X-Line product developments
So, apart from the obvious investments in research and development, how exactly has Michelin improved its XLine highway tyre range’s wet grip and rolling resistance? And what do we know about why these tyres perform throughout the life of the tread?
In a nutshell, there are three new improved tread designs plus the application of a five rib structure and 25 per cent wider side-ribs on the front axle. Looking specifically at the tread, this means the inclusion of what Michelin calls TowerPump and Delta sipes on the drive axle as well as hidden groove technology and the addition of “Carbion” in trailer tyre compounds. In addition all positions feature EnergyFlex casings on all positions. This technology is said to offer improved heat management extending the products life, endurance and – importantly – its rolling resistance characteristics.
You may not have thought that sipes make all that much difference or that the small cuts in a tyre’s tread patter are most effective in wintry conditions. And they certainly are an effective way of increasing the number of biting edges on a tread patter and therefore improving grip, especially in wet and wintery conditions. However, as much as this is true, Michelin researchers are also increasingly deploying a range of siping technology to solve both environment and performance challenges put forward by hauliers and fleets.
This began with the addition of so-called raindrop sipes to its truck tyre toolbox with the advent of Michelin durable technologies in 2005. This particular approach, which is still in use in the latest generation of truck tyre technology, was a precursor to Michelin’s current emphasis on worn tyre performance as it offered a way for the tread pattern to be regenerated through the patented “rain drops” as the tyre wore. And the logic behind this approach is pretty water tight too – after all who can argue with the fact that a truck tyre spends more time worn than in a freshly cured, full treaded state?
Now with the latest generation of truck tyres, Michelin is employing further siping approaches, namely TowerPump and Delta sipes. The TowerPump technology, which was introduced on the Multiway 3D earlier this year, combats the decreased water evacuation properties of a tyre that are inevitable when grooves are narrowed – something that has been added to certain products in the truck line-up in order to decrease void ratio and increase block stability as a way of offering improved rolling resistance performance through reduced deformation. TowerPump sipes are designed to increase wet grip in a damp road situation (an environment that will be very familiar to any British trucker) by putting pin-width voids in particular parts of the tread. Together with a further wider but shallower recess around the entrance of this hole, this feature acts as plunger sucking up the covering film of surface moisture and thus improving braking performance.
Lower tread depth + better wear rate = A-grade trailer tyres
However, perhaps the most marked development can be found in the new generation of X Line trailer fitments. As we have already mentioned, the 385/55 R22.5 fitment scores AB 70dB on the European label, which is of course the highest mark for rolling resistance a high grade for braking and respectably quiet noise score. Apart from the structural and tread developments we looked at earlier, it appears that the addition of Michelin’s patented and trademarked Carbion ingredient in the rubber compound has made all the difference in the design of this product.
By virtue of the inclusion of Carbion Michelin reports that the compound alone offers a huge 40 per cent better wear rate than predecessor (X Energy Saver Green), which was not shabby in this respect itself. The point is that with a low hysteresis compound as effective as this built on a casing that is as much as two kilos lighter, Michelin had enough of a wear rate improvement in its new design to be able to reduce the tread depth and improve rolling resistance performance.
The crucial part is that because of all these developments, Michelin also claims that, although it may have reduced tread depth, the tyre actually lasts longer than its predecessor in terms of mileage. Once adjustments for wet-grip and other characteristics had been worked, in the end result is said to offer between 8 and 12 per cent improvement in overall tyre life. These details are key to the product narrative of the latest Michelin range because lower tread depths will inevitably be seized upon by the competition as weak point in their approach. However, the likely answer brings us back to Michelin’s renewed emphasis on whole life cost and whole life performance. Company representatives will no doubt ask: while others may reduce tread depths or improve rolling resistance/wet grip on the label can they a) do this without compromising the progress of other criteria and b) maintain performance levels throughout the life of the tyre?