In the second in our series on tyres and fuel efficiency, we spoke with Steve Howat, Technical Services General Manager at Continental Tyres in the UK
Continental’s Steve Howat explains how tyres are critical to fuel efficiency
To our simplistic question of how does tyre construction impact upon fuel efficiency? Do more belts make a difference? Howat responded; “The way that a tyre is constructed can have a positive impact on fuel efficiency. It’s not necessarily to do with the number of belts used within a tyre, or indeed that more of them make a bigger difference. Rather, it is how they are configured, which helps to control the tyre contour and influence the contact pressure distribution. This is what impacts rolling resistance. Generally, the lower the rolling resistance of a tyre, the more fuel efficient it is. Of course, other innovative technology, such as advancements in cap and base rubber compounds, energy efficient carcass materials and advanced polymer technology also have a significant impact on maximising fuel efficiency.”
Howat gave further explanation of rolling resistance and how it can make a considerable difference to a truck’s fuel efficiency.
“Rolling resistance,” says Howat, “can be defined as the amount of energy a tyre uses over a defined distance. It is one of five forces – along with climbing resistance, aerodynamic drag, inertia and mechanical friction – that must be overcome for a vehicle to move forward. There are a number of factors that affect rolling resistance, mentioned in the first question, which include the bead, belt, sidewall and tread designs. This is as well as the inflation pressure of the tyre itself, the vehicle’s load and how it is distributed, the road surface conditions and the weather. The rolling resistance and aerodynamic efficiency of the tyres directly impact the energy consumption of a vehicle. Lower energy consumption equates to greater sustainability – regardless of the type of drive system. In combustion-engined vehicles, this is reflected in lower fuel consumption and lower CO2 emissions. It also means better energy efficiency and, therefore, greater range. Reducing rolling resistance by 1 kg/t would increase an electric truck’s range by some two to three percent.”
Once again we asked about the impact of rubber compounding, that magic art that tyre manufacturers like to keep behind closed doors. Does rubber compounding have a role to play in fuel saving?
“Absolutely!” Says Howat. “The tread contributes around 50 – 60 per cent to the tyre’s overall rolling resistance. In the tread, it is not just about the compound but also the tread pattern. If we reduce the pattern void (the negative space between the tread blocks) by 1 per cent, then that directly correlates to a one per cent improvement in rolling resistance. This is a balancing act in tyre design, as the void has a role to play in water removal and overall handling characteristics.
“The type of compound used also has a significant effect on fuel saving and can be improved from a rolling resistance perspective by focusing on advanced polymer technology. Using the latest silica fillers, which reduces energy loss, is an important element of our base compounds.”
Continental is one of the market leaders in digital tyre management, and the focus in the system is on the tyre pressure monitoring. We asked Howat what the effect of incorrect tyre pressures on fuel efficiency might be?
“When a tyre is underinflated, the contact patch becomes larger,” says Howat. “As a result, a greater part of the wheel load acts on the outer edges of the tyre, with reduced pressure on the centre of the tread. Depending on the speed and weight of the vehicle, this variation in the distribution of forces causes the tyre to flex more and reach temperatures in excess of 150°C. We know that a tyre that is around 15 – 20 per cent underinflated can increase fuel consumption by up to 3 per cent, depending on how many tyres are in this condition on the vehicle.”
Retreading is the final element in a tyre’s operational life and there have been many arguments over the years about the benefits, or otherwise, of retreading. Is there a loss of performance in a second life retreaded tyre on a manufacturers own casing? If there is, does the cost saving on the retread tyre compensate for any reduction in fuel efficiency?
“Continental is leading the way when it comes to matching the technology used in our first life tyre within our retreads. We are already manufacturing low rolling resistance tyres as part of our ContiRe retread range, using advanced compound technology. From our perspective, we believe the loss of efficiency is negligible.” Concludes Howat.
