Feature: the tech behind tyres
A visit to a tyre research and development department reveals what goes into that rubber on your car ... and what the future holds
TWO black rubber balls, identical in size and appearance, are handed to me at Continental’s tyre research and development centre in Stöcken, Germany. My host, Ryan Visagie, the product communications manager for Continental South Africa, asks me to bounce them on the floor. The first ball goes head high, but the other barely leaves the ground. This is what a difference in rubber compound can achieve and proves that not all tyres are the same. Invited to attend the bi-annual Continental Techshow by the famed company, CAR gleaned insights into the future of tyre development.
TYRE MATERIALS
A tyre typically consists of between 10 to 20 materials. By varying the percentage of each component and the curing criteria, a tyre’s characteristics can be altered. Continental has developed more than 10 000 compounds in its material lab and creates more than 10 000 samples each year to be tested. Think of it as the test kitchen for the tyre compounds. Once tested in the laboratory until the chemists and engineers are happy, the new compound samples are then sent for prototype tyre testing. Continental not only tests the samples for overall performance properties, but also employs state-of-the-art microscopes (including the electron variety) to investigate the materials on a molecular level. It is important that the tyre material is a homogeneous mixture of the various elements to ensure consistent behaviour of the nal product.
TYRE PERFORMANCE TRADE-OFFS
“What is the best tyre?” It’s a common question posed by a customer to a tyre dealer. There is no simple answer because it depends which tyre characteristic is important to the buyer. This may include grip on dry and wet roads, tyre noise, longevity, rolling resistance and cost. The conundrum is that you can have some of these properties in a tyre, but not all. A tyre with high-mileage capability is going to sacri ce excellent grip and, therefore, a tyre manufacturer needs to decide the performance targets for a certain tyre range.
The new wave of electric vehicles demand low rolling resistance to decrease parasitic losses and improve driving range. In the past, a low-rolling-resistance tyre lacked grip in wet road situations, but Continental is addressing the issue by using less rubber material in non-critical areas (the exing of unnecessary rubber wastes energy). This improves rolling resistance, but still allows a rubber compound with favourable wet-road performance to be used.
When autonomous driving and the connected car become a reality, tyre manufacturers will be able to decrease the rolling resistance further, albeit at the slight expense of of grip. According to Continental, machines plan better ahead more ef ciently and make fewer mistakes than humans.
“WHAT IS THE BEST TYRE?” THERE’S NO SIMPLE ANSWER BECAUSE IT DEPENDS WHAT’S IMPORTANT TO THE BUYER
TYRE TESTING
Even before a new prototype tyre is tested, the manufacturer uses software simulations to predict the tyre’s behaviour. In advance of a tyre entering production, actual tyre testing is still necessary to verify the simulation result. This testing includes indoor valuations in test laboratories, driving test vehicles on proving grounds, and then finally fleet testing by customers to support the findings. The number of tests conducted on tyres is mindboggling and I’ll focus on the tests demonstrated at the tyre test facility on the day of our visit.
TYRE CHARACTERISATION
1 Footprint analysis. All a vehicle’s acceleration and steering forces are generated at the tyres’ contact patches on the road. It is therefore important to analyse the behaviour of a tyre’s footprint under varying conditions. We witnessed static and dynamic tests where tyres are fitted to machines capable of replicating actual road scenarios. This included increasing the normal force on the tyres, varying the rolling speed between zero and 250 km/h, and changing the camber, caster and slip angle of the wheel relevant to the surface it was rolling on. The footprint can be measured via pressure sensors under the rolling surface or by optical or laser-measuring techniques. A contact patch shape that is not stable during these tests results in unpredictable tyre behaviour.
2 Force and moments. It is important to measure the possible forces a tyre can generate in the longitudinal and lateral directions. To do this, Continental has a machine that runs a tyre on a drum covered with 80-120 grit sandpaper to simulate a road surface. You can change the wheel’s orientation to mimic steering and the forces measured at the spindle of the machine. It can also measure acceleration and braking forces and, because these tests are done under controlled conditions, you can also compare different tyre compounds.
3 Rolling resistance. The quest for increased vehicle efficiency has led to tyres’ lower rolling resistance being a key development criteria. The international standard for testing the rolling resistance comprises of a machine that spins a wheel on a drum and then measures the resistance torque as a result of the frictional losses. Although measuring on a flat, moving surface, is more accurate, the industry sticks to the described method for comparative reasons.
Electrical resistance. Measuring a tyre’s electrical resistance or conductivity is an interesting one. This is important because a tyre tends to build up static electricity on the move and this can be both a safety hazard during refuelling, as well as an annoyance for occupants when they exit a car and get a mild shock. Like most manufacturers, Continental tyres allow static electricity to discharge to the ground.
4 Tyre durability and longevity.
The most peculiar tyre-test machine on display was the tyre-wear rate device. It consists of a large drum with six test tyres running on the circumference. Each tyre’s pressure, attitude towards the drum, and normal force is accurately controlled with the drum surface speed varying between 90 and 120 km/h. The idea is to subject different tyres to exactly the same conditions and compare the wear rates after a week of running 24 hours a day. The mileage for the test is around 14 000 km, which is enough to identify wear patterns and rates. This is a non-destructive test and uses high-tech laser-measuring equipment to gauge not only the overall wear rate, but also the wear on the individual tread blocks.
Intelligent tyres. A subject on which Continental refused to answer any specific questions was on embedded sensors in the carcass of the tyres. Naturally, the manufacturer doesn’t want opposition tyre manufacturers to get insight on what it’s up to. The concept is not new, but it is clear that Continental is not only using these sensors to measure tyre pressure, but I suspect they can read wear rates and even grip levels, too. This would allow the vehicle’s ECU to use the information to fine-tune the ESC system’s behaviour in real time for all road surfaces.