@
Thorin Cain
Tyre Dynamics/Contact Patch
Why do different tyres have different levels of grip?
A tyres level of grip is determined by two factors:-
Tread Pattern/Surface area: This is the amount of rubber in contact with the road at any given moment. The more rubber touching the road, the more potential grip you have. This is determined by the tread pattern of the tyre which varies in GT6 in 3 categories:-
Comfort: Comfort tyres represent standard road tyres such as you would find on normal everyday cars. These have a tread pattern designed to allow for a multitude of driving conditions. There are deep lines and patterns cut into the surface that allow for good water dispersal as well as adequate grip on loose surfaces such as gravel or shallow mud. A down side of this is that the total surface area is reduced substantially, all those cuts and grooves are gaps where the tyre isn't touching the road and therefore not aiding traction.
Sports: Sports tyres represent the kind of tyre you would find on performance cars and road legal track cars. These have a tread pattern that is less deep and there is less pattern across the surface. This means that it will have a higher surface area because more rubber is touching the road at any given moment giving it higher potential traction. The downside is that the reduced pattern and depth means that they will have less grip on loose surfaces and a lower capacity for water dispersal.
Racing: Racing tyres represent what you would see fitted during a high level professional racing event. These tyres have almost no tread pattern and therefore offer the highest surface area and grip possible. As a downside they will not work on anything except perfect track conditions. The lack of tread means that water can not be adequately dispersed and the tyre will skate over the top of loose gravel and debris offering almost zero grip.
Compound: To illustrate this point I always find a water balloon to be the easiest to relate to example.
Imagine you have three balloons, one filled with water, one filled with flour and one filled with water and flour.
The one filled with flour represents a hard compound of rubber, if you poke it it will deform a little but you have to push fairly hard. If you stab it with a pin not much will happen.
The one filled with water represents a soft compound of tyre. It is very malleable an can be deformed easily but if you stab it with a pin it pops very easily.
The one filled with flour and water represents a medium tyre. It resists being deformed less than flour but more than water and if you stab it with a pin it will slowly drain out rather than explode.
Hard: A hard compound tyre is made from a stronger and less flexible compound of rubber. This means that it is very resistant to the abrasive nature of constantly being rubbed against the track and will have a longer potential lifespan. As a downside of the rubber being tougher and less flexible means it cannot deform to fit the road surface efficiently which will reduce the total surface area of the tyre.
Medium: A medium compound tyre is a compromise between the flexibility of the material and the resistance to abrasion. It will deform to fit the surface better than the hard compound and offer more total surface area but will also degrade degrade quicker through use giving it a shorter potential lifespan.
Soft: A soft compound tyre is focussed purely on performance and has a high level of deformation which gives it the highest total surface area and potential grip. The downside of this is that it will degrade far faster than the others giving it the shortest potential life span.
This combination of tyre pattern and compound gives a total surface area which we use to gauge how much traction a tyre has and from this we can determine how much total force a tyre can take before slipping.
Because a tyre is round, there is only a small amount of this total surface area in use at any time. The amount of this total surface area that we can use is determined by what is known as the contact patch.
What is a contact patch?
The tyres are quite obviously the only point of contact between the track surface and the vehicle you are driving. They are arguably the most important part of how a car accelerates, brake and steers, without them driving would be impossible. For this reason I believe that it is important to discuss what they do and how they do it.
The most important part of a tyre is what is known as the Contact Patch, this is quite simply where the rubber hits the road, the cars footprint so to speak. The contact patch describes the size and shape of this area, and this in turn dictates how hard you can accelerate, brake and turn.
The size of the contact patch is determined by a very simple equation:
Load/Tyre PSI = Contact patch area
Because PSI (tyre pressure) is one of the parameters of this equation and we have no option for altering this, we have to accept that we cannot manually alter the size of the contact patch.
We must also assume that when we change the weight of the car (Load) that the tyre pressure is automatically changed to keep the size of the contact patch constant for the style (Comfort/Sports/Racing) and compound (Hard/Med/Soft).
If we can't increase or decrease the size of the contact patch then what is the point of camber?
Well, we may not be able to alter the size of the contact patch but we can change the shape of it to better suit our needs and enhance our potential performance in various situations.
We use what is known as the “Circle of Traction” in conjunction with tyre data to show how the shape of the contact patch will affect our potential grip level when in motion.
Here we have a circular diagram that shows all of the forces encountered while driving using G-Forces as a measure.
As a simplified example, if we have a tyre that can take a maximum total force of 1.5 G before breaking traction and we are accelerating with a force of 1 G, this means we still have 0.5 G worth of grip to corner with before we start losing grip.
Lets imagine we have a car that can produce 0.8 G of acceleration when going from 0-60. Its currently using a hard tyre that can handle a total of 0.5 G, when we nail the accelerator we will get wheel spin because the force is exceeding the grip limit. Now we put a Soft tyre on that has a 1.0 G grip limit, when we nail the throttle this time the car grips immediately and accelerates at 0.8 G. We are getting maximum traction because we are operating within the tyres limits. If we attempt the same test again on the soft tyre but this time attempt to turn left or right while accelerating we will again experience wheel spin because we are adding force in the form of lateral G to the equation and exceeding the tyres limitations.
When we use camber we are changing the shape of our contact patch to best suit the forces acting upon the tyres, we cannot change the total amount of grip but we can change the percentage of that total grip that is available in a particular axis.
Lets now have a look at what camber is doing in order to achieve this.
Camber Theory
What is Camber?
Camber is, in its simplest form, the amount of lean a wheel has in relation to the vertical angle when viewed from the front or rear of the car.
In the image above we have a car displaying 0.0 camber, this means that when the car is at rest (no extra forces acting on the suspension) the wheels are aligned vertically at 90° to the road surface.
This car is showing what is known as negative camber. This means that the wheels are leaning in towards the body at the top and away at the bottom. This is the kind of camber we can set in GT6 using the tuning options.
Here we have a car displaying positive camber. This means that the bottom of the wheels lean in towards the body further than the tops. We cannot set positive camber in the tuning options but we do sometimes encounter it whilst driving.
Why do we use camber?
To simplify as much as possible, we use camber to alter the way the tyre contacts the ground to maximise its efficiency and grip during various phases of driving. There are a multitude of forces to consider so I will try to explain them as we go.
Here we see how the downward force of gravity is working on the tyres in various states of camber.
Here we see that the wheel is perpendicular (at 90°) to the road surface and the downward forces are acting equally across the face of the tyre. This gives us a contact patch that is wider than it is long.
If we take this contact patch and compare it with our circle of traction we will begin to understand which conditions this shape suits best.
In the diagram we see that the contact patch can take higher lateral (left/right) stresses but reduced linear (Accel/Decel) limits. This means that the car will have improved grip during hard cornering but reduced grip available for acceleration and braking. Ideally we want our tyres contact patch to be this shape near the apex of a corner. Conversely this shape is not ideally suited to straight line acceleration or braking where the linear forces are higher.
Here we see a negatively cambered wheel, it is leaning towards the inside edge so the downward forces are collecting on that side. If the wheel was positively cambered then the forces would be acting on the outside edge instead. The contact patch is now longer than it is wide, it is the same amount of surface area exhibited in a different shape.
If we consult our traction wheel again we will see where the strengths and weaknesses lie.
In the diagram we see that the contact patch can take higher linear (Accel/Decel) stresses but reduced lateral (left/right) limits. This means that the car will have improved grip during acceleration and braking but reduced amounts of cornering grip. Ideally we want our tyres contact patch to be this shape when we are accelerating down the straights or braking in a straight line.
By changing our camber settings in the tuning options we have changed the shape of our contact patch while the car is sat still in the garage, this is what is known as Static Camber.
Next we need to see how camber angle is changed when forces are applied to the car during what is known as Active Camber
What is Active Camber?
The term active camber basically describes the way that camber angle changes in relation to forces acting on the suspension and changing its geometry. It is important to remember that a suspension system is basically a bunch of frames attached to the chassis at fixed points that allow the wheels to move up and down independently.
Here we see a car with 0.0° of static camber. While the suspension is at rest in a neutrally loaded position defined by the ride height the wheels are parallel to the car body. The suspension mounting points (black dots) are fixed points and cannot move. The suspension arms (purple) can move in an arc around these mounting points but are solid so cannot extend or compress. The red thing is the spring/damper combo which can move in the same way as the suspension arms but can compress/extend when needed. The wheel mount (grey) works independently of the chassis but is connected by the suspension arms.
Here we see the same car being pushed into the ground by downward forces which are causing the springs/dampers to compress and the geometry of the suspension to change. Because of the way the suspension is designed the car gains negative camber during compression.
If we apply the opposite forces we see that the car has gained positive camber during suspension/damper extension.
Generally the amount of positive camber gained during extension is less than the amount of negative camber gained during compression due to the way the angles work. I will save the theories of suspension geometry for another day though.
During cornering the suspension can be simultaneously experiencing extension and compression on different sides of the car and both positive and negative camber as a result.
Here we see a car turning right which is causing compression on the outside (left) wheels and extension on the inside (right) wheels. The suspension is designed to keep both wheels in contact with the road as best as possible at all times.
Another thing we notice in the picture above is that the tyre is always directly below the car body in relation to the road. This is important because of the extra leverage forces gain during body roll.
What is body roll?
Body roll is a side effect of lateral (sideways) forces being changed into vertical (up and down) forces by the suspension during cornering. The weight distribution shifts across the car sideways and essentially makes one side heavier than the other.
As a rule, all force is lazy and always takes the shortest route between A – B, usually in the form of a straight line
As we can see above, when the car is level and stationary the downward force of gravity acts equally across the width of the car.
Here we can see a car turning right and encountering body roll. The body is leaning out over the tyre on the left hand side and because the forces are travelling straight down they are forming a leverage point which is helping to lift the inside wheel and reduce overall grip.
In real life this would usually result in a roll over if the cornering forces were high enough but in GT this would be more difficult to achieve, I think the gravity value is a little bit low in the physics engine. While the roll over might not be a risk in game, the resultant potential for grip loss is still a factor
How does camber affect body roll?
One of the effects of camber that is most visibly obvious is that it widens the track (axle width) or stance of the car. If the bottom of the wheel is sticking 1” further out with camber than it was at 0.0 then you have effectively widened the base of the car by 2” overall.
This means that the car would have to lean over even further in order to create the same negative leverage effect as before.
Now we can see that the wheels are directly underneath the downward forces which allows them to do a better job of opposing them. The weight is also pushing down on the tyre and forcing the contact patch of the tyre into the preferable wide/short pattern which is suited to cornering.
Will changing the track width of my car affect anything else?
This is a bit of a tricky one to explain as the physics involve a baffling amount of variables that vary from car to car. Some cars are wider at the front and some are wider at the rear by design for various reasons involving weight distribution and natural handling characteristics. It basically affects how a car will rotate.
I can only attempt to show you visually what I am talking about when discussing track width so you have some idea what is going on.
Here we see a few illustrations to show how track width affects a car visually, it basically means that one set of wheels is following a different path to the other. The effects of this are very complicated and there are a colosal amount of variables that could affect the outcome on different cars so I will not be discussing this in depth.
The most common theory is that the car should be wider at the driven wheels to promote stability and traction but this is not always true so don't take it as a fact. My advice would be to try it each way and see which feels better on you.
What are the major points to consider when tuning my car with camber?
Overall aim – We are aiming to use camber to get the best possible contact patch on the road at any given moment. We want it to be leaning on the inside edge of the tyre when travelling in a straight line and spreading the load when cornering to give us the most useful grip when we need it.
Camber angle – There is no such thing as a perfect angle for all cars and all conditions. Pick a sensible number in relation to the fitted tyres, set it equally at both ends of the car. Take the car for a few laps and see how it performs. Increase or decrease the numbers equally and try again, if it performs better then keep moving in that direction, if it feels worse then try the other way. Once you feel you've found the best number, try adjusting the front and rear independently and look for any improvements. Sometimes the best results will be with equal front and back, sometimes it will be better when they're at vastly different figures, it all depends how your car is setup and what you want it to do.
Tyres- Different types of tyres work better between certain values in the same way that springs do.
Comfort: Between 0.0 - 2.0
Sport: Between 1.0 -3.0
Racing: Between 2.0 - 4.0
Ride height - This setting may be called ride height but in this context it should be treated more like the amount of suspension travel. The higher the ride height, the more the suspension geometry will change and add negative camber during compression. The lower the ride height, the more constant the angles are.
Springs/Dampers/ARB - Much like the ride height, these settings will directly affect how much active camber is gained during compression by controlling the amount of movement in the suspension. As before stiffer settings will reduce the amount of geometry change and softer settings will increase it.
Toe angle – When we change the angle of a wheel in one axis we affect other settings that also rely on angles to perform. Toe angles may change in feel when camber is applied and may also need adjusting. My general thought would be to reduce toe angle as more camber is applied.
Track Surface: If the track you are racing on has banked/cambered corners then you may wish to run a little less camber than you would on a flat track in order to maintain your contact patch.
Rim Size - I'll only mention this briefly as I cannot confirm or deny if it is modelled in the game. The theory is that a the taller tyre sidewall that you would find on a standard size rim is more flexible and easier to deform than the shorter stiffer sidewall you would have on a +2” rim. Always worth checking when you are looking to put the finishing touch on your setup.
), With the Version 1.09 update arriving and bringing us some new physics changes for us to deal with. It's pretty clear that the following changes have brought with them some new variables for us to consider. 
) And I was reading about the relationship between camber and toe in maintaining or obtaining the right shape of contact patch during each phase of a corner. Once more I find that the idea makes a lot of sense but I was wondering if there are any general rules of thumb when adjusting these two settings to achieve the correct contact patch?
) now that Camber works, is what you have written into your guide relevant to gt6? Sorry I'm not trying to say anything bad about your guide. I want to use it, i just wanted to make sure that you think everything you wrote will work. because it looks like you wrote it prior to camber working
You've definitely earned a spot as a well respected tuner in my book.
I just want to be confident that if I do "blank" it will help the car do "blank". Call me lazy, but that was one of the things I liked about Hami's GT5 guide, he explained well and kept it easy for the simple folk like me!
PHUUTTUWIIEE i was afraid of that. Oh well, if its anything like the rest of your guide it will be easy to read and apply. So far all i understand is that you can increase camber with better tires. right? hehe
