Archive for March, 2007

Tyres and Formula 1

We have seen many press articles being published lately, commenting, assessing, analysing the impact of the new Formula 1 rule about tyres.

To explain briefly the concept of the new rule; Bridgestone will be the sole tyre supplier this year, providing each teams with identical specifications and quantities of tyres. All drivers will be required to use two different compounds during each race; making the tyres an even more important component for success. (more about the new F1 tyre rule)

The Australian Grand Prix in Albert Park, Melbourne, is always the big test for all teams, and the extreme conditions there make the track really demanding for the tyres. Bridgestone was having trouble to choose between the hard/medium and medium/soft compounds for the race.

To make any sense at all of this treatise, we recommend that first you go to our “all about tyres” section on CarbonBlack, then click on the section “Tyre construction Q & A”, and finally browse down to “Let’s get back to where this heat comes from”, and “what’s rubber”. Having done your homework, you will then be prepared for this rational discussion on what makes a tyre tick under the extreme conditions of car racing.

Rubber compounds are comprised generally of around 12 chemicals, mainly carbon black, rubber, and the vulcanisation system of sulphur and other chemicals. Others are added to protect the rubber, aid its processing, or improve it resistance to a perceived hazard.

Rubbers used in tyres are generally styrene-butadiene co-polymers, natural rubber, or polybutadiene. These can be blended in whatever ratio is desired. The styrene content can be varied to give a hard wearing rubber, or a high styrene cling rubber to maximise wet grip at the expense of heat build up. Everything is a compromise aimed at giving the best performance for a particular application. For example, when a new circuit is laid down the surface is very abrasive, and polybutadiene has a superb abrasion resistance to sliding on sharp surfaces. However, it is hopeless in the wet, since grip suffers appallingly. In car racing of course, grip is everything. However, there is one famous case where a car won one of the last Phillip Island 500 mile races, by changing only one tyre, whereas everyone else changed 12! The tyres had polybutadiene treads, but were 3 seconds a lap slower on the newly laid circuit, particularly so at the ocean side of the circuit. But they didn’t call the now 89 years old Harry Firth “the FOX” for nothing.

The second most important variable is the carbon black type that is used. There is a huge range of carbon blacks, derived from burning oil in a specially designed furnace in insufficient air for complete combustion. The “soot” that is gathered is carbon black, which may vary from the ultra-fine types used in printing ink, to the ‘soft’ blacks used in the casing compounds of a tyre. As a general rule, the finer the carbon black, the higher the abrasion resistance, and the higher the heat build-up in the rubber compound in service. There is another variable, the “structure’ of the carbon black, a measure of the agglomeration of the particles, but no further correspondence will be entered into on this, as it’s getting a bit too technical. Most tyre compounds will contain 25% to 35% carbon. It’s the carbon that reinforces the rubber, improves abrasion and tear resistance, tensile strength, and lots of other characteristics.

The third variable is the “state of cure”. In other words, you can make “hard rubbers” merely by making adjustments to the level of “curatives” – sulphur and accelerators added to the mix. Add all these variables together, and the usual range of tread rubber hardness can vary quite considerably. It is measured using a simple penetrating tool called a Shore A Durometer. What is significant is that this hardness varies with the temperature of the rubber. This affects other properties as well. You are probably all familiar with the range of squash balls and their different colored dots, signifying different resilience or rebound. However, all change their rebound characteristics with temperature, and they get hot when you bash them up against a wall. Race car drivers are quite used to this, and adopt techniques to “load their tyres up” during slow periods of the race under the pace car discipline, for example.

Formula 1 go even further by wrapping their tyres in the pits in electric blankets to warm them, so that the driver won’t be caught out by an abrupt transition from race hot tyres, to cold newly fitted tyres, which don’t grip as well.

As the temperature of the tyre changes, so does the dynamic qualities of the tyre. If it gets TOO hot, the amount of heat being generated cannot escape to the cooling airstream quickly enough, rubber being a very good insulator, the heat builds up at either the thickest part, or the part under most stress, for example the outside front tyre on a banked circuit, and the tyre “goes off’ in race car speak. It loses some of its rubbery characteristics, reverts to a puggy dough almost, and will probably blow apart. Tyre technicians monitor the temperature at the thickest part of the tread by inserting a needle pyrometer, which gives a digital readout of the temperature at the point of the needle inside. The tyres have a dimple on the buttress to indicate where the needle should be inserted to a calibrated depth. Being race tyres, the tread is not very thick, so this has to be done carefully, and quickly.

An interesting development in Formula 1 has been the compulsory adoption of grooved tread patterns. The tyres are grooved circumferentially, rather similarly to the patterns used on aircraft tyres. They have one purpose- to slow the cars down! There is less rubber on the road than a slick tyre. A high proportion of the drag generated by an F1 car comes from the tyres. The downforce is controlled by the spoiler or wing on the rear of the car, plus other “aerodynamic aids” placed at critical points around the car, following wind tunnel testing, designed to hold the car on the ground.

These tread grooves cannot be placed over the edges of the reinforcing belts in the casing, or they will quickly cause the tread to crack circumferentially, which will “throw the tread”- a catastrophic failure. Recently, one of the presenters on the BBC show “Top Gear’ crashed a jet powered car at high speed due to a tyre failure on the front wheel. Wait for the full show, so that you can freeze frame the blowout, but it looked very much like that sort of failure on the film clip seen so far.

However, even though all tyres now have a tread pattern, there are still “wet weather” and “dry weather” compound tyres fitted during the course of a race, as circumstances dictate. This is a measure of the absolute ‘coefficient of friction’ developed by the rubber compound on the road, particularly after it has removed the film of water from under the tyre.

When to change from wet to dry, or the reverse, is dictated by experience, the lap times being recorded, the weather forecast, and the ‘lap of the gods’. That’s why all the gurus in the pit lane all seem to have grey hair, or none at all. The tyre technicians can advise, test to their hearts content on indoor test wheels at impossible speeds, and at outdoor circuits, have access to all the computer aided programs they desire to optimise any particular property of the rubber compounds they may be seeking, but in the long run, someone has to make a decision on what is the most suitable tyre for the race on the day. What works at Albert Park in Melbourne, will be different indeed to the new circuit at Bahrein, which is very abrasive on tyres.

The difference can be the difference between finishing first, or tenth, or worse.


March 19, 2007 at 11:01 am Leave a comment

Tyre Review Interpretation by Allan Henry

Allan Henry is the “Major Accounts And Business Development Manager” of Assist Australia. Today, he writes about the interpretation of “tyre reviews”.

Carbonblack offers tyre reviews from experts, tyre dealers and tyre buyers to make it easy for you to buy tyres. But the most important thing is to interpret correctly these tyre reviews… Read this article and make the right tyre choices.

Tyre Performance Parameters:

  • Wet grip
  • Dry grip
  • Wet braking
  • Steering response
  • Noise level
  • Tread wear.

Ranking of importance based on:

  1. Safety – the first priority
  2. Ability to control the vehicle – also a safety issue
  3. Comfort & fatigue factors – on long trips, also a safety issue
  4. Cost factors

Note that cost factors may be very important to some drivers, but less so to others who may be prepared to pay a higher price to gain greater safety.

Criteria Why is it important? Ranking of importance (more stars = more importance)
Wet grip Affects steering & braking on wet roads ***** Safety issue
Dry grip Affects steering & braking on dry roads ***** Safety issue
Wet braking Ability to stop on wet roads ***** Safety issue
Steering response Affects driver’s ability to steer the car **** Driver control issue
Noise Comfort and Fatigue factor *** Fatigue issue
Treadwear Cost issue Individual – important to many drivers

1. Wet Grip

Refers to a tyre’s level of grip on a wet road, when cornering, braking or accelerating.

Obviously, the water depth on the road surface and the speed of the vehicle are very significant factors in the level of wet grip. However, the tyre tread design, tread rubber compound, and tyre construction all have a significant affect on a tyre’s wet grip, as does the remaining tread depth, or amount of tread wear. Operational factors – tyre load and pressure, and environmental factors such as ambient temperature also play a part. The type of road surface – bitumen, or concrete, and macro and micro surface roughness, and amount and type of surface contaminants (such as oil) also have significant effects. Generally, coarser road surfaces improve a tyre’s wet grip. However, a factor within the control of all drivers – the speed at which the vehicle is driven – is one of the most crucial factors.

Most people have heard of the term “aquaplaning”, and some understand that it results in a loss of control of the vehicle. This is because the tyre tread is unable to clear away the water on the road surface, and the tyre in effect, “rides on a cushion of water”, much like the planing hull of a speedboat. It is necessary for the tyre to make contact with the road surface so the driver can control the vehicle’s direction and speed.

When there is water lying on a road surface, the tyre tread must squeeze the water out of the contact area (or “footprint”) as the tyre rolls along the road to make contact with the road surface. This takes a small but finite amount of time. As the speed of the tyre increases, the amount of time the tyre has to remove the water becomes less and less. Within the “footprint” of the tyre, the proportion of the area in contact with the road gradually becomes less as the speed increases, and when aquaplaning occurs, there is no contact at all. Note though, that at typical highway speeds in heavy rain, the “footprint” area in contact with the road surface can be less than 50% of the normal contact area. The tyre’s grip is also commensurably reduced.

It is sobering to consider the amount of time the tyre has to remove road surface water from under the tread at normal vehicle speeds – see the table below, calculated for a typical tyre footprint length of 160mm:

Speed Time
to travel footprint length Seconds
km/hr m/sec
60 16.67 0.0096
80 22.22 0.0072
100 27.78 0.0058
120 33.33 0.0048

The time the tyre takes to travel one footprint length, is the maximum time it has available to squeeze out the water on the road surface, before all contact with the road surface is lost!

2. Dry grip

Refers to a tyre’s level of grip on a dry road, when cornering, braking or accelerating.
The level of dry grip basically determines how hard the tyre can brake, accelerate or turn the vehicle through a corner or curve. The level of grip available is affected by many factors, including:

  • Tread rubber compound and tread pattern design,
  • Tyre shape, aspect ratio, and construction
  • Interaction with a vehicle’s suspension
  • Operational factors – load on the tyre, inflation pressure, and
  • Environmental factors – the road surface, contaminants, and weather conditions

3. Wet Braking

Refers to a tyre’s level of grip on a wet road when braking.

Refer to “Wet Grip” for more information.

4. Steering Response

Usually refers to how quickly a tyre responds to a sharp steering input from the steering wheel, as in (the first part of) a lane change manoeuvre.

This is a tyre performance parameter that helps the driver control the vehicle, particularly when the unexpected happens and an evasive manoeuvre is necessary. Up to a point, the faster the steering response, the better, but there is an ideal level. If the response is too quick, it can make the tyre/vehicle combination “twitchy” or over-sensitive to driver inputs. Car and tyre manufacturers go to enormous trouble to ensure the steering characteristics designed into a car and tyre combination, suit the intended purpose of the vehicle. A sporty car and tyre package will have different steering response designed in, than would be the case for a family sedan.

Generally speaking, the steering response of low “profile” or low aspect ratio tyres is quicker than higher profile or high aspect ratio tyres, which is why low aspect ratio tyres are specified by car manufacturers for their sports oriented models.

5. Noise Level

Refers to the volume of noise generated by the tyre when a vehicle is moving. A tyre generates noise as it rolls along the road surface, mostly from the tread pattern of the tyre.

The aim of tyre designers is to design the tread of the tyre so that it generates a noise as close to “white” noise, and with as low a noise level, as possible. That is, the noise will have no significant tonal characteristics, and be very quiet. The original tyres fitted to basic family sedans tend to be the quietest tread designs. There are a number of reasons for this. One is that these vehicles have less noise reduction material fitted (and car manufacturers therefore specify a quieter tyre for the vehicle), another is that the mix of tyre performance parameters will be different from that required for a sporty or prestige vehicle. High levels of wet grip for example, generally requires a more “open” tread design, which will usually result in a noisier tyre. As a general rule, the more aggressive or “sporty” the tread design is, the more likely it is that the tyre noise will be louder and more annoying. Some SUV or 4WD tyre designs have very aggressive tread designs to provide good grip in off-road, muddy conditions. These designs can be very annoying on bitumen roads, and tiring for the passengers during a long trip on sealed highway roads.

Tyre noise also varies significantly on different road surfaces. On smooth, polished road surfaces, noise generated by the tyre tread predominates, whereas on coarse, new road surfaces, tyre construction and materials also have a significant influence.

If tyre noise, or the lack of it, is important to you, it may be best to replace your worn tyres with some of a similar design and quality to those originally fitted by the car manufacturer.

6. Tread Wear

Usually refers to the distance the tyre has covered before the tread is legally worn out, when the Tread Wear Indicators (TWI) are level with the worn tread surface.

Many, many factors affect the tread wear of a tyre. Tyre tread design, tyre construction and materials, the load on the tyre and the inflation pressure, the speed of travel, wheel alignment, driver inputs (gentle or aggressive steering, braking and acceleration) and many environmental factors all have a greater or lesser influence on the tread-wear of a tyre. Even the age of a tyre (since it was manufactured), and the remaining tread depth have an influence on the rate of tread-wear.

Motorists generally cannot control the environment in which they drive – the type of road surface and layout (smooth or rough, straight and level or curved and hilly), and the weather conditions (wet or dry, hot or cold), but can maximise the tread-wear from their tyres by:

  • Maintaining the correct tyre pressure (check at least monthly). If the size of tyre fitted to the car is listed on the tyre placard, use the recommended pressure as the minimum pressure to use.
  • Regularly “rotating” the tyres’ position on the vehicle (every 10,000 km is usually a reasonable frequency)
  • Maintaining the vehicle wheel alignment to the car manufacturer’s specifications.
  • Braking, accelerating and cornering smoothly and gently

Low tyre pressures increase the rate of wear on a tyre, as well as reducing or eliminating the tyre’s reserves of safety. Poor wheel alignment can also cause very rapid wear to all or part of the tyre tread surface, and render the tyre unroadworthy. The worse the tyre misalignment is, the more rapid the rate of wear. Similarly, rough or aggressive driving will also significantly increase the rate of wear. For example, a small increase in cornering speeds will result in a much greater rate of wear.

March 12, 2007 at 9:24 am 3 comments

The Romance of Rubber

There are probably a few myths interwoven into this tale, but a brief history of the development of the tyre industry wouldn’t be complete without a tribute to the early pioneers of the rubber industry.

First there had to be a source of the material itself. The tree hevea braziliensis, the name gives a clue where it was from, bled a milky liquid sap (called latex), which when dried in the sun and smoked, became rubber. The South American “Indians” used to wrap this sticky material up into shapes approximating a football, and kick it around, so that’s where football came from?

The early explorers returned to Europe with this interesting material, but really couldn’t find a use for it except as a curiosity because of its bounce, and it found use as a pencil eraser, hardly earth shattering.

A Scotsman discovered that it dissolved in petroleum based solvents, and could be spread on fabric to make water-proofed clothing, called “macintoshes”, but these stuck together if they became warm, so of limited use. Later, a means of “cold vulcanisation” by dipping the fabric in chemicals was developed. Cold vulcanisation is still used today, most commonly in puncture repair kits

Enter Charles Goodyear, around the 1840’s. He was a “chemical tinkerer” according to legend, and experimented with many materials as an additive to rubber, trying to convert it into something more useful. Eventually he struck pay-dirt by combining rubber with sulphur, and cooking it under pressure. Pressure had to be applied to prevent the material becoming porous. By combining sulphur and rubber, an irreversible chemical change was initiated which made the product stronger and retained its elasticity. Combining it with a much larger percentage of sulphur (around 35%) gave a very hard material called ebonite, which immediately found applications. It was the forerunner of modern plastics, in a way.

Nearly fifty years later, John Boyd Dunlop wrapped his bicycle wheels with proofed fabric, inflated the resulting tube with air, and started winning bike races because pneumatic tyres were easier to push than bicycles shod with solid tyres. This was in 1888, four years before the first Daimler-Benz was made, called Mercedes after his daughter. The bicycle tyre industry took off, as the bicycle was the most popular individual form of transport. Components to manufacture bicycle tyres were shipped from the U.K. to South Melbourne as early as 1892 for assembly here, so you can see that the take-up was rapid worldwide.

The introduction of the motor car changed everything. Many entrepreneurs started building cars, and despite their many limitations, pneumatic tyres were quickly adopted on them, (though truck tyres continued on solid tyres for many years afterwards.) This occurred most rapidly in the U.S.A., and the Seiberling brothers started a tyre company, calling it after Charles Goodyear, and another famous name of the period was Harvey Firestone. Both names survive today. Goodyear built the first factory of theirs outside the U.S.A. in Sydney in 1927 at Granville.

You may think of the radial tyre as a recent invention, but Gray and Sloper invented the design in the early 1900’s, but couldn’t figure out a way of stabilising the construction, nor the means of building it.

The 1920’s saw many rapid advances in the technology of rubber. The make up of the various formulations was a closely guarded company secret. Materials were coded to disguise their identity, and factories were closed to visitors. In some, communication between departments of the same factory was restricted. In some companies today, these practices still survive, though the means to chemically analyse the complete structure of a rubber compound exist.

Around that time in the 1920’s, chemicals were being developed that speeded up the vulcanisation process markedly, and others that delayed rubber from “perishing”. Some of these proved to be pretty toxic and were later withdrawn, but left an unfortunate legacy behind.

A story of the time tells of a clergyman visitor who was admitted to counsel one of his flock, and who expressed great wonderment at what he was seeing, and asked for a sample of rubber being processed. When approved, he drew out his pocket knife to cut a sample, and LICKED IT FIRST. He was immediately escorted out the door, because he knew too much, that wet rubber cuts easily. . So industrial espionage is not new either!

March 6, 2007 at 9:49 am Leave a comment

Inflating Tyres Safely

Today’s Passenger and R.V. tyres, are tubeless. In order to get the beads to seat and seal, specialised equipment is needed, with a blast of air into the tyre casing, sufficient to move the beads outwards till they contact the rim. Virtually the only way this can be done without this equipment, is to fit a tube, and pump away till the tube walls do the job for you. That is why dedicated off-roaders always carry a spare tube, tyre levers, a pump, and if they are wise and experienced, some tyre lubricant.

So assuming that the tyre is still inflated, and only needs a top-up, it’s down to the local servo you go. Join the queue (you can feel virtuous because they’re probably won’t be one). Uncoil the hose from its stand. Unscrew the valve cap, give the valve a blast of air by depressing the trigger and the stem in the centre of the airhose to clean the area of the valve. Unscrew the metal or plastic valve cap, and top up the air pressure. Then on the first tyre of the set that you do, check the pressure against the gauge that you carry in the glovebox. After that, move on to the next wheel, but not before you have screwed the valve cap back on.

That’s your first line of defence against air loss.

It’s surprising the number of motorists who realise that they have a slow air leak a week or so after they have topped up their tyres. Commonly, dirt under the valve stem is the problem. Detect this with “the spit application test”. If a blob of glottal applied with the finger over the valve orifice bubbles, then the valve core needs replacing. It only costs a few cents, but a slotted valve cap, or core removal tool, is needed. Ask your friendly service station operator for help, because the tyre has to be almost deflated, unless he’s quick!

March 1, 2007 at 11:13 am Leave a comment