Tubeless Tyre Valves

The little rubber and brass valve that holds the air in your tyre, and admits new air, is one of the world’s most successful inventions. William Schraeder designed its fundamentals nearly 120 years ago.

The little “springy thingy”, called the “valve core”, that screws into the brass valve really hasn’t altered all that much in that time, and all you need to remove it and let the air out, is a slotted valve cap. Or you can just depress the little button in the centre and you get the same effect, only slower.

Yet when you buy a new tyre, the fitter always replaces the valve. Why does he bother?

The modern tubeless snap-in valve is compressed into a hole in the rim to provide a seal. A brass stem is adhered to a rubber skin, with a domed shape on the inside of the wheel to prevent it being blown through the hole by the air pressure.

 Over time, the degree of compression is lowered (it doesn’t fit as tightly). It may even crack around the groove in the rubber which lodges in the rim hole due to flexing.

The valve actually flexes as the wheel revolves, particularly if it is a long one designed to protrude past the wheel trim. Ultra-high-speed photographs have shown the valve actually touching the rim at right angles at very high speeds. Also the heat during service causes the bond of the brass to the rubber to deteriorate, and if this bond ruptures, the stem blows out, and the tyre goes down quickly.

So reliability is what it’s all about. It’s much better in the long run to replace it after one tyre life.

You can contribute by using dust caps or valve caps, and giving a blast of air around the valve before you clamp on the air chuck, which you should do monthly. If you suspect a leaking valve, a “dob of spittle” on the end of your finger into the brass stem is the tried and true method. If it bubbles, first check the valve core is tight. If it is, loosen it, let some air our, then retighten to dislodge any dirt that might be there.

If it still leaks, replace the core. Unscrewing the core right out will let all the air out, and coincidentally clean the seat that the “springy thingy” seals on. To do this, you need a slotted metal valve cap, or a valve tool, and a kindly service station operator to assist if needed.

The metal clamp-in valves are different. These are used in some alloy wheels, where the thickness of the metal around the hole is too great for a snap-in type. But they are even more desirable when high speeds are the norm. Unlike a snap-in, they do not flex, and they sandwich two air seal washers under compression to get the air seal. So even though they cost more, they last longer, because it is not as necessary to replace them after every tyre life.

Want to know more? See our “All about tyres” section or our “Inflating Tyres Safely” post.

Brad Pitt falls off his Chopper

So Brad Pitt fell off his “chopper” motorcycle. Unfortunately for him as he was in view of the paparazzi.

Hasn’t anyone told him that motorcycles with very high castor angles on the front forks (laid back at an acute angle) have very poor stability at low speeds.

They fall over.

That’s why BMX bicycles and trail bikes have their front forks ALMOST vertical, so they can be manoeuvred at low speeds. If they are vertical, then steering at high speeds becomes very twitchy.

In contrast, high castor angles steer very much in a straight line at higher speeds. Think Peter Fonda (who? say the younger generation) and his “Easy Rider” motor bicycle. Man, was that laid back.

That’s why shopping trolley front wheels always have a small, but positive castor angle on the steering wheels. Otherwise they just jiggle from side to side, and are a pain. Hence why Brad felt!

Your car’s “alignment” incorporates all of the above to keep you safe and in control, and hopefully without the paparazzi.

Should Tyres have a use-By Date?

Channel 7’s “Today Tonight” program on Friday 5th December, picked up on earlier publicity originating from an American T.V. program “Twenty-twenty”. An aggrieved customer in South Australia complained that he had been sold Light Truck tyres that were already 14 years old when fitted. One tyre had separated its steel belts from the tread ring, causing damage to his mudguard, and raised the risk of an accident.

The British Rubber Manufacturers have recommended that tyres more than six years old should not be sold, but there is no law requiring this anywhere in the world at present. The American Rubber Manufacturers Association states that there is no scientific evidence to support a six-year limitation on the life of a tyre.

The Channel 7 program cut pieces from the sidewall of the tyre, and did a “tensile test”, pulling on the test piece till it broke. Pieces cut from the (used) 14 year old tyre broke at a lower tensile than from a new tyre. Why they tested the sidewalls, which are a different rubber compound to the tread/steel belt area, it is not known, but it is not surprising that testing two tyres made 14 years apart would give different test results. The reason? The tyres were different!

Tyres are warranted for their life by the manufacturer. Occasionally tyres, like many products, are subjected to a recall program. To enable identification of these, a code is branded into the sidewall, which is used world wide, and is a requirement of the American Department of Transportation. It is called the DOT code. Practically all tyre manufacturers worldwide use this code.

The code details the actual factory in which the tyre was made, the design, and among others items, the last appearing group lists the week and year the tyre was made. 3 digits for the ninetees, four digits for the noughties. Examples then are 489 for the 48th week of 1989, 2604 the 26th week of 2004.

Tyres are generally 6 months to 2 years old by the time they are fitted to your car as replacements. The original equipment tyres are generally one week to six months old, dependent on whether the car was made here, or imported.

The Australian tyre market is so fragmented, with many makes and models of vehicles sold, that the supply chain for replacement tyres is very long, and large stocks are held at distribution points to meet market requirements. For example, the 11 hectare distribution centre at Somerton, Victoria, can hold up to 11 million tyres. Naturally, efforts are made through inventory control to ensure quick turnaround of stock going into the store, to reduce holding costs.

Eventually, tyres are shipped out to your local tyre store. Here they should be stored in racks, in a “cool, dry place”. Many tyre storage areas paint their tyre storage area windows with blue paint to screen out U.V. This is because tyres get harder with age. The vulcanisation process continues at a very slow rate, and protective agents such as antioxidants and antiozidants incorporated into the mix diminish in effectiveness with prolonged storage. Walk into a darkened tyre store, and you can smell the rubber. A somewhat doubtful farming practice used to be that tractor tyres were stored by the farmer to “harden them up”, and possibly improve tread wear. Really, all it did was increase the risk of buttress cracking.

Unless stored correctly (read “All About tyres/Storing a tyre” on our www.carbonblack.com.au site), the tyres will eventually craze or crack most severely where the tyre is resting on the pipe rack. This is because stretched rubber is attacked by ozone in the air. Ozone is generated by electric motors and lightning, so maybe the shop compressor is the culprit. However, tests done in the past have never been able to show that tyres stored this way will not give a satisfactory life. The deformations caused by the pipe rack run out as soon as the tyre gets run in on the vehicle- say 10 kilometres, depending on the temperature.

The real sleeper in all this is your spare wheel. Stored in the boot, or under the tray of a light truck, it is subjected to high summer temperatures, and may lay there undisturbed for six years or more if you don’t have to use it. Our discussion on what to do about that is contained in “All about tyres/original equipment”. Basically, it has missed out on six years of design improvements whilst sleeping in the car boot, or lying in the dealer’s racks waiting for a sale, or in the South Australian’s case, 14 years.

So should tyres have a “Use by Date?” It would appear that provided they have been stored correctly, there is not a problem with tyres encountered in the usual course of trade. Besides, somewhere out of Broken Hill or Wilcannia or somewhere like that, you will be pleased to find that the tyre service has your badly needed tyre, even if it is a bit dusty.

All that applies to tyres also applies to automotive car batteries of course, for all the same reasons, except that a lead acid battery does in fact have a finite life, and has to be stored correctly with its charge maintained until it is sold. The warranty period then kicks in once it is sold.

Mazda 3 outstripped Holden VE and Toyota Corolla, previous market darlings

Someone once said “Build a better mousetrap and the world will beat a path to your door”.

Build a pretty little car that looks good, drives well, and doesn’t cost a fortune to run, and it will attract buyers into the showrooms faster than a plain Jane, reliable, but conservative looking car.

It’s all about emotion- and you must admit, the Mazda 3 is a pretty looking motorcar!

January sales of the Mazda 3 outstripped Holden VE and Toyota Corolla, previous market darlings. The Holden defeat could be explained by the fact that fleet sales are always low in January. Petrol prices remained high for most of January, when there didn’t seem to be any logical reason why it was so.

The Australian dollar hovered around the US$ 65 cents mark, and crude oil around US $40 a barrel, so some price gouging of touring holiday makers seemed apparent. Yet prices as low as 97 cents/litre, and as high as 127 cents/litre, were recorded in Sydney in that period.

No wonder sales of small cars are booming, as it’s apparent that high petrol prices will be around for some time. Just can’t see them driving Sydney to Melbourne comfortably in 8 hours with a full load of passengers and luggage to see the Australian Open, or the Formula 1 Grand Prix. Yet that is what’s happening with the newer designs of small cars. Bring them on!

NSW demerit points are the go!

Faced with the prospect of a huge voter backlash as motorists reap their harvest of demerit points for a huge variety of driving misdemeanours, the N.S.W. State government has started to back-pedal on the consequences of their actions. A rumoured 40,000 motorists on Sydneys North Shore have accumulated so many de-merit points that their next indiscretion will cost them either a 3 month’s suspension of their driving licence, or force them into an undertaking to be good for the next twelve months, or double the penalty if they offend again.

The new NSW Minister for Transport says he’ll look into it – he promises.

Regular Sydney commuters know where the speed cameras are, either from the GPS or from local knowledge. What throws their calculations out is when a new camera is installed at a new location. They reap a harvest for the first month, until the grapevine catches up. Pity the poor country motorist who comes to town rarely, and has their hands full already negotiating Sydney traffic. Throw in some rain, or a thunderstorm, or a huge truck blocking your vision, and six points can go out the window in a flash.

Average traffic speed in Sydney is 65 km/hour. Because this is 15 kms over the 50km subrurban speed limit,  it puts the fine bracket up to the next level – $243 dollars instead of the lesser penalty.

But beware, in Queensland, it’s 13 km/h over the posted limit that puts you up to the higher penalty

Car sickness? Blame the bacteria

According to a recent study commissioned by insurance.co.uk, the typical car has 283 different types of bacteria present in every square centimeter.

Microbiologists from Britain’s Aston University found the dirtiest part of the vehicle was the gear stick, home to 356 germs on a square centimeter, while one car boot in a random survey of 25 cars had 850 bacteria in a square centimeter.

“Whilst most of the bacteria we’ve found are unlikely to cause serious health problems, some cars, particularly those which regularly carry children and animals, play host to potentially harmful germs,” said Anthony Hilton, director of Biology and Biomedical Science, at Aston University.

“People would be horrified at the thought of eating off their toilet seat, but few realize eating off their car dashboard is just as likely to make them sick,” he added in a statement.

When quizzed about the most peculiar items drivers had found in their car, a whole host of unusual and downright unpleasant objects were revealed, including:

Top 5 – insects, animals and excrement

Mice (dead and alive)
Dog poo
The neighbour’s cat
Body parts from a dead seagull which a dog had smuggled in
Maggots for fishing that were forgotten about and didn’t die, but reproduced and grew

Top 5 – food

A joint of beef in the boot, which had fallen out of shopping bags weeks ago
A 3 year old, green sandwich
A baby’s bottle under a seat, which had been there for at least 6 months
A very old chicken nugget, found lodged under a childs car seat
A Cadburys Wispa, which had been left long before the re-launch

Top 5 – miscellaneous

A pair of knickers belonging to a husbands ex girlfriend
A used condom in a just-bought second-hand car
Childs vomit in a door pocket, which had gone unnoticed for days
The results of a toddler picking his nose
Mushrooms growing in the floor

Time to get the inside of your car cleaned……

Ageing Tyres and Road Safety

A recent survey carried out for the RAC Foundation in the UK has revealed that although nine out of ten drivers understand the link between tyre age and road safety, up to an estimated three million in the UK- do not.

According to the research, owners of low-mileage cars, vintage and classic models, caravans, motor homes and trailers need to be aware of the risk of tyre fatigue. The spare tyre is also at risk of age-related deterioration, as it is often unused even though other tyres may have been replaced over the years.

Simplifying the checking process could be one answer to the problem, as seven out of ten motorists said they would like to see the current age coding system replaced by an easy-to-read ‘year of manufacture’ date on the tyre.

The Foundation was also concerned that 45% of drivers questioned did not know the minimum legal tread depth for car tyres and among women drivers, this figure rose to 60 %.

Although it is quite easy to check a tyres’ age from the sidewall code it only tells you when the tyre is made, not its physical condition.The danger signs of ageing can include:

- cracks or crazing on the sidewall

- tread separation, cracks or bulges

- deformation of the tyre carcass

- discolouration and fading of the rubber

In response to these findings the UK RAC and the UK National Tyre Distributors Association have launched an eight-week tyre safety campaign urging drivers of low-mileage vehicles to get their tyres inspected.

Our Experts on: Tyre pressure, part 1

Given that tyre pressure is one of the few things about a tyre that you, the average driver, have direct control over, it’s no wonder that a lot of people take an interest in it. Tyre pressure can have a surprising influence on your car’s performance and fuel efficiency, so it’s worth understanding.

Originally, back in the days of bias tyres, your tyre pressure was highly important to the health of your tyre. If you over-inflated a tyre it wore heavily on the centre of the tread, and if you under-inflated it wore on the shoulders (edges) of the tyre. This was before those clever Frenchmen invented radial tyres and front wheel drive (traction-avant) motor-cars. The steel belts of a radial tyre are laid criss-cross under the tread, bracing it. The tread rubber, and the tread pattern particularly, are then held stable, and the pattern is able to perform its major function of providing drainage channels for water trapped under the tyre to escape

So what is the role of tyre pressure? First, and most obviously, it is the air that carries the load. The air pressure inside the tyre and rim creates tension, which allows the tyre to support the weight of the car. The quickest way of proving this is the rather extreme method of letting all the air out and seeing how far you get. Incidentally, a tyre has to be below about 17 p.s.i. for it to look “flat”.

We’ve established what not enough air can do, what about too much air? First off, it shortens the footprint (area of tyre in contact with the road), which lessens the time available for the tyre to drain water out from under it. In compensation, it increases the pressure under the contact patch, increasing grip. Whether it entirely compensates for the drop in drainage time is a matter entirely for the design of the tread pattern, the speed, depth of water, texture of road surface, and how much tread pattern depth remains on the tyre. Naturally, the less pattern depth, the more drainage is impaired- worn tyres don’t perform as well as new tyres in the wet.

With extra pressure in the tyre, a turning input from the steering will get to the road surface with more sensitivity as well. Things happen quicker and more predictably if the tyre is pumped up “hard”. The tyre distorts less in a sideways direction under extreme cornering forces too – sporting drivers say that the car “handles”. That’s something to notice – the steering response (ability to change direction quickly, as in negotiating a course of witches hats) gets better as tyre pressure increases.

High performance and premium quality tyres have complex bead and lower sidewall structures and low profiles, so that the message can get to the road quicker WITHOUT the necessity to run high pressures. A tyre with extra pressure can give a bone shaking ride, and transmit a lot of thumps and bumps from concrete road joins and the like to the cabin – not exactly ideal for the driver. There are more components in premium tyres to accomplish this feat, which is why they cost more.

Next on the CarbonBlack blog, we use our newfound knowledge of tyre pressures in some detective work.

Our Experts on: Aircraft Tyres

While we’re mainly focused on car and truck tyres on CarbonBlack, occasionally something comes along that piques our interest. In this case it was a question posted to our tyre expert David Matthews on aircraft tyres. Here’s David’s response:

The job that aircraft tyres have to do is very simple, but very specialised. They only have to track in a straight line, and operate within a narrow range of speeds. The epitome of this is, of course, a jet aircraft tyre. These have three layers of nylon built into the tread crown to hold the tread on at very high speeds (around 230 knots) – the nylon shrinks when hot, strengthening the hold.

The real issue is the amount of deflection they have to absorb on landing. Around 50% of the tyre section height (the distance between rim and ground) is lost on impact. The tyre flattens out, wears out after around 200-230 landings, (leaving furry bits of nylon protruding) and is retreaded, with the nylon replaced. While taxi-ing, the tyre deflection (percentage of section height lost) is around 30% on a jet, so some airports have limitations on plane weight when it has to taxi a long way in high temperatures.

The qualifying test for an aircraft tyre used to be (I have no recent knowledge, but it wouldn’t be any less today) that the tyre did 50 simulated landings without flaps at one hourly intervals – from memory around 180 knots. This is all done on a machine under controlled conditions.

The tyres operate at about 230 p.s.i on massively strong rims bolted together with massively strong bolts. This is possibly a bit removed from recreational aircraft tyres. What finally brings an aircraft tyre undone after six or seven retreads is fatigue in the lower sidewall, where the massively strong bead wire bundles (3 a side) are tapered into the flexible sidewall. So speed is not what it’s all about- reliability is. Comforting for recreational flyers!

What’s the relationship between love and tyres?

More metaphysical observations can be found on CarbonBlack’s tyre bloopers page.