Tyre Review Interpretation by Allan Henry

March 12, 2007 at 9:24 am 3 comments

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.

Entry filed under: Choosing the Right Tyre, Installing & Changing Tyres, Our Experts, Safety, Tyre Industry, Tyre safety & maintenance, Tyre Technology, When to Replace your Tyres. Tags: , , , , , , .

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3 Comments Add your own

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  • 2. Michael  |  May 25, 2009 at 7:46 am

    Our mazda 6 currently has 215/45 x17 tyres. The rim is 7JJ which I presume is 7 inches wide. Can I increase the tyre wide on this rim to 225 or 235?

    Reply
  • 3. Ian  |  September 10, 2009 at 12:32 pm

    I have a Kia Carnival 2.7 auto lEX May 2007 you say use Mich’s I always used them in U.K. but search say 13 to 15 mine are 225/70R-16.when car was new tyres where Kumho now there are Nexen.so what long lasting tyres can I use around town and short weekend driving.I am slow driver 60-90 kph.Kumho’s lasted 1.5 yrs. and 22,000 K’s.

    Reply

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