BMW Z4 M40i explained: the straight-six roadster
The BMW Z4 M40i is a straight-six roadster with M Performance tuning. The B58 engine, automatic and manual gearboxes, its link with the Toyota Supra, driving feel and buying tips.
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The BMW Z4 M40i is the most powerful version of the G29 Z4 roadster. It combines a 3.0-litre straight-six, rear-wheel drive and a fabric roof that opens in seconds, making it one of the most enjoyable open cars BMW has built.
It is an M Performance model rather than a full M car, and it shares its platform with the Toyota GR Supra. In this article we explain the engine, the gearboxes, the driving experience, practicality and what to check when buying a Z4 M40i.
The G29 Z4 and its roots
The G29 Z4 was launched in 2018, continuing the Z roadster family that started with the Z1 and continued with the Z3 and earlier Z4 generations. Our article on the Z3 M and Z4 M explains the M versions of earlier roadsters.
The G29 was developed together with Toyota, which used the same basic platform for the GR Supra coupé. Both cars are built by Magna Steyr in Austria. The Z4 is an open roadster with a fabric roof, while the Supra is a fixed-roof coupé with its own styling and tuning.
The BMW Z4 M40i engine
The BMW Z4 M40i uses the B58 3.0-litre straight-six with a single twin-scroll turbocharger. In Europe it produces around 340 hp, while some markets received a version with more power.
The engine delivers strong torque from low revs, a smooth power delivery and a pleasing straight-six sound, especially with the roof down. It is known as a robust engine. Our comparison of the N54, N55 and B58 explains how the B58 developed from earlier BMW turbo straight-six engines.
Automatic or manual
At launch, the Z4 M40i was offered with an eight-speed automatic gearbox, which is quick, smooth and efficient. It suits relaxed cruising and fast driving equally well.
Later, BMW also offered a six-speed manual gearbox for the Z4 M40i in some markets, responding to requests from enthusiasts. The manual adds involvement and is a strong reason to choose this car for many buyers.
Our article on BMW transmission fluid explains maintenance for automatic gearboxes, and our article on the BMW dual-mass flywheel explains what to know about manual gearboxes.
Driving feel
The Z4 M40i has a low centre of gravity, a short wheelbase and wide tracks. It feels agile and eager to turn, with strong grip from wide tyres. An electronically controlled M Sport differential helps traction out of corners on many cars.
Adaptive suspension allows a comfortable setting for longer journeys and a firmer setting for twisty roads. With the roof down, wind noise is well controlled, making it a pleasant car for long trips. It is less sharp than a full M car, but more relaxed and comfortable.
Practicality
The Z4 offers a surprisingly usable boot for a roadster, because the fabric roof folds into a compact space and does not reduce luggage capacity when open. The cabin is comfortable for two people, with modern infotainment and driver assistance systems.
The fabric roof opens and closes in a few seconds, even at low speeds. It keeps the weight low and preserves the boot space compared with folding hard tops.
Z4 M40i vs Toyota GR Supra
The two cars share much of their technology, but they feel different:
- Z4 M40i: an open roadster, more comfortable and refined, with a BMW interior.
- GR Supra: a fixed-roof coupé, stiffer and more focused, with Toyota's own styling and tuning.
Both use the B58 engine in their most powerful versions. Choose the Z4 if you want open-air driving and comfort, and the Supra if you prefer a coupé and a sharper feel.
Buying tips
When buying a used Z4 M40i:
- Check the service history and oil changes with the correct oil.
- Inspect the fabric roof for damage, and test the opening and closing several times.
- Check for water leaks in the cabin and boot. Our article on BMW water leaks explains the causes.
- Look at tyres and brakes, which wear faster on cars driven hard.
- Ask about modifications, because the B58 is often tuned.
Our complete checklist for buying a used BMW covers the other checks.
Is it a good choice?
The Z4 M40i offers a rare combination: a smooth straight-six, rear-wheel drive and open-air driving in a modern, comfortable package. For many buyers, it is the ideal weekend car that can also be used every day.
It does not have the raw edge of a full M car, but it offers much of the fun with lower running costs and more comfort.
BMW Z4 M40i key facts
| Item | Details |
|---|---|
| Internal code | G29 |
| Launched | 2018 |
| Engine | B58 3.0-litre straight-six, single twin-scroll turbo |
| Power | Around 340 hp in Europe |
| Gearboxes | 8-speed automatic; 6-speed manual added later in some markets |
| Roof | Fabric, quick operation |
| Related model | Toyota GR Supra, same platform |
Frequently asked questions
Is the BMW Z4 M40i a real M car?
It is an M Performance model, tuned by BMW M, but not a full M car.
Does the Z4 M40i have a manual gearbox?
At launch it was automatic only. A six-speed manual was added later in some markets.
Is the BMW Z4 the same as the Toyota Supra?
They share a platform and many parts, but the Z4 is a roadster with its own design, interior and tuning.
What engine is in the Z4 M40i?
The B58 3.0-litre straight-six with a single twin-scroll turbocharger.
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