Manufacturing a modern 4x4 tyre is much more complicated than you think...
The rubber fitted to your 4x4 can make or break your vehicle’s performance, both on- and off-road. However, have you ever given thought to the extensive research and development that goes into producing that tyre? We visited the Continental Tyre SA factory in Port Elizabeth (home of General Tire) to learn how a 4x4 tyre is designed and constructed.
1. Research and development
A tyre comprises more than 10 individual components and the decision regarding the types of materials, rubber compounds and construction methods is its own science. Computer simulation work has become paramount to the process because actual testing with prototype tyres is costly and time-consuming. Initial tests are conducted under controlled conditions in a laboratory (we covered this in the article Tech behind tyres in the August 2017 issue) before on-road testing commences.
An interesting subject when it comes to off-road tyres is tread-pattern design. The general perception that the topography of the tyre is mostly for aesthetic appeal cannot be further from the truth. Every little edge, chamfer and block is there for a reason, and nowhere is this more evident than on off-road tyres with bold patterns. Below are some of the features on General Tires’ X3.
The downside of an aggressive tread pattern is increased road and wind noise at speed, as well as a rolling-resistance penalty (resulting in increased fuel consumption). The general trend is for less-aggressive patterns to meet stringent UNECE 30 tyre regulations without losing off-road performance in the process (bad news for enthusiasts craving that aggressive look).
2. The production process
The smell of fresh rubber hangs in the air as I enter the production facility. What grabs my attention is how labour-intensive the process is to create a single tyre. This is not because of local labour law or absence of the latest high-tech machinery. According to Ahmed Boualam, production manager, the same method of tyre production is employed locally and internationally (Germany). The reason for this is a tyre – especially an off-road example – is a complex item with many components, and so requires extensive human input.
3. The raw materials
Approved rubber compounds arrive in bulk at the extruders. They are then heated and forced through a specific die creating a green rubber profile (tread or sidewall). The tread consists of three types of compound: the base, the cap (running surface) and the wing strips located beyond the tread shoulders. These three co-extruded compounds are overlaid to form a continuous assembly that is cut into specified lengths for the tyre circumference.
Although each tyre carries a barcode documenting its production history, paint of different colours is applied to the tread in thin stripes as a visual aid to distinguish between tyre designs (explaining the colours on the tread of some new tyres). Sidewalls as well as tyre-reinforcement materials arrive in bulk rolls and must be cut to size and specified angles before being joined with the tread. Even the hoops of steel wire (bead cores) anchoring the ply and securing the tyre onto the wheel rim are created on site by winding steel wires in a pattern and enclosing them with more rubber.
The building of a tyre is done in two stages. Firstly, a casing is made consisting of an inner liner, ply(s), bead, apex, sidewall and, in some cases, reinforcement and shoulder pads. The casing is then expanded on a second-stage build unit, where the tread assembly is applied. The tyre slowly takes shape but still appears alien to the eye; touching the “green” product reveals it’s soft and tacky. No adhesive is used between the component layers, as the vulcanisation of the rubber during the curing process forms the permanent bonds.5. Curing and tread
The tyre is inflated with a bladder before it is heated internally with steam. The specific data is proprietary but it is a function of pressure, temperature and time for the tyre to set in its final form, losing that tackiness, with the desired rubber properties. However, it still resembles a racing slick with no tread. Time for more heat in an oven, where the tread moulds are clamped on the tyre from the outside, forging the rubber into the required shape. More time elapses before a final product exits the oven in a haze of steam: a tyre is born.
6. Quality testing
Each tyre goes through a visual-inspection phase and then endures rigorous testing before it is allowed to leave the factory. This includes mounting it on a rim and testing natural balance at speed. A low scrap rate is essential to save both cost and the environment.
Choose your tyres carefully
User profiles directly influence the choice of tyre, so make sure you get peak performance where you need it. We compare three popular General Tire options to highlight the differences in performance.
As interesting as manufacturing a 4x4 tyre is, it’s crucial to test the claims. We put General Tire’s Grabber AT3 to the test in soft, sandy conditions to show how tyre pressure influences traction
Test vehicle: Ford Ranger DC 3,2 TDCi XLT 6AT 4x4 HR
Test: Start on a soft, level sandy surface with the Ranger’s transmission in second gear and low range engaged. Level the engine speed at 2 000 r/min before flooring the throttle and trying to scale the sandy incline. Tyre pressure is lowered in steps from 3,0 bar to record the difference in vehicle speed versus distance (with Racelogic’s VBOX) to depict the available traction.
- 3,0 bar: The over-inflated tyres offered very little traction and the vehicle got stuck after only a metre.
- 2,4 bar: The recommended on-road tyre pressures allowed the Ranger to scale the sandy hill but with plenty of wheelspin. The vehicle nearly became stuck at three metres but just pulled through.
- 1,6 bar: This recommended sand-driving pressure allows dynamic cornering without the risk of popping a tyre off a rim. The traction was markedly improved with less wheelspin and a higher speed when scaling the hill.
- 1,0 bar: The recommended tyre pressure for soft sand (lower pressures are possible under extreme conditions, but the risk of a tyre popping off a rim is high). In comparison with the other pressures, the traction was much improved and the Ranger scaled the hill as if it was paved.
Author: Nicol Louw