BMW Z4 M40i (G29)

A six-cylinder soft-top roadster

The BMW Z4 M40i is the top version of the third-generation G29 Z4, a rear-wheel-drive two-seat roadster with a fabric roof. BMW says the car is built for the company by Magna Steyr in Graz, Austria. Our catalogue lists a 3.0L turbocharged inline-6 petrol (B58) engine producing 335 bhp and 500 Nm, with 0 to 100 km/h in 4.5 seconds and a 250 km/h limited top speed. We have not driven this model for this article. This is a desk-researched ownership guide built from the BMW Group press release for the updated Z4 of September 2022, a PistonHeads used buying guide published in January 2023 and the government recall check. Both written sources are a few years old, so read their reliability reports as an early picture of the car and confirm everything on the example in front of you.

Checking the figures

BMW's release gives the M40i 340 hp and 500 Nm of torque (369 lb-ft), with 0 to 62 mph in 4.5 seconds and a 155 mph top speed that it marks as electronically limited. The 340 hp is the metric rating, which converts to the 335 bhp in our catalogue, and 155 mph is the 250 km/h limit. The release states that its figures are provisional and refer to the German market, so UK and other buyers should read the output on the car's own documents. PistonHeads gives the same power, torque and acceleration figures and lists a weight of 1,610 kg for the M40i, while warning that weight and power data are hard to pin down with certainty. On dates, BMW says the third generation went on sale in 2018, whereas PistonHeads lists the car as on sale from 2019. Our catalogue uses 2019, so check the build date and first registration rather than relying on a model year.

Engine and gearbox

BMW describes the six-cylinder in-line engine with M TwinPower Turbo technology and claims that it is unmatched by any rival in the class. PistonHeads describes it as a lusty unit with plenty of lunge from low revs and no objection to higher ones, and says its 4.5 second time is quicker than a 718 Boxster and only just behind the Boxster S. The only gearbox at launch was the eight-speed Steptronic Sport automatic. A six-speed manual arrived on the 20i in spring 2019 in some markets, but the guide suspects it was not sold in the UK and found no manual G29 on British selling sites. The engine note is partly artificial, since the car uses sound augmentation, and the guide notes that dropping the roof gives more of the real exhaust.

The most common reports concern a flat spot or throttle hesitation when pulling away from stationary or crawling speeds. PistonHeads says this affects four-cylinder and six-cylinder cars and the closely related Toyota GR Supra, and that nobody has pinned down the cause. Suggestions include fuel quality, the high-pressure fuel pump, the throttle position sensor, engine management software, stability control and gearbox software. Some owners say it began after the brake disc recall work, and some cars show long cranking times. Test drive for it from cold and warm, and ask whether a dealer has investigated it.

Servicing was sold as either a pay-monthly plan or a service-inclusive plan covering the first four years, excluding brake pads, discs and the MOT. According to the guide, a minor service covers oil, oil filter and cabin filter, a major adds the engine intake filter and spark plugs, and brake fluid is due three years from the build date and then every two years. Ask for dated invoices that show which service was done and when.

Chassis, brakes and tyres

BMW lists a two-joint spring strut front axle and a five-link rear axle, with variable sport steering as standard. The M40i adds adaptive M suspension with electronically controlled dampers, M Sport brakes with blue or red painted calipers and an M Sport differential at the rear axle. PistonHeads says the chassis is a large step on from the second-generation Z4 but that the ride is stiff even in Comfort, so on poor British roads you may find it compromised. It explains that Eco Pro and Comfort use the soft damper setting, while Sport and Sport Plus use the firm one.

Smaller points from the guide: cars lowered on aftermarket springs can show ride height warnings, which BMW's ISTA-D diagnostic tool can usually recalibrate, and stones caught in the brakes can cause a loud noise. The wheel and tyre sizes vary. BMW's release lists 18-inch M wheels with mixed-size tyres among the new standard-equipment additions and 19-inch wheels as an option, but it does not say which wheels the M40i itself gets, so check the specification of the car you are viewing. Front and rear tyre sizes differ on mixed-size sets, so check each axle separately, look for kerb damage on the rims and ask when each pair of tyres was replaced.

Roof, body and cabin

The fabric roof is electric and BMW says it opens or closes in about 10 seconds at up to 31 mph. PistonHeads reports squeaks from behind the driver's head or at the screen, worse in cold weather, which BMW attributed in one case to trim panels de-bonding, and which adjusting the trim, adding foam tape and lubricating the roof mechanism usually cured. At least one owner had a roof that stopped in the first six inches of its downward travel, linked to window and module error codes, and the manual release is not always reachable depending on where the roof stopped. Some owners found windows dropped halfway on garaged cars. Other reported faults include automatic door locking that did not work, intermittent door mirror dip and fold, and headlight condensation. Run the roof up and down several times, with the windows, and look at the seals and the headlining for signs of water.

The guide says accident-damaged Z4s are not uncommon and that Frozen matt paint panels are notoriously hard to match, so look carefully at panel gaps and paint finish. Inside, the boot holds 281 litres and the driving position and cabin space are good. BMW fits two 10.25-inch screens with Live Cockpit Professional. PistonHeads says the screens collect light scratches, the sat nav can zoom at random or misplace the car until it is reflashed, the climate system sometimes needs a replacement control module and one owner had an amplifier failure that took out the radio, navigation and voice control. Expect some creaks from plastic trim, rattling driver's windows, wireless phone connections that glitch after updates and a wireless charging pad that can run hot. Holding the power button down for 20 to 30 seconds restarts iDrive.

Recalls and history

PistonHeads mentions a brake safety recall for incorrectly manufactured discs, a recall in late 2019 for an out-of-specification engine counterbalance shaft crankcase bushing, a recall for a fuel tank leak and another for a potentially faulty steering tie rod. The guide does not say which markets these recalls covered, so some may apply only to US cars; it also does not say which cars were affected, so use the DVSA recall service with the registration and ask the seller for dealer paperwork showing that any open work was completed. Also ask for a full service record, evidence of accident repair and any modifications.

Buying decision

The PistonHeads verdict is that the Z4 became an accomplished and capable two-seater, handsome in the right colours, better suited to stylish cruising than to outright cornering speed, and that a used Porsche Cayman or Boxster may suit buyers wanting a purer sports car. It also suggests the G29 is likely to be BMW's last Z4. Its price examples date from January 2023, so we have not repeated them: compare several current adverts for mileage, options and condition.

The best car has a complete service history, a roof that cycles quietly with no error messages, smooth throttle response from a cold start, even tyre wear, no crash repairs and every recall closed. Paying a little more for that car may save you chasing roof, electrical and drivability faults on a cheaper one.