Tread mills
Why do car and motorcycle tyre manufacturers keep coming up with such varied tread patterns? Every time I look at a tyre, the design seems different. Why is there no standard, proven pattern?
鈥� There are only two physical requirements for a car tyre tread pattern. It must provide traction for acceleration and braking and it must move surface water out of the way so that the tyre can touch a wet road without aquaplaning, which is where a vehicle slides uncontrollably on a wet surface.
A simple block pattern is great for off-road traction, but the front and back of each block wears quickly on tarmac. Circumferential ribs, edged with tooth-like indentations, give extra traction without increasing the overall wear. Regularly spaced cross-tyre features, however, generate a loud noise so irregular patterns are used.
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At 100 kilometres per hour in moderate rain, a car tyre has to displace five litres of water every second just to maintain contact with the road. Crosswise cuts in the tyre lift water off the road, which is then squirted out sideways through tunnels in the side ribs.
With motorcycle tyres, the oval cross-section of the tread cuts naturally through water, so aquaplaning is rarely a problem, and noise levels for the rider are hardly an issue given all the other noise. All that is needed is traction.
It is clear that these requirements can be fulfilled by many different patterns. In fact, most variations in tread design are decided by the tyre makers鈥� marketing people.
Reinhard Reading
Wendover, Buckinghamshire
鈥� In the late 1980s I worked on three-dimensional CAD/CAM design software for a top tyre manufacturer.
The software allowed the designers to create almost lifelike pictures of tyres based on two-dimensional drawings of the tyre section and the treads.
The designers told me that this saved them a lot of time, because many of the hundreds of designs they produced every year were turned down by the marketing department purely because of their appearance. Tread patterns were described as 鈥渘ot sexy enough鈥� or 鈥渘ot masculine enough鈥� and were sent back to the drawing board.
Only when the marketing department agreed with the general look of the tyre and its tread pattern could a set of test tyres be produced. These were cut by hand, because of the high cost of a mould, and then tested.
Experienced tyre designers knew what made a certain tread pattern perform well for a given type of tyre and could therefore deliver surprisingly new and different designs again and again that satisfied the marketing department鈥檚 desire for new products but also still behaved well during the tests.
Andre de Bruin
Sonoma, California
Curious cuppa
When you add a few drops of lemon juice to a cup of black tea, the colour of the tea lightens considerably and very quickly. Why?
鈥� The simple answer to this question is that adding lemon juice alters the acidity of the tea and the colour change is an indication of this, in the same way that litmus paper changes colour.
A similar effect can be observed by substituting the tea with some cooked red cabbage juice.
Aron
Toronto
鈥� Tea leaves are rich in a group of chemicals known as polyphenols that amazingly account for almost one-third of the weight of the dried leaf. Both the colour of the tea and much of its taste are due to these compounds.
One group of polyphenols, the thearubigins, are the red-brown pigments found in black tea and constitute between 7 per cent and 20 per cent of the weight of dried black tea.
The colour of black tea is also influenced by the concentration of hydrogen ions in the water. Thearubigins in tea are weakly ionising acids and the anions (negatively charged ions) they produce are highly coloured. If the water used to brew tea is alkaline, the colour of the tea will be deeper due to greater ionisation of the thearubigins.
If lemon juice, which is an acid, is added to the tea, the hydrogen ions suppress the ionisation of thearubigins, and that makes the tea lighter.
Interestingly, the theaflavins 鈥� the yellow-coloured polyphenols 鈥� in black tea are not involved in the change in colour that is associated with a change in acidity.
Johan Uys
Bellville, South Africa
This week鈥檚 questions
Hanging tunes
A few years ago I was lying on the floor in my living room, absent-mindedly playing with two wire coat hangers. I was holding them both above my head, allowing them to touch each other. All of a sudden I heard, very loudly and clearly, about three lines of the Michael Jackson song Ben. Naturally I dropped the coat hangers, sat up and panicked, wondering what had happened. There were no televisions or radios playing and no one else was in the house.
In my experience as a molecular scientist, the only explanation I can come up with is that I am either slowly going mad because of excessive chloroform intake or somehow I received a radio signal. How could I have heard it and how did the event occur?
Clare Lanyon
Liverpool
Honey monster
How can an unopened jar of runny, clear honey suddenly begin to turn into a hardened block of sugar with no obvious external stimulus?
Jars that have remained clear for years can, over the space of a couple of weeks, change into solid sugar while the jar remains motionless on its shelf. Temperature does not seem to be a factor 鈥� the process can occur in either winter or summer.
Billy Gilligan
Reading, Berkshire
Let鈥檚 twist again
Given that the average person twists and turns up to 100 times during a night鈥檚 sleep, why is it so unusual for anyone to fall out of bed? Does the human brain have a built-in warning system that is triggered when one鈥檚 body goes near or over the edge?
G. Rowlands
Purley, Surrey
Dairy dilemma
In England a decade ago, pasteurised bottled milk would go sour very quickly, especially during hot weather. Specially treated UHT milk would keep far longer but it tasted pretty awful. Now pasteurised milk keeps fresh for weeks, and UHT milk tastes almost the same as pasteurised. What revolution in milk technology has caused this?
Keith Ross
University of Gloucestershire Cheltenham