This year McLaren have had the option to alter rear brake cooling during the pit stops in a race. As a result they can vary brake temperatures and potentially alter tyre temperature slightly. This latter effect being possible from the heat conducting from the red hot brake discs through the wheel and into the tyre. This system has been used at various races and each driver appears to have preference when to use it. This system has been especially useful this year, as the tyres dropping below their operating temperature window will see grip their levels fall dramatically. At the British GP one of the mechanical updates McLaren have brought, is the front brakes now also have this adjustability.
The front brake duct appears to use the same mechanism as the rear. A flap opens up to uncover the brake disc, this allows more heat to pass out of the outer brake drum. To accomplish this, a small telescopic adjuster is fitted to the outer drum to move the flap.
Images taken over the Friday practice sessions also showed the mechanism hanging loose from the duct assembly. These images show the mechanism has a hydraulic fluid line and a bleed nipple, providing the surprising proof that the mechanism is hydraulic. As explained in the previous rear brake duct post, the ducts are altered centrally from an adjuster near the fuel filler flap.
It was previously presumed to be a cable operated system, using hydraulics may make the packaging of the system easier, as you don’t need to find smooth routes through the car for a bowden cable.
It’s also likely that this is a separate hydraulic circuit for this purpose, rather than a part of the cars high pressure electro-hydraulic system or the cars brake circuit. Using hydraulics over a cable is not a legal issue, as long as the system is operated when the car is at a stand still, then the adjustment mechanism is not an issue.
Now having front and rear adjustment to brake cooling , McLaren will be able to react to brake temperature issues, play with KERS harvesting without fear of overheating brakes and also alter the tyre temperatures front or rear, allowing for a better balance to be found during the race. With the weather expected to be mixed this weekend having this option will be extremely useful for the Race Engineers.