With plethora of terms revolving around describing 4×4’s, the marketing jargon does tend to make one feel dumb. In fact lot many of us tend to fall for the mini and micro SUV concept being sold like hot cakes in a SUV-famished market like India. People consider these cars as tru-blue SUV’s and end up getting stuck on the easiest of off-roading trails. Based on my research, I can say that these cars are simply 2 wheel drive hatchbacks with higher ground clearance. Well undoubtedly, ground clearance does help when things get tricky, the lack of wheel articulation and a 4×4 drivetrain makes it challenging for such cars to venture out on the trails. Since many of us are inclined towards SUV options, the marketers are finding this as an opportunity to get the customers off-track from the facts.
Let me quickly clear some air around basic 4×4 terminologies that we see in cars around us. A good 4×4 car is a not a function of one but a combination of several things – Drivetrain, Chassis, Ground Clearance, Approach and Departure Angles, Weight, Engine Output in terms of Power to Weight Ratio, Wheelbase, Suspension Setup, Differentials, Tyres and Transmission. Allow me to take you through basic drivetrain concepts and the rest shall be covered in subsequent write-ups.
I have always had a keen eye for the badges found on SUV’s around us. Some of them say 4WD, Full Time 4WD, AWD, 4Matic, Quattro etc. I shall quickly take you through the facts behind these badges and their effect in our daily driving.
Any vehicle that is capable of providing torque to all its wheels may be termed as a 4×4. In layman terms, each wheel is getting its share from the engine output; contrary to a 2WD, where 2 wheels are dragged along by the wheels that are powered. A 4WD vehicle carries a transfer case and differentials over a standard 2WD car.
Full Time 4WD
This one powers all 4 wheels at all times. Though this definitely helps in traction and go-anywhere ability, it takes a toll on the fuel economy due to higher fuel consumption and added weight of such a system. Let me ring the bell for you all, remember, the old Toyota Fortuner proudly carried this badge on its boot.
So are all SUV’s Full Time 4WD? Before answering this, you need to understand that all wheels in a car do not rotate at the same speed at all times. Imagine a car taking a U-Turn – In such a scenario the wheels on the inside would rotate at a lesser speed than the wheels on the outside as the outside wheels cover a greater distance while taking a U-Turn. These rotational differences are made possible through differentials. In the absence/locking of a differential, the tyres shall rotate at same speed and would lead to wear and tear for the tyres covering greater distance in this case.
Now the Answer – No, not all SUV’s are full time 4WD. Such cars have a Centre Differential in addition to front and rear differentials that allows for rotational differences between front and rear axle of a full time 4WD car. In layman terms, absence of a centre differential shall mean excessive wear and tear for the tyres and drivetrain as the wheels try to rotate at a similar speed on a high traction surface while taking a turn. This is where AWD and Part time 4WD cars come into picture.
Part time 4WD
Such a car has an option to engage 4WD when required. Most modern day cars have a button/dial to control 2WD/4WD modes. While driving in 2WD shall ensure lesser fuel consumption and adequate traction when on tarmac, you may engage 4WD on the go when things get slippery for stability. Important to note that driving such vehicles on tarmac (read high traction surface) in 4WD mode shall mean excessive wear and tear for the tyres and the drivetrain. This is due to absence of a centre differential in such cars. Examples of cars using such a setup include Isuzu VCross and Tata Safari.
A proper Fulltime/Part-time 4WD system shall be equipped with a low-range transfer case too. This enables these cars to generate much higher torque output at low RPM’s to overcome steep inclines and obstacles and also complement their towing capabilities. You may select 4L by simply moving a lever or rotating a knob. A car with a low range transfer case would normally have 3 modes.
2H – 2 Wheel Drive Mode – Useful on Tarmac
4H – 4 High or 4WD mode with engine suited to high-speed driving. Not for high traction surfaces. Suitable in Sand, Snow and Slush.
4L – 4 Low or 4WD mode with engine producing much higher torque at low RPM to overcome obstacles easily. Suitable for extreme off-road driving/crawling.
Last of the lot are AWD systems, that are relatively new and involve complex technologies and computer systems to regulate torque between all 4 wheels. These may be found in hatchbacks, sedans and SUV’s too. A chip dictates the amount of power being sent to any wheel basis throttle input and available traction. XUV 500/Compass are cars where the system stays in 2WD in high traction conditions and distributes power to all wheels in split seconds in case of loss of traction on any wheel. Important to note that such systems use sophisticated technologies such as pressure plates to regulate wheel movement and distribute torque. These are most suited for on-road driving in tough weather conditions like extreme rain, snow/sleet or mild slush. Some proprietary technologies include Quattro by Audi and 4matic by Mercedes. However, in my opinion, these are still no match for part time 4WD systems equipped with low range transfer cases.
Pertinent to note that manufacturers nowadays are offering a fusion of these systems, such as equipping AWD systems with low range, ability to lock/unlock differentials on the go and giving part time 4WD systems a centre differential ; the basics remain same though.
By now you would have understood subtle nuances of all these systems. So the next time you see these badges on a car, you would know what the car is capable of!
And until we meet next, take care and drive safe!
— Ankit Mahajan ©