Preamble

Besides audible noises, in any car some ‘vibrations’ are inevitable. These are defined as ‘noises’ that can be ‘felt but not heard’ – though with ongoing advances in technology today’s cars are a lot ‘smoother’ than their decade old predecessors.

Unfortunately, it can be difficult for an average owner-driver/passenger to distinguish between normal or abnormal vibrations. So let’s try and explore them.

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Causes of Vibration

Prime source of vibrations in any car is its engine (we’re not talking of diesels here !), followed by wheels and road undulations transmitted to its body by its suspension. Let’s look at each of them.

The Engine

The ‘reciprocating’ nature of pistons’ movement in an engine is converted to rotary one of its Flywheel by the ‘Crankshaft’, which is linked to them by ‘Connecting Rods’. Therefore, unless each one of these ‘constituents’ is individually well balanced over the entire operating speed range of the engine, it will be prone to excessive vibrations.

Despite, some vibrations are inevitable. These are ‘damped-out’ by ‘foundations’ between car body and engine/gearbox. Such foundations are crafted out of suitable grades 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/felt at the steering if – i) its ‘idling speed’ is below normal, ii) it’s over loaded at any speed due to inappropriate 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 – either due to fuel starvation, unsatisfactory spark plugs/‘HT’ leads, or premature compression loss due to piston/rings or valve failure.

Wheels

Until the advent of Maruti-800 in mid ‘80s, the concept of ‘wheel balancing’ was relatively unknown in India and confined to some speciality garages in Metro’s mostly for ‘imported’ cars. A wheel being an ‘assembly’ of its ‘rim’, tyre/tube, is invariably unbalanced to some degree even when brand new coz 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 dia ones of yore. Given the overall ‘lightness’ of cars nowadays incl its suspension members/steering links, such unbalance in wheels produces unwanted vibrations in an otherwise ‘smooth’ car. Worse still, it makes the steering ‘wobble’ at higher speeds, depending upon extent of unbalance in them.

It’s worthwhile to remember that a wheel once ‘balanced’ won’t stay so for all times to come coz of daily and uneven wear going on the tyres due to accelerating/braking/cornering etc. Worse still, as the ‘balancing weights’ are ‘clip-on’ or ‘stuck-on’ types, they can and do fall off for many reasons. So it’s advisable to get one’s wheels re-balanced, say, every 5,000 kms in our conditions.

Further, it’s a popular misconception that only front wheels need re-balancing coz their deterioration immediately reflects as steering wobble. Nothing could be farther from truth coz any unbalance in the rear ones, even if not felt as such, resultant vibrations will certainly eat into 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 too and then if it’s unbalanced, one’ll have a wobbly steering damaging the front suspension/wheel bearings/steering linkages all the way home/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, even if it was balanced only recently/before going flat. For once a tyre is dismounted from its rim, it can hardly ever be put back in same position. Besides, while doing so, some existing balance weights inevitably get dislodged from their earlier positions.

A finer nuance towards need to have one’s 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 at the steering wheel and consequently, car’s ‘rolling’ resistance and hence fuel consumption stand to go up !

Suspension

From foregoing, it can be visualised that well-balanced wheels can add significantly to lives of a car’s original suspension and steering gear. However, given our road conditions, a car’s suspension has the most arduous task to perform. Any flaws in it by way of worn out bushes, ball joints, shock absorbers can lead to abnormal vibrations even on reasonably good roads – by way of excessive/‘bouncy’ suspension ‘travel’ and resultant uneven tyre wear. The latter, once set in, is impossible to ‘iron-out’ even by completely re-furbishing the entire suspension. So it’s of great importance keep a close watch on one’s suspension before it’s too late.

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