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Trail Savvy: Wheelbase & Angles

What is wheelbase, and how does it affect your rig off-road? We take a look at the pros and cons of different vehicle lengths, and how to alter your driving approach to match.

People with shorties are always adamant that their vehicles are the best off-road. Lighter, nimbler in tight situations and in general more fun. Long wheelbase pundits claim extra packing space and more stability under certain conditions. So, what exactly are the strengths and drawbacks of a short or long wheelbase vehicle and what would best suit your needs?

The driver of this Discovery approaches the obstacle at an oblique angle, allowing its front right wheel to climb up first, lifting the nose of the vehicle and preventing the bumper scraping as it would have had if the vehicle attempted the obstacle head on.

First things first: wheelbase simply refers to the distance between the centres of the wheels of your vehicle. A short wheelbase (SWB) version of the same vehicle will handle and react to inputs completely differently to a long wheelbase (LWB) of the same design.

SWB pros and cons

Generally speaking (and it may change depending on opinion) a short wheelbase 4×4 is anything less than 100 inches (254cm) or the length of a Land Rover Discovery 1/2. Anything shorter than this takes you into the realm of the Defender 90, Pajero SWB (also around 250cm), Suzuki Jimny or two-door Wrangler.

Had this short wheelbase Jeep Wrangler not been attached to a winch, it would almost certainly have toppled over backwards. Longer wheelbase vehicles did not have such issues up this steep climb in the Cederberg.

The clear benefit of a short wheelbase vehicle, given the same ground clearance, is an improved breakover angle – which means you’re less likely to get hung up on rocks or over humps on the centre of your vehicle. A smaller turning radius also makes a shorty a joy to handle in tight, technical sections (and even the local parking lot).

Unfortunately most good things come at a price, and that short wheelbase has an effect on balance, steering and loadability. Physics dictates that steering inputs will turn a shorter wheelbase vehicle slightly more than a longer one, and they are also more prone to tipping over, as overall height is a higher percentage of overall length. These factors make a short wheelbase vehicle relatively more unstable at high speeds or on steep descents/ascents.

For example, when going down a steep slope in a shorty, if one front wheel falls into a hole, the rear is likely to become light and at least one rear wheel may lift off the ground, whereas a longer vehicle’s hind legs would stay planted. This instability has resulted in rollovers and it’s a caution for the less experienced driver. Needless to say, a heavy load on the roof of a short wheelbase vehicle will exacerbate its instability rather more than the same load would on an equivalent long wheelbase vehicle.

LWB pros and cons

Apart from the obvious added storage capacity, and the fact they are less twitchy when driving faster as they are less reactive to steering inputs, longer wheelbase vehicles also have a few surprising benefits off-road. The first and most obvious one is stability, especially useful when they have had a suspension lift.

As an example, we recently went on a trip through the Cederberg and Karoo and one chap, in his short two-door Rubicon, had extreme difficulty up the steepest hills; his lifted Jeep would simply rear off its front wheels and threaten to roll over backwards. An equally lifted long wheelbase four-door Rubicon, on the same trip, had no such issues and climbed much more easily. This advantage was of course lost in tighter sections or where maximum breakover angles were necessary, because even though both Jeeps shared the same ground clearance, the longer Rubi had a tendency to scrape its belly over humps.

This brings us neatly into our next point.

Ramp/breakover angles

The ramp or breakover angle is the maximum possible angle that a vehicle can drive over without the apex of that angle touching the underside of the vehicle – this angle is measured from the centre of the contact patches of the tyres to the approximate centre of the vehicle as viewed from the side.

In effect, if a LWB and a SWB vehicle of the same type with the same ground clearance were to drive over a large hump, the longer vehicle would be the first to scrape its belly.

This gigantic 2500 Dodge RAM was the only vehicle to get stuck on this relatively small obstacle due to its long wheelbase, negatively affecting its breakover angle.

Off-road, the breakover angle your vehicle can achieve is an important factor in clearing large obstacles, and can of course be improved by lifting the suspension, fitting larger tyres, or both.

A useful driving trick to improve your vehicle’s relative ramp/breakover angle is to turn sharply at the top of an obstacle so that your vehicle traverses it at an angle. By reducing the difference in height between your front and rear wheels by packing rocks/recovery tracks before and after protruding obstacles, you may also be able to save yourself body damage. I always find that by driving with my window open and looking closely at my wheels, I can avoid damage to the undercarriage most of the time.

 Approach & departure angles

Approach and departure angles refer to the maximum angle of a ramp that a vehicle can climb onto from a horizontal plane, without scraping. When approaching an obstacle the first thing limiting your approach angle is usually your front bumper or recovery points, while when departing an obstacle, your tow hitch usually hits the deck first.

The 76 Series Cruiser’s long rear overhang threatens to touch terra firma.

The approach and departure angles of a vehicle often dictate how large an obstacle it can tackle, though, in many cases, approaching an obstacle at an angle and letting one wheel climb the obstacle first, may improve the approach angle compared to just heading at it straight on.

Long wheelbase vehicles, such as bakkies or campers, generally have poor departure angles due to the fact that their load bays hang far over the rear wheels to allow for more space and gear to be loaded. Large overhangs, tow bars, modern plastic front bumpers and low-slung radiators or intercoolers are the enemy of a good approach or departure angle.

Lifted suspension, a body lift or larger tyres are all effective methods of improving your approach, departure and breakover angles, while more extreme methods include cutting the rear of a vehicle clean off. All modern off-road specific aftermarket front or rear bumpers are designed in such a way as to improve approach or departure angles.

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