Ground clearance and traction: key features of a good 4X4

Illustration showing the different angular clearances of a typical 4WD vehicle

Illustration showing the different angular clearances of a typical 4WD vehicle

Two weeks ago, we tackled the matter of all-wheel drive (AWD) and four-wheel drive (4WD), two systems that separate the men from the boys. Now, we will tackle what makes a ‘good’ 4WD and what’s a ‘great’ 4WD system. For one, it is not about having the most engine horsepower (HP). If you think that having the most powerful engine is the best option, then you are wrong.

For 4WD off-road operations to be safe and less damaging to the vehicle, bear in mind that there is a bell curve wherein too much modification done to improve a vehicle’s performance will translate to sacrificing safety and durablility of a 4X4 in on-road use. Also take note that when it comes to tackling difficult terrain safely and with the least amount of damage, the two key areas of concern is for your vehicle to have good ‘ground clearance’ and ‘traction.’

Ground clearance
Let’s start with ground clearance. It is the amount of space between the underside of the chassis and the ground. Yes, it is that simple. The height of your vehicle will dictate how big a rock one can crawl over, or how cavernous a hole one can drive over, or even how deep a river one can wade through. In off-road driving, the three key ground clearance issues are: approach angle; break-over angle; and departure angle.

‘Approach angle’ is the degree between a forward line on a flat or level surface where the front tires make contact with the ground and another line from that point where the front part of the bumper can make contact with an obstacle.

The ‘breakover angle’ is the maximum possible angle that a vehicle, with at least one front wheel and one rear wheel, can drive over an obstacle without the apex of that agle touching any point of the underside of the chassis.

The ‘departure angle’ is the angle from the last point of where the rear wheels make contact with the ground and the point of the rear-most point of the vehicle, usually the bumper, that is likely to make contact with the ground or an obstacle.

Another key feature of having a good 4WD car is ‘traction.’ Traction is the ability of your 4WD vehicle to maintain grip depending on the driving surface. If your tires slip on any driving surface, that means you are applying too much power on your throttle/gas pedal and your tires are not biting on the driving surface. Sounds simple, right? Wrong. There are many variables involved in getting traction: tire type; weight distribution; gear ratio; driving surface; applied traction; and traction aids.

Tire type
The type of tires you have, be it mud, all-terrain or road-oriented tires. The type of tires used is crucial on what driving surface you are in. You can have 100 percent traction on a driving surface but having so can be detrimental to your forward progress. So understand what to apply to your driving surface.

Weight distribution
How much down force or weight is being applied on each tire. Critical here is how much weight to put on each tire, with the bottom line of maintaining your vehicle weight distribution even by keeping all four wheels in contact with the driving surface.

Gear ratio
The average 4WD has five forward gear ratios, from 1st gear to 5th. With your 4WD’s “four-low” range gear engaged, one can multiply the vehicle’s choice of gears by two, making a five-speed transmission, a 10-speed. Always choose a gear that is the most appropriate for the driving surface.

In a motorsport event I recently participated in, the starting point was a slippery mud surface. All the participants started in first gear and took off by just slipping and sliding due to the slippery surface. I, on the other hand, started on second gear. Guess who won the event because of picking the right gear ratio to start with?

Driving surface
Are you driving on a hard dry surface with perfect traction? Are there any dips or holes on the surface? Is traction good or bad due to rain or mud on the hard driving surface? How much water weight is in front of your vehicle when water crossing? Do you have enough gear ratio and engine torque to push that water weight in front of you? Bottom line is, know your vehicles capacity and capability. It’s not all about engine power.

Traction aids
Not all 4WD vehicles are equal in terms of traction aids. 10 years ago, a ‘limited-slip differential’(LSD) equipped 4WD was the best traction aid available on locally sold 4WD vehicles. Nowadays, there are 4WD vehicles equipped with ‘electronic traction control’ and ‘differential locks’ that provides optimum traction on different driving surfaces.

We have barely scratched the surface on ‘ground clearance’and ‘traction.’ We can fill a whole chapter of a book just going through these. For more questions about 4WD, feel free to e mail me at Happy trails and stay safe.


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