Vibrations in a Car

Preamble
Besides noises, in any car some ‘vibrations’ are inevitable. These are ‘noises’ that can be ‘felt’ but not heard. It can be difficult for an average person to distinguish between normal or abnormal vibrations. So let’s try and explore them…

Causes of Vibrations
It’s elementary physics that any rotating mass will vibrate if its weight is not evenly distributed around its ‘axis of rotation’. Their ‘intensity’ is proportional to such ‘unbalance’ AND speed of rotation. If vibrations are not contained to ‘safe’ levels, ‘metal-fatigue’ sets in a machine, eventually leading to its wreckage.

Prime source of vibrations in a car is its engine – followed by wheels and road undulations transmitted to its body by its suspension. Let’s look at each of them.

Engine
The ‘reciprocating’ movement of pistons in an engine is converted to a ‘rotary’ one by its ‘Crankshaft’, which is linked to them by ‘Connecting Rods’. Therefore, unless each one of these parts is individually well balanced, it will vibrate.

Despite, some vibrations are inevitable. These are ‘damped-out’ by flexible ‘foundations’ between the engine/gearbox and the car body. Such foundations are made of rubber fused on metal anchors but in more expensive cars, ‘hydraulic’ foundations have become a norm.

However, even a well designed engine can vibrate if – i) its ‘idling speed’ is below normal, ii) it’s over loaded due to improper gear selection, iii) its foundations are damaged or misaligned, and iv) if one or more of its cylinders is not producing right amount of power compared to others.

Wheels
Until the advent of Maruti-800 in mid ‘80s, concept of ‘wheel balancing’ was unknown in India. A wheel being an ‘assembly’ of its rim, tyre/tube, is invariably unbalanced even when brand new, because of permissible manufacturing ‘tolerances’ of its constituents.

And when the wheel diameters get smaller, their ‘rpm’ for a given road speed goes up compared to larger ones. Given the overall ‘lightness’ of cars nowadays, such unbalance in wheels produces unwanted vibrations in an otherwise ‘smooth’ car. Worse still, it makes the steering ‘wobble’ at higher speeds.

It’s worthwhile remembering that a wheel once ‘balanced’ won’t stay so for long because of daily/uneven wear going on its tyres due to braking/cornering etc. Worse still, the ‘balancing weights’ can and do fall off for many reasons. So it’s advisable to get one’s wheels re-balanced, say, every 5,000 kms.

It’s a popular misconception that only front wheels need re-balancing because that immediately reflects as steering wobble. Since any unbalance in rear wheels also produces vibrations and these, even if not felt as such, do eat into the lives of rear suspension bushes, shock-absorbers AND wheel bearings.

Like wise for Stepney – for simple reason that one may need it any time upfront and if it’s unbalanced, one’ll have a wobbly steering till re-balanced. From this point of view, it makes a lot of sense to have a wheel re-balanced immediately after puncture repairs before stowing away as spare.

A finer nuance to have all the 5-wheels in good balance all the time is that if they’re not, the front ones will inevitably wobble a bit even if not perceptible. Consequently, car’s ‘rolling’ resistance and hence fuel consumption stand to go up!

Conclusion
From the foregoing, it can be visualised that a well tuned engine and all the five wheels in good balance can add significantly to the overall life of a car.