Tests and User Surveys

Several different tyres where brought to the Swedish Road and Traffic Institution to measure the slipping characteristics of Green Diamond Tyres on wet ice and to compare with regular tyres and studded tyres. The main objective with this specific experiment was to measure the traction characteristics on ice close to 0°C when there is a water-film formation on the surface. Both Green Diamond Tyres  and studded tyres out-performed regular tyres. Several measurements where made on each tyre. The results from studded tyres and Green Diamond Tyres overlapped in all cases. The average result of studded tyres had the advantage when the wheels locked during braking. However; the Green Diamond Tyres had a clear advantage when using ABS (anti-lock braking system).

The BAST laboratory personnel drove granulated tyres in special drums for 250.000 circles and measured the general wear of the drum surface and compared it to the wear generated from studded tyres tested the same way. Using an average of nine different types of studs they concluded that Green Diamond Tyres wear the road 14 times less then studded tyres do.  With the bus drivers endorsing the product on the grounds of better road traction, better snow grip and increased safety. In addition the fleet manager was very content with the wear of the tyres.

An independent acoustic specialist measured the comparative noise generated from Green Diamond Tyres and from same type of tyres with and without studs fitted made on the same day with the same compound by driving the same car past measuring equipment at 60 k.p.h on a dry surface with the engine switched off. The Icelandic Police assisted in measuring the exact speed of the car. The result was that Green Diamond Tyres produced the same noise level as normal tyres whilst the studded tyres produced double the noise of the other two types.

Green Diamond Tyres have now been tested in service in the most rigorous conditions in Iceland since 1995 with outstanding results. In the first user survey conducted, 18 out of 20 users, including 16 police officers on duty, concluded that they would prefer these tyres over studded tyres during the winter time in Iceland. The wide acceptance of the market in Iceland and Sweden is also a strong indication of the performance of Green Diamond Tyres.

Using Green Diamond Tyres made by Vacu-lug Traction Tyres Limited on the Reykjavik town bus fleet during a whole winter, some excellent results where achieved with the bus drivers endorsing the product on the grounds of better road traction, better snow grip and increased safety. In addition the fleet manager was very content with the wear of the tyres.

Purpose: Trials of tyres custom-moulded for New Industries Ltd.

The purpose of the visit was to establish, using reliable measuring equipment, whether mixing of hard granules into all-weather tyres has an impact on their surface resistance, especially on icy roads.

After the tyres had been delivered they were prepared for testing by mounting them on the tyre rims, then chilled to adapt them to real winter conditions

The testing equipment is a 60-metre mobile track mounted in a refrigerated stockade. When the track has been refrigerated to below freezing-point, it is covered with several layers of water until a suitable thickness of ice is created.

The tyres are tested individually and attached to a metering device. When the test commences, the track is moved beneath the meter at a speed of 30 km per hour. The load on the tyres can be adjusted, as can the vertical angle and turning angle. For the last 40 meters of the track, a brake is gradually applied. The friction of the tyre is then measured both in the direction of the track and at right angles to it (to measure sideways sliding friction). The data measurement recordings are processed by a computer which calculates the friction co-efficient for both static friction (when the tyre moves with the track) and sliding friction (when the tyre has braked but the track continues to move).

Tests were conducted on three tyres with granulated treads and a regular tyre, which was produced using the same equipment as the granulated tyres to provide a standard reference. One of the three types of granulated tyres produced noticeably the best performance, confirming prior findings from tests conducted in Iceland.

The test results offer strong support for earlier hypotheses that hard granules could lead to substantial increases in tyre skid resistance. Granulated tyres outperformed regular tyres in all measurements, and the difference seemed to become more pronounced as the toughest ice conditions were approached, namely at 0°C. At a temperature of -1°C the difference in static friction between the reference tyre and granulated tyre measured a minimum of 22% and maximum of 52%. The difference in sliding friction under the same conditions was a minimum of 10% and maximum of 34%.

The real difference in performance lies somewhere between these two points and cannot be determined with a reasonable degree of certainty except by very extensive, repeated measurements. In comparable tests between nailed tyres and the reference tyre, the difference in static friction was a minimum of 14% and maximum of 39%. The difference in sliding friction ranged from a minimum of 32% to a maximum of 73%.

Conclusion:

Granulated tyres clearly perform much better than regular tyres in icy conditions. Measurements show that, as a rule, granulated tyres are probably better than studded ones when the tyres are rolling along the road, without sliding. This applies in particular to bends and, for example, anti-braking systems which prevent the wheels from locking completely. Under conditions where the wheels lock, studded tyres seem to have the edge in performance over granulated tyres. It should be reiterated that more tests will need to be conducted before these findings can be confirmed.

RETURN TO GREEN DIAMOND WEB SITE