At Silverstone (as in Barcelona and at Paul Ricard), Pirelli brought a special thinner
tread version of their tyres after testing suggested the new surfaces at these tracks
might cause overheating problems.
The head of F1 at Pirelli, Mario Isola, said that testing showed them the new tarmac at
the Circuit di Catalunya ‘has [in the tyres] a lot of grip, low wear and low degradation.’
This allowed for much faster lap times but caused temperatures in the tyres to skyrocket.
Pirelli’s solution was to shave 0.4 mm of rubber from the treat of the tyres they brought
to Spain, France and Britain.
But how did this work?
First let’s look at how tyres heat up in the first place.
To remind you: tread is the rubber part around the outside of the tyre - the part that contacts
the surface of the track.
It’s a few centimetres thick and sits above the belt and the rest of the inner body of
the tyre.
The rubber interacts with the track in two main ways:
Firstly through braking and acceleration: driving the car’s energy into the track
to change the speed of the car.
Secondly in a lateral direction when cornering, absorbing incredible forces to allow the cars
to change direction so quickly.
Now, as you know, tyre tread is made of rubber - a soft synthetic rubber that deforms very
easily at optimum working temperatures.
In the direction of travel, the rubber deforms in a spiral direction, with the inside of
the tyre pulling the rotation of the tyres such that that inside of the tyre drives the
outside.
When changing direction, the rubber is pulled and stretched across the body of the tyre
at the point the rubber contacts the track surface, and is then released as the tyre
rotates that part of the rubber away from the contact patch.
It’s this stretching and releasing of the rubber that causes the treat to heat up dramatically.
See rubber is made of long molecule chains called polymers which act sort of like springs.
When in a relaxed state, these chains are all bundled and twisted up together.
When we stretch the rubber, by deforming it as discussed through driving and cornering,
a certain amount of energy goes into stretching these chains out.
As rubber is elastic, when we stop putting this stretching force into the rubber it springs
back to its relaxed, tangled, resting shape.
But in both the act of stretching the molecule chain out and in releasing it again (which
is what’s happening when we load and unload the tyre), some of the energy is lost into
the rubber as heat due to the internal friction of the molecules.
This heat spreads through the tyre, through the rubber tread and can cause accelerated
degradation or blistering.
See, the energy the tyres absorb in accelerating and turning the cars has to go somewhere.
The three main places energy is transferred to are:
In deforming the rubber In degrading the tyre
Into heat, or thermal energy What Pirelli found was that their tyre compounds,
when put to work on the newly laid tarmac, were not wearing very quickly despite the
huge amounts of grip being provided to the tyre.
Huge grip means huge energy being put through the tyre and this means more heat being allowed
to build up and build up as the tyre went on longer and longer stints without problem.
Excessive heat build up leads to thermal degradation or blistering.
Thermal degradation is just the chemical nature of the rubber changing due to high energies
allowing the breaking down of the long molecule chains within the rubber tread
Blistering occurs when pockets of very high temperatures occur within the rubber and cause
a local expansion of air or molten rubber, which rips the tread apart from the inside
causing large chunks to break loose.
Experts in the field will tell you that holes in your tyre tread are less than ideal.
So how does shaving the tyre tread down a little help this?
Well we can use a classic tool - a ruler and the edge of a desk - to illustrate how this
works.
If you hold a long length of ruler over a desk and twang it, you’ll see it gets a
proper wobble on.
Shorten that length, however, and its wobble is also cut down to size.
Such as it is with tyre rubber.
Trimming the thickness of the tread a bit gives the tyres a bit less flexibility.
This means the rubber is being stretched and distorted less, which means a bit less heat
build up and slightly shorter stint life.
As in - the slow wear rate will have less rubber to wear through, forcing an earlier
pit stop and less time building up the heat.
This worked so well that even Ferrari, who initially saw the thinner treaded tyres as
a pro-Mercedes move, admitted the shaved tyres were the right call after trying both in Barcelona.
And in Austria this year we saw blistering rear its head again, even after last year’s
race was disrupted by blistering tyres.
Drivers like Lewis Hamilton questioned why the Austrian Grand Prix didn’t get the slim
tyres as it was clear that blistering was a known risk.
So it was clear that these thin tyres were a solution that worked well, without debate.
Pirelli have shown no sign that the shaved tyres will return in 2018, but looking at
the bigger picture, there does seem to be a sense of Pirelli behaving in a very reactive
way, trying to be everything to everyone instead of driving a clear, well-constructed mission
through their tyre philosophy.
But that’s a topic for another day!