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This is a CMST widebody carbon-fibre build on a BMW Z4 roadster (E89-generation), mixing dry-carbon show panels with FRP arches and bumpers to widen the track and sharpen the aero. It is a complete fast-road transformation — carbon bumpers, bonnet, fenders, skirts and wing, FRP widebody arches, a carbon-trimmed cabin, two-piece forged wheels and a valved cat-back exhaust — and every major panel is mirrored across CMST's catalogue, so the look can be copied piece by piece. The full parts list, materials and fitment notes are below.

• Vehicle: BMW Z4 roadster (E89-generation long-nose, short-tail two-seater)
• Fitment: Shaped to the Z4 body; a workshop fit built around a wider wheel and tyre package
• Materials: Dry carbon fibre (bonnet, fenders, lip, skirt centres, rear wing, tips, interior trim) and FRP (widebody arches, bumper shells)
• Key pieces: Carbon front bumper, vented carbon bonnet, carbon fenders, widened side skirts, FRP front and rear arches, carbon rear bumper and wing, valved cat-back exhaust, two-piece forged wheels
• Finish: Gloss carbon weave under clearcoat; FRP primed for colour-matched paint; brushed SUS304 exhaust with carbon tips; forged wheels with red barrels

The build at a glance

The donor is a BMW Z4 roadster, the long-nose, short-tail two-seater with a folding hard top. It carries good proportions from the factory but lacks width and aggression, and that is the gap this CMST programme fills with a full widebody. Two materials run through the car. Dry carbon fibre — pre-preg carbon cured under heat and pressure in an autoclave — is used for the show panels, while FRP (fibreglass-reinforced plastic) handles the bumper shells and the four widebody arches, where the shapes are deep and the panels get painted body colour anyway. AME stocks the full CMST catalogue alongside the dedicated CMST body kit for BMW range this build draws on.

The full parts list

Every panel is a discrete component, which is what lets an owner copy the build in stages. Materials are noted because they drive both the cost and how each piece is finished.

• Front bumper (FRP & carbon): reshaped front end with a dry-carbon lip and carbon canards.
• Rear bumper (FRP & carbon): deeper rear with a dry-carbon rear lip and diffuser-style centre.
• Widened side skirts (FRP & carbon): extended skirts with a carbon centre linking the arches.
• Carbon bonnet: lighter dry-carbon panel with two raised vents (the "eyes") for heat extraction.
• Carbon front fenders: vented guards for under-bonnet cooling and front-end detail.
• FRP front and rear arches: flared widebody guards covering the wider track and tyres.
• Carbon rear wing: fixed dry-carbon wing replacing the boot spoiler.
• Carbon steering wheel and interior trim.
• CMST valved cat-back exhaust: brushed SUS304, twin dual-exit, carbon tips.
• CMST two-piece forged wheels: five-point-star spoke with red barrels.

Front end: bumper, lip and canards

The FRP-and-carbon front bumper is the centrepiece of the nose. A dry-carbon front lip follows the lower edge and pushes the leading edge forward, which lowers the apparent ride height and reduces the air slipping under the front of the car, where lift builds at speed. Flanking it are two carbon canards — small winglets that shed a controlled vortex off each front corner, giving a less plain front face and a small reduction in front-axle lift. Owners building the front first can match these parts through the CMST front lip for BMW collection.

Bonnet and fenders: carbon where heat and weight matter

The steel bonnet is replaced with a dry-carbon item carrying two raised vents. Beyond the styling, the change does real work: carbon removes weight from the highest, most forward part of the car — the best place to lose mass for handling — and the vents let hot air escape the engine bay instead of building up under sealed steel. The carbon front fenders follow the same logic — vented behind the wheel so high-pressure air trapped in the arch can bleed out, easing front-end lift and helping cooling. Bonnet and fenders are the panels people notice first, so they are formed in carbon rather than FRP.

Going wide: arches and side skirts

The widebody conversion is the heart of this build. Flared FRP arches overlay the standard guards front and rear, adding clearance for a wider track and broader tyres. CMST moulds these in fibreglass for a reason: the deep, compound curve of a widebody arch is far easier and cheaper to form in FRP than in autoclaved carbon, and since the arches are painted body colour, a carbon weave would be hidden anyway. Linking them is a widened side-skirt set with a carbon centre that ties the front and rear flares into one line down the flank. The trade-off to plan for is the wheel and tyre package: offset, tyre width and ride height must be set so the tyre clears the new arch through full suspension travel and steering lock.

Rear end and wing

At the back, the FRP-and-carbon rear bumper deepens the tail and houses a dry-carbon rear lip with a diffuser-style centre that frames the new exhaust exits. Above the boot, a fixed dry-carbon rear wing replaces the standard spoiler. A raised wing sits in cleaner air above the bodywork and generates rear downforce, which matters most at higher speeds, where it improves stability and balances the front aero so the car does not feel light at the back.

The exhaust: a valved CMST cat-back

The car runs a CMST valved cat-back exhaust in SUS304 international-standard stainless steel with a brushed finish and carbon tips. Its headline trick is converting the factory twin single-exit layout to a twin dual-exit, so each side shows two tailpipes. SUS304 is the grade widely used for performance exhausts because it resists corrosion and tolerates heat well, and a purpose-built cat-back is generally lighter than the restrictive factory system, with a smoother flow path.

The valve is the part owners interact with most. Closed, exhaust gas takes the longer, quieter route that preserves some back-pressure and keeps the car torque-friendly at low rpm. Open it — by choice or as engine speed rises — and the gas takes a straighter path for a louder, free-flowing note up top. That dual personality is why valved systems suit a road car that occasionally gets driven hard. A freer-flowing cat-back can help an engine breathe, but gains depend on the wider setup, so we avoid quoting figures this system has not been measured to deliver. The same range is available through the CMST cat-back exhaust collection.

Wheels and interior

The build sits on CMST two-piece forged wheels with a five-point-star spoke and red barrels that contrast the dark body. Two-piece forged construction — a forged centre bolted to a separate barrel — lets the wheel be built to a specific width and offset, exactly what a widebody car needs to fill the new arches. Forged wheels are also generally lighter and stronger than cast equivalents at the same size, and cutting unsprung weight helps the suspension keep the tyre planted. Confirm sizing against the final arch and tyre package; CMST forged options sit in the CMST wheels for BMW collection. Inside, a carbon steering wheel and carbon trim continue the theme, with the red barrels tying back to the cabin's red detailing.

Owner takeaways if you want to copy this build

• Plan the wheels and tyres first. Lock in width, offset, tyre size and ride height before the arches go on so everything clears through full travel and lock.
• Budget for paint. The FRP arches and bumpers arrive primed and need spraying to match your Z4's colour.
• Look after the carbon. Clearcoat degrades under prolonged UV — park undercover, wash with pH-neutral products and consider a ceramic coating or paint protection film.
• Stage it. Every panel is separate, so start with the front lip and canards and commit to the full arches and wheels later.

Frequently asked questions

Which BMW Z4 does this CMST widebody kit suit?

It is built for the BMW Z4 roadster, the long-nose, short-tail two-seater with the folding hard top (the E89-generation car). The panels are shaped to that body, so confirm your Z4 matches before ordering and have fitment checked by a workshop, as a widebody conversion is not a driveway job.

Why are some parts carbon fibre and others FRP?

Dry carbon fibre is autoclave-cured pre-preg carbon: light, stiff and showing a visible weave, so CMST uses it for the bonnet, fenders, front lip, skirt centres, rear wing, exhaust tips and interior trim. FRP (fibreglass) is heavier but forms deep, complex shapes economically and paints well, so it is used for the widebody arches and bumper shells, which are colour-matched to the car anyway.

How does the valved exhaust work?

The CMST cat-back uses a valve in the pipework. Closed, it routes gas through a quieter path that keeps some back-pressure and protects low-rpm torque; open, it lets gas flow more directly for a louder note at high rpm. The owner can switch modes manually or have the valve respond to engine speed. It is built from SUS304 stainless with a brushed finish and carbon tips, and converts the factory twin single-exit to a twin dual-exit.

What does the widebody conversion involve?

Fitting flared FRP arches front and rear to cover a wider track and broader tyres, then matching wheel offset, tyre width and ride height so the tyres clear through full suspension travel and steering lock. Depending on the final wheel and tyre choice, some guard rolling or trimming of the OEM metal can be needed, so it should be fitted by a workshop experienced with widebody builds.

Are the two-piece forged wheels worth it on a widebody?

Yes, and they are close to essential. A two-piece forged wheel pairs a forged centre with a separate barrel, so it can be built to the exact width and offset the new arches need. Forged wheels are also generally lighter and stronger than cast ones at the same size, and cutting unsprung weight helps the suspension keep the tyre planted.

Can I buy the parts separately and build it over time?

Yes. The kit is a set of discrete components, so you can stage the build: start with the front lip and canards for an early change, then add panels and finish with the full widebody arches and forged wheels. Contact AME Motorsport to confirm current availability of single pieces for your Z4.

Build your Z4 widebody with AME Motorsport

If you are planning a carbon widebody for a BMW Z4, AME Motorsport can supply the CMST panels, exhaust and forged wheels and help you sequence the build. Browse the BMW body kit range to see what fits, then get in touch to confirm the right wheel and tyre package before any panels are painted.