Abu Dhabi, UAEWednesday 20 June 2018

The decoder: Crawl ratio for off-road vehicles 

 Explaining the gear-ratio term that is important to off-roading ability

Crawl ratio. Courtesy Jeep
Crawl ratio. Courtesy Jeep

Imagine being faced with a rocky incline so steep that you couldn’t possibly walk up it. What would you do? In all likelihood, you would get down on all fours and clamber up the precipice using your hands and knees.

Extending this analogy to a four-wheel-drive vehicle, they are already using all fours (tyres, in this case) to generate their forward propulsion, but when faced with extreme terrain, even this isn’t enough on occasions. Hence the provision in dedicated off-roaders of low-range gearing, which gives you a crawl ratio for when the going gets gnarly.

What on earth is this? Well, it’s basically a means of enabling the engine to spin faster than the axles, which means a lot of torque (twisting force) is transmitted to the wheels even at very low speeds. This in turn enables you to literally "crawl" over boulders and large obstacles, because trying to conquer this terrain using sheer momentum would be a sure-fire recipe to break your vehicle.

The specs

Price, base / as tested Dh100,000 (estimate)

Engine 2.4L four-cylinder 

Gearbox Nine-speed automatic 

Power 184bhp at 6,400rpm

Torque 237Nm at 3,900rpm

Fuel economy, combined 9.4L/100km