The Smart Roadster 60kW returns 40–50 MPG in real-world mixed driving, against an official combined figure of around 58 MPG. The 45kW Lite manages similar numbers, while the Brabus variants typically see 35–44 MPG due to higher boost and a heavier right foot temptation.
Smart Roadster fuel economy MPG is one of the most searched topics among owners — partly because the official figures look so attractive, and partly because real life has a habit of falling short. With a 698cc turbocharged three-cylinder mounted mid-rear and a Softouch automated-manual gearbox that has opinions of its own, the Roadster rewards those who understand it. This guide covers the real numbers, the mechanical factors that influence them, and the practical steps you can take to close the gap between what the brochure promised and what your fuel gauge is telling you.
What Smart Roadster Fuel Economy MPG Looks Like in the Real World
Smart quoted a combined 58.9 MPG (NEDC) for the 60kW variant when new. That figure was achieved under test conditions that bear little resemblance to British A-roads, urban commutes or spirited weekend runs. In day-to-day use, owners consistently report 40–50 MPG for mixed driving, with pure urban use dropping into the mid-30s and relaxed motorway cruising — where the tiny engine is spinning hard just to maintain 70 mph — hovering around 44–48 MPG.
The Brabus 74kW is the thirstiest. Its higher base boost pressure of 1.43 bar and the irresistible urge to use that extra performance conspire to push real consumption toward 35–42 MPG. The 45kW Lite can match or slightly exceed the 60kW in economy terms, but its omission of an oil cooler makes it a poor long-term choice regardless of fuel bills.
Tracking your own consumption accurately matters. Fill to the brim, reset the trip meter, repeat. The Roadster’s small 33-litre tank means even modest inefficiency becomes noticeable quickly. If you’re averaging fewer than 38 MPG in mixed use, something is wrong — either mechanically or in technique.
Mechanical Factors That Hurt Smart Roadster Fuel Economy
Before adjusting your driving style, rule out the hardware. A car that is out of tune will consume more fuel regardless of how gently you drive it.
Spark Plugs and Ignition
The 698cc triple uses three spark plugs on a short service interval. Worn plugs cause incomplete combustion, forcing the ECU to enrich the mixture to compensate. Replace them on schedule — typically every 20,000 miles — with the correct NGK or equivalent specification. Iridium plugs are worth the modest extra cost for their consistency over time.
Air Filter Condition
A blocked air filter restricts the intake charge and forces richer fuelling under load. It is one of the cheapest maintenance items and one of the most overlooked. If you have not changed yours recently, our step-by-step guide to keeping the intake clean and unrestricted walks you through the process in about 15 minutes.
Fuel Filter
The fuel filter on the Roadster sits in a location that surprises many owners, and a partially blocked filter starves the injectors of consistent pressure, leading to compensation strategies from the ECU that cost economy. Full details on location and when to replace it are covered in our guide to fuel filter replacement on the 452.
Tyre Pressures
Under-inflated tyres increase rolling resistance significantly. The Roadster’s staggered tyre sizes — 175/55 R15 front, 205/50 R15 rear on most variants — mean pressures differ between axles. Running even 4 PSI low all round can cost 2–3 MPG. Check pressures cold, weekly if you drive daily. Our complete tyre pressure and sizing reference gives the correct figures for every variant.
Coolant and Thermostat
An engine that never reaches proper operating temperature runs rich as a matter of design — the ECU applies cold-start enrichment until the coolant sensor reads correctly. A stuck-open thermostat can keep the engine in this partially enriched state indefinitely, quietly destroying your MPG. If your temperature gauge seems lower than normal, investigate promptly.
How the Softouch Gearbox Affects Fuel Economy
The Softouch is not a conventional automatic. It is an automated manual — a traditional six-speed with a hydraulic actuator managing the clutch and gear selection. Understanding this distinction transforms your fuel consumption. In full auto mode, the gearbox holds gears longer than an efficient driver would, particularly under light throttle. It also downshifts aggressively when it detects even modest acceleration demand, often unnecessarily.
The single most effective technique for better economy is using manual mode (the + and − paddles or gate) to upshift earlier than the gearbox would choose. At 30 mph, you want to be in fourth. At 50 mph, fifth or sixth. The engine is torquey enough from low revs thanks to the turbocharger — trust it. Keeping revs between 1,500 and 2,500 RPM in normal driving covers the sweet spot. Our detailed walkthrough on getting the best from the Softouch transmission covers this and much more, including the critical pause technique when pulling away to avoid clutch slip.
Driving Style: The Biggest Variable in Smart Roadster Fuel Economy MPG
Mechanical condition and gearbox technique aside, how you drive accounts for the largest swing in real-world MPG — potentially 10–15 MPG between an aggressive and a measured approach.
Anticipate, Don’t React
The Roadster’s short wheelbase and light weight mean it responds quickly to inputs, but the Softouch needs a moment to react to sudden throttle demands. Smooth, progressive inputs are both faster in practice and significantly more economical. Read the road ahead, coast to junctions where safe, and avoid unnecessary acceleration followed immediately by braking.
Avoid Unnecessary Boost
The turbocharger is what makes the 698cc engine usable, but boost is expensive in fuel terms. The Garrett 1238S spools quickly at even modest throttle openings, and once it is spinning, the ECU enriches the mixture to protect the engine. Keep throttle openings below roughly 30% for everyday town use and you will rarely trigger meaningful boost, keeping economy strong.
Motorway Speeds
Aerodynamic drag increases with the square of speed. The Roadster’s low frontal area helps, but 80 mph consumes dramatically more fuel than 60 mph. If economy genuinely matters, a disciplined 60–65 mph cruise on the motorway returns noticeably better figures than 70–75 mph.
Maintenance Schedule and Fuel Economy: The Connection
A well-maintained Roadster is an economical one. The two are inseparable. Oil viscosity matters — the engine specification calls for 5W-40 fully synthetic, and using a heavier or degraded oil increases internal friction and hurts fuel consumption. Fresh oil after every 9,000-mile or annual service interval is not optional for economy or longevity.
Oxygen sensor (lambda sensor) health is equally important. The Bosch MEG 1.1 ECU relies on the upstream lambda sensor to trim fuelling in closed-loop operation. A lazy or failing sensor causes the ECU to default to a richer open-loop map, which costs both economy and power. If your long-term fuel trims are significantly positive, investigate the sensor before assuming driver error.
Reviewing the full maintenance schedule for the 452 is the best way to ensure none of the economy-relevant service items have been missed by a previous owner.
Fuel Quality and Choice
The 698cc engine requires a minimum of 95 RON unleaded. Using supermarket own-brand fuel is not inherently harmful, but premium fuels from Shell (V-Power, 99 RON) or BP (Ultimate, 97–99 RON) contain additional detergents that keep injectors and intake valves cleaner over time. On a direct-injection or port-injection engine running a turbocharger, injector cleanliness has a measurable effect on atomisation and therefore combustion efficiency.
E10 fuel, now the UK standard at forecourts, is compatible with the Roadster’s fuel system components on post-2003 cars. However, ethanol has a lower energy density than pure petrol — approximately 34% less per litre — so E10 will deliver marginally fewer MPG than E5 (super unleaded) even if all else is equal. If maximising fuel economy is the priority, filling with 97–99 RON E5 super unleaded is the correct choice. The UK government’s E10 compatibility guidance confirms the Roadster is listed as compatible, but the energy density trade-off remains real.
For background on how air-fuel ratio management interacts with the turbocharger and ECU fuelling strategy, Bosch’s technical resources on engine management offer authoritative reference material on the MEG family of ECUs that underpin the Roadster’s fuelling logic.
The Wikipedia overview of fuel economy measurement is useful for understanding why NEDC figures diverge so substantially from real-world results — the test cycle’s low average speeds and absence of meaningful acceleration phases are the primary culprits.
Frequently Asked Questions
What is the real-world MPG of a Smart Roadster 60kW?
Most 60kW owners report 40–50 MPG in genuine mixed driving. Urban-only use can drop this to the mid-30s, while steady motorway cruising at legal speeds can reach 48–52 MPG. The official NEDC figure of around 58 MPG is not achievable in normal conditions.
Does driving in manual mode improve Smart Roadster fuel economy?
Yes, meaningfully so. Manually upshifting earlier — into fourth by 30 mph and sixth by 55–60 mph — keeps revs in the efficient 1,500–2,500 RPM band. The Softouch in auto mode tends to hold gears longer and downshift unnecessarily, both of which increase fuel consumption.
Does tyre pressure really affect Smart Roadster MPG?
Significantly. Running 4 PSI below the recommended pressure on all four tyres can reduce fuel economy by 2–3 MPG due to increased rolling resistance. The Roadster’s different front and rear tyre sizes mean each axle has its own correct pressure — check both regularly with a calibrated gauge.
Is E10 petrol safe for the Smart Roadster and does it reduce MPG?
E10 is compatible with the Smart Roadster 452. However, ethanol’s lower energy density means you will typically see a small reduction in MPG compared to E5 super unleaded. If economy is the priority, premium 97–99 RON E5 fuels are preferable and also benefit injector cleanliness.
