Throw One’s Weight Around
Last year Vredestein unveiled the newest big gun in its UHP arsenal, the Ultrac Sessanta. Designed and marketed as a cut above the existing Ultrac range, the new tyre was the Dutch-Russian tyremaker’s response to the ever growing high performance vehicle segment, and with a low profile wide-tread design, Y speed rating and styling by Italy’s Giugiaro Design, the Ultrac Sessanta fitted comfortably into the upper end of Vredestein’s range. However this series of performance car tyres only partially catered for the performance market, and those wishing to drive vehicles the size of small trucks at incredible speeds found themselves without a suitable Ultrac Sessanta offering.
As of March 2007 all this would change: Enter the Ultrac SUV Sessanta, Vredestein’s UHP tyre for 4×4 sport utility vehicles. Based upon the Ultrac Sessanta, this latest tyre takes into account the unique qualities possessed by vehicles that are both fast and very heavy. The Audi Q7, for example – a vehicle Vredestein expressly states the Ultrac SUV Sessanta is ideally suited to – in its 4.2 litre petrol-engine guise has a top speed of close to 250km/h combined with a kerb weight of two and a quarter tonnes. So it goes without saying that the demands these vehicles place upon a tyre when cornering and stopping are far above the norm.
To handle this additional force, Vredestein has reinforced the Ultrac SUV Sessanta’s sidewalls with two rayon carcass layers. The tyremaker calls this feature HTS+ (Handling Tuned Sidewall) and first used it on their Sportrac 2 tyre back in 2004. Since then the principle has been tweaked first for use in the Ultrac and later the Ultrac Sessanta. The greater axial rigidity the HTS+ double layer provides keeps sidewall deformation due to lateral forces at a minimum when negotiating sharp curves.
In fact the entire steel belt structure has been designed to possess maximum rigidity. This has been done by keeping the distance between the belt and the road surface as small as possible through applying rubber to only one side of the nylon overhead as opposed to the standard double-sided application – less rubber between the cord layers equals less distance between belt and road surface, and this in turn equates to a more direct contact with the road.
According to Vredestein, the rubber compound used in the Ultrac SUV Sessanta is made using carbon particles with a large active surface area, providing a strong reinforcing bond with the polymers contained therein. Vredestein claims this particular quality allows for a compound with outstanding handling on both wet and dry surfaces. The compound has its own official name and acronym – the people at Vredestein’s marketing department seem to have been working overtime lately – and we should thus speak of it as Handling Tuned Tread Compound (HTTC).
Asymmetrical but Non-Directional
The Ultrac SUV Sessanta’s tread is asymmetrical, with a wide circumferential groove running near the tread’s inside shoulder. Positioned along this groove at an angle of about 45 degrees are a series of curved grooves that fan out towards the outer edge of the tread. Therefore the tyre has four longitudinal grooves, three of them running at a slight angle, and because of this the Ultrac SUV Sessanta does not behave like a directional tyre. Vredestein calls this feature Sophisticated Longitudinal Design (SLD) –another acronym, but it does mean that vehicle owners are not faced with the inconvenience of requiring specific left and right tyres.
Additionally, the Ultrac SUV Sessanta features different air ratios – the proportion of air to rubber visible in the footprint – on its inner and outer edges. The air ratio is lower on the tread’s outer edge, meaning that approximately 25 per cent more rubber is in contact with the road compared with the inside edge. Vredestein report cornering grip and stability is thus enhanced, as the forces affecting this part of the tread (which in vehicles of this size are considerable) can be more effectively absorbed, allowing corners to be taken at greater speed. The tyre’s large contact surface also, naturally, contributes to more predictable handling in both corners and straight sections of road.
P3DD – Simplified Design
Vredestein has voiced their desire to manufacture the Ultrac SUV Sessanta range in a wide variety of fitments, and have shown their commitment to doing so through their debut release of 12 sizes. The provision of this comprehensive size range has been made possible due to the use of Parametrical 3D Design (P3DD), a 3D CAD system that works in conjunction with a database that calculates the structure of a tyre. When using P3DD, the dimensions for every desired tyre size are automatically optimised and the most suitable contact surface are is automatically calculated. The use of this system saves considerable time when designing a new addition to a tyre range and enables Vredestein to quickly respond to market demands.
The Ultrac SUV Sessanta range is currently available in a dozen sizes between 17 and 22-inches, with V, W and Y speed ratings. Vredestein claims they intend to gradually expand the number of tyres included in the range over time.