Maintenance Guide for Earthmover Tyres: Different tyre constructions
The solid tyre
Solid tyres have been used on lift trucks for a long time.
The solid tyre is made up of different rubbers bonded one on top of each other, the specific properties of each combining to give the required adhesion and traction.
Its limitations become apparent under intensive use: rapid wear, due to a significant increase in internal temperature of the rubber and the risk of damage through driving over obstacles. The solid tyre “breaks”.
The bias tyre
A conventional diagonal-structured tyre is made up of textile plies, for example in nylon or rayon, criss crossed on top of each other and bonded together by a rubber compound.
The carrying capacity increases with the number of plies.
In a diagonal tyre, the movement between the plies leads to damaging temperature increase. At the same time, there is distortion in the contact patch due to distortion from the sidewalls, resulting rapid wear and reduced adhesion.
This type of structure also presents lower resistance to punctures.
The radial tyre
The ideal solution was to separate the work of the tyre’s sidewalls and crown, making each part of the tyre more specialised and thereby enhancing performance. This is exactly what is achieved by MICHELIN’s radial structure; metallic or textile plies, going from one bead to the other, are combined with an inextensible steel belt which reinforces the tyre’s crown.
To sum up, the radial construction reduces tyre tread movement and energy consumption; it improves adhesion and lessens wear, while its steel belt provides much better puncture-resistance.The casing of the radial tyre is made up of one or more steel plies going from one bead to the other.
3 or 4 circumferential steel breaker strips or crown plies encircle the casing; the radial structure separates the work of the crown from that of the sidewalls.
This separation of functions is the main reason for the radial tyre’s main qualities, as each of its parts can be specialised. It provides greater adhesion
by minimising slip, thereby reducing the rate of wear. A steel belted radial tyre resists damage and punctures. Its deep tread gives it long life.
Its sidewalls, being more flexible,offer greater comfort, without compromising on stability. Safety is also improved.
The Tubeless radial tyre
The tubeless tyre is mounted on a special rim equipped with a suitable valve.
From the outside, the tubeless tyre looks like its tube-type counterpart.It is identical as far as the structure is concerned, but inside, a layer of special rubber (butyl) makes it completely airtight.
There are numerous advantages:
- There is no longer any risk of nipping the inner tube.
- There is no air trapped between the tyre and the inner tube.
- There are no more sudden deflations (in most cases air-loss is slow; it is not necessary to repair the tyre on the spot; there is time to reach the repair workshop).
- As the unit is perfectly sealed, there is no risk of the rim rusting provided the inflation air is dry.
Tyre markings and size Designations
can distinguish several categories of earthmover tyre, characterised by their H/S (aspect ratio) (the ratio between the height of the sidewall and the width of the tyre).
Standard base tyres (100 series)
The H/S ratio is approximately equal to 1.
The section width is expressed as a whole number of inches with two “00” after the decimal point.
Example: 18.00 R 33
80 Series or wide base (fig. 2)
The H/S ratio is approximately equal to 0,80.
The section width is expressed:
– either as a whole number and fraction of inches
Example: 20.5 R 25 or 37.25R35
– or as a whole number of inches followed by the number 80.
Example: 59/80 R 63
Tyres with an H/S ratio < 80 or extra wide base (fig. 3)
Example: Series 65
The H/S ratio is approximately equal to 0,65.
The section width is expressed as a whole number of inches or a whole number of millimetres, followed by the number 65.
Example: 35/65 R 33 650/65 R 25
The different types of tread rubber
In Earthmover, there are various types of tread rubber. The choice of compound depends on the applications and the nature of the ground.
TYPE A4: particularly resistant to cuts, tears and abrasion on very rough surfaces.
TYPE A: particularly resistant to cuts, tread tearing and abrasion, at higher average speeds than for A4 type.
TYPE B4: compromise between abrasion resistance and average speed on rough surfaces (available in sizes 49 inch and above).
TYPE B: higher resistant to internal heat generation on non-aggressive surfaces.
TYPE C4: for running on long cycles at high speeds on well maintained roads.
TYPE C: very high resistance to high average speeds long cycles run on well-maintained roads.
Different tread depths
There are four main categories of earthmover tyre, characterised by their different tread depths; the choice between them is determined by their applications and the nature of the ground.
It should be noted that earthmover, tyres for construction applications and industrial tyres carry either a load/speed index (as above), or one or more stars and sometimes a number followed by the letters PR.
- The load/speed index is shown onsome tyres.
- PR means Ply Rating: the numberpreceding the letters PR was anindex referring to the number ofplies used in the construction oftyres (originated at the beginning of the tyre industry). It is now a measure of capacity.
- Star ratings give an indication of tyre strength that defines the purpose for which the tyre was intended.
– “One star” indicates that the tyre can be used on working machines (surface loaders, graders, etc.)
– “Two stars” indicates that the tyre can be used on transport vehicles (rigid dumpers, scrapers, etc.)
Note: Some sizes (24 and 25 inch) carry the three-star marking. These tyres are intended for specific applications, such as underground mining, for example.
The type of rubber (A, A4, B, B4, C and C4) and the tread depth (SUPER, D1 and D2) are usually shown.
Classification of earthmover tyres in accordance with the standard codes (ISO -E.T.R.T.O. – T.R.A. – J.A.T.M.A.)
All earthmover and construction tyresare codified and may carry a code on their sidewall, made up of:
- letter indicating the application
– C: Compactor
– G: Grader
– E: Earthmoving (transport)
– L: Loader and Bulldozer
- figure indicating the tread depth
– 1: slick, ribbed (smooth surfaces)
– 2: traction (regular)
– 3: rock (regular)
– 4: rock (deep tread)
– 5: rock (extra deep tread)
– 7: flotation (operation on soft ground)
- and sometimes a further letter
– S: indicating that the tread is smooth (for very difficult conditions)
- MICHELIN tyres carry an additional letter, further specifying their application.
– T = Traction
– R = Rock
– V = Speed
– F = Flotation
– P = Multi-purpose
– S/R = Smooth/Rock
Example: L3T, loader tyre, rock (L3: standardised identification code) and traction (T: MICHELIN code)