How BMW’s Genius ‘Pendulum Brake’ System Beat an ABS Ban in Racing

Anyone who says regulation stifles innovation clearly knows as little about business as they do about motorsport. Necessity is the mother of invention, and every rule ever made to slow cars down has been twisted, exploited, and brilliantly circumvented in ways that are the stuff of legend—or remain confidential to this day. One of the lesser-known rule-bends was brought about by BMW, which deployed a novel “pendulum brake” to get an edge in Super Touring. But as clever as it was, it was an invention of the kind that might have helped kill this legendary category of racing. The 1990s were arguably the heyday of touring cars, and one of the most popular categories was Super Touring. Based on the British Touring Car Championship’s 2.0-liter class, Super Touring cars replaced Group A in circuit racing around the globe starting in 1992. According to Super Touring Register, BMW was on board from the beginning with its new 3 Series, the E36, which it was keen to build on the pedigree of the E30. It was only modestly successful though, with early chassis winning some smaller regional championships, but not in the countries with the most competitive fields. What BMW needed was a leg up on the competition, and apparently, it turned to McLaren for the answer. 1997 BMW E36 Super Touring. Race Cars Direct According to an old for-sale listing for a Super Touring E36 on Race Cars Direct, BMW Motorsport enlisted McLaren to improve its car for 1997. It’s unclear what all McLaren did to upgrade the car, with its suspension being the only part specified in the ad. But it’d be a strange coincidence for McLaren not to have had a hand in the ’97 Super Touring E36’s new “pendulum brake,” not with what was going on in its Formula 1 team that year. You may remember 1997 as the year of the “fiddle brake” controversy. In short, McLaren rigged up an extra brake pedal to drag on the inside rear wheel, which significantly improved both agility and stability. It would eventually be banned, but a similar idea may have pollinated the E36 program, whose pendulum brake is a bit more complex. The pendulum brake’s function was outlined in a video by Schnitzer Classic, which supports the old race cars of Schnitzer Motorsport, a historic BMW race team that campaigned these E36s. Underneath the dashboard, there’s a proportioning valve that adjusts brake balance plumbed into the hydraulic lines of the front brakes. Normally, these are just used to adjust bias front-to-rear, but here, the adjustment is lateral and controlled by a pendulum that swings from side to side. When the driver turns the steering wheel, that pendulum swings to the outside, directing more braking force to the outer wheel than the inner one. That may sound counterintuitive if you know how modern torque vectoring works; it often drags on the inside wheel to cull understeer, not the outer one. Many commenters reacted the same way, believing the pendulum brake would make trail braking into a corner impossible. But as kart racer Javier Fichera points out in the comments, turning in transfers weight to the outer wheel. We’ve all seen cars lock their inner wheel while braking into a corner, and in the absence of ABS (which Super Touring prohibited), that’s what this system was designed to prevent. Still, you may be wondering why the proportioning valve isn’t attached directly to the steering column for quicker response. This is just speculation on my part, but the lag is the entire point of the pendulum: Lateral brake bias changes in sync with the weight transfer, not ahead of it. Brake balance only changes when the grip is there to use it. So how’d it do? Well, from looking into the careers of ’97-onward E36 Super Touring chassis, it seems the improved E36 was significantly more competitive from the get-go. But its reign would be limited because in December 1997, BMW succeeded the E36 with the E46. This was also near the end of the peak for Super Touring, as the editor of 1990sBTCC.com, Alex Clarke, explained to The Drive. On top of brand politics as makes acquired one another, costs spiraled out of control and led to manufacturers withdrawing—in part, no doubt, due to tricks like BMW’s pendulum brake. But successful or not, new ideas are the lifeblood of motorsport. Win with them, and you’ll change the game. Fail that, you’ll at least give people something to talk about—and remember you by, regardless of where you finish. Got a tip or question for the author? You can reach them here: james@thedrive.com