General Enquiries (Q&A)

General Enquiries (Q&A)

Questions & Answers

Here you have the opportunity to ask all kinds of questions simply by filling in the Ask us form.  We will reply to you and publish the Q & A on this page in the future.

1.  What is the difference between a radial and a conventional (cross-ply) tyre?

The radial tyre is distinguished by the plies that form the carcase being radially oriented. This means that they run across the tyre from side to side, at 90° to the direction of travel. In a cross-ply tyre the carcase plies intersect and form an approximate 45° angle to the direction of travel.

The result of manufacturing tyres with these quite different types of construction can be summarized as follows:

The radial construction has a very flexible sidewall but a stiffer tread area. The cross-ply construction has much stiffer sidewalls with a more flexible tread area.

The resulting performance of the different construction types is very important if we consider wear, traction and stability, particularly during road transport.

2.  What does ply rating mean?

It is a measure of resistance of the tyre's plies to the internal pressure, determining the permissible load. 

The historical reference goes back to the days when they ply layers were made of heavy duty canvas, then the only material available. In those days to improve the tyres' carrying capacity more internal pressure was required, and therefore more ply layers to resist the internal pressure/load, hence the expression 2ply, 4ply etc.

With the development of new carcase materials such as rayon, nylon and steel it was possible to decrease the actual ply numbers while keeping unchanged, even improving, the tyre's resistance to internal pressure, and therefore load carrying capacity. For this reason, we should really talk about ply-rating rather than just ply numbers.

3.  What does "double traction" mean?

It means that the driving power of the tractor is transmitted by both axles, front and rear, in other words 4wd. This is an almost inevitable consequence of the increase in tractor horsepower and weight. 

When energy has to be converted to driving power it needs mechanical transmission, transmission shafts, axle shafts, reduction gears, differentials etc.

All these have a natural resistance to rotation plus a limit on the power that can be transmitted through them, particularly in 2wd. Therefore when the requirement is the ability to transmit high horsepower, manufacturers generally choose to spread the power through both front and rear axles, hence the growth of 4wd.

The 4wd choice is now the predominant type of tractor or agricultural vehicle, and therefore is the type most concentrated on by manufacturers when reserarching new materials, electronics, or variable transmissions. 

We must not forget however that the 4wd tractors behaviour on both field and road is considerably affected by the tyres fitted, and the tyre maintenance applied.

5.  To what pressure should I inflate my tyres?

There is no single answer to this question as pressure settings vary depending on the tyre size, the load carried and the type of work.  To assist operators, Trelleborg Wheel Systems' catalogues and technical handbooks list a recommended maximum load and pressure for every tyre and tyre size offered.  If you need assistance in establishing the correct pressure for your specific tyres, please contact us direct for advice.

6.  What is the minimum pressure at which my tyres can be run?

The answer to this will depend on several different factors such as operating speed, surface conditions and the type of work being carried out.  

For comprehensive advice, please contact Trelleborg Wheel Systems.  If appropriate, arrangements can be made for a visit by a technical representative.

7.  How do I determine the maximum load that my tyres can safely carry?

A tyre's maximum load is expressed using an internationally-accepted Load Index (LI) code number to be found on the sidewall of the tyre adjacent to the Speed Index code. 

The LI code shown is the maximum advised load for that specific tyre, irrespective of its type or its size.  Again, a full listing of LI codes and their meanings can be found within sales and technical literature available free of charge from Trelleborg Wheel Systems.

8.  What is the meaning of all the numbers to be found on the sides of modern tyres and how do I relate current tyre sizes with those fitted to my older tractors and machines?

In common with all tyre manufacturers, Trelleborg Wheel Systems uses a combination of metric and imperial measurements to describe the size of every tyre in the TM Radial and Trelleborg ranges.  

The company will be happy to provide customers with the equivalent modern size for a superseded older tyre, although it is a comparatively easy calculation for owners and operators to make.  

Take, for example, a new tyre marked with the designation: 420/70 R 28 TL.  The figure 420 is the maximum sidewall to sidewall measurement (the section width) expressed in millimetres.  To convert to inches, simply divide the figure by 25.4 (420 ÷ 25.4 = 16.5 ins).  

Moving along, the next figure (70) indicates the tyre's profile, expressed as the height of the sidewall as a percentage of the tyre's width.  The letter R shows that the tyre is of radial construction and the letters TL indicate that the tyre is designed for use without an inner tube. 

The most confusing figure to most tyre users is the 28, which is the diameter of the wheel rim in inches.  If you have any doubts or need help in deciding the correct replacement TM Radial or Trelleborg tyre size to specify, please contact us direct.

9.  Are my tyres suitable for use at 50 km/h?

This can be checked easily by looking on the sidewall of the tyre for the Speed Index (SI) code, an international designation indicating the maximum speed at which the tyre should be used.  

For speeds of up to 40km/h, the SI code is expressed as a letter and a number.  For example, A5 = 25 km/h and A8 = 40 km/h.  For speeds greater than 40 km/h, the SI code is expressed solely as a letter.  

For example, B indicates a maximum speed of 50 km/h.  A full listing of SI codes and their individual speed ratings can be found in sales and technical literature available from Trelleborg Wheel Systems. 

For further questions fill in the Contact us form.


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