As the Formula One season returns to Europe for round eight at the Valencia street circuit, it's another debut for Pirelli.

For the first time the new medium tyre will be seen in competition, having been tested by all the teams during free practice in Canada. The medium tyre, used as the prime compound in Valencia this weekend, is distinguished by white markings so is known as the PZero White.

At the Spanish street circuit, the tyres will face one the hardest workouts of the year on a track with more corners than anywhere else on the Formula One calendar. We take a look at some of the most important ones...

The 3.367 mile circuit takes in 25 corners, as well as four straights where the cars reach nearly 190 mph. Turn 2 is taken at relatively low speed with reduced aerodynamic downforce. The grip comes mainly from the tyre, which manages to generate adhesion through steering and traction. The new medium tyre provides increased grip as well as durability, which is absolutely crucial at this point to prevent understeer. The softer compound is more biased towards grip and performance.

Turn 9 is a key point of the lap. The inconsistent track surface heading onto the bridge means that grip is a fundamental issue here. The same problem applies at the exit of the bridge, amplified by an immediate tight right-hand corner. All the engine's power is then unleashed up to seventh gear on the straight, using KERS as well to boost ultimate top speed. The tyres have to generate the maximum traction possible under full power.

Turn 17 is a sharp corner that helps bring the tyres rapidly up to temperature on an out lap. When using the soft tyres, the driver can attack the most demanding sequence of corners of the lap with the maximum grip possible, controlling the car's reactions perfectly. This sequence of bends is taken in seventh gear, so it is important to stick to the line and take the perfect trajectory, driving as neatly as possible to avoid excessive wear. After heavy braking, the driver eases the car into the final corner before the start-finish straight, where the engine's full power is released once more...

Blistering

One of the main problems that drivers can encounter with their tyres is a phenomenon known as 'blistering'. All of the PZero tyres undergo a chemical treatment to minimise the risk of this happening, which is essentially caused by overheating.

There are several reasons why the tyres can overheat, mostly to do with the tyres sliding too much and generating too much friction. This can be caused by a lack of downforce, problems with the car set-up or a driving style that is too aggressive.

Blistering begins at the innermost edge of the tyre, which is most stressed and runs at the highest temperature. The phenomenon occurs when the rubber close to the carcass overheats, creating small air pockets within the tyre that gradually begin to pull the compound apart in various different areas.

If uncorrected, sections of rubber detach themselves from the surface of the tyre, in different sizes depending on the amount of both heat and mechanical stress they are subjected to. These leave quite large and visible blisters on the tread surface, that often go down to the carcass. The look is very similar to a human blister, hence the name.