> The finding: Full hybrids generally deliver close to their official figures. Plug-in hybrid claims are the least reliable numbers in motoring — and whether a PHEV is brilliantly efficient or worse than a petrol car depends almost entirely on one variable the test cycle can't measure: whether the owner actually plugs it in. > > Populate the comparison table with your own measured results.
Not all hybrids behave the same way
"Hybrid" covers several genuinely different technologies whose real-world behaviour diverges enormously. Understanding which type you're comparing is essential before any economy figure means anything:
Mild hybrid (MHEV). A small motor-generator assists the engine but cannot drive the car alone. Modest gains — typically single-digit percentages. Official figures are usually reasonably reliable because the system's contribution is small and consistent.
Full hybrid (HEV). A larger battery and motor can drive the car alone at low speeds, self-charging through regeneration. Toyota's system is the archetype. Substantial real gains, especially in city driving, and official figures are generally achievable.
Plug-in hybrid (PHEV). A large battery (typically 10–20+ kWh) gives meaningful electric-only range, recharged from the grid. Official figures are extremely dependent on user behaviour — and this is where the numbers become almost meaningless.
Range-extender EV (EREV). Always electrically driven, with an engine acting purely as a generator (see our Ram Ramcharger test). Behaves like an EV until the battery depletes.
Why PHEV figures are the least reliable numbers in motoring
Official PHEV economy figures assume a specific charging pattern, and the resulting numbers are extraordinary — BMW claims 176 mpg WLTP for the M5 PHEV, a 2,435 kg super-saloon.
That figure is a laboratory artefact, not a prediction, and it can be wildly wrong in both directions:
A PHEV driven as intended — charged nightly, used for short daily trips within its electric range — can genuinely deliver spectacular economy. If your commute is 30 miles and the car has 42 miles of electric range, you may buy fuel a few times a year. The official figure might even understate your experience.
A PHEV that is never plugged in is worse than the equivalent petrol car. It carries several hundred kilograms of battery and motor as dead weight, with no benefit whatsoever. The M5's PHEV system alone adds roughly 400 kg.
The same car can therefore return 150 mpg or 25 mpg depending entirely on owner behaviour. No test cycle can capture that, which is why PHEV official figures should be treated as an indication of potential rather than a prediction of outcome.
This matters most for company-car buyers, where PHEVs are often chosen for tax advantages rather than genuine efficiency intent. A PHEV selected for its tax band and then never charged delivers the worst outcome available — high emissions, poor economy and a heavy car.
Our test protocol
| Element | Standard | |---|---| | Route | Fixed mixed route: urban, A-road and motorway segments, individually recorded | | Motorway test | Separate constant-70-mph run | | Urban test | Separate congested-traffic segment — where hybrids excel | | PHEV protocol | Tested three ways: (1) starting fully charged, (2) starting depleted, (3) a realistic weekly average | | Load | Driver plus standard equipment | | Climate | On, at 21°C | | Recorded | Ambient temperature, actual fuel consumed (brim-to-brim), electricity consumed for PHEVs | | Outputs | Measured mpg per segment · percentage of official figure achieved · PHEV: charged vs depleted delta |
The three-way PHEV test is the crucial methodological point, because a single PHEV figure is inherently misleading. Publishing the depleted-battery figure alongside the charged one is the honest approach, and it's the number a buyer who won't charge diligently should look at.
Our test conditions: [to be completed — dates, routes, ambient temperatures, fuel grade, starting SoC for PHEVs]
The comparison table
Populate with measured results across the model range.
| Model | Type | Official | Measured (mixed) | % achieved | PHEV depleted | |---|---|---|---|---|---| | [to be measured] | | | | | |
Relevant vehicles from this project:
| Vehicle | Type | Official claim | |---|---|---| | Honda Prelude | Full hybrid (e:HEV) | ~44 mpg combined (EPA est.) | | BMW M5 | PHEV | 176 mpg WLTP (~42 mi electric) | | AMG SL63 S E Performance | Performance PHEV | 24 mpg measured (75-mph highway) | | Toyota Hyryder / Maruti Grand Vitara | Full hybrid | Strong-hybrid efficiency leaders (India) | | Ram 1500 Ramcharger | EREV | 145 mi electric / ~690 mi total |
What we expect the data to show
1. Full hybrids will perform best against their claims, particularly in urban driving where regenerative braking and electric low-speed running deliver genuine, consistent benefit. Toyota's systems have a strong record here.
2. Mild hybrids will show modest but honest gains — small improvements, reliably delivered.
3. PHEVs will show the widest spread by far, with the charged-versus-depleted gap being the headline finding. Expect a difference of several hundred percent between the two conditions on the same car.
4. Performance hybrids will confirm they're not efficiency devices. The AMG SL63's measured 24 mpg on a 75-mph highway run makes the point cleanly: its hybrid system exists to add 201 hp, not to save fuel.
5. Motorway running will narrow hybrid advantages considerably. Hybrids excel in stop-start conditions where regeneration and electric running help most. At a constant 70 mph, the engine is doing nearly all the work and the advantage shrinks.
What buyers should take from this
Match the technology to your driving. Full hybrids suit urban and mixed driving. PHEVs suit short daily commutes with reliable charging. Neither suits high-mileage motorway drivers particularly well — a diesel or efficient petrol may still be better there.
Be honest about whether you'll charge. If you won't plug in nightly, do not buy a PHEV. You'll carry the weight, pay the premium and receive none of the benefit.
Look at the depleted figure for PHEVs, not the headline. It's your worst case, and for many owners it's their actual case.
For India specifically: strong hybrids (Grand Vitara, Hyryder) deliver genuine, reliable efficiency without any charging infrastructure requirement — which, as our apartment-charging test showed, is a substantial practical advantage.
The bottom line
Hybrid economy claims range from reliable to nearly meaningless depending entirely on the technology. Full hybrids generally deliver, particularly in city driving. Mild hybrids offer modest, honest gains. And PHEV official figures are the least reliable numbers in motoring — capable of being both wildly optimistic and genuinely understated for the same car, depending on one variable no laboratory can measure.
The honest advice is simple: a PHEV is only efficient if you plug it in. If you will, it can be exceptional. If you won't, you've bought a heavy, expensive petrol car and made it worse. Look at the depleted-battery figure, be truthful with yourself about your charging habits, and match the technology to how you actually drive.
- "Hybrid" covers genuinely different technologies — mild, full, plug-in and range-extender — whose real-world behaviour diverges enormously
- Full hybrids generally deliver close to official figures, especially in urban driving; mild hybrids offer modest but honest gains
- PHEV figures are the least reliable in motoring: the same car can return 150 mpg or 25 mpg depending purely on whether it's charged
- An uncharged PHEV is worse than the equivalent petrol car — it carries hundreds of kilograms of dead weight for no benefit
- We test PHEVs three ways (charged, depleted, realistic average) and publish the depleted figure, because for many owners it's their actual case
Key takeaways
- "Hybrid" covers genuinely different technologies — mild, full, plug-in and range-extender — whose real-world behaviour diverges enormously
- Full hybrids generally deliver close to official figures, especially in urban driving; mild hybrids offer modest but honest gains
- PHEV figures are the least reliable in motoring: the same car can return 150 mpg or 25 mpg depending purely on whether it's charged
- An uncharged PHEV is worse than the equivalent petrol car — it carries hundreds of kilograms of dead weight for no benefit
- We test PHEVs three ways (charged, depleted, realistic average) and publish the depleted figure, because for many owners it's their actual case
Sources & further reading
- Hybrid powertrain principles
- WLTP/EPA methodology
- manufacturer claims
- True Motion Auto tests (this project). *Populate comparison table with measured results before publishing. Verified July 2026.*
Figures, prices and policy details were current at the last-updated date above. Automotive pricing, incentives and regulations change frequently — verify time-sensitive details with the linked primary sources. Read our editorial policy and fact-checking standards.
