Are you looking for a way to help improve your car’s driving performance in the rain? Rain tyres, as the name implies, can help provide better performance on wet surfaces. Here, we explore what makes tyres perform better in this area and how you can find the best rain tyres for your car.
What are rain tyres?
The simplest way to divide car tyres is to put them into two seasonal divisions - summer tyres and winter tyres. Looking at these two groups, there is a clear, significant difference between them and this lies mostly in the composition of the compound (used in the tyre construction), as well as the tread pattern used.
Consequently, the concept of “rain tyres” applies to summer tyres. Specifically, it applies to those with a composition designed to ensure excellent behaviour on wet surfaces. This includes the addition of filler particles, allowing the rubber compound to “fit in” better with the coarse areas of the road. This effectively increases the contact area between the tyre and the road surface, as the tyre ‘bites’ into the uneven sections with greater ease.
Climatic conditions and the selection of tyres
Weather conditions are not always perfect for driving. The UK is well known for its abundance of rain and, on a wider European scale, there are around 140 rainy days every year. More than 30% of accidents also occur in rainy weather, so it’s clear that many drivers wish to select tyres that can cope in these elements.
Sometimes, the rainfall is so profuse that the risk of aquaplaning rises, increasing the need for the right choice of tyre. In these situations, wet roads can often become a dangerous zone for drivers, as a wedge of water in front of the tyre can cause a loss of traction with the road surface, consequently causing a possible loss of control with the car. According to research, around 70% of European drivers expect the best grip from their tyres on a wet road surface.
Rain tyres: Uniroyal brand tyres are the most popular tyres for a wet road surface.
Why are some tyres better on wet surfaces than other?
The success of rain tyres lies mostly in the use of an appropriate compound. More active silica, for example, is known to help and this is a common inclusion in the composition of Uniroyal tyres, which are well known as being reliable rain products.
Similarly, the right tread pattern, or tyre surface, also helps. A directional V-shape, as seen on the likes of the Uniroyal RainSport 2, is optimal. The tread ribs on this pattern allow for an ideal distribution of tyre pressure on the surface, allowing for higher pressure away from the tread centre. This allows water to be more effectively removed via the tread grooves.
While this occurs in directional tyres, this pattern is not always the best solution. Such a pattern is most optimal for tyres with a tread width of roughly 215 mm. In wider tyres, the distance water needs to cover, from the under the front of the tread, is similar to that of asymmetrical tyres. However, rain tyres still typically feature a directional tread, due to its many other benefits.
Apart from having a symmetrical design, directional treads have minimally weaker traction, which is most noticeable when driving quickly through a bend. Asymmetrical tyres, on the other hand, feature outer tyre flanks that are closed. This is, of course, connected with each pattern’s ability to remove water.
Tread depth and water removal
With this in mind, it’s also vital to mention the depth of the tread pattern. The deeper this is, the larger volumes of water that can be removed from underneath the tyre. Consequently, a deeper tread is better as reducing the risk of aquaplaning.
The graph presents the lengthening of the braking distance with a decrease in the tread depth. Source: MIRA (Motor Industry Research Association) report – ‘An Investigation into the Effects of Tyre Tread Depth on Wet Road Braking and Cornering Performance ‘ (MIRA-1002250)
The above graph shows how the braking distance changes on a wet and smooth concrete surface depending on the tread depth. At a depth of 6.7 mm, the braking distance from 50 mph, to a complete stop at 0 mph, is less than 29 m. At 1.6 mm - the legal minimum allowed in the UK - it takes 42 m. The distance has increased by 44.6%.
As a result, as in the case of any tyre, it’s important to undertake regular tread inspections. While 1.6 mm is the legal minimum, we recommend fitting new tyres when the treads reach around 3 mm. This is also more critical in the winter, when the thicker treads are required to cope with snow, slush and other severe weather conditions.
Now that you know which tyres matter the most - those with excellent water repulsion, a thick tread and a directional V-pattern - you can more readily determine if any given product has the qualities you need. If it does, there’s a good chance it could be the best rain tyre for you!