The role of tyres in fuel economy

  • Author: OPONEO.CO.UK

In times of rising fuel prices, it is worth looking for ways to make savings through other means. Fuel consumption is one such way, as using less fuel saves money, and various car tyre features can contribute to this factor. In fact, every component part of a tyre has the potential to cause a significant increase or decrease in the use of fuel.

For some time, manufacturers have been offering “eco-tyres”, which claim to offer a low rolling resistance and, consequently, lower fuel consumption. These are products which really do enable savings to be made, but only if certain conditions are met. One of these is the need to adopt a relaxed driving style.

We advise those who drive dynamically and aggressive not to buy ecological tyres, but rather stick to high-range traditional tyres.

However, this doesn’t mean that a traditional tyre will lead to much greater fuel consumption. This parameter is influenced by numerous factors. You could encounter a poor made and used ecological tyre, or a well designed and used traditional tyre. In this case, it is rather likely the lower-standard eco-tyre will provide a greater consumption of fuel than the good traditional equivalent.

Overall, when looking at the factors that influence fuel consumption, we can look at five principle areas:

1. Tyre structure

2. Tyre size

3. Tyre wear (technical condition)

4. Tyre pressure

5. Conditions of tyre use
 

Apart from rolling resistance, every car is subject to the following resisting forces while travelling:

  • Aerodynamic forces
  • Internal friction
  • Gravitational forces
  • Inertial forces

To overcome each of these forces, energy is required and this is provided by the fuel source. A tyre’s motion involves hysteresis (a loss of energy in the form of accumulated heat due to compression of the tyre). The rolling resistance is an effect of this phenomenon. A very high level of hysteresis offers excellent grip, while a very low hysteresis creates a low rolling resistance. This hysteresis factor is determined by the viscosity and elasticity of the materials used in the tyre construction. Aside from rolling resistance (which in turn changes the fuel consumption), tyres also make another contribution when it comes to the vehicle’s aerodynamic resistance.

Overcoming resisting forces accounts for up to 35% of a vehicle’s fuel usage. Depending on various factors, rolling resistance makes up anywhere between 10% and 70% of this. There are also various other forces, such as those that apply when turning with a front-wheel steering system or 4x4, but these aren’t included for the purposes of fuel consumption.


refueling

The rolling resistance of tyres is one of the elements affecting fuel consumption.


Tyre Structure

  • Radial tyres have at least 20% lower rolling resistance than diagonal tyres
  • A smaller quantity and thickness of tyre elements, as well as a thinner tread and sides, leads to less rolling resistance
  • The smaller the mass of the tyre, the lower the rolling resistance can be. A lighter tyre can be produced using materials of a smaller thickness, by reducing the quantity of material and the width of the tyre, as well as raising the profile.
  • Other elements of the tyre design include the proper selection and mutual positioning of materials, as well as the quantity of supplies used and the angle of reinforcements and belts.
  • The shape of the tyre’s contact patch, the tread pattern and the materials used in its manufacture all contribute. In fact, the tread structure contributes up to 60% of the rolling resistance.
  • The position of blocks and other elements in the tread. An optimum design of this tyre part reduces the compression and deformation.
  • The rubber compound used to produce the tyre. Modern tyres are made from various sources, including polymers (such as butadiene, natural and styrene-butadiene rubbers), fillers (such as soot and silica) and a vulcanizing agent, such as sulphur.  Also, a greater number of butadiene parts and larger particles of filler (this works best with silica in a binder form of silanes) will help lower the rolling resistance.
  • The process of producing the compound, such as its temperature and duration.

Of course rolling resistance isn’t the only factor that matters. When making a purchase, you should always choose a product that will offer good values across a range of performance parameters.

New tyre

A tyre must offer good values for a range of parameters, not only rolling resistance.


Tyre Size

  • The lower the tyre height, the more rigid it will be and this results in a lower rolling resistance
  • A tyre which is narrower by 1 cm has approximately a.1.5% lower aerodynamic resistance.
  • Changing the rim width may also influence the tyre’s rigidity and, consequently, affect its deformation and rolling resistance.

Because of these factors, a low tyre profile will reduce the tyre’s rolling resistance. However, low profile tyres have their own pros and cons, which should be considered before choosing this option.


Tyre Wear (Technical Condition)

  • The more worn a tyre is, the lower the rolling resistance
  • In the case of a worn tyre, its mass decreases and it undergoes a lesser degree of compression during travel, increasing its rigidity
  • Of course, a worn out tyre has other issues, such as a lack of grip and a decreased resistance to aquaplaning.
A tyre with tread depth of 1.6 mm

A tyre with a tread depth of 1.6 mm may have 20% less rolling resistance than a new product. At the same time there is a decrease in its grip on wet surfaces.


Tyre Pressure

  • Low tyre pressure causes a greater compression of the tyre and less squeezing of the tread blocks when in contact with the road surface.
  • As a result, a reduction in pressure by 0.3 bar means a 6% rise in rolling resistance
  • A reduction in pressure by 1 bar results in a 30% rise in rolling resistance, increasing fuel consumption by several percent.

Conditions Of Tyre Use

A higher ambient temperature causes a reduction in rolling resistance. The reason for this is due to the increase in pressure and the attainment of the tyre optimum working temperature. This is especially true during the warmer months and, thus, with summer tyres.

The impact that tyres can have on fuel consumption is a fact, resulting from the influence of various factors. Because of this, it is something that drivers should always consider and modern EU tyre labels indicate a tyre’s given rolling resistance (in fact, the labels are part of an initiative to encourage better rolling resistance across all tyres).

However, you should also remember that it is not just the tyres that influence a vehicle’s fuel consumption. Naturally, buying tyres with a low rolling resistance is beneficial, but it is also necessary to drive in an economical fashion. Eco-driving experts recommend:

  • Do not warm up the engine while stationary
  • Do not accelerate rapidly or dynamically (such as changing to higher gears as soon as possible)
  • Using the engine to brake

Ultimately, there are quite a few conditions to consider. When it comes to tyres, a lower rolling resistance has some drawbacks, so you should also look for tyres that compensate this, such as asymmetrical and directional tyres.
 

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