BMW Z4 G29 used: which roadster engine to buy

A BMW Z4 G29 used (2019 to 2024) gives you a folding-fabric roadster that splits cleanly down the middle: the four-cylinder sDrive20i and sDrive30i on one side, the straight-six M40i on the other. The right pick depends on whether you want cheap open-top miles or the soundtrack of BMW’s B58 six. Here we set out the engine split, the Toyota Supra link, the soft-top and run-flat realities, and what a UK buyer should check before paying a deposit.

The engine split that decides everything

The G29 range is built on two engine families. The sDrive20i and sDrive30i share BMW’s B48 2.0-litre turbocharged four-cylinder, rated at 197PS and 258PS respectively. The M40i runs the B58 3.0-litre turbocharged straight-six at 340PS. That is the single most important decision on a used Z4: a four-pot car is a relaxed weekend roadster, while the six turns it into a serious quick convertible with a 0 to 62mph time in the low-4-second range. Power figures are per BMW’s published specifications. If your shortlist also takes in a hard-top coupe, our BMW 4 Series G22 used engine and year guide walks the same B48-versus-B58 choice in a different body.

Why the Toyota Supra link matters to a used buyer

The G29 was developed alongside the fifth-generation Toyota Supra (A90) under the BMW-Toyota joint sports-car project, and both are assembled by Magna Steyr in Graz, Austria. For a buyer that is reassurance, not a gimmick: the M40i’s straight-six, ZF eight-speed automatic and rear suspension are shared engineering with a car Toyota was happy to badge as a Supra. The practical upshot is a healthy independent-specialist and parts network, because mechanics who know one know the other. It also means the Z4 drives like a proper rear-driven sports car rather than a softened cabrio. The Supra connection is confirmed by BMW and Toyota’s own launch material.

Soft-top roof: the return to fabric

The previous Z4 (E89) used a folding metal hardtop. The G29 went back to a fabric soft-top, and that is a deliberate gain: it is lighter, packages into a smaller stack, and leaves a usable 281-litre boot that does not shrink when the roof drops. The roof operates electrically in around 10 seconds at up to 31mph. The trade-off is the one owners mention most: with the roof up, motorway road noise is higher than a tin-top coupe, and the fabric needs occasional reproofing to keep water out. Check the roof cycles fully, sits quiet at the seals, and shows no staining or perished edges before you commit.

Run-flat tyres and the ride question

The Z4 ships on run-flat tyres and carries no spare wheel, which keeps the boot clear but firms up the low-speed ride, especially on the M40i’s larger wheels. Owners who find the ride too sharp often switch to conventional tyres at the next change and report a meaningful improvement, accepting that they then need a mobility kit or breakdown cover for a puncture. Budget for tyres as a running cost: a set of staggered run-flats for the six-cylinder car is not cheap, and uneven wear is common if the alignment has drifted. The salary-sacrifice EV crowd will recognise this trade-off from our piece on salary sacrifice EV hidden costs including tyres, where run-flat and performance rubber quietly inflate the monthly sums.

The gearbox reality: automatic for almost everyone

Here is the detail that catches buyers out. For nearly the whole used run, every G29 in the UK is a ZF eight-speed automatic. A six-speed manual was offered on the sDrive20i only, from July 2019, and it is rare; the manual M40i (the Handschalter) arrived only at the very end of production in 2025 and barely exists used. So if you want three pedals, you are hunting a scarce four-cylinder car and should expect to travel for it. For most buyers the ZF auto is no hardship: it is the same smooth, quick-shifting box used across the BMW range and shared with the Supra. Verify the transmission in the advert rather than assuming, because US-market manual availability does not map onto UK stock.

Real UK used prices and the M40i premium

On a June 2026 scan of UK classifieds, early 2019 to 2020 sDrive20i M Sport cars start around £19,000 to £23,500, mid-range sDrive30i examples sit a few thousand higher, and 2021 to 2022 M40i cars run from roughly £33,000 to £37,000 (UK classifieds, June 2026). That is the M40i premium in plain numbers: the straight-six commands £10,000 or more over a four-cylinder of similar age and mileage, and it holds that gap because the engine is the car’s headline act. Our verdict on whether that premium is worth paying comes later, but the residual strength of the six is real. For a sense of how engine choice drives premium-roadster values elsewhere, the Porsche 718 Cayman and Boxster used buyer’s guide shows the same flat-four-versus-flagship split.

BMW Z4 G29 used: faults by year and pre-purchase checks

The G29 has been a reliable design, but it is not faultless. Early 2019 cars occasionally needed infotainment software updates and the odd electrical niggle ironed out under warranty; from the 2023 facelift onward the iDrive system and trims were freshened. Across the run, the recurring owner themes are tyre wear, the occasional soft-top motor or seal issue, and brake discs that wear faster on hard-driven M40is. None of these is a structural flaw, but each is a bargaining lever. Before deposit: confirm full BMW or specialist service history, run the VIN through the DVSA vehicle recall checker, inspect the roof through a full cycle, check tyre dates and wear evenly across the axle, and on the M40i lift the car to look at disc lip and pad life.

Running costs: insurance, economy and servicing

Economy is better than the roadster image suggests. Honest John Real MPG, drawn from 24 owner submissions, records 39.0mpg for the sDrive20i, 39.6mpg for the sDrive30i and 36.5mpg for the M40i, so even the six is genuinely usable daily. Insurance is where the engines separate again: the M40i sits in high insurance groups and shares the cost profile of other performance BMWs, a pattern we cover in our look at why BMW M and Audi RS insurance costs so much. Servicing follows standard BMW intervals, and a manufacturer-backed plan via the BMW, Audi and Mercedes approved-used warranty comparison is worth weighing against an independent specialist for a car of this value. You can browse comparable roadster guides through our used buying guides hub.

Specs and used data at a glance

Our take

Buying a BMW Z4 G29 used comes down to honesty about how you will use it. If the Z4 is a weekend toy and a second car, the sDrive20i is the value play: cheap to buy from around £19,000, 39mpg real-world, and every bit the open-top BMW for the money. If it is your one indulgence and you want the noise and the pace, the M40i is the one to stretch for, and its B58 straight-six is the reason it holds value so much better than the four-cylinders. We would skip the sDrive30i unless one turns up cheap, because it costs more than a 20i without matching the six. Whichever you pick, the deal-makers are boring: documented service history, a soft-top that cycles cleanly, healthy run-flat tyres and a clear DVSA recall check. Pay for the paperwork, not the colour.