AP Racing on the Evolution of GT3 Race Car Brakes

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Source: This excerpted from a Professional Motorsports World post written by Lawrence Butcher after he spoke with AP Racing executives.

The most populous global racing class is GT3, with dozens of manufacturers producing customer cars, raced by both professionals and gentleman drivers alike. The category has ballooned over the past decade and the technology deployed has advanced at a considerable rate. Gone are the days when a GT3 car bore any resemblance to its roadgoing base; current machines are bespoke in almost every way.

This observation applies to the braking system as much as any component group. PMW caught up with AP Racing’s business development manager, Ian Nash, and Paul Hayden, a technical support engineer at the company, to find out how brake technology has evolved to meet the changing demands of GT racing’s second tier.

Commenting on the shift in engineering ethos, AP Racing’s Nash observes, “I think the first car I got involved with in GT3 was the Nissan GTR [c.2013]. And I remember that having standard rear brakes on it. I think it also had the standard front uprights and we just upgraded the front calipers. Things have developed a long way since then. Nearly all of the cars now have bespoke uprights and there is no OEM running gear. Then you have things like changes to the FIA regulations in areas such as seat position and adjustment.”

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This latter point drove companies such as AP to produce adjustable pedal boxes, to allow for easy accommodation of different drivers. Coupled with adjustable reach steering wheels, most drivers can be fitted to most cars without the need to move seat mounts. According to Nash, AP is now on its second generation of adjustable pedal box, having been first to market with a design when the rules first changed. The latest offering incorporates feedback from users and a modular design, giving greater flexibility of pedal layout.

Hard stopping

One particularly challenging aspect of GT racing for brake manufacturers is the widespread use of ABS. “It’s very nice for gentlemen drivers and for non-professional drivers, but very hard on the brakes,” remarks Nash. “The drivers are just taught to just stand on the brakes as hard as they possibly can. Therefore, it is maximum braking effort on every stop. It’s also hard on the master cylinders, which see very, very high pressures from the ABS system. As a result, we have put a lot of developments into the master cylinders.”

Due to the nature of operation for an ABS system, it is only the master cylinder that sees sustained high-hydraulic pressure, not the caliper. The challenge, explains Nash, is handling the excess braking pressure that the ABS bleeds from the caliper to prevent the wheels locking. “That needs to be removed from the system before the next application. The pressure comes back up the system and needs to be vented to atmosphere; the only way to do that is through the reservoir, via the master cylinder.”

On a traditional master cylinder, this process places significant stress on the seals, with Nash noting that in the past, rapid seal wear has been an issue. To counter this, AP has now developed its Centre Valve master cylinders, which are ABS specific and feature a dedicated seal design to ensure reliability.

The nature of how GT cars are built amplified some of the early challenges for suppliers such as AP. Constructors tend to buy in components from many sources, and there is not necessarily any direct dealing between companies like Bosch, which supplies the most ABS hardware, and brake manufacturers. Therefore, compatibility issues may not be apparent until cars start track testing. For example, the early evidence of seal problems manifested as an issue with wear particles blocking the hydraulic filters on the ABS units.

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