Setting up Racing Tyres — a brief overview.
Since Pirelli took over Bridgestone as the official manufacturer for Formula 1 in 2011, a big part of their deal was to explicitly design their tyres with less durability (cliff edge) — to create a show.
This cliff is VERY DIFFICULT to manufacture — Pirelli use a steel belt construction, rather than kevlar, helping keep the tyre structure stable at peak loads of >5G, but steel is heavier and creates more heat.
The result is a very sensitive tyre.
In general, tyres consist of a carcass (internal) and surface.
Tyre surface and carcass temperatures are measured via a myriad of thermal imaging cameras. During free practise, it’s not uncommon for teams to bulk on extra sensors. (see below).
Tyres degrade in 2 ways:
- Thermal degradation
- Physical abrasion
Thermal degradation is thermal performance loss in the tyre, which results in under/overheating — deteriorating the compound.
Racing tyre compounds (soft, medium and hard) all are designed to give optimum life and grip within a specific temperature band, on a sliding scale. The life of the tyre is significantly affected by the way the compound is heat cycled during its break in. We often see this in qualifying, with drivers wanting to save a fresh set of softs for their final run — a used set would’ve been put through its heat cycle, giving less performance.
Physical abrasion is the actual wear of the tyre from running on the tarmac. Think a rubber eraser — after a while it gets smaller and deteriorates.
During the course of this season, Formula One visits 18 race tracks, each of which has its own distinctive surface. From the public roads of Monaco, to the dedicated motorsport surfaces of the permanent race tracks, each one has its trademark fingerprint.
Two main track factors determine the allocation of tyre compound for a circuit: the layout and the roughness of the track surface.
Bahrain is known for having an abrasive surface.
Run the tyre too long and the outcome will look similar to this:
These two factors are both usually linked. Inescapably, running the tyre too long causes the tread to wear down, reducing the distance between the carcass and the surface. This creates a temperature imbalance.
Blistering is when this temperature imbalance has a much hotter carcass, creating air bubbles beneath the surface. These bubbles explode, internal pieces of rubber rupture — leaving a hole. This is mainly due to too high tyre pressures, or other factors which heats up the tyre too quickly.
Graining is when the surface is too hot, resulting in pieces of rubber in the flex at the furface to build up and stick to the tyre. This is uusally caused due to unsufficient grip from the tyre, causing the driver to overdrive and ‘slip’ the front tyres too much.
The 2 main tabs to control the tyre and mitigate the aforementioned, are:
- Tyre Pressures
- Suspension Geometry
Tire orientation throughout a lap is a function of the suspension kinematics, so the trick for the engineers and drivers is to compromise on the best setup for the anticipated race conditions.
Tyre Orientation = f(suspension kinematics)
For simplicity, I will explain the following, all other things being equal.
Tyre Pressure (the easy one) — measured in psi
General rule: Go as low as you can. Pirelli mandate minimum pressures to reduce the likelihood of blowouts.
Greater pressure = more heat, less structural flex. The tyre can heat up quicker, but wont give in as much when you turn.
Lower pressure = less heat, more structural flex. Too much structural flex means less overall grip, they will deform more and place greater stresses on the shoulder join
Deflated tyres will initally have a greater contact patch, so it’ll hug the tyre like your favourite granny, but the downside is the additional hysteresis (delay in input to output).
Cornering at high speeds with too much hysterisis (delay) can cause a multiplier effect, as the tyre can scrub, generating additional heat — eventually losing grip.
Suspension Geometry
Camber Angles— when tyres are NOT perpendicular to the tarmac.
Camber (denotated in degrees) is the angle that which the tyre is standing, comapred to the vertical axis. It can be tilted inwards, or outwards.
Think those JDM cars with ridiculous wheel angles.
Negative camber is common in race cars to improve grip through corners, as it creates a camber thrust.
First, a quick physics lesson:
When accelerating at a green light, inertial forces push you back into your seat. The same intertial forces are applied to tyres.
When turning for a right hander, the weight transfer pushes you to the outside of the corner. This force is also transmitted to the tyres.
See below.
The tyre reacts to this inertial force with its own lateral force. This is the cornering force on the tyre, and it is centred towards the corner — we want to maximise this to increase grip.
You can now imagine how, when going through high speed corners, as the tyre deforms, a wider axle track will compensate this great load.
Negative camber attempts to optimise grip in corners by increasing the contact surface of the tyre, as the lateral forces and elasticity of the tyre cause it to deform and stretch.
0˚ camber = perfectly vertical wheels.
Increasing negative camber˚ generates more camber thrust, which increases cornering force, as the weight of the car can more easily lean on the outside of the tyre.
With all the benefits, too much camber means more scrub on the tyres. Remember, the tyres are not not aligned with the movement vector of the car, so the tyres will be slightly scrubbing on the straights. When extreme, this reduces traction and can cause slippage under braking, so everything is a compromise.
Still with me?
Toe — think penguin feet.
Similar to camber, whether it be toe out or toe in, you’re increasing the surface that will be dragging and scrubbing against the tarmac, as the rolling axis of the wheel is further misaligned from the movement vector of the car.
With cambers, we were dealing with cornering forces and reducing slip. Now with toe, we are discussing initial responsiveness when turning, not necessarily grip when at peak loads.
“Toe-in” and “toe-out” are important in setting up a car. Toe in is an adjustment of wheels where the distance from the centre of the left wheel to the centre of the right wheel is less at the front of the wheels than at the back of the wheels. A slight amount of toe-in is usually specified to keep the front wheels running parallel on the road by offsetting other forces that tend to spread the wheels apart. The major force is the backward thrust of the road against the tire tread while the vehicle is moving forward. Other factors include play in the tie-rod assembly and allowance for angular changes caused by wheel bounce or variations in road conditions. Toe out is obviously the opposite setting and is mostly unwanted. Both settings are measured in fractions of an inch or millimetres.
So why use toe?
It’s again all to do with the compromises in balance, and grip — usually reducing understeer, and managing oversteer.
It works like this. We know already that when the car goes through a corner, there are lateral forces which push the tyre to the outside, causing the tyre to deform. This is a lateral deflection of the tyre.
A general rule is that front wheel cars run toe out and rear wheel drive cars run a little toe in.
Now, regularly speaking, a racing car’s front wheels are set-up in such a way that they toe-out slightly, meaning they are pointing outward by a few milimeters to improve handling in the corners.
Thanks for reading, now enjoy some satisfying tyre scraping. Tyres are scraped at the end of each session to get accurate measurements of the tread wear. There are a number of holes across the face of the tread which they measure the height of.
