Our resident mechanical engineer addresses gearbox, suspension and tyrerelated queries this month.

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What is “mechatronics” and what does it have to do with the gearbox?

My mechanic says my car’s mechatronics module in the dual-clutch gearbox is defective and needs to be replaced.

But it is rather costly. Are there any alternatives to replacing it?

The term “mechatronics” is derived from a combination of mechanisms and electronics.

Essentially, it is a mechanical system which is controlled by computerised electronics.

In a dual-clutch transmission, the electronic part receives information from a number of sensors, so that the controller can pick the optimal gear.

The mechanical hardware is a hydraulic system comprising a high-pressure pump, oil control valves and piston-type actuators.

With electronics controlling the function of these components and hydraulics providing the necessary force to work the clutches and shift gears, the system can function with precision and speed.

The mechatronics module is a compact unit fitted on the gearbox.

When there is a problem, the exact cause may be impossible to trace. Dismantling and repairing it will be even more complicated.

Hence the best way to solve the problem is to replace the module with a new one.

While I was driving out of a carpark, I misjudged a turn and one of the front wheels mounted the kerb.

Although this happened at low speed, the thud was quite sickening.

Now, my car keeps drifting to the left on straight roads unless I keep tugging at the steering wheel. Do you think the damage is serious, and will it be dificult to fix?

On a separate note, why are turns set at 90 degrees, and why can’t kerbs be tapered and not so high?

Your car may have sustained a mild, unnoticeable bending of the tie rod arm, which maintains front-wheel alignment.

In this case, a re-alignment will most likely fix the problem. If the tie rod is bent severely, it will have to be replaced. On cars with complex multilink suspensions, more elements of the suspension could be damaged during an impact with a kerb.

Colliding with a kerb at higher speeds can distort the suspension’s lower arm or even the suspension strut. The damaged parts will have to be replaced.

Have the workshop show you the distortion or crack before you agree to replacements.

On the subject of the kerb height and the sharpturn set-up, we can only sympathise with you. Just be more mindful in future.

I recently watched a video showing how a new tyre can already be past its sellby date and is therefore dangerous to fit on a car.

How true is this? How serious can the consequences be?

While the video is an illustration of an extreme situation, it is nonetheless important to be aware of a tyre’s deterioration over time – even when it is new and unused.

The rubber compound used in tyres experiences gradual, natural degradation. This continues whether or not the tyres are fitted to a vehicle that is in regular use.

After several years on a shelf, the rubber in a tyre’s compound will lose its pliability. Tiny cracks will begin to form.

The compound’s diminished integrity and flexibility will, in most cases, lead to sudden side-wall failure or tread delamination.

However, it would take around four years or more before a tyre deteriorates to this point. Most tyre shops do not hold stock for that long.

Before buying tyres, you can check their age by looking for a four-digit mark on the side-wall.

You will find it on every tyre and it identifies the week and year of its manufacture. For example, “4717” means it was produced on the 47th week of the year 2017.

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What has a greater effect on fuele  efficiency as far as wheels and tyres are concerned? Is it the width or the diameter?

When wheels and tyres are concerned, weight and diameter can directly influence momentum.

For any given speed, an increase in either will increase momentum. This means more torque will be needed and hence more fuel will be consumed by the engine.

Unless a larger diameter wheel is of a lightweight design, upsizing will affect fuel economy adversely. But moving up one size, say from 17 to 18 inches, is not likely to cause a significant deterioration in fuel efficiency.

An example of how a manufacturer enhances fuel efficiency can be seen in BMW’s choice of wheels and tyres for its electric i3 model.

They are lightweight 19-inch wheels shod with tyres that are unusually narrow. Having narrow tyres has two advantages – reduced rolling resistance and minimal frontal area and hence lower air resistance.

But it is hard to say whether wheel size or tyre width has the bigger influence on efficiency.