During a recent cycle ride I was passed at some speed by an ancient Rolls-Royce car, which was far and away the quietest vehicle I encountered all day. Given the huge advances in engineering, materials and design techniques in the 60 or 70 years since that car was built, why can’t today’s car manufacturers get close to crafting a car with such a quiet engine, so little tyre noise and a lack of discernible wind noise?
• Your questioner was impressed by the silence of the ancient Rolls-Royce, but perhaps it’s first worth mentioning the car’s fuel consumption or its wet-weather handling.
That old Rolls-Royce is propelled by a woefully inefficient, low-revving petrol engine with huge cylinders. The pressure generated by the exploding fuel-air mix in these big cylinders is quite low. This makes it very quiet because there are fewer exhaust pulses per minute, and the exhaust pressure is low. An old Rolls-Royce is also a big car with room for a big exhaust silencer.
Modern car engines have smaller cylinders and run faster, and the exploding fuel produces higher pressure in the cylinders. More exhaust pulses, a higher exhaust pressure and a smaller silencer make it noisier, but it gets far more miles per gallon.
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Modern tyres are noisy, too: this is a by-product of tread designs calculated to pump water away from the interface between tyre and road. As long as tyres have a legal amount of tread on them and are properly inflated, however, this provides predictable and safe handling on wet roads.
The modern car is also better built where it matters than the old Rolls-Royce. The Rolls-Royce engine will need an overhaul every 30,000 to 50,000 miles, whereas a modern car engine, built for a fraction of the cost, should manage 150,000 miles with only routine maintenance.
Richard Ellam, Bristol, UK
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