Is F1’s water cooling tyre trick paranoia or a real battleground?

The latest Formula 1 technical hot topic that sparked up at the Brazilian Grand Prix was over internal water cooling of tyres. Here’s a delve into the factors in play and whether it is speculative or cause for concern

In a Formula 1 season dominated by technical intrigue between the top squads, attention was grabbed at the Brazilian Grand Prix by suspicions over a potential trick involving the internal water cooling of tyres.

The speculation follows hot on the heels of wild rumours we have seen throughout 2024 of asymmetric braking systems, flexi front wings, McLaren’s ‘mini-DRS’ and Red Bull’s front bib adjuster as the battle between F1's big teams gets ever more intense.

One of the games played when performance closes up at the front is to try to hold back the performance of your main rival through politicking, rather than waste effort trying to pursue something similar – which would cost a lot more resource.

This latest story revolves around questions Red Bull has had over whether some teams might be adding a very small quantity of liquid when inflating their tyres, in order to help control temperatures.

While the accusations are centred on several unidentified teams - sources suggest that Red Bull’s main interest involves closest rival McLaren - which has denied any behaviour like this.

It comes with Red Bull being well versed in the tactic, because it is understood to have employed it in the past before doing so was outlawed in an FIA technical directive a few years ago.

However, this is where the matter could fall into a bit of a grey area because TDs are only advisory – and it is ultimately down to the stewards to interpret the wordings of the regulations as they see fit to determine if teams have breached the rules.

And in this case, F1’s technical rules regarding tyre treatment only detail the removal of moisture from the tyres – not adding it.

Article 10.8.4 states:
a. Tyres may only be inflated with air or nitrogen.
b. Any process the intent of which is to reduce the amount of moisture in the tyre and/or in its inflation gas is forbidden.

So in theory, inflating the tyres with moist air does not appear to be strictly prohibited.

From Pirelli’s perspective, it supplies the teams with tyres that are inflated with ‘dry air’ inside.

Head of car racing and F1 Mario Isola said: “We have a dryer connected to our system, and they get all the tyres with dry air, as in the regulation. In the technical directive, it's written that any modification to this is forbidden, and it's quite clear.”

Red Bull however approached the governing body regarding this matter, because it believes teams may have been able to seek some advantage from altering the air’s composition and inject some cooling liquid – either water or another substance - through the valve.

Evidence of this tactic was alleged to have been spotted with water and watermarks seen inside some rims after tyres had been stripped at Pirelli's base post-race in Singapore.

The motivation appears simple as Pirelli’s tyres are sensitive to temperature and they are designed to thermally degrade over the course of its lifespan.

This results in the teams and drivers constantly trying to find the right balance between the bulk and tread temperature of the tyre. If a driver can keep the tyres cooler than their rivals, so they do not spike out of the operating window, then that results in improved performance and increased stint length.

A considerable amount of time, money and effort is expended by the teams to understand and harness the relationship between the associated components that can impact the tyre's thermal degradation.

The wheel rim is now a spec component, supplied to all the teams by BBS, which means that any tricks, such as knurling on the wheel rim’s surface, changing spoke design and altering the geometries of the surfaces can no longer take place.

Meanwhile, the outer wheel cover and a great deal of the brake duct fence design are also specified, further limiting how they can be used for individual aerodynamic or thermodynamic benefit.

However, the brake assembly and internal drum design, while more limited than it has been in the past, still provides a playground for the engineers in terms of how they manage the heat generated by the brakes and how it is transferred to the tyre's bulk temperature, via the wheel rim.

Each team has its own methods for dealing with the heat exchange between components, which obviously means some will do so better than others.

The introduction of a coolant into the tyre would be expected to help with this process, as it will alter the humidity level, which should in-turn impact the bulk temperature and pressure.

The most likely upshot here is that the temperature will be less than if it was just pure dry air, but there will also be a parallel increase in pressure.

This might look like a net loss in the short term, as teams traditionally try to run as close to the minimum tyre pressures prescribed by Pirelli as possible, as that should yield more performance.

However, given that this regulation set favours a car that’s less sensitive to ride height fluctuation but also requires cars to be as low as possible to reap benefits, it might make sense to have more pressure than might otherwise be ideal.

This is a sentiment echoed by Mario Isola, who suggests that teams have opted for a similar direction in the past, in order to gain aerodynamic performance at the short term detriment of a loss of grip from the tyre.

“I remember a few years ago most of the teams were increasing the front pressure to have a stiffer tyre and go lower with the ride height,” he said.

“They accepted to have this smaller contact patch, because the aero set-up of the car was better. So the balance between the two was about performance - because of the downforce they were able to achieve”.

It is understood that the FIA inspected tyres and rims closely at the Brazilian Grand Prix to see if there was any evidence of extra moisture – but nothing was found.

And while this increased focus will almost certainly mean that if anyone was playing around with this tactic then they will not be doing it any more, it will not stop intrigue over whether anyone got away with it earlier in the year.