How much grip does a road bike tyre have? And what's the best way to find out? Simply riding is not enough, because you rarely push the tyres to the limit and if you do, it's more by chance. But the limit range and how the tyres behave there is particularly interesting. Because we want tyres that display the limits in a good-natured way, have a wide limit range and of course offer as much grip as possible.
Tyre test: How the TOUR test works
One test method goes like this: riding faster and faster around a bend until the tyres slip or break loose. For many years, this was the standard testing practice at TOUR. We had constructed a special tyre scooter for this purpose, a kind of scooter for racing bike tyres, with which we pushed the limits on lonely public roads. The method had strengths and weaknesses. The strength: the cornering was real, there were no driving forces at work, the real surface interlocked with the tyres. The weakness: the limit situation lasted only fractions of a second and the procedure was extremely stressful for the testers, because you never knew whether you would get through with your skin intact. There was a lot of hard scratches and even the best motorbike suit was worn through after a while.
That's why we copied our current test method from the tyre manufacturers Michelin and Pirelli: Our bike for the tyre test is a modified e-bike from Merida with a Mahle hub motor. The bike accelerates at the push of a button and the maximum speed can be programmed in advance. We ride faster and faster on a watered circular track until the tyres give feedback that the grip limit has been reached. We record the speed reached, but focus our attention primarily on the behaviour of the tyres at the limit. This is because the tyres react very differently. Some tyres are good-natured, pull their course safely and slide over both tyres in a controlled manner, others hop, but some slip away abruptly, which is of course unfavourable. We base our rating on the speed achieved and the tyre's behaviour.
Tyre test: Data provides information
The subjective feedback from the test driver can usually also be verified in the data record. The driver can move trustworthy tyres stably at the limit. Treacherous tyres, on the other hand, can be recognised by fidgety driving records, as the driver has to constantly intervene to regulate them. The advantage of riding in a circle: crashes are less frequent than with a scooter and the limit range can be experienced more extensively, which makes the whole thing more reproducible. But even if the new tyre test method is not as crazy as the scooter ride, it is still stressful. The man on the handlebars needs courage, nerves, a lot of sensitivity and a pinch of luck that the tyre doesn't grab grip again while sliding, then a highsider threatens, a catapult-like flight over the handlebars, which TOUR test director Jens Klötzer has already experienced himself during a ride on the Pirelli test site near Milan. It was a minor incident, but the risk remains.
Adhesion varies
Our data from the tyre test tells you which tyres are good-natured. This good-naturedness is important because the grip of roads can vary greatly. There are stretches with an incredible amount of grip and slippery roads. Sometimes the conditions change quickly. Assessing this reliably in advance is an art. Zones where cars brake or accelerate are particularly slippery. If there is soft rock in the tarmac, the road becomes really polished and very slippery, especially in wet conditions.
In our tyre test, we only test in the wet because the grip level of good tyres is very high in the dry and the risk of injury would increase accordingly.
