BMW stopped building the Z4 and shelved any plans for a successor. Andreas Bovensiepen had 99 of them squirreled away before the line went cold.
Those 99 cars, all pulled from the final four weeks of G29 production, are now becoming the Bovensiepen Spider. Each one gets rebuilt by hand into a 435 hp, rear-drive roadster that BMW never had the nerve to make. The price is €115,500 in Germany, and when the 99th car is finished, that’s it.
We rode shotgun with Bovensiepen up the Bernina hill climb in Switzerland, where the company showed the car publicly for the first time at the Bernina Gran Prix. It is the third model from Bovensiepen’s young company, following the Zagato-bodied M4 and the M5 Touring-based 05 GT. But the Spider is the leanest idea of the three.
A two-seat roadster, open top, inline-six, rear wheels only, at a moment when Jaguar and Porsche have both abandoned the formula.
The B58 3.0-liter six-cylinder gets its extra muscle through better breathing on both ends. A ram-air intake hides in the grille, feeding pressurized air through a second tube into a larger filter housing. The effect builds with speed.
On the exhaust side, Bovensiepen threw out the particulate filter entirely, claiming the car still passes emissions without it. Less restriction, more power, sharper throttle response.
Frank Stephenson Design handled the exterior rework, which falls somewhere between a deep facelift and a proper reskin. New front fenders carry functional air outlets. A wind tunnel-developed rear spoiler generates real downforce, balanced by a new front splitter.
The car still reads as a Z4, but the proportions look stretched and more purposeful.
Underneath, the changes are surgical rather than sweeping. Low-speed bound damping is stiffer, addressing a specific weakness in the standard car’s composure over dips. The rear gets a longer rubber auxiliary spring.
Tires are wide, 255s up front and 295/30s at the rear, and the car tips the scales at 1,585 kg. Bovensiepen says it will still light up the rears in first gear with stability control off.
Braking is handled by 395 mm drilled Brembo front discs. An optional Performance Package pushes top speed from 260 to 295 km/h and adds an aluminum differential cover with cooling fins and extra oil capacity. That fix was born from autobahn testing where the stock diff ran too hot at sustained pace.
The ZF eight-speed automatic stays, and Bovensiepen left BMW’s shift calibration untouched. No manual option. He has said a manual gearbox would have limited how much torque the engine could produce, which is a defensible engineering argument but still stings for the audience most likely to buy a car like this.
Inside, the cabin gets Lavalina leather across more surfaces than the factory Z4 offered. The steering wheel uses Bovensiepen’s signature parallel stitching. Our car wore a platinum and violet two-tone center console that was easily the most memorable detail in the cockpit.
Every Spider starts as a brand-new, never-registered Z4. They were built to Bovensiepen’s specifications before the production line shut down. That distinction matters.
These aren’t used cars getting a tuner makeover. They are bespoke machines using the last available donor bodies, a supply that cannot be replenished.
At roughly €97,000 before tax, the Spider costs more than double what a Z4 M40i listed for. But the Z4 M40i no longer exists, and BMW has made clear nothing is coming to replace it. Bovensiepen is selling scarcity as much as engineering, and 99 units is a number small enough to make both arguments stick.
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