There are few more unsettling feelings for a driver than arriving at a corner and being unable to trust that the brakes will slow them down. A long pedal that means apexes cannot be attacked with appropriate vigour carries a clear lap time penalty, and over a stint such inconsistency can make all the difference between victory and mid-pack anonymity.
“Front-wheel-drive performance is all about your brakes and how you can manage them to load up the front axle, keep the weight over the nose and control the balance,” explains Aron Taylor-Smith, the British Touring Car Championship’s Independents’ title winner in 2024 with the Power Maxed Racing Vauxhall squad.
But braking systems are a package deal. Disc and pad wear isn’t the only brake-fade catalyst. Even the best pad/disc combination will have limited use if not complemented by effective brake fluid, the often-overlooked hydraulic element that transmits the force from the pedal.
“The only connection between your foot and the calliper is the brake fluid,” points out Dan Stafford. The chief chemist at Halo by Orthene, the racing sub-brand of the family-owned Orthene company that has since 1976 developed brake fluids, says their significance shouldn’t be overlooked.
“You want the brake fluid to have a very low compressibility,” he explains. “Force transfer has to be consistent. On a straight, you have a massive cooling effect, then in a braking and cornering event you get instantaneous heating of the brake system. If the fluid can’t adapt to those dynamic temperature ranges and has changed its compressibility in any way, you’ll get control issues.”
All the same, in the experience of Halo by Orthene chief marketing officer Mike Biscoe, there is a tendency for mechanical and electrical engineering to completely overshadow chemical engineering approaches when it comes to unlocking lap time.
“There are teams and engineers who understand the importance of brake fluid, but I’d suggest they’re a minority,” says Biscoe. “When it comes to braking, everyone thinks about the mechanical components at that calliper end, not about the fluid that transmits that force.”
However, that may not be the case for much longer. As both Stafford and Taylor-Smith recognise, demands on braking systems are only growing as the trend of adding weight shows no signs of abating. When this is combined with greater electrification – regen, so fundamental to extending battery life, occurs under deceleration – the heat that racing braking systems must cope with is extreme.
Not meeting this reality face-on can have serious consequences. When brake fluid boils, bubbles form and the fluid becomes more compressible, with the resulting loss of pressure making it harder to stop. This explains the mind-bending 341C boiling point of Halo P1, the company’s latest motorsport-focused product.
One of the first measures PMR identified for improved braking consistency was in brake fluid, and Taylor-Smith believes his overall podium finishes at both circuits this year “is probably no coincidence”
Sensors on a master cylinder measuring pedal travel across different temperatures are a great indicator of how compressible the brake fluid is. For Stafford, very low and stable compressibility over a wide temperature range is one of P1’s core traits, its high temperature lubricity the other.
“Having a fluid where the boiling point is that little bit higher, the compressibility is that little bit better,” says Taylor-Smith, who has used the new-for-2024 P1 formulation in his Astra this year.
The Irishman cites Donington and Oulton Park as examples of circuits with multiple back-to-back heavy braking zones that afford little opportunity for cooling where brake fade was “a huge issue”. One of the first measures PMR identified for improved braking consistency at these tracks was in brake fluid, and Taylor-Smith believes his overall podium finishes at both circuits this year “is probably no coincidence”.
“Other brake fluids might be able to replicate a one-lap pace when all the fluid is fresh,” he says. “But I’ve found with P1 that in the last few seconds of qualifying, when the track is at the grippiest, you still have the peak of brake performance.”
Unlike road-going brake fluid, which is subject to prescribed standards to ensure it can perform at extremely low temperatures, racing brake fluid involves fewer compromises that Biscoe notes “allows us to push the envelope of performance”. Top teams will ‘flush’ the systems multiple times over a race weekend, Stafford explains, “not just to ensure you’ve got fresh fluid in there, but to remove any elastomer dust” generated when new or rebuilt brake systems are bedding in.
Stafford notes that additives present in automotive fluids to prevent corrosion, potentially resulting from water entering the brake fluid after encountering puddles, “doesn’t come into it” with racing, and longevity of the fluid itself isn’t such a concern either. But the right degree of viscosity, lubricity to avoid unduly wearing components, as well as compatibility with the varied exotic metallurgy used in those components, are also important qualities.
Halo by Orthene is already exploring options for new formulations. Stafford points out that motorcycles “need slightly different properties” to cars since there is far less brake fluid and the dynamics flowing through the system are very different. “We’ve been working with a team in British Superbikes and they’re looking for a very particular characteristic with the brake fluid which we managed to solve,” he says. “From a chemical perspective, we’ll probably start to see some divergence.”
As motorsport continually strives for faster lap times, so in its unseen way, will brake fluid evolve to play its own part?
