Coming straight after another Technical Directive from the FIA, Red Bull have again had one of their designs ruled on by Charlie Whiting. It’s now the Front hub design that has stretched the rules to the point where a clarification was required. Uniquely Red Bull duct air through the front hub to vent it out through the wheel for aerodynamic benefit. This appears to contravene the regulations on air ducts forming part of the brake system.
All teams use a hollow front stub axle (hub); the hub spins on bearings within the upright. Although hollow, the hub is not normally used to duct airflow to the brakes, instead air is ducted around the upright to enter the drilled brake disc.
In Red Bulls case the hub has air fed through it and then exits through two areas on the hub outboard of the disc. Firstly through drillings in the larger diameter section of hub and secondly in an open section outboard of the threads that hold the wheel nut on.
The air that vents through these outlets will exit through the centre of the wheel and does not really contribute to any brake cooling function. It’s clear a lot of effort has been expended on these vents, particularly the outboard vents. The six vents waist away the outer section of hub to almost nothing. These show how the inner section of the nut retention system being pointed to divert the flow out of these vents. Reinforcing the fact that these are vents and not simply drillings for weight saving.
I suspect the aim of this ducted flow is to aid the general flow out of the wheel. This will help improve the airflow that passes around the wheel off the front wing, which will reduce drag and probably also aid airflow to the rear of the car for more rear downforce. But any gain will be a small one, just a few points of aero efficiency. As with the tyre squirt slots in the rear of the floor, not even tenth of a second performance gain. Often with aero gains, it’s a compound effect of several gains in many areas, which really brings lap time benefit.
Back in 2009 teams fitted static wheel fairings to the front wheels; these also aided the airflow around the front tyre. These fairings were banned for 2010, by a series of rules that prevented any bodyworkbrake duct outboard of the wheel. These rules are the same ones that Red Bulls design appears to contravene.
Three sections of regulation 11.4 ban these fairings and apply to the current Red Bull design. Firstly that any air ducts are considered part of the brake system, secondly that the air duct must not rotate and lastly that the duct must not protrude outboard of the wheel nut. Regulations do not consider brake ducts as bodywork, also the rules are not specific what constitutes a brake duct, be it carbon ducting or the hub itself. Equally the rules do not demand any air duct forms any form of brake cooling function, but all are merely considered part of the brake system.
Red Bulls hub is clearly acting as an air duct, regardless of not being any form of brake cooling. We can then apply either the ‘rotating’ wording to all of the drillings in the hub or the ‘outboard of the wheelnut’ to the outer drillings.
Red Bull have now been asked to close off these drillings, which has been done temporarily with tape. For subsequent races Red Bull may choose to redesign the hub or make a more permanent solution to replace the tape used in Canada.
11.4 Air ducts :
Air ducts around the front and rear brakes will be considered part of the braking system and shall not protrude beyond :
‐ A plane parallel to the ground situated at a distance of 160mm above the horizontal centre line of the wheel.
‐ A plane parallel to the ground situated at a distance of 160mm below the horizontal centre line of the wheel.
‐ A vertical plane parallel to the inner face of the wheel rim and displaced from it by 120mm toward the car centre line.
‐ When viewed from the side the ducts must not protrude forwards beyond a radius of 330mm from the centre of the wheel or backwards beyond a radius of 180mm from the centre of the wheel.
‐ The ducts may not rotate with the wheels nor may they, or any of their mountings, protrude axially beyond the outer face of the wheel fastener.
‐ No part of the car, other than those specifically defined in Articles 12.8.1 and 12.8.2, may obscure any part of the wheel when viewed from the outside of the car towards the car centre line along the axis of the wheel.