Every tuner who has ever chased wheel hop out of a rear-drive build knows the drill: stiffer bushings, a better-located axle, damper valving that stops the tire from skipping across the pavement like a stone. Hop is what happens when the suspension and the driveline start arguing at a frequency the tire can’t resolve. You engineer it out.
BMW has a patent filing that goes the other direction. The idea is to use the active suspension to shove the rear unsprung mass upward in a single sharp impulse, briefly dumping load off the rear tires so the car will break traction with almost no throttle. Deliberate, timed, one-shot axle hop as a drift button.
Before deciding whether that’s brilliant or heretical, it’s worth understanding why it would actually work, because the physics has already been documented in detail — in a patent pointing the opposite way.
The math already exists, running backward
There’s a recently issued U.S. patent covering a method to increase tire traction by using an active suspension element to fire a downward impulse into the wheel. Same hardware, opposite sign. And because the inventors had to prove the effect was real, the filing shows its work.
Their worked example: a 2,000 kg vehicle, body raised 50 mm above its base ride height, then dropped. On very stiff springs, maximum traction jumps from about 3,430 N to roughly 10,400 N per tire. That’s a 204 percent increase. On merely stiff springs, 50 percent. On soft springs, 10 percent.
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Read that as an engineer and the drift application writes itself. Vertical load is the input variable for grip, and a suspension actuator can move it by triple digits in percentage terms. If you can add 204 percent, you can subtract a meaningful chunk of it just as fast. Unload the rear contact patches and the torque required to spin them collapses.
The same document gives you the other number that matters: duration. The enhanced-traction window lasts roughly half the suspension’s natural period. In their example that’s about 150 milliseconds on very stiff springs, 315 ms on stiff, and 700 ms on soft.
That’s the whole ballgame. A drift-initiation impulse would give you a grip-reduction window measured in tenths of a second, and it scales inversely with spring rate — the stiffer the car, the shorter and sharper the window. A human being cannot reliably meet a 150-millisecond aperture while also managing steering, throttle and the yaw that’s about to arrive. A controller can hit it every time.
That’s the actual argument for the patent, and it’s a better one than “drifting for people who can’t drift.”
BMW has been circling this for over a decade
This filing isn’t a bolt from nowhere. BMW’s drift training assistance system, filed by Philipp Reinisch and Moritz Werling with a January 2013 priority date, proposed handing steering and throttle to an assistance system so a driver could learn each input separately instead of failing at both simultaneously. It granted in the U.S. as US10077051B2.
That document also contains the most useful piece of chassis theory I’ve read in a patent this year. When the assistance system holds a course, BMW says the best reference point isn’t the center of gravity — it’s the center of percussion, located a distance d = J/(m·l_h) ahead of the CG, where J is the yaw moment of inertia, m is vehicle mass, and l_h is the distance from the CG to the rear axle.
Why there? Because a change in rear-axle lateral force produces no lateral acceleration change at that point. The car’s course is instantaneously preserved at the moment the rear steps out, which means the steering correction can be applied later and more calmly. That’s the difference between a drift that looks composed and one that turns into a save.
The same patent catalogs how humans do it: the pendulum entry, where you weave to load and then unload the rear; the handbrake, useful both for initiating and for extending a slide when the rear is trying to regain grip; and the old trick of dropping the rear axle onto the grass beside the track to lose adhesion, then bringing it back onto asphalt once the entry angle is set.
Look at that last one. It’s the exact same input the new filing describes — a momentary loss of rear grip, externally supplied. BMW is proposing to replace the grass with an actuator.
Everyone is filing on this
The drift-assist patent shelf is getting crowded. Ford holds US10513254B2 on methods providing vehicle drift. Toyota Research Institute has US11858497B2, covering an ECU that initiates a stable drift and then provides corrective assistance to keep the driver out of an unstable one. Mercedes-Benz filed DE102022003544A1 on driver assistance during a drift maneuver. Audi has held a drift assistance patent since 2016. GM published a drift assistance system application in March. ZF published one on drift support in May.
Nobody else in that list is manipulating vertical wheel load to do it. They’re working through torque, brakes, steering and yaw control. Reaching for the suspension is the genuinely novel move, and it’s the one that requires hardware most cars don’t have.
What it would cost you to own
If this ever ships, the maintenance conversation is not trivial. An impulse actuator capable of moving unsprung mass hard enough to unload a tire is doing violent, repeated work on components that are usually asked to move smoothly. Bushings, top mounts, wheel bearings and driveshaft joints all see a shock load every time the driver pushes the button. Track-day users would be cycling that hardware dozens of times per session.
Active suspension actuators are also among the most expensive individual components on a modern chassis, and they are not serviceable at the corner shop. A drift-initiation function is a wear feature dressed up as a party trick, and out of warranty it lives on the wrong side of the repair-cost ledger.
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There’s a subtler issue too. Suspension components that get regularly shock-loaded develop play, and play changes toe and camber compliance under load. A car whose whole premise is precisely metered grip reduction depends on knowing exactly what the rear axle does when you unload it. Worn bushings make that number a moving target.
The part nobody wants to say
A patent filing is not a product. Automakers file to fence off ideas they may never build, and this one would require active suspension hardware that isn’t standard equipment across the M range.
But the concept is sound, the physics is documented, and the timing problem it solves is a real one that no amount of practice fully eliminates. The honest objection isn’t engineering. It’s that drift initiation is the part of the maneuver where the driver actually finds out whether they can do it, and a machine that hands you the entry hands you a slide you didn’t earn and may not be able to finish.
Which is a philosophical complaint, not a technical one. And it has never once stopped a feature from reaching production.