Why do rough roads cause more wear and faster ageing?

We all recognize that cars wear out faster when used on rough roads. But all the moving parts go round and round and up and down in much the same way, rough or smooth, so what is causing more damage and overall ageing?

Rough or smooth, the factors of “movement and work” that cause wear (and ultimately failure or breakage) include friction, heat, impact, vibration, torsion, abrasion, load, corrosion, materials fatigue, etc.

And, as you rightly surmise, cars are designed to deal with all of those…within limits…and if/while those designs are maintained in good working order.

Read: Must-have tools in your car when driving off the beaten track

Rough roads increase the movement and intensify the work in both frequency and degree (in different ways on different components), so there is more intrinsic wear, limits are more likely to be exceeded (especially vide the suspension, mountings, joints, and tyres).

Some extra wear is inevitable, and so there is greater possibility that the design could be compromised (loose nuts, torn lubrication seals, misaligned wheels, fatigued springs, cracked bushes etc). 

But extra wear need not be severe… if the car is diligently maintained and sympathetically driven. Rough roads might marginally increase the wear and tear factors, but what will make them excessive (beyond the design limits) are neglect and abuse. Those two factors can cause premature ageing even on smooth roads.

Motorists who understand that are fastidious about regular service maintenance, pre-safari checks, tyre pressures, lubrication levels, cooling system condition, and attend immediately to any rattles or other unusual noises.

Rough-road mileage

They know what conditions or driving actions are outside the limits, and how to avoid them, and how to prepare themselves and their vehicles for them. Many have vehicles of considerable age and rough-road mileage that are still in better condition than cars used exclusively on tarmac. 

They also know that bad “on-roads” can be far more damaging than most “off-roads”, primarily because of the speed at which they are negotiated. And thereby hangs a salutary tale: 

Many years ago I was invited by American Motors Corp to tour their assembly plant at Toledo, some way from Detroit, to see how well-built and strong their Jeep C5 was, and then to drive one on the Rubicon Trail – an off-road route over the top of the Sierra Nevada! – deemed so tough it is nicknamed “The Devil’s Highway”. It’s main aim is to demonstrate and promote the extreme off-road agility, power and toughness of Jeep. 

Read: I want a roof hatch, will it affect value of my vehicle?

The setting is truly spectacular and the hospitality sumptuous (we slept overnight in the open air, but were also served a four-course dinner, and a helicopter delivered dancing girls and a rock band after pudding). The route certainly tested power and agility, but was conducted mostly at walking speed and did no harm at all.

To cut short a much, much longer list of incidents and amazements both before and after the drive, at the end I was asked if I thought the Jeep would “do great” in Kenya. 

Rock-and-roll technique

My answer: there is lots to like and admire about the Jeep CJ5, but to test how “tough” it is you need to drive it, well laden, on our “Devil’s Highway” – from Isiolo to Marsabit and back, in a day. If it does that without a problem, the CJ5 might have what it takes to succeed in our conditions. 

In those days that Great North Road was not tarmacked; it was a hell-run of heat and dust and mud and deep sand and rocks and holes and washaways and massive corrugations sculpted by heavy trucks.

It either had to be driven so slowly that it would take a week, or at high enough speed to iron out the surface… a process that guaranteed a superabundance of heat, impact, vibration, torsion, load etc. 

Methinks they did not try that, or if they did then the answer to the outcome lies in counting the number of Jeeps on our safari roads today. 

Read: Are Manumatic gearboxes the best of both worlds?

In the same era, Mercedes built an elaborate, multi-section test track to go with their assembly operations in South Africa. The toughest part, used primarily for destruction testing, was nicknamed “The Kenya Road.” 

Nearer home, the track from my shamba to the nearest tarmac is about 2 kms, made by the local council using the rock-and-roll technique, without the roll or any other surface material or treatment.

Any vehicle can get from one end to the other, whatever the load or weather. I drive that several times per week. I also do a fair number of safaris, well-laden and sometimes off-road in remote places. There is no doubt that the farm track inflicts more wear-and tear than all the safaris combined. 

The moral of these examples: bad on-road does more harm than rough off-road.