travel. Too much toe-in causes accelerated wear at the outboard edges of the tires, while too much toe-out causes wear at the inboard edges.
So if minimum tire wear and power loss are achieved with zero toe, why have any toe angles at all? The answer is that toe settings have a major impact on directional stability. The illustrations at right show the mechanisms involved. With the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect each other. Under this condition, the wheels are at odds with each other, and no turn results.
When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If it's a minor disturbance, the disturbed wheel will steer only a small amount, perhaps so that it's rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still don't describe a turn. The wheels have absorbed the irregularity without significantly changing the direction of the vehicle. In this way, toe-in enhances straight-line stability.
If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.
With toe-in (left) a deflection of the suspension does not cause the wheels to initiate a turn as with toe-out (right).
The toe setting on a particular car becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted by toe-out. Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. So street cars are generally set up with toe-in, while race cars are often set up with toe-out.
With four-wheel independent suspension, the toe must also be set at the rear of the car. Toe settings at the rear have essentially the same effect on wear, directional stability and turn-in as they do on the front. However, it is rare to set up a rear-drive race car toed out in the rear, since doing so causes excessive oversteer, particularly when power is applied. Front-wheel-drive race cars, on the other hand, are often set up with a bit of toe-out, as this induces a bit of oversteer to counteract the greater tendency of front-wheel-drive cars to understeer.
Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This is another reason why many front-drivers are set up with toe-out in the front. Likewise, when pushed down the road, a non-driven wheel will tend to toe itself out. This is most noticeable in rear-drive cars.
The amount of toe-in or toe-out dialled into a given car is dependent on the compliance of the suspension and the desired handling characteristics. To improve ride quality, street cars are equipped with relatively soft rubber bushings at their suspension links, and thus the links move a fair amount when they are loaded. Race cars, in contrast, are fitted with steel spherical bearings or very hard urethane, metal or plastic bushings to provide optimum rigidity and control of suspension links. Thus, a street car requires a greater static toe-in than does a race car, so as to avoid the condition wherein bushing compliance allows the wheels to assume a toe-out condition.
It should be noted that in recent years, designers have been using bushing compliance in street cars to their advantage. To maximize transient response, it is desirable to use a little toe-in at the rear to hasten the generation of slip angles and thus cornering forces in the rear tires. By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system.
THE EFFECTS OF CASTER
Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.
Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The mechanism that causes this tendency is clearly illustrated by the castering front wheels of a shopping cart (above). The steering axis of a shopping cart wheel is set forward of where the wheel contacts the ground. As the cart is pushed forward, the steering axis pulls the wheel along, and since the wheel drags along the ground, it falls directly in line behind the steering axis. The force that causes the wheel to follow the steering axis is proportional to the distance between the steering axis and the wheel-to-ground contact patch-the greater the distance, the greater the force. This distance is referred to as "trail."
Due to many design considerations, it is desirable to have the steering axis of a car's wheel right at the wheel hub. If the steering axis were to be set vertical with this layout, the axis would be coincident with the tire contact patch. The trail would be zero, and no castering would be generated. The wheel would be essentially free to spin about the patch (actually, the tire itself generates a bit of a castering effect due to a phenomenon known as "pneumatic trail," but this effect is much smaller than that created by mechanical castering, so we'll ignore it here). Fortunately, it is possible to create castering by tilting the steering axis in the positive direction. With such an arrangement, the steering axis intersects the ground at a point in front of the tire contact patch, and thus the same effect as seen in the shopping cart casters is achieved.
The tilted steering axis has another important effect on suspension geometry. Since the wheel rotates about a tilted axis, the wheel gains camber as it is turned. This effect is best visualized by imagining the unrealistically extreme case where the steering axis would be horizontal-as the steering wheel is turned, the road wheel would simply change camber rather than direction. This effect causes the outside wheel in a turn to gain negative camber, while the inside wheel gains positive camber. These camber changes are generally favorable for cornering, although it is possible to overdo it.
Most cars are not particularly sensitive to caster settings. Nevertheless, it is important to ensure that the caster is the same on both sides of the car to avoid the tendency to pull to one side. While greater caster angles serve to improve straight-line stability, they also cause an increase in steering effort. Three to five degrees of positive caster is the typical range of settings, with lower angles being used on heavier vehicles to keep the steering effort reasonable.
Like a shopping cart wheel (left) the trail created by the castering of the steering axis pulls the wheels in line.
WHAT IS CAMBER?
Camber is the angle of the wheel relative to vertical, as viewed from the front or the rear of the car. If the wheel leans in towards the chassis, it has negative camber; if it leans away from the car, it has positive camber (see next page). The cornering force that a tire can develop is highly dependent on its angle relative to the road surface, and so wheel camber has a major effect on the road holding of a car. It's interesting to note that a tire develops its maximum cornering force at a small negative camber angle, typically around neg. 1/2 degree. This fact is due to the contribution of camber thrust, which is an additional lateral force generated by elastic deformation as the tread rubber pulls through the tire/road interface (the contact patch).
To optimize a tire's performance in a corner, it's the job of the suspension designer to assume that the tire is always operating at a slightly negative camber angle. This can be a very difficult task, since, as the chassis rolls in a corner, the suspension must deflect vertically some distance. Since the wheel is connected to the chassis by several links which must rotate to allow for the wheel deflection, the wheel can be subject to large camber changes as the suspension moves up and down. For this reason, the more the wheel must deflect from its static position, the more difficult it is to maintain an ideal camber angle. Thus, the relatively large wheel travel and soft roll stiffness needed to provide a smooth ride in passenger cars presents a difficult design challenge, while the small wheel travel and high roll stiffness inherent in racing cars reduces the engineer's headaches.
It's important to draw the distinction between camber relative to the road, and camber relative to the chassis. To maintain the ideal camber relative to the road, the suspension must be designed so that wheel camber relative to the chassis becomes increasingly negative as the suspension deflects upward. The illustration on the bottom of page 46 shows why this is so. If the suspension were designed so as to maintain no camber change relative to the chassis, then body roll would induce positive camber of the wheel relative to the road. Thus, to negate the effect of body roll, the suspension must be designed so that it pulls in the top of the wheel (i.e., gains negative camber) as it is deflected upwards.
While maintaining the ideal camber angle throughout the suspension travel assures that the tire is operating at peak efficiency, designers often configure the front suspensions of passenger cars so that the wheels gain positive camber as they are deflected upward. The purpose of such a design is to reduce the cornering power of the front end relative to the rear end, so that the car will understeer in steadily greater amounts up to the limit of adhesion. Understeer is inherently a much safer and more stable condition than oversteer, and thus is preferable for cars intended for the public.
Since most independent suspensions are designed so that the camber varies as the wheel moves up and down relative to the chassis, the camber angle that we set when we align the car is not typically what is seen when the car is in a corner. Nevertheless, it's really the only reference we have to make camber adjustments. For competition, it's necessary to set the camber under the static condition, test the car, then alter the static setting in the direction that is indicated by the test results.
The best way to determine the proper camber for competition is to measure the temperature profile across the tire tread immediately after completing some hot laps. In general, it's desirable to have the inboard edge of the tire slightly hotter than the outboard edge. However, it's far more important to ensure that the tire is up to its proper operating temperature than it is to have an "ideal" temperature profile. Thus, it may be advantageous to run extra negative camber to work the tires up to temperature.
Positive camber: The bottoms of the wheels are closer together than the tops.
Negative camber: The tops of the wheels are closer together than the bottoms.
4. Suspension A
Spring weights – Tuning TIPS
Spring Rate is the amount of weight needed to compress a spring a certain . Springs are rated in LB/in (in metric system kg/mm), or specifically, how many pounds of weight are required to depress the spring by one inch. To convert LB/in to kg/mm international, you must divide divide figure by 56.
Consider you have 2 springs having different spring rates: One with 345 g/mm and the other with 480 g/mm. So what does it mean?
It means the 1st spring will compress 1 mm if you put a load of 345 grams, while the 2nd one will not. The 2nd one will need a 480 g. load to compress 1 mm. According to this, we can say that the 2nd spring is harder than the 1st one, or we can state that:
Springs that have a low Spring Rate are soft, while springs that have a high Spring Rate are stiffer.
If there are 2 different values listed, it means that the spring starts at one rate, and ends at another rate under full compression.
For example: a 10lb to 25lb progressive spring will need 10lb to compress it the first inch, then 13lb the next inch, and so on, until the end of the travel; it will take 25lb to compress it the last inch. The benefit of this is that the spring can be soft enough at the start of the travel to offer a soft ride yet be stiff enough at the end of the travel to performance well during hard braking and turning.
What Affects the Spring Rate?
There are 3 things that affect the spring rate:
1. Diameter of the wire: Diameter of the wire itself affects the spring rate because when diameter of the wire increases it gets stronger, meaning a wire which is harder to compress. So, if we know that a wire becomes harder when its diameter increases, we can say that:
When wire diameter increases, spring rate increases.
When a suspension does not gain camber during deflection, this causes a severe positive camber condition when the car leans during cornering. This can cause funky handling.
Fight the funk: A suspension that gains camber during deflection will compensate for body roll. Tuning dynamic camber angles is one of the black arts of suspension tuning.
2. Diameter of the spring: That is in fact 'the mean diameter of the spring', achieved by subtracting the diameter of the wire from diameter of the spring:
The overall outside diameter of the spring (mm) - diameter of the wire (mm)
When diameter of the suspension spring increases, the spring rate decreases.
3. Number of Active Coils (length / height of the coil spring): Determination of the active coil number varies according to spring design. Total coil number -2 for springs with both ends closed. Count the total coils -1 for springs with one end closed and one end open.
As the number of active coil decrease, the spring rate increases.
Normal Springs has a fixed spring rate.
Step Linear Springs are springs which have 2 different spring rates.
Progressive Springs have a variable spring rate.
Ride height – F1 Technologies.
The importance of ride height
"Ride height" is essentially the distance between the base of the car and the ground. By adjusting suspension and aerodynamic characteristics correctly, it is possible to get a very low ride height. Why is this desirable though?
Why have a low ride height?
Having a low ride height is desirable for a number of reasons. Obviously, lowering the car in any way lowers the centre of gravity. A low centre of gravity is important because it helps to make the car pitch and roll less.
The main reason for a low ride height however, is for aerodynamic reasons. Lowering the ride height increases a car's downforce without any significant increase in drag. Cars are normally set up to have the front ride height of the car (measured at the front axle) lower than the rear ride height of the car (measured from the rear axle). This relationship is known as "rake". There is an optimum rake at which cars run though and there is a point beyond which any extra reduction in ride height may actually increase drag and promote lift.
Assuming a car's ride height is set up correctly, how does this generate downforce?
Basically, the low clearance of the car causes the air travelling under the car to speed up (and go faster than the air travelling above the car). The total pressure at any point in an air stream is the sum of the static pressure plus the dynamic pressure. The faster moving air under the car means its total pressure comprises of a larger dynamic pressure component, resulting in a smaller static pressure component to keep the total pressure the same. The air travelling over the car however, has less dynamic pressure and more static pressure. This static pressure difference means there is an overall downward force on the car - downforce. This principle is much the same as that which dictates how wings can be used to generate downforce, only in the case of a wing it is the aerofoil geometry which results in the pressure difference across the upper and lower surfaces.
Setting ride height
Setting up a car's ride height seems like an easy enough task, but it certainly isn't. Ride heights are measured while the car is stationary and they'll invariably change once the car is out on the track doing some reasonable speed. Downforce, pitch, roll, suspension stiffness and other factors will cause the real distance between the bottom of the car and the ground to change from the measured ride height.
One way to make sure the "moving ride height" remains close to the stationary, measured ride height, is to run extremely stiff suspension. This is not always desirable as the car will often be too nimble for the drivers and tyre wear will be high.
Running softer suspension is not really the answer either, as if the suspension is too soft and the ride height is too low, the car is going to "bottom out". Not only will this slow the car down,
A compromise between stiff and soft suspension has to be made.
Glossary
Roll - The angle between the car's body and a longitudinal axis. Roll is caused by centrifugal forces and "uneven" track surfaces.
Pitch - The angle between the car's body and a transverse axis. Pitch is caused by the car's accelleration or decelleration. It is most noticeable under heavy braking, with the car tending to angle forward. The diagram shows a car pitching due to acceleration (exaggerated).
5. Suspension B (by Neil Roberts)
We will discuss the damper adjustments which can be used to change the behavior of the car in each phase of a corner. We will begin by defining each phase of a corner and apply some
sensible simplifications, then list the relative damper adjustments
available to produce the desired handling change.
For the purposes of this discussion, we will assume the racing surface
to be perfectly flat, smooth, and uniform. So, all damper velocities
will be relatively low, assuming a smooth driving technique. We will
assume a simple road course setup, with no asymmetric adjustments.
The damper velocities and travel directions resulting from each
cornering phase affect the distribution of load among the four tires.
This change in load distribution changes the cornering balance. We will
focus primarily on the effects of diagonal weight transfer due to
damper forces and the resultant change in cornering balance.
CORNERING PHASE DEFINITIONS
PHASE 1: Increasing braking + increasing steering
This phase is the first part of a fast decreasing radius turn. This
phase will not occur at all if maximum braking is achieved before
turning in. Since weight is being transferred both forward and outboard,
the outside front damper moves in the bump direction. Also, the inside
rear damper moves in rebound. The other two dampers do not move as much
or as rapidly, so their effects are minimal. For our purposes, we will
consider the inside front and outside rear dampers to have a fixed
position during phase 1.
PHASE 2: Decreasing braking + increasing steering
This is the turn in phase of a slow corner. This phase may or may not
occur depending on the type of turn and driving technique. Weight is
being transferred outboard and aft, so the outboard rear damper moves
in bump and the inside front damper moves in rebound. The other two
dampers are considered to be stationary.
PHASE 3A: Increasing steering at constant throttle
This phase can be a course correction, a slalom turn in, or a turn
entry taken at full throttle. Weight is being transferred outboard, so
both outside dampers travel in bump and both inside dampers travel in rebound.
PHASE 3B: Decreasing steering at constant throttle
This is the opposite of phase 3A. During a slalom, this phase occurs
while the steering is changing away from the current cornering
direction. As soon as the lateral acceleration passes through zero, the
car reverts to phase 3A. This is part of why so many spins occur in slaloms.
PHASE 4: Decreasing steering + increasing throttle (or decreasing braking)
This is the apex-to-exit phase. Weight is being transferred inboard and
aft, so the outside front moves in rebound and the inside rear moves in
bump. The other two dampers are considered stationary.
EFFECTS OF DAMPER INDUCED WEIGHT TRANSFER
At all times, cornering balance is affected by the distribution of load
between the two front tires. Because the efficiency of a tire decreases
with increasing load, a larger difference in load between the two front
tires increases understeer. Also, a smaller difference decreases
understeer. The same concept applies to the two rear tires.
To illustrate the effect of damper adjustments, consider a phase 3A
flat out turn entry. If the front dampers are adjusted to increase
either bump or rebound damping, more weight will be transferred across
the front tires during entry. The same result occurs if the rear
dampers are adjusted to decrease either bump or rebound damping. This
increased front load transfer increases understeer during turn in, just
as a larger anti-roll bar increases understeer in steady statecornering.
The same increase in understeer results from diagonal weight transfer
from the inside rear to the outside front. The fact that the two
diagonally opposite dampers move in opposite directions allows us to
modify cornering balance with damper adjustments.
Note that we are only considering longitudinal weight transfer if
accompanied by steering change. Longitudinal weight transfer without
steering change moves both front and both rear dampers in the same
direction at the same speed, so damper adjustments cannot change the
diagonal weight distribution. Obviously, longitudinal weight transfer
affects cornering balance. But, since the dampers cannot affect balance
unless accompanied by roll, we will ignore this effect for damper tuning.
The following table presents the damper adjustments available to modify
the cornering balance in each phase. Each entry lists the phase, the
damper travel directions, the desired change, and the damper
adjustments available to produce that change. "+" indicates stiffer damping
"-" indicates softer damping. IF is inside front, OF is outside front.
PHASE
DIRECTIONS
More UNDERSTEER
More OVERSTEER
Phase 1 entry
OF bump
F bump +
F bump -
OR rebound
R rebound -
R rebound +
Phase 2 entry
IF rebound
F rebound +
F rebound -
OR bump
R bump -
R bump +
Phase 3A entry
OF&OR bump
F bump +
F bump -
IF&IR rebound
F rebound +
F rebound -
R bump -
R bump +
R rebound -
R rebound +
Phase 3B exit
OF&OR rebound
F bump -
F bump +
IF&IR bump
F rebound -
F rebound +
R bump +
R bump -
R rebound +
R rebound -
Phase 4 exit
OF rebound
F rebound -
F rebound +
IR bump
R bump +
R bump -
As you can see, none of the available adjustments affect only one
cornering phase. This is where the balancing act begins. Notice that
the same adjustments that increase phase 2 entry understeer also
increase phase 4 exit oversteer. Compromise is necessary even in the
case of a constant speed slalom.
It is worthwhile to spend some time studying the table to figure out
how to fix more than one balance problem at the same time. For example,
consider a car that has phase 1 oversteer, phase 2 understeer, and
phase 4 understeer. Can this combination of problems be corrected by
damper adjustments alone?
Careful, focused analysis of the behavior of the car during each phase
is necessary to begin real damper tuning. Then, the correct decisions
must be made concerning which phase(s) are most important and require
damper adjustments to improve cornering balance. The adjustments made
will alter performance in other phases, so the magnitudes of damper
adjustments must be selected accordingly.
As you can imagine, it is rather difficult to accurately remember the
balance of the car in each cornering phase for each corner of the
track. This process can be assisted considerably by an in-car video
camera and/or a data acquisition system.
A truly optimum damper setup is only possible with highly developed
active dampers. The optimum compromise with conventional racing dampers
is difficult to determine. This should not deter us from trying.
The restriction to symmetric damper adjustments is the source of many
of the required compromises. If you have followed the discussion to
this point, you can work out for yourself the amazing cornucopia of
damper adjustments available to oval track tuners. If a particular road
course features all or most of the important corners in the same
direction, asymmetric adjustments can be used to fine tune the setup to
that track.
6. Downforce – Wikapidia
The term downforce describes the downward pressure created by the aerodynamic characteristics of a car that allows it to travel faster through a corner by increasing the pressure between the contact area of the tire and the road surface, thus creating more grip.
Fundamental principals
The same principle that allows an airplane to rise off the ground by creating lift under its wings is used in reverse to apply force that presses the race car against the surface of the track. This effect is referred to as "aerodynamic grip" and is distinguished from "mechanical grip," which is a function of the car mass repartition, tires and suspension. The creation of downforce by passive devices can only be achieved at the cost of increased aerodynamic drag (or friction), and the optimum setup is always a compromise between the two. The aerodynamic setup for a car can vary considerably between race tracks, depending on the length of the straights and the types of corners; some drivers also make different choices on setup. Because it is a function of the flow of air over and under the car, and because aerodynamic forces increase with the square of velocity, downforce increases with the square of the car's speed and requires a certain minimum speed in order to produce a significant effect. But some cars have had rather unstable aerodynamics, such that a minor change in angle of attack or height of the vehicle (for example, caused by a bump on the track or slipstreaming over a crest) has caused the car to experience lift, not downforce, sometimes with disastrous consequences
Two primary components of a racing car can be used to create downforce when the car is travelling at racing speed:
- the shape of the body, and
- the use of airfoils.
Most racing formulae have a ban on aerodynamic devices that can be adjusted during a race, except at pit stops.
The body
The rounded and tapered shape of the top of the car is designed to slice through the air and minimize wind resistance. Detailed pieces of bodywork on top of the car can be added to allow a smooth flow of air to reach the downforce-creating elements (i.e., wings or spoilers, and underbody tunnels). The underside of the body is similar in shape to an inverted wing and creates an area of low pressure between the car and the track, pressing the car to the road. This is sometimes called a ground effect and has been the subject of many rule changes over the years in different racing series.
Airfoils
The amount of downforce created by the wings or spoilers on a car is dependent primarily on two things:
- The shape, including surface area, aspect ratio and cross-section of the device, and
- The device's orientation (or angle of attack).
A larger surface area creates greater downforce and greater drag (also known as air resistance). The aspect ratio is the width of the airfoil divided by its depth. The aspect ratio formula is written like AR=b squarded/s, where AR=aspect ratio, b=spand squared, and s=wing area. Also, a greater angle of attack (or tilt) of the wing or spoiler, creates more downforce, which puts more pressure on the rear wheels and more drag.
Front
The function of the airfoils at the front of the car is twofold. They create downforce that enhances the grip of the front tires, while also optimizing (or minimizing disturbance to) the flow of air to the rest of the car. The front wings on an open-wheeled car undergo constant modification as data is gathered from race to race, and are customized for every characteristic of a particular circuit (see top photos). In most series, the wings are even designed for adjustment during the race itself when the car is serviced.
Rear
The flow of air at the rear of the car is affected by the front wings, front wheels, mirrors, driver's helmet, side pods and exhaust. This causes the rear wing to be less aerodynamically efficient than the front wing, Yet, because it must generate more than twice as much downforce as the front wings in order to maintain the handling to balance the car, the rear wing typically has a much larger aspect ratio, and often uses two or more elements to compound the amount of downforce created (see photo at left). Like the front wings, each of these elements can often be adjusted when the car is serviced, before or even during a race, and are the object of constant attention and modification.
Brakes
Brake Bias 101
By Dan Wagner (As seen in Circle Track magazine)
Understanding your brakes will not only help make your car safer; it can also help improve your lap times. Correct brake bias will help you maximize the braking force available from your car, allowing you to brake harder, deeper and more confidently.
Safety First
Proper brakes are one of the most important safety features on you race car. There are plenty of ways to reduce the cost of racing, your brakes are not one of them! No car should ever race without separate brake systems for the front and rear, period.
Separate systems are easily achieved using either dual master cylinders or a production style tandem master cylinder. Tandem master cylinders use one cylinder bore with two pressure ports and pistons. They are designed so that if pressure is lost in either port, the other port maintains its pressure. Dual master cylinder set-ups completely isolate the two hydraulic systems. However you choose to do it, dual brake systems will still provide braking from one system even if the other one completely loses pressure.
Bias Defined
What exactly is brake bias and how will it help you? Brake Bias is just a fancy way to describe how the total braking force is distributed between the front and rear tires.
Many factors affect the amount of braking force a tire can generate. The most important one is the force (weight, downforce, etc) pushing the tire against the ground (see sidebar on friction). As your car decelerates, weight is transferred from the rear to the front tires. This weight transfer reduces the amount of braking force the rear tires can produce. Apply too much braking to the rear wheels and they will lock up causing the rear end to lose traction and possibly swing around violently.
For most of us, losing traction on the rear end is one of the last things we want to have happen. However, some people actually use the knowledge of this principle to their advantage. Rally drivers use quick applications of the parking brakes to turn tighter corners. How many of us haven't used the parking brakes to spin "doughnuts" in a freshly snow covered parking lot? For now though, we will concentrate on getting the maximum braking force from all four of our tires without losing control.
Losing traction on the front tires is not as bad as on the rear. You usually plow forward in in the original direction until the driver lightens up enough on the pedal to regain control. As a general rule, 60% of your braking capacity should be on the front tires. Whatever the percentage is for your particular car, the front tires should lock up slightly before the rear tires.
Overview of the Braking System
Braking force is applied to the brake pedal. The force is multiplied by the pedal output ratio (typically three to four) and the power brakes if present. The output force from the pedal is transferred to the master cylinder(s), either directly or through a balance bar. As the master cylinders' piston moves forward, the fluid pressure rises until the force applied to the face of the piston equals the force from the balance bar assembly. The fluid pressure is then applied to the face of the calipers' pistons causing the calipers to squeeze the pads on the brake rotors.
We will be talking a lot about torque and pressure. So, let's make sure we are all talking about the same thing.
Torque
Torque is a twisting force caused by the multiplication of a force by a lever arm. Torque is usually expressed as inch-pounds (in-Ibs) or foot-pounds (ft-Ibs). The inch or feet refer to the lever arm length and pounds are a measure of force. For a given torque, the shorter the lever the larger the force and the longer the lever the smaller the force.
TORQUE = FORCE x LENGTHRemember when you were a kid trying to use your dads' hammer? If you tried to hold the hammer at the end of the handle it kept twisting out of control. So, you ended up holding the hammer close to the head. What you really did was shorten the lever arm thereby reducing the torque. Now that you're hands are stronger, you hold the hammer the correct way to maximize the force on the nail due to the increased torque.
There is another example of torque that we all have experienced one time or another. It seems there is always at least one bolt that you just can't twist loose. You put a pipe over your good ratchet and easily twist the bolt (or your only socket). Why did the bolt turn more easily? You increased your "leverage" by using a longer lever arm. The torque increased while the force you supplied stayed about the same. Remember that torque is force times a distance.
Pressure
Pressure is force spread over a given area. It is typically expressed in pounds per square inch (psi). Pounds for force and square inches for the area. As a force is spread over a larger area, the pressure goes down. If a force is concentrated on a smaller area, the pressure goes up.
PRESSURE = FORCE / AREAAirplanes provide some great examples of pressure. Airlines want sturdy strong floors that don't weigh too much. Interestingly, the biggest problem they have is usually not heavy people but ladies with stiletto heels. Heavier people tend to wear shoes that spread their weight over their feet reducing any localized pressure. Even with a lighter woman wearing stiletto heels, the smaller force concentrated over a such a small area can cause enough pressure to puncture the floorboard.
Pressure applied over an area results in a force. Just a few psi pressure difference applied to the wing of a 747 can lift it into the air. Remember, pressure is force over an area and pressure applied to an area results in force.
Now that we have those definitions out of the way, let's examine each of the components that make up the braking system individually. This along with the use of the computer spreadsheet included at the end of the article, will help you understand how each component affects the overall system.
Brake Pedal
The brake pedal multiplies and transfers your force to the master cylinder(s) either directly or through a balance bar. A typical brake pedal will increase your force three or four times. If you run power brakes, the power booster is between the pedal and master cylinder(s). The booster provides another multiplication of your force on the pedal.
Balance Bar
A balance bar (also called a bias bar) on dual master cylinder systems, divides the force from the brake pedal to the two master cylinders. It is called a "balance bar" because that is exactly what it does. The torque on one side of the bar must balance the torque on the other side of the bar. Remember that a force applied over a distance causes torque. Therefore, the master cylinder closer to the pivot point on the bar has a shorter lever arm and will receive a higher braking force.
Balancing bars take force from one side and give it to the other.
Brake Proportioning Valve
Brake proportioning valves on tandem master cylinder systems act much like a balancing bar on dual master cylinder systems. The proportioning valve is usually used in the rear brake line. It can reduce the pressure by 0 to 50% (typically). Proportioning valves only reduce the pressure in one system unlike balance bars that take from one side and give to the other
Master Cylinders
The size of the master cylinders' piston has a direct result on brake fluid pressure. However, it may not work like you would think... higher line pressure will build up on a smaller master cylinder piston to react the force applied by the pedal. A smaller master cylinder will create more brake fluid pressure but will also increase brake pedal travel. The smaller diameter cylinder requires a longer stroke to move the volume of fluid necessary to move the caliper pistons during braking.
Larger master cylinders will create less pressure but will require less travel.
Calipers
Greater piston area on the calipers, whether by using larger pistons or more of them, will cause greater squeezing force on the rotor. More caliper piston area also increases master cylinder movement. Different brake pad compounds will affect the friction developed between the pads and the rotor Larger brake pads will not significantly increase braking capacity but can improve wear, lower temperatures etc.
Brake Rotors
A larger rotor has a bigger lever arm increasing brake torque on a wheel. Smaller diameter rotors will reduce brake torque. Ventilated rotors will not significantly increase brake torque but do improve cooling.
Tires
The rotor diameter and the amount of squeeze from the caliper determine brake torque on a wheel assembly. The torque caused by the friction forces developed between the tire and the ground must balance the torque from the brakes or slipping will occur. The result is that a larger diameter tire (bigger lever arm) will actually have less braking force where the tire meets the pavement.
I'm sure that last statement will ruffle a few feathers. Please bear with me on this one. Many things (including contact patch size, tire compound, temperature, etc) will affect the amount of traction available from a tire. More traction means more torque will be required from the brakes to lock up the tire. Bigger (diameter) tires will require bigger brakes. It is all about torque.
Originally Posted by s14unimog
