4X2 or 4X4?

By Paolo San Mateo Philippine Daily Inquirer June 12,2019

Time and again, we are bugged by questions on what makes a 4×4 ride better, or even safer, than a 4×2.

The price difference is quite a lot but through this article, we’d like to share some technical aspects that will tell us that the upgrade is quite worth it.

Do you need four-wheel drive?

It depends on where you are going or what you want to do with your vehicle.  If you intend to use your vehicle for off-roading then, period, you do. The few off-roading scenarios where four-wheel drive isn’t required is if you’re building a 2wd high-speed Prerunner, dune buggy or 2wd rally car on purpose. Recreational off-roading isn’t also called ‘four-wheeling’ for no reason. If you use 2wd for ‘four-wheeling,’ then you’re asking for trouble and simply making life difficult for yourself.

For traditionalists and off-roaders, four-wheel drive (4WD) means that both of a vehicle’s axles receive drive power via a 2-speed transfer case.  Four-wheel drive usually meant ‘go-anywhere’ and all-terrain capability.  However, developments and consumer demands have developed products that have ‘four-wheel drive’ but aren’t really all-terrain capable.  These pavement-oriented four-wheel drives are called all-wheel drives.  An all-wheel drive vehicle (AWD) is designed with a driveline that also sends power to all four wheels (usually on a full-time basis) but only through a single-speed transfer case without low-range capability. Though some are truck-based, most all-wheel drives are car based with emphasis on all-weather capability (rain, ice and snow), and on-pavement handling. Variants of the Toyota RAV4s and the Honda CRVs are all-wheel drives. The RAV4’s Dynamic Torque Control AWD the CRV’s Real Time AWD system remains front-wheel driven until slip is detected and power is sent to the rear wheels. A Porsche 911 Turbo also has all-wheel drive but most of the driveline power is sent to the rear wheels rather than the front.  For high-horsepower applications, this is better for traction because weight transfers to the rear during strong acceleration.

All-wheel drive has its place and it has its purpose but for those who wish to take their vehicles off-road and venture miles beyond the nearest Starbucks–four-wheel drive with a low-range transfer case is the only way to go.  The main types of four-wheel drive systems are Part-time and Full-time.

Part-time 4WD

This is the most common four-wheel drive system.  A part-time system is designed to be used off-pavement and on low-traction surfaces only.  The part-time system lacks any mechanism that will allow speed differentiation between the front and rear axles.  If a part-time system is used on dry pavement, driveline bind will result and cause some tire squeal, adverse handling, and increased driveline wear.  Off-road, driveline bind is released by the low-traction situation.

Most modern part-time 4WD systems allow the driver to shift from two- to four-wheel drive while in motion. This is called ‘shift-on-the-fly.’

To provide shift-on-the-fly function, many part-time 4WD systems use some sort of front axle disconnect.  The front axle disconnect normally forms part of the front differential assembly.

As part of a shift-on-the-fly four-wheel drive system, the front axle disconnect serves two functions.  First, in two-wheel-drive mode, the front wheels are disengaged from the driveline to lessen wear and tear, since the driveline is not dragged by the rotation of the front wheels.

Second, when shifting from two- to four-wheel drive “on the fly” (while moving), the front axle disconnect utilizes a synchro mechanism to match the front driveshaft speed with the rear driveshaft speed before engagement.  This allows seamless shifts into and out of four-wheel drive while in motion (but usually below 100 kph).

The common drawback of the front axle disconnect system is complexity which can lead to less reliability.  A front axle disconnect often utilizes some type of vacuum or electrical element to engage to front drive shaft.  This type of system can be less reliable than the simpler but obsolete manual-hub set-up.

Full-Time four-wheel drive (4WD)

A full-time 4WD vehicle provides drive power to both of its axles all the time-whether on or off pavement.  To differentiate full-time 4WD from all-wheel drive, full-time 4WD is understood to have a 2-speed transfer case with low-range.  Full-time 4WD requires a center differential to provide speed differentiation between the front and rear axles.  While full-time 4WD provides increased traction at all times, it can also reduce fuel economy.

What do we have?

Well, most pickups like Rangers, Navaras, Stradas and Hiluxes have part-time 4wd.  Nothing bad about this since this is an efficient and cost-effective system.  Land Rovers and some Land Cruisers (LC200 and Prado) have full-time systems.

If you’re not an off-roader and simply want to get from point A to point B, then you don’t need four-wheel drive and a 2wd will suffice.  Four-wheel drive has its disadvantages under normal road use.  The system adds weight, decreases fuel economy and increases maintenance costs.  All that hardware adds more places to leak oil and is heavy.

And, if you’re simply buying a car and not a pickup or Suv then a 2wd drivetrain makes for a stronger argument.  In 95% of places where cars can drive on, 2wd is enough.  That number goes up to 99% in the Philippines because we neither have ice nor snow. Unless you’re buying a Subaru, there aren’t many all-wheel drive (AWD) options for cars unless you’re talking about Porsche 911 Turbos, Nissan GT-Rs, E63 AMGs and the like.  These cars need AWD to get way over 500hp to the ground for sling-shot acceleration.

With modern 2wds now having limited-slip differentials and traction control, four-wheel drive becomes less necessary unless your idea of fun is really ‘four-wheeling’. Posing is a different story.

Disclaimer: The comments uploaded on this site do not necessarily represent or reflect the views of management and owner of Cebudailynews. We reserve the right to exclude comments that we deem to be inconsistent with our editorial standards.