One of the defining stories of this 2013 F1 season has been the rise of Mercedes and the way they not only grabbed pole position in eight of the first 12 qualifying sessions (by getting the most out of the Pirelli tyres), but also got on top of heavy tyre wear issues in races to allow Rosberg to win twice and Hamilton once.
Analysis by former Williams chief engineer and JA on F1 technical adviser Mark Gillan of photos of Mercedes wheels, taken by leading F1 photographer Russell Batchelor of XPB Images, shows the complex internal design which Mercedes has evolved to master thermal management of the tyre. It is F1 innovation in action.
Mercedes’ steady improvement in tyre management in races has not happened without controversy, as they took part in a 1,000km Pirelli test in May which landed them in the FIA International Tribunal, where they were found to have breached the Sporting Regulations, but the Tribunal found that the breach had been made in “good faith” based on communications with the FIA.
Here is Mark Gillan’s analysis:
Take a look at what the regulations say about wheels (at the bottom of this post).
As the wheels are easy for other teams to look at one is always very careful to ensure that their legality is crystal clear and if there are any ‘grey areas’ then one will run the idea past Charlie Whiting at the FIA to ensure that there are no problems. Whilst wheels are relatively inexpensive to manufacture (per item) the manufacturing lead times are relatively long and one typically needs 30+ sets of wheels (i.e. 120+ wheels) to remain operationally efficient at races so wheel upgrades during a season are not too common.
The Mercedes wheels in detail
In my experience conjecture about what a team is actually doing with a particular design is often wide of the mark.
What one can say is that to modify a wheel a team needs a good reason to do so because of the lead-times and quantities involved. As tyre thermal management has been a major performance differentiator this season all teams have been working on mechanisms/process to get the tyres into their operating temperature window as soon as possible and then keeping them in this window for as long as possible. The thermal window is quoted by Pirelli as typically 20C to 25C, with running temperatures of between 90C to 135C, depending on compound.
Mercedes has been evolving what it does inside the wheels. Mercedes now has a new set of front and rear wheels which were captured very clearly in Monza by photographer Russell Batchelor. On the inner surface of the wheel there is a complex dimple pattern, which is actually fully integral to the wheel itself and almost certainly there solely for thermal management purposes in order to get and keep the tyres within their optimal temperature window.
This complex dimpled and scalloped pattern (see close up of the front tyre, below) is not straightforward to manufacture and therefore indicates a lot of research and development has gone into developing this component and proving its benefit before committing to its manufacture.
This type of pattern is quite common on modern heatsink designs, where dimples have been shown to give up to 25 to 30% thermal transfer improvements over the smooth surface variant. Only Mercedes will know whether the effort was worthwhile and how good the correlation was to their simulation and rig programme, but one has to applaud their ingenuity and effort.
What the F1 regulations say
Firstly, Article 12 of the 2013 Technical Regs determines what a team can/cannot do with the design of their wheels. The regulations are pretty prescriptive, but the main points can be summarised as:
i) Wheel must be made from a magnesium alloy (AZ 70 or 80);
ii) The width and diameter of the complete wheel (wheel and tyre) is specified within a range;
iii) The wheel minimum thickness is 3mm increasing to 4mm at the bead;
iv) The wheel must not be handed i.e. the left and right wheels on a given axle must be identical;
v) Surface treatments are only allowed for appearance and protection e.g. painted/clear coated to avoid corrosion and allow for livery schemes.
vi) One can then add to the wheel a limited number of items such as spacers, balance weights, tyre pressure and temperature monitoring systems, pegs etc