Goodyear’s LHT II – Low Rolling Resistance Without the Drawbacks?
Newton’s First Law of Motion states that ‘every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it’. For tyres, this external force is seen in rolling resistance, and it is primarily caused by the repeated deformation and recovery of the tyre as it comes into contact with the road surface. Reducing rolling resistance is, in theory anyway, relatively simple – yet achieving a reduction in rolling resistance without compromising on other essential tyre qualities is another matter entirely. In designing its latest generation trailer tyre, the Marathon LHT II, Goodyear referred to this as “mission impossible”. Yet through much research and development work the tyre maker believes it has achieved this seemingly unreachable goal.
“The tyre that we have here today, our target was to be best in rolling resistance and best in wet grip,” comments Henry Johnson, Goodyear’s vice president Commercial Tyres Europe, Middle East and Africa. “I worked very closely with our technical people and, believe me, many of them a year ago didn’t think this was possible. What we’ve achieved is a tyre that will deliver just alone, if you don’t change the tyres on the tractor unit, a three per cent fuel saving. And if we take an average fleet in Europe, of let’s say 400 vehicles, on an annual basis that’s nearly one million euros with that three per cent fuel saving. In addition, the tyre will give five per cent better mileage than its predecessor. On top of that – something that’s quite incredible, I think – it is seven and a half kilos lighter than the predecessor, which will give additional payload capacity; it gives around 45 kilos per tractor and trailer unit, plus it gives excellent braking on wet roads.”
One of the factors shaping development work on the LHT II was upcoming European legislation. Regulation 661, set to come into effect in November 2012, sets maximum standards for rolling resistance and noise. In addition, July 2012 is the scheduled date for the introduction of tyre labelling. “That labelling is for rolling resistance, wet grip and noise, so obviously you need to succeed in each of these areas, and our mission impossible as we saw it was to succeed in all of those areas,” remarks Johnson.
Explaining the significance to the fleet industry of a reduced rolling resistance tyre such as the LHT II, Georges Feider, chief engineer, Construction Development at the Goodyear Innovation Center in Luxembourg points out that “when looking at a typical line haul vehicle we see that of the total rolling resistance coming from the tyres, when divided up between the various axles, about a sixth comes from the steer tyres, a third from the tyres on the drive axle, and about half the total rolling resistance comes from the trailer. That’s why it’s so important in tyres like the LHT II that this rolling resistance in minimised.” Furthermore, explains Feider, a direct correlation between rolling resistance and fuel consumption can be observed: “When we reduce rolling resistance in a tyre by ten per cent, the fuel savings is three per cent. So lower rolling resistance to lower fuel consumption is ten to three.”
Feider asks the question: Why is improving rolling resistance without harming other qualities a ‘mission impossible’ for tyre designers? “What we want to achieve is an improvement in the overall level of our tyres,” he states. “We don’t want to make an improvement in one aspect that deteriorates the performance for some other criteria. It is very easy to make a tyre that grips like glue to the road – a lot of blades, a very sticky compound – but then it will be very lousy in terms of mileage. And we don’t want to compromise safety just to improve rolling resistance.”
So how does the Goodyear tyre design team claim to have solved this ‘mission impossible’? Referring to the LHT II, Feider reports that the focus was on rolling resistance with no compromise in any other area. “To achieve this, we left no stone unturned; we have first of all worked on the shape of the tyre, on the shape of the imprint, the footprint, on the road. We also looked at the internal construction – what the customer normally does not see.
“We looked at a whole list of ideas on how to minimise deformation so that we can reduce energy loss,” Feider continues. “The idea here really was to reduce deformation, take all the weight out that we don’t need, take all the material out that we don’t need and put the material where we really need it. So we had a whole list of ideas which simulated what the effect would be, we selected the most promising and then we took prototypes and tested them and developed and refined them.”
The nuts and bolts of the LHT II – the parts, as Georges Feider says, the customer doesn’t see – include a casing in which the component gauges have been redesigned in order to lower both temperature and rolling resistance, while the steel wire belts in the tread area are designed to enhance stability and reduce tyre inertia energy losses. The carcass shape and bead area is intended to further improve stability and rolling resistance, with the added advantage that retreadability is said to have been enhanced in the LHT II. As for the tread, Goodyear says the LHT II’s compact tread design allows low energy dissipation, again favouring very low rolling resistance and reduced fuel consumption. Blading density and distribution is intended to optimise wet braking performance, rolling resistance reduction and minimise noise emissions. We can’t report on the exact composition of the tyre’s compound – Georges Feider quipped he’d have to shoot us if he told us – although we can mention it features a high silica content that Goodyear says provides the ideal balance between rolling resistance, wet braking and mileage. As he comments: “We have latest generation steel cords in the crown and also in the carcass, so when we took out the weight we did not compromise the stability. We did not want the tyre to become so soft that movement is always occurring. So we have instead achieved this weight saving by using new materials.” Henry Johnson sums up the construction of the LHT II by saying “it contains fewer materials, but better materials.”
Much of the development and testing work for the LHT II was carried out at the Goodyear Innovation Center, located in Colmar-Berg, Luxembourg. At the centre, which employs some 900 scientists, engineers and technicians from 24 countries and is responsible for developing products for every region apart from North America, the new tyre was tested by the company’s Tire Vehicle Mechanics Laboratory and Product Evaluation Division. Static tests were carried out on a range of devices including the high speed uniformity machine, dynamic footprint machine and noise lab, and on-vehicle tests were performed at Goodyear’s on- site proving ground. The LHT II was then handed over to Austrian long-haul logistics company Zeller Transporte for field testing. During the final quarter of 2009 Zeller tested the tyres over a total distance of 55,000 kilometres, comparing performance with the predecessor tyre, the LHT+. “We measured an average fuel consumption for the LHT+ of 33.41 litres per 100 kilometres, with the LHT II we have 32.17 litres,” reports Feider. “This is a reduction of 1.24 litres for every 100 kilometres – a 3.7 per cent saving. If you take a vehicle that does about 200,000 kilometres per year and assume a fuel price of 1.2 euros per litre, then we have a savings potential of over 3,300 euros per truck per year.”
That is unarguably an impressive saving. But can the LHT II really deliver the decrease in rolling resistance, and through it the fuel savings, that Goodyear says it can? Feider has a reply to any such skepticism. “We always have people who don’t believe what we show them, that’s why we requested TÜV in Germany, an independent company, to purchase tyres and test them. We didn’t provide the tyres – we asked them to go out and purchase the tyres. Then they measured them for us.
“With the first result they laughed, they said it’s impossible, so they went out and purchased a second set of tyres and tested them again but found the same results,” Feider continues. “The LHT II has 26 per cent less rolling resistance than the LHT+. When we looked at the rolling resistance coefficient (rolling resistance divided by the load), it was 3.27 for the LHT II. This is not the final result that we can take for labelling and homologation because there is still some discussion going on, but it is not hard to imagine what the result will be. As you may be aware, the overall limit is 8; to qualify for class A (for truck and bus tyres under the EU tyre label) it must be 4 or less – so you can imagine was this will probably mean for this tyre.”
The first three sizes in the LHT II range – 385/55R22.5, 435/50R19.5 and 385/65R22.5 – will be available from September 2010 with a price about 10 per cent above the predecessor tyre. The LHT II is, as Henry Johnson comments, the latest addition to a range of “new generation” truck tyres introduced to the market since 2007; tyres that he refers to as being “better for the pocket and better for the planet.”
Once more referring to the new tyre’s environmental benefits, Johnson states: “If you equip a truck today that was equipped with our previous generation tyres with this generation tyres, the CO2 saving per year represents 5,200 kilos per truck, which is significant. If you want to put that into context, if all long haul trucks in Europe were fitted with these tyres, it’s equivalent to over 6,000 football pitches of trees as an offset.
“So, in conclusion, in what has been a very challenging environment we’ve continued to innovate, and we’ve set what we consider to be a new benchmark for the industry, with very innovative products. The Marathon LHT II combines low rolling resistance with excellent wet grip, and this will give optimum fleet operating costs – which is, at the end of the day, what we’re concerned about.”