Twenty to One

Croft begins not with a corner, but with the boost allocation table. During Saturday’s qualifying session and Qualifying Race, championship leader Ash Sutton will receive additional turbo boost for just one second per lap, and will only be able to activate it above 140km/h. Tom Ingram gets three seconds from 135km/h; Dan Cammish, five from 130. Gordon Shedden, eighth in the standings, and everyone below him can use the boost for 20 seconds from a threshold of 105km/h. The difference becomes even starker in Sunday’s opening race: Sutton gets one boost-enabled lap, Ingram two, Cammish three, while eighth place and below get ten. There is no misprint. The air is being measured out by the teaspoon.

At some circuits, part of this arithmetic can be hidden inside the corners. At Croft, that is considerably harder. The cars leave the final hairpin at almost the lowest speed of the lap and accelerate along the start-finish straight. Another important acceleration begins after the chicane on the run towards Tower. Here, extra boost is not a decorative light on the dashboard: it directly affects terminal speed, the ability to defend and the length of the following braking zone.

The activation threshold matters just as much as the duration. A car from the lower half of the table receives boost from 105km/h - roughly when the driver begins to unwind the steering and the tyre is gradually released from its lateral work. Sutton must wait until 140km/h and then has a single second available. He will just have time to notice that the engine has become more cheerful; a rival with 20 seconds can carry the higher boost through several acceleration zones on the same lap.

Extra horsepower does not, however, turn into lap time automatically. In a front-wheel-drive car, the front tyre must steer, accelerate the car and endure the loss of vertical load as the mass transfers rearwards. Apply the boost too early and part of the advantage disappears into wheelspin, heat and power understeer on corner exit. In the rear-wheel-drive BMW, the same longitudinal weight transfer presses the driven tyres harder into the road while the fronts get on with their proper job.

That is one reason why Croft has long been West Surrey Racing territory. The team has won 22 races here since 1997, five of them with the current BMW 330i. Daryl DeLeon added another useful clue in the spring by setting the fastest time in pre-season testing: 1m20.417s. None of this guarantees victory, but it tells us where to look when the cars leave the hairpin.

Reducing Croft to a rear-wheel-drive circuit would nevertheless be far too convenient. Beyond Tower, the task is almost reversed. The Jim Clark Esses and Barcroft are taken at high speed, and the car must remain composed through several rapid changes of direction before braking for Sunny. Horsepower matters less here than a stable aerodynamic platform, an accurate front end and a body that can settle before the driver reaches the brake pedal.

Then everything changes again. Sunny, the Complex and the hairpin demand low-speed rotation, compliance over the bumps and traction under power. Stiffen the suspension to control the platform through the fast middle sector and the car may begin to bounce off the kerbs, losing contact patch precisely where the driver wants to deploy the boost. Make it too compliant in search of mechanical grip and the Esses bring more roll, slower responses and an earlier lift.

Croft is gloriously immodest in its engineering demands. One half of the lap asks the chassis to be held with an iron hand; the other wants the wheels to be allowed to lead lives of their own.

Hence the importance of Saturday. The new Qualifying Race will be held on the regular Soft tyre, and its result determines the entire starting order for Sunday’s opening race. Sutton arrives with a 98-point lead over Ingram, but that is precisely why he receives the poorest boost allocation. Cammish is only five points behind Ingram and is also placed on starvation rations. Behind them, Adam Morgan, Ricky Collard, Dan Rowbottom and Charles Rainford receive seven, nine, 11 and 15 seconds per lap respectively. Eighth-placed Shedden gets the full 20.

Sutton’s main technical opponent, therefore, need not be Ingram - or even one of his immediate championship rivals. It could be anyone from the maximum-boost group capable of inserting themselves between the leaders on Saturday. Shedden has all 20 seconds. Josh Cook trails him by only one point and receives the same conditions. DeLeon combines maximum boost with rear-wheel drive and a car that has already demonstrated its pace at Croft.

The winner of each Sunday race will then have their allowance reduced for the next one, because the allocation is recalculated from the result of the previous race. A car may remain quick throughout the day, yet its engine will be served a different ration of air each time.

The tyres add the widest available strategic split. Goodyear’s Soft becomes the standard tyre, with the Hard as the mandatory option. Teams receive two sets of Softs and one set of Hards, and may also bring three carry-over sets from previous meetings. The Qualifying Race must be completed on the Soft, while every driver must use the Hard in one of Sunday’s three races.

The difficulty is that the sole practice session must be divided between setting up the car and learning the Hard compound. Running it provides valuable information about its Sunday behaviour, but also ages the only available set. Saving it leaves the tyre fresh, but means making its serious acquaintance for the first time during a race.

That trade-off is particularly sharp at Croft. A cold Hard front tyre will hurt braking and initial rotation; trying to recover the lost time with earlier throttle will merely add wheelspin. On the Soft, the danger is the opposite: overwork the front axle through the Complex, then discover that the car is negotiating the fast corners largely through an act of goodwill.

For the moment, the rain has decided not to take part. After heavy showers on Thursday evening, Friday should allow the track to dry. Saturday is expected to bring sunny intervals, with temperatures rising from about 12°C in the morning to 17-18°C during qualifying and no more than a five-to-ten per cent chance of rain during the sessions. Sunday should feel almost summery: around 21°C for the opening race and as much as 23°C later in the afternoon.

The wind, however, will strengthen. Gusts may reach 27mph on Saturday and 31mph on Sunday. On an exposed former airfield this is not background scenery: a changing crosswind can alter the aerodynamic balance through the Esses and Barcroft, particularly when a car is travelling in another’s wake.

The cold morning should help the front-wheel-drive cars put energy into their front tyres. During the warmer Sunday races, the advantage may pass to those that do not also ask the same tyres to transmit the engine’s torque. Once again, the BMW appears in the equation: rear-wheel drive, a strong Croft record and maximum boost for DeLeon form a combination rather too promising to ignore.

Yet DeLeon may have been fastest here in the spring, but Sutton is still the man leading the championship. Croft should therefore reveal more than which car is best. It will show how far a good car - and the driver inside it - can compensate for 20 seconds of somebody else’s boost with one second of its own.

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