Permanent vs on-demand 4x4: the differences in everyday driving

• Permanent four-wheel drive drives both axles all the time, with a differential or a controlled clutch splitting power between them. On-demand four-wheel drive mostly drives just one axle and a multi-plate clutch engages the other when needed.
• On a snowy road you will notice little difference. Modern clutches, such as the one in the Škoda Octavia Combi III 4x4, engage the rear axle predictively, before the wheels start to spin. Permanent drive has the edge under prolonged load, in deep snow and when getting a stuck car out.
• Disconnecting the drive saves only tenths of a litre of fuel. For its quattro ultra system, Audi quotes a saving of 0.3 l/100 km compared with conventional all-wheel drive. Weight barely changes, as the car carries the drivetrain components around at all times.
• The clutch of an on-demand system needs oil changes. Škoda specifies a three-year interval for its 2018 clutch. It is an inexpensive job compared with repairing a neglected clutch.
• Part-time four-wheel drive with low range, as on the Suzuki Jimny IV, is a category of its own. Its 4x4 mode belongs only on slippery or loose surfaces.

In used-car adverts, permanent four-wheel drive is seen as technically superior and on-demand drive as the more economical compromise. That distinction does not help much when choosing a used car, though. Over the years, different designs have hidden behind a single trade name, and similarly named systems behave differently in everyday use. For daily driving, it matters more to know how the system engages the second axle, how this shows on snow and in fuel consumption, and what maintenance it needs. Specific used cars by body style are covered in our guide to the best 4x4 cars.

Permanent all-wheel drive sends power to both axles continuously. In the classic design, a centre differential allows the front and rear wheels to turn at different speeds in a corner. The split of power between the axles changes according to grip, and on newer systems it is controlled by electronics.

Automatically engaged four-wheel drive brings in the second axle with a controlled multi-plate clutch. When driving calmly on a dry road, it drives mainly one axle. When pulling away, accelerating or on a slippery surface, the clutch engages and sends part of the power to the rear. The driver does nothing.

Part-time four-wheel drive is found on off-roaders and pickups. The driver chooses between one or both axles being driven, and low range where fitted. In 4x4 mode the axles are rigidly linked, so the speed difference in a corner has to be absorbed by the tyres slipping. On dry tarmac this puts strain on both the drivetrain and the tyres.

A multi-plate clutch does not in itself determine the type of system. In on-demand drive it engages and disengages the second axle; in some permanent systems it continuously splits power between the axles, as on the automatic Subaru Forester III in the table below.

Hybrids and electric cars drive the rear axle separately with an electric motor. The Toyota RAV4 V Hybrid AWD-i in its 2019 specification uses an additional electric motor for this. The details are covered in our article on electric and hybrid 4x4s: drive, range and winter driving.

On-demand drive does not wait for wheelspin

The old idea is that the front wheels have to spin first and only then does the rear axle start to pull. That no longer applies to modern systems. The electronics monitor the accelerator position, steering angle and the car's movement, and preload the clutch in advance.

Škoda states that the electronically controlled multi-plate clutch in the Octavia Combi III 4x4 and Kodiaq I 4x4 in their 2018 versions works predictively. When pulling away normally on a snowy road, the driver therefore does not notice the rear axle engaging. There is no single figure for the delay. The speed of response depends on the clutch generation and software. Older clutch generations react noticeably more slowly than the predictive ones.

Permanent drive keeps traction even under prolonged load

When dry and snowy stretches alternate, or when accelerating on a slippery climb, permanent drive does not have to engage anything; it simply redistributes power. Its responses are smooth and easy to predict.

The difference shows when getting a car unstuck over a long period, in deep snow or with repeated wheelspin. A controlled clutch heats up and the electronics may temporarily disengage it to protect it. The car then pulls with just one axle. Permanent drive does not suffer from this limitation, but it too has its limits, set by the diff locks, slip control and ground clearance.

When braking, the type of drive makes no difference. All-wheel drive does not shorten braking distances. When slowing down on snow, speed and tyres are what count.

Drivetrain parts that turn constantly cause mechanical losses. A system that disconnects part of the drivetrain and lets it stand still reduces them. For its quattro ultra system, Audi quotes an average saving of 0.3 l/100 km compared with conventional all-wheel drive in everyday driving. The difference is roughly of that order. Choosing a type of drive for the sake of fuel consumption is therefore not worthwhile.

With used cars, it is also easy to end up comparing two different cars instead of two systems. A different engine, gearbox, tyres or weight can easily mask the difference in drivetrain. It only makes sense to compare the same model with the same engine.

What about weight?

Both concepts need extra parts: power transfer between the axles, a propshaft, a rear differential and driveshafts. An on-demand 4x4 carries them even when it is not driving the rear axle. In terms of weight, on-demand drive does not behave like a front-wheel-drive car. The saving comes from less friction, not lower weight.

The table shows examples of designs, not buying recommendations. The Suzuki Jimny is included as a contrast to the road-going systems.

How to identify the system on a specific car

Trade names such as quattro, 4Motion, xDrive or AWD do not refer to a single, unchanging design. Manufacturers have used them for different systems across generations and engine versions. You can determine the type of drive from the combination of generation, engine and gearbox. The most reliable source is the factory specification by VIN, which an authorised dealer workshop can print out.

The Subaru Forester III shows why knowing the model and generation is not enough. With a manual and with an automatic it has two different systems. So do not trust the description of the drivetrain in an advert until the car's specification confirms it.

Neither system is maintenance-free. They differ in what gets replaced and what goes wrong.

For the 2018 multi-plate clutch, Škoda specifies an oil change every three years. Other generations and makes have different intervals, and some older clutches even shorter ones. A Haldex clutch oil change is an inexpensive job compared with a clutch repair. The price depends on the size of the oil fill, the oil used and how much labour the particular gearbox family requires, and it varies from country to country and workshop to workshop.

A skipped oil change is the most common route to an expensive repair on on-demand drive. A worn clutch or faulty pump costs considerably more than regular servicing. On permanent drive, oil changes are less frequent. Any repair to the differential or final drive is also among the more expensive jobs, though. On a used car, the drivetrain's service history therefore matters more than its type.

• Do not confuse automatic engagement with manual. A road-going 4x4 with a clutch can be driven on dry tarmac without restriction. Manually engaged 4x4 mode on an off-roader destroys the gears and tyres on the same surface.
• Permanent drive does not have a fixed torque split. The ratio between the axles changes, and individual designs cope with wheelspin with varying success.
• Tyres must be the same size and have similar wear on all wheels. Different wheel circumferences put constant strain on the drivetrain. For xDrive systems with the ATX13-X transfer case, BMW describes judder or shudder when cornering and pulling away at low speed, and warns that badly worn tyres can keep the drive permanently engaged.
• A name in the equipment list says nothing about condition. Even an advanced system can have a faulty clutch or a worn propshaft bearing. For cars offered by Carvago, the condition of the drivetrain is checked by diagnostics and a test drive as part of CarAudit™.

For normal road driving, there is no reason to reject modern on-demand drive out of concern about slow responses. Permanent drive makes sense for those who often drive on mountain roads with changing grip or expect prolonged load. A part-time system only belongs on the shortlist if the car really will be driven off made-up roads.

With all-wheel drive, the exact version is what counts: generation, engine and gearbox. Carvago offers roughly a million used cars from dealers in several European countries. That means you can find the specific version with the system you want, rather than settling for whatever happens to be available nearby.

Every car is inspected by a technician before sale as part of CarAudit™ with up to 270 checkpoints. The inspection covers the technical components, diagnostics and a test drive, which reveals any judder, noises or an axle that fails to engage. You know the result before you decide to buy. Carvago guarantees the condition stated in the CarAudit™ certificate.

Every car comes with a free extended warranty. On a used 4x4, where a clutch or differential repair is among the more expensive items, it is a useful safeguard. Before sale, Carvago buys the car from the original seller and takes on its risks, so you buy directly from Carvago.

Does a Lock button mean a mechanical diff lock?

Usually not. On systems with a multi-plate clutch, Lock mode simply keeps the clutch more firmly engaged and the axles more tightly linked, usually up to a certain speed. Mechanical diff locks are found mainly on off-roaders and pickups.

Which axle do snow chains go on with a 4x4?

The manufacturer specifies this in the owner's manual. On cars with on-demand drive derived from a front-wheel-drive platform, it is usually the front axle. Some all-wheel-drive cars do not allow chains with certain tyre sizes because there is too little space around the wheel.

How should a 4x4 be towed?

On a flatbed recovery truck with all four wheels off the road. Towing with one axle lifted can damage the clutch or the centre differential.

1. https://www.audi-technology-portal.de/en/drivetrain/quattro_en/audi-quattro-with-ultra-technology-en
2. https://cdn.skoda-storyboard.com/2018/02/3_Press_Kit_SKODA_4x4_en_Benefits_of_all-wheel_drive_.pdf
3. https://www.subaru.co.jp/en/news/archives/contents/pdf_en_41806.pdf
4. https://www.globalsuzuki.com/globalnews/2018/0705.html
5. https://newsroom.toyota.eu/2019-the-new-rav4/
6. https://static.nhtsa.gov/odi/tsbs/2025/MC-11019579-0001.pdf
7. https://www.auto-motor-und-sport.de/reise/so-gut-ist-allradantrieb/
8. https://carvago.com/caraudit
9. https://carvago.com/car-delivery
10. https://carvago.com/how-carvago-works