CMST BMW Z4 E89 Widebody Carbon Kit & Forged Wheels
The CMST widebody Z4 build turns a BMW Z4 E89 roadster into a wide-track, carbon-bodied street car by combining a flared FRP-and-carbon body kit with two-piece forged wheels and a valved SUS304 exhaust. The E89 already has the long-bonnet, short-deck roadster shape and a folding hard-top; CMST adds width, downforce-oriented aero and exposed carbon weave on the highest-value panels. This article treats the kit as one complete transformation, because the stance, wheels and exhaust were specified to work together.
- Vehicle: BMW Z4 (E89, 2009–2016) two-seat roadster with retractable hard-top
- Kit type: Widebody aero kit — flared arches plus carbon and FRP aero panels
- Materials: Dry carbon on headline panels; FRP on the wide arches and bumper structure
- Key pieces: Front bumper (carbon lip + canards), rear bumper (carbon lip), widened side skirts, vented carbon bonnet, vented carbon front fenders, FRP arches, carbon rear wing
- Add-ons: CMST valved SUS304 cat-back (twin dual-exit, carbon tips) and CMST two-piece forged wheels with red barrels
- Interior: Carbon-fibre steering wheel and carbon trim
Why the Z4 E89 suits a widebody build
The Z4 E89 is a front-engine, rear-drive roadster with a folding hard-top, so its proportions are already dramatic: a long bonnet, a cab-rearward cockpit and a short tail. That shape carries width well, but the standard car runs narrow guards and a restrained factory aero treatment — the gap a widebody kit fills. Flaring the arches and dropping a carbon lip under the nose gives the E89 the planted, track-derived stance its silhouette always hinted at.
Because the E89 is rear-driven, the aero logic is straightforward: a front lip and canards manage lift over the nose, while a raised rear wing adds load over the driven rear axle. Get that balance right and the car feels settled rather than nervous as speed climbs. If you are mapping out a full carbon programme, AME stocks the complete CMST range alongside the broader CMST carbon fibre body kit catalogue.
The stance: forged wheels and widebody arches
The transformation starts at the corners. CMST fits two-piece forged wheels with a five-point-star spoke pattern and red-anodised barrels that contrast against a dark body and tie back to the red interior. A two-piece forged wheel bolts a separately forged centre to a spun or forged outer rim, so it can be sized and offset precisely for a widebody car. Forging aligns the aluminium's grain, making the wheel generally stiffer and lighter for its strength than a cast equivalent; lighter unsprung mass sharpens how the car reacts over bumps.
Those wheels need somewhere to live, which is where the FRP arches come in. They widen the guards so the car can run a wider track and broader tyres without fouling the bodywork. CMST moulds them in FRP because fibreglass forms the deep curves economically and is built to be sprayed to body colour. Setting offset, tyre width and ride height so the tyre clears the arch through full travel and steering lock is the most important fitment decision on a widebody Z4. Owners can compare the CMST BMW wheels listings.
Carbon aero, panel by panel
With the stance set, the aero panels do the styling and airflow work — dry carbon where light weight and a visible weave matter, FRP on the wider structural pieces.
Front bumper, carbon lip and canards
The front bumper is an FRP-and-carbon assembly carrying a carbon front lip and a pair of carbon canards. The lip integrates with the factory bumper line and extends slightly forward to reduce the air slipping under the nose. The corner canards add aggression and create small vortices that help trim front-end lift. To start at the nose, the CMST BMW front lip range is the logical first piece.
Vented carbon bonnet
The steel bonnet is replaced with a dry-carbon item carrying two recessed vents — the "eyes" that define the car's face. The vents let hot engine-bay air escape and shed weight from the highest, most forward part of the car, where removing mass helps the way a roadster turns in. As with any aftermarket carbon bonnet, confirm the factory latch or bonnet pins engage securely before driving. Browse comparable panels in the CMST BMW bonnet collection.
Vented carbon fenders and widened side skirts
The carbon front fenders use a louvred vent design that increases heat extraction from the front of the car and echoes the bonnet vents. The widened side skirts carry a carbon centre section and run between the arches, visually lowering the car and tying the flares into one continuous line. Together they make the widebody read as a designed whole rather than bolt-on flares.
Rear bumper, carbon lip and rear wing
At the back, the FRP-and-carbon rear bumper houses a carbon rear lip that adds a diffuser-style lower section and pulls the tail visually towards the road. Above it sits a dry-carbon rear wing in place of the factory boot-lid treatment. A raised wing sits in cleaner air than a ducktail and generates rear downforce, which on a rear-drive roadster aids high-speed stability and balances the front aero. The same philosophy runs across AME's CMST carbon fibre programme, where aero and rolling stock are specified as a set.
The CMST valved exhaust: SUS304, twin dual exit
The exhaust changes how the car feels and sounds rather than how it looks. CMST's valved cat-back replaces the factory twin single-exit layout with a twin dual-exit system finished in carbon tips, so the rear shows four pipes instead of two. It is built from SUS304 stainless steel with a brushed finish, resisting corrosion and saving weight over the heavier factory system while smoothing exhaust flow.
The valve is the clever part. An electronically controlled valve lets the driver, or engine load and rpm, set the exhaust character. Closed, it routes gas through a longer, quieter path with more back-pressure, keeping the cabin civil and looking after low-rpm tractability. Open, it gives a straighter, free-flowing path with a louder note for higher-rpm work. That dual personality is what makes a valved cat-back so popular on a roadster you actually street-drive. Match it to your build through the CMST cat-back exhaust range.
Carbon inside the cabin
The interior carries the theme inward with a carbon-fibre steering wheel and carbon trim. On the E89, these lift a cabin that, in standard form, leans more luxury roadster than focused sports car. Paired with the red leather and red wheel barrels, the carbon reads as a coordinated colour story rather than a random collection of upgrades.
Dry carbon vs FRP: what goes where, and why
This build mixes two aftermarket materials on purpose. Knowing which is which sets your expectations on weight, finish and care.
| Material | Where CMST uses it | Strengths | Trade-offs |
|---|---|---|---|
| Dry carbon fibre | Front lip, canards, bonnet, fenders, skirt centres, rear lip, wing, tips, interior | Lightest and stiffest; visible twill weave under clearcoat | UV-sensitive clearcoat; higher cost |
| FRP (fibreglass) | Wide front and rear arches, bumper structure | Forms deep arch curves economically; easy to paint | Heavier than carbon; needs colour-matched paint to finish |
The practical upshot: the weight-saving show panels — bonnet, fenders, lips, wing — are dry carbon, while the wide arches that get sprayed to body colour anyway are FRP. That keeps the build affordable without giving up the carbon look where it counts.
Fitment and finish in Australia
Carbon and FRP panels are made to tighter, more brittle tolerances than the factory bumpers, so a widebody Z4 is a workshop job. A few points are worth planning before you book it.
- Paint-matching the FRP: the arches and bumper structure arrive primed and must be sprayed to your Z4's colour, including any metallic or pearl, so the flares disappear into the body.
- Dry-carbon clearcoat care: the exposed weave sits under a clearcoat that degrades under prolonged UV. Park undercover, wash with pH-neutral products, and consider a UV-stable ceramic coating or PPF to stop the weave yellowing under the Australian sun.
- Wheel and tyre package: confirm offset, tyre width and ride height before the arches go on so the tyre clears through full travel and lock.
- Roof clearance: the E89's hard-top stows into the boot, so check that any rear-bumper or wing hardware does not foul the roof mechanism or boot.
Because the kit ships as discrete pieces, a competent body shop can trial-fit and correct panel gaps in stages, working around your painter's schedule.
Frequently asked questions
Which BMW Z4 does this CMST kit fit?
This is a widebody kit for the BMW Z4 E89, the second-generation roadster built from 2009 to 2016 with the folding hard-top. It is shaped to the E89 body, so confirm your car is the E89 generation before ordering; it is not designed for the earlier E85/E86 or the later G29 Z4.
What is the kit made from?
The headline aero panels — front lip, canards, bonnet, front fenders, side-skirt centres, rear lip and rear wing — are dry carbon fibre, the lightest and stiffest option, with a visible twill weave under clearcoat. The widebody arches and bumper structure are FRP (fibreglass-reinforced plastic), which forms the deep arch curves economically and is painted to match the body.
Do the widebody arches need cutting or rolling?
The flared arches cover a wider track and tyre. Depending on your final wheel offset, tyre width and ride height, some guard rolling or trimming of the factory metal can be required so the tyre clears the arch through full suspension travel. Confirm your wheel and tyre package and have the work done by a workshop experienced with widebody conversions.
How does the CMST valved exhaust change the car?
The SUS304 stainless cat-back converts the factory twin single-exit to a twin dual-exit with carbon tips. Its electronic valve switches between a quieter, higher-back-pressure mode that protects low-rpm drivability and a louder, free-flowing mode for higher-rpm driving, so the same car can be civil on the commute and aggressive when you want it.
Why two-piece forged wheels rather than cast?
Forging aligns the aluminium grain, so a forged wheel is generally stiffer and lighter for its strength than a cast wheel, reducing unsprung mass and sharpening the roadster's responses. The two-piece construction also lets CMST set rim width and offset precisely to suit the wider widebody track.
Should I have it professionally fitted?
Yes. Carbon and FRP panels are more brittle than the flexible factory bumpers, and correct panel gaps, secure mounting, colour-matched FRP paint and a properly set widebody wheel package all need a body shop. Professional fitment protects the parts and delivers the flush, coordinated result the kit is designed for.
Build your widebody Z4 with AME Motorsport
If you are planning a complete carbon transformation for a BMW Z4 E89 — widebody arches, carbon aero, two-piece forged wheels and a valved SUS304 exhaust as one package — AME Motorsport can supply the CMST pieces and advise on staging the build. Start with the CMST BMW body kit range, then get in touch to confirm fitment and the right wheel and tyre package for the arches.