Will Gray

Tech Talk: Playing the tyre management game

Will Gray

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This year's Pirelli tyres are hard to handle and have led to some dramatic degradation for some teams and drivers — but are teams now finally getting to grips with the key to tyre management?

The dramatic descent through the field that Kimi Raikkonen experienced earlier this year was a classic demonstration of just how the Pirelli tyres can drop off when they hit 'the wall'.

Since the early races, however, teams have been gathering data on how the tyres behave and while it still seems the trends are hard to spot, engineers are becoming wiser and wiser.

The key is the narrow operating temperature window — stay too low and you get little grip but go too hot and you will quickly eat up the tyres and be forced into an early stop.

While it's not easy to manage this sensitive area, many of the top teams now use innovative brake ducting systems and ducted wheel hubs to help increase those temperatures but on the flip side they also need to manage braking and traction to avoid overheating and with the levels of grip changing corner by corner this is a highly complex issue.

During a lap, the location through which the downforce is acting moves around and its location at any given point plays a crucial role in tyre degradation.

Managing this is now one of the keys to getting the most out of these Pirelli tyres, and it's all about the grip point between tyre and the track.

Loaded tyres, which are pushed down into the track more, will be able to cope with a greater braking force than unloaded tyres, which will lock up much more quickly when the braking force is applied and cannot cope with as much braking pressure.

When the tyre locks, rather than gripping and working with the track surface it is sliding across it — like a pencil eraser on a pad of paper — and that not only wears down the tyre compound material on the surface but it also heats up the tyre, potentially pushing it out of its narrow preferred operating range.

The more this happens, the sooner the tyre will wear out and the sooner a driver will need to pit for a new set.

The braking force comes from a combination of three elements — a classic braking system that uses hydraulics to make a calliper grip a carbon disk; the engine braking torque; and the KERS harvesting (spinning up the KERS motor to store energy).

The team can modify engine torque using electronic engine mapping, but only by a limited amount, while the way KERS handles its regeneration can be adjusted by the driver using a number of dials on the steering wheel.

The hydraulic system, meanwhile, provides a set force that is spread between front and rear brake systems and the driver can alter the balance front and rear not just lap by lap but corner by corner, to cope with the changing acting position of the forces on the car.

For example, at the end of a high-speed straight, there is a lot of braking potential because the downforce is high and is pushing the tyres into the track.

As the brakes are applied, the car pitches forward and the acting position of the downforce moves forward. This extra force on the front tyres gives them more braking potential while reduced force on the rears lowers their capability to grip the track under braking.

With a 50/50 brake balance, the rear tyres would lock earlier than the fronts because they cannot cope with the amount of braking force put through them - but at that point plenty more braking power could still be put through the front tyres before they started to lock.

In this situation, a driver would have to come off the brakes due to the locking rears, and would lose a significant amount of braking potential.

Instead, by changing the brake bias more towards the front, more of the available braking power from the front tyres can be harnessed before the rears lock — significantly improving lap time and, importantly, reducing the tyre wear.

At low speed, where there is less pitching in braking and therefore a more even force balance across the tyres, using the same brake balance as in the high speed corners would result in the front tyres locking. To cope with this, a driver would alter the brake balance back to more of a mid-level position.

Once into the corner, things are even complex as the lateral (sideways) loading creates different loads on different sides of the car and when a tyre becomes unloaded (most noticeably the inside front but often more problematically the inside rear) it will quickly lock.

The corner-by-corner adjustment can be made using brake balance knobs on the steering wheel that can alter the position by a set percentage for each turn of the knob or using levers that can quickly and simply modify the hydraulic balance corner by corner.

So while driving style is key to taking care of tyres, mastering the brake management is also vital in F1 2012.

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