Flatspotting Tyres

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Have you ever felt a vibration or steering “shimmy” during the first couple of kilometers after you first drive your vehicle since it’s been parked for a few days? Then, after driving for a few kilometers, the sensation goes away and the ride returns to normal – than you have experienced what’s known as flatspotting, where flatspots in the tyres tread develop when a vehicle is parked.

Whilst flatspotting is usually temporary (because the flattened area of the tyre rounds itself out), it can be permanent in some cases.

Why does flatspotting occur?

Whilst driving down a road at an average speed of 60km/h, as your tyres roll they transform to and from an unloaded state to a loaded state roughly 500 times during a single kilometer (that’s around 8 times per second!).

This constant cycle of load/unload results in what’s known as tyre deflection, whereby friction within the body of the tyre causes it to heat up and expand. Afterwards, When you’re vehicle is stationary (or parked), the heat in the tyre gradually cools down. As this cooling occurs, the area of the tyre making contact with the surface beneath the vehicle begins to flatting out as the weight of the vechile presses the tyre into the ground, adopting the shape of the surface. It is this shape or “flat spot” that causes the vibration and shimmy the next time you drive.

After you drive for a few kilometers the tyre begins to warm up again, and the flat area of the tyre will regain it’s original shape.

The severity of flattspotting can be increased by a number of factors, mainly:

  • Period that the vehicle remains stationary
  • Low tyre pressures
  • Low ambient temperatures
  • Heavy loads

Low Aspect Ratio Tyres

Due to shorter sidewalls and because the bulk of their load capacity gets absorbed by the deflection of their wider tread, low aspect ratio tyres have a reduced amount of flex, which means they are more susceptible to flatspotting.

How to minimise flatspotting

Whilst there is no clear way to absolutely prevent flat spots from occurring, the ability to predict what will happen to a tyre under certain conditions helps to reduce the inconvenience caused by flatspotting.

During winter months, or when you have not driven your vehicle for a few days, flatspotting may be noticeable, although typically these flatspots your sort themselves out during the first few kilometers. During the day time, the warmer temperatures should prevent noticeable flat spots from occurring.

Parking or storing vehicles for long periods

This is when flatting will occur the most. Before putting your vehicle in storage you should make take the time to make sure the tyres are fully warmed up and then but the car up on blocks when you reach the storage destination. This will help you to avoid permanently flatspotting your tyres.

Getting your car serviced

Whenever you are taking your vehicle in for a service to do with your tyres (rebalancing, tyre rotation etc), you should ensure that you drive around for 5-10 kilometers beforehand to ensure flatspots do not prevent your mechanic from identify the source of any problems.

Tyre Placard

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Since 1973, in order to be compliant with strict design started introduced in 1971 (ADR 24), all vehicles in Australia are required to have a tyre placard installed which outlines the specific wheel and tyre combination that is recommended by the vehicles manufacturer. This can usually be found inside the glove box.

Along with details for optional and recommended tyres and wheels, the tyre placard also details the recommended air pressure, speed rating and load capacity for the vehicle.

Changing tyres

You may fit tyres to your passenger vehicle (under 4.5 tonne) other than those outlined on the tyre placard and still be compliant with ADR 24, providing:

  • The load rating does not fall what’s outlined on the placard
  • Where the speed rating required is higher than S, the speed rating on the tyres fitted must be at a minimum 180 km/h (S)
  • For off-road usage, where the speed rating required is higher than N, the speed rating of the tyres fitted bust be at least 140 km/h (N)
  • Any other type of vehicle must have a speed rating of at least 120 km/h

There are some instances where the speed rating is allowed to be lower than the rates outlined above when the speed rating of the tyre is greater than the max speed of the vehicle.

Replacement tyres

When you are purchasing replacement tyres, the following requirements must also he adhered to:

  • The manufacturer must rate the tyres are suitable for on road use
  • Tyre size and construction must match for each axle

Retreaded tyres

If you are planning on using retreaded tyres, than it is required that they are retreaded and clearly marked according to the provisions of Australian Standard AS 1973 – 1993 Pneumatic Tyres – Passenger Car, Light Truck.

Space Saver Spare Tyres

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Space savers (or temporary use tyres) are common place these days in new cars, with a full sized traditional spare becoming a rarity.

Infact many vehicle manufactures provide no spare at all, with space-saving, speed limited tyres or run-flat tyres with an inflation kit deemed good enough.

Overview

Typically consisting of both a wheel and rim and smaller than your average tyre, space savers are spare tyres specifically designed by vehicle manufacturers to be used as a replacement in the advent of a punctured tyre. First introduced for sports cars as a way of maximising the boot space, the now come as standard equipment in most new vehicles as way to reduce costs.

They are a small, lightweight substitute for the traditional fitted tyres and are usually instantly recognisable by a bright red or yellow rim and slender/compact size. As such they are strictly to be used in emergency situations only, and should be used as a permanent replacement for a standard road tyre.

It is important that you do not use space saver tyres for extended periods of time, at high speeds or for long distances. Once a space saver has been temporarily fitted, you should drive to the nearest tyre store as soon as possible and purchase a replacement tyre.

Safety

It is highly recommended that you pay attention to any recommendations outlined by the vehicle’s manufacturer, specifically in relation to speed limits, tyre pressures, travelling distances and vehicle load as driving on a space-saver tyre dramatically alters the behaviour of your vehicle – increasing stopping distances by nearly 50% and reducing corning grip by up to 13%. Generally the maximum speed rating for space-saver tyres in 80 km/h.

For further information, see the placard found near your spare tyre or the vehicle’s operating handbook, however generally it’s important to note the following guidelines when using a temporary spare tyre:

  • Be sure you ONLY fit spare tyres that have been provided by your vehicles manufacturer for your specific make and model or replacement tyres recommended by your local tyre dealer that are a direct match for the original equipment specifications outlined by the manufacturer.
  • Be aware that temporary use tyres such as space savers and run-flat tyres are not designed to be driven on for extended periods or long distances.
  • Always check the condition that the spare tyre is in before driving.
  • Never fit a space saver to another rim.
  • Always check the tyre pressure of the spare, noting that the inflation pressure will NOT be the same for a space saver as your normal tyre.
  • Always read the manufacturers instructions and drive your vehicle accordingly.

 Roadworthy requirement

Driving with a space-saver tyre is perfectly acceptable under all state and territory regulations in Australia, providing that the tyre has been fitted and is being used within the specifications outlined by the vehicle’s manufacturer (found in your handbook).

Please note that in order for your vehicle to pass a roadworthy inspection, you must not have more than one space-saver tyre (or other type of temporary use tyre) fitted to your vehicle at any given time.

Insurance claims

In most instances, incidents involving space-saver tyres will be treated the just like any other insurance claim in that all the contributing factors will be taken into account and looked at individually for each case. Although the use of space-saving tyres will not automatically exclude a claim from being approved, your insurer may look at whether the tyre was used in accordance with the manufacturers specifications (e.g. speed rating, distanced travelled) with review a claim.

Run Flat Tyres

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An increasingly popular choice on new vehicles, Run flat tyres (also known as Mobility Tyres or RFT) are characterised by their ability to support a vehicles weight in the event of a puncture or loss of tyre pressure. This safety design enables the driver to retain control of the vehicle and remove the need for a tyre to be changed immediately when tyre pressure is lost – meaning you can still drive to a tyre retailer for a replacement of the damaged tyre (subject to distance limitations).

Overview

Unlike conventional tyres that rely on pressurised air contained within a  tyre to support a cars weight, run flat tyres can support the cars weight by themselves for a short period of time.

Available in two variants, Run flat tyre systems may be equipped with a hardened sidewall or an internal support ring that’s mounted to the inside of the rim. Regardless of which type you have installed, both of these systems can be driven on without stopping when a puncture occurs.

Under normal operating conditions, runflat tyres continue to behave just like conventional car tyres. Run-flats still contain air which helps lighten the load the run flat system has to bear, spreading the weight of the vehicle evenly on the surface of the road and maximising the contact area formed between the car and the road.

One limitation is that run flat tyres cannot be fitted to every make and model as the vehicle manufacturer needs to specifically design the car to fit run flats. To find out if your car it suited it’s best to speak with your local dealer.

Safety

Developed specifically with increased safety in mind, Runflat tyres help minimise the risks associated with a punctured tyre. A puncture often causes the driver to lose control of their vehicle as a tyres shape and structure changes as it deflates, however in the event of sudden deflation, vehicle stability and therefore driver control are able to be maintained with run flats.

It’s fair to say most drivers, at one time or another, will be  inconvenienced by a punctured tyre. Changing a tyre on the roadside is laden with risks, especially when it occurs on the freeway, during peak hour, a busy road, at night and work needs to be carried out on the roads shoulder.

And whilst a puncture is usually more of an inconvenience and an unwanted expense, the dangers involved with a tyre failure at high speed are far more serious – such as losing control of the vehicle.  Using air pressure, the sidewall of a conventional tyre is securely pressed up against the wheel, however once this pressure is lost the tyre will seperate from the wheel and fall into the well of the wheel/rim causing the driver to lose control. Run-flat tyres on the other hand have been designed to keep all components of the tyre secure and in place when damaged or without pressure.

Tyre Pressure Monitoring System

A Tyre Pressure Monitoring System (TPMS) is an essential piece of safety equipment for any vehicles with Run-flat tyres installed. As run-flat tyres are designed to minimise the difference in ride quality when a tyre is punctured, especially on the freeway where little cornering takes place it can be hard to know when a tyre has lost pressure.

In the event that the driver is unaware of the damaged tyre, they are likely to continue driving at a speed above the safety limit outlined by the tyre manufacturer. Therefore it is essential that a Tyre Pressure Monitoring System be installed in conjunction with run flat tyres so that the driver is alerted (usually on the dash) when any loss of pressure occurs.

Advantages

Convience
As previously stated, the core advantage of runflat tyres is there ability to function without air over short distances at low speeds, as they are able to retain their overall shape thanks to its built in rigid components. This rigidity helps the driver maintain control of the vehicle if the tyre loses pressure, and removes the need to change a tyre immediately.

No need for a spare
Generally there is no need to carry a spare tyre with run flats, this reduces weight and frees up space in the boot.

Increased safety
The ability to stay in control and continuing driving on a run flat tyre means there is no need for you to change the tyre in unsafe conditions, such as the side of a the road. Generally you can drive at 80 km/hr for around 80 kms but you should refer to the manufacturers guide for more information.

Cons

Harder ride
Compared to a regular pneumatic tyre the ride is much harder.

Increased cost
Run-flats cost roughly 50% higher than your regular tyre.

Availability
At the time of publishing, run flat tyres are only able to be fitted to late model luxury & sports cars that have low profile tyres.

Repairs
Run-flats may only be repaired where the tyre is re-inflated as soon as the Tyre Pressure Monitoring System (TPMS) dashboard indicator lights up as driving with a flat tyre can often damage the sidewall beyond repaire.

Tyre Speed Ratings

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When buying tyres it’s important that you always select tyres with the correct speed rating for your vehicle.

Regardless of brand, all tyres have a speed rating indicated by letters which are outlined on the sidewall of your tyres. If you are unfamiliar with how to read tyres, than you should take a minute to read our guide.

The speed rating is an indication of the maximum speed at which the tyres can be safely used. Theoretically, the speed rating of your tyres should be lower that the maximum speed of your vehicle - in the unlikely event that it is ever driven at that speed.

The easiest way to determine the speed rating you require is to look at your existing tyres and use that as a reference when purchasing replacements for your vehicle. Otherwise you can always check in your vehicle manual/handbook or get in touch with your local dealer where possible.

When looking at your tyre size, the speed rating should be the very last letter written on the side of the tyre. For example, if the tyre’s size is “P205/65 R1 5 94V” than V would be the speed rating you are looking for.

Changing your Speed Rating

Even though the speed rating outlined for your vehicle may be a much higher speed than you’d ever consider safely driving at, we strongly recommend that you do not choose to buy lower speed rated tyres than outlined by the vehicle’s manufacturer. Infact it is illegal and quite dangerous to do so and considering a higher speed rating often results in improved car handling there is no need to do so.

Feel free to select an alternate model or brand of tyre, but try and stick to the same size and speed rating as if you ever choose to sell you vehicle, the new owner may be unaware of the change you made and may not choose to drive the vehicle in the same safe manner as you do.

Modifying your vehicle

If at any time your vehicle has been modified or the wheels/rims have been changed than you may need to find new tyres to fit the wheels, but the speed rating should still remain higher than the top speed your vehicle is capable of driving at.

Replacing tyres

Tyre manufactures do not recommended that you mix and match tyres that have different speed ratings. It is strongly recommended that you always replace your speed-rating tyres in a complete set of 4.

If you are planning on replacing 2 tyres only, the replacement tyres should be the same speed rating or higher.

Multiple Speed Ratings

If you end up with different speed rated tyres of your vehicle than you are advised to have them installed in pairs on the same axel – regardless of the driving axle as this helps to prevent oversteering.

In this instance, the speed rating for your vehicle becomes that of the lowest rated tyre by default.

Speed Rating table

Below is a table of speeds and there corresponding letter:

Speed Symbol Maximum speed (km/h)
N 140
P 150
Q 160
R 170
S 180
T 190
U 200
H 210
V 240
Z 240
W 270
Y 300

How to read your tyres

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Knowing how to read the information printed on the sidewall of your tyres is a crucial undertaking, as it enables you to correctly order the right tyre for your car.

If you look closely at the writing on the sidewall you’ll see the something similar to P205/65 R1 5 94V.

Tyre Size

Width (205)

The first number refers to the tyres section width in millimeters, which is measured from the bottom of the tread to the rim (sidewall to sidewall).

Profile (65)

After the forward slash, the next number is refering to the height of the sidewall, which is also known as the Aspect Ratio as it is a percentage of the section width.

For example, the height of this tyre is 65% of of the tyres width (205mm).

Low profile tyres mean there is a smaller aspect ratio percentage.

Tyre Construction (R)

Indicates that the tyre has Radial tyre construction, which essentially refers to the way it has been constructed.

Almost all passenger tyres are radial tyres.

Rim Size (15)

Indicates the diameter (size in inches) of the wheels rim, which is helpful when you are purchasing rims for existing tyres.

Speed Rating (94v)

The final symbol represents the maximum load capacity and speed rating at which it’s safe to use the tyre, subject to correctly fitted tyres, sound condition and appropriate tyre inflation pressure.