DLG says CGS tractor tyres are quieter

Tyre makers’ main task may be to produce tyres capable of maximising grip and utilising the power produced by the tractor, but other considerations have to be borne in mind too. There’s wear rate, compaction, operating pressure, wall flexibility, lug shape, lug angle, and so on – not to mention such basics as tyre width and diameter.

Last Autumn tyre maker CGS has added another parameter and that’s to reduce the noise generated by the tyre as it travels at speed on a metalled road surfaces.

This has not been a major issue for the industry in the past but CGS says that modern tractors’ ability to travel at speeds over 50kph has created a new threat to driver welfare in the form of cab boom. This is caused by the interaction between road, rear tyres and vehicle.

Five years of development work has produced the Continental SilentSpeedTyre SST which, for the first time, has been designed to reduce noise levels and therefore make the tractor driver’s life more comfortable.

Do they work though? The DLG, an independent German test organistion, has tested the tyres and has some anmswers.

Firs, a bit of background. The SST is a conventional radial design which aims to achieve lower noise levels by using a casing that is designed to dampen out the vibration caused by the lugs as they hit the tarmac.

Tractor cabs apparently have a natural noise frequency of between 110Hz and 120Hz which is induced according to the frequency with which the lugs strike the road. A 650/65 R 38 tyre – the size of the STS tyre being tested – rotates at about 2.5 times/second when travelling at 50kph.

With 44 lugs, the noise frequency will be 110Hz (2.5 x 44) which, without any specific dampening, results in a large increase in cab noise due to sympathetic/harmonious vibration.


Analysing the frequencies showed that the highest noise levels occurred at 125Hz

Analysing the frequencies showed that the highest noise levels occurred at 125Hz

The DLG measured the noise levels generated by the tyres as they travelled on a flat stretch of road without any load on the tractor. Tyres used for comparison – the ContiContract AC65 – had the same size and tread pattern, and were operated at the same inflation pressure.

A John Deere 6930 AutoQuadPlus tractor was driven on a smooth asphalt surface at speeds from 40-54 kph in jumps of 1kph with two noise level measurements taken in the cab at each stage, once with the rear window open and another with it shut.

Noise level measurements taken at all speeds revealed that, with the rear window closed, the average noise level was 2.4 dBA lower than with conventional tyres. With the rear window open, the average difference was 2dBA. The maximum differences of 3.6 dBA and 2.8 dBA were recorded at speeds of about 47kph.

Analysing the frequencies recorded revealed that the highest noise levels occurred at 125Hz – which is within the lug frequency range of the rear tyres. In fact the difference in the noise levels recorded become even more pronounced, with the difference extending up to 7.5dBA when compared with standard tyres – which is a significant difference in noise levels bearing in mind that an increase of just 1dBA represents an increase in noise by a factor of 10.

For the tractor operator, long distances driving a tractor on the road need not now mean having to endure excessive cab booming – the loud droning that lasts the duration of the journey.

The STS tyres were given a test mark of “very good” by the DLG – the highest rating allowed in the test scheme.