Rallying is an interesting form of motorsport. It’s extremely exciting watching cars go around corners sideways, shooting down the straights with sheer drops on either side. However, in order to drive in this way, rally cars need special tires.
Rally tires are specifically designed based on the stage they need to run at. They come in different types and compounds, and the tires rally cars use are usually designed by Michelin and DMACK. These tires can take a huge amount of wear and tear, making them perfect for racing on dirt and gravel.
Rally cars put a lot of pressure on their tires as they drive as fast as possible over multiple different road surfaces in every stage. In some cases, they also drive in severe rain and snow, and tires need to be designed to sustain these conditions. Let’s take a closer look at rally tires.
How Are Rally Tires Different From Road Tires?
Rally tires are completely different to standard, everyday road car tires. Firstly, rally tires are designed with performance in mind. This means that they do not last nearly as long as daily road tires, which are designed to be very durable, with less of a focus on performance.
Tires used in rally stages need to provide the maximum amount of grip on different surfaces and in different conditions. This means that the tires need to be designed in such a way that they will offer the best possible traction for the car at all times.
Tough Skin
The biggest difference between rally tires and your average road car tires is the fact that they are built to be tougher. Rally tires are designed with a thicker ‘skin’. This involves a reinforced tire wall which helps to protect them from the myriad hazards found during a rally stage.
Everyday street tires on the other hand have an extremely soft sidewall which is designed for comfort. The softer sidewall gives your car a smoother ride on the roads and there is no risk of tire failure due to going across some bumps and potholes. This would make rally tires uncomfortable if they were your daily driver.
Tread
Rally tires are designed with bigger tread blocks than normal tires. This allows the tires to dig into the loose surfaces and down to the harder surfaces that will provide more grip and traction for the car.
Rally tires are also designed in different forms than standard road tires. They have different compounds, ranging from soft, medium and hard. On top of that, they have specialized options for tarmac, gravel, rain and snow.
Suppliers
Rally tires in the official WRC series are supplied by Michelin and DMACK. Pirelli is an additional tire supplier for the junior WRC series. Each manufacturer has a different way of designing the tread on their tires.
The common theme, however, is that all tires will have two different types of tread blocks on their tires (for gravel and snow). Firstly, they have straight edge treads that face perpendicular to the road, and these assist the car with accelerating and braking in a straight line.
The second set of tread blocks are cut at an angle for lateral grip, these help the car to grip while it is turning and sliding. Each manufacturer designs these differently. For example, Pirelli might have their straight-line tread in the middle of the tire, while Michelin will have theirs on the inside of the tire.
How Do Different Surfaces And Conditions Affect Tires?
Just like they would affect your road car, different road surfaces and different weather conditions will affect the amount of grip you have. However, unlike on the roads, rally cars need to go as fast as possible at all times.
Road tires are designed to be able to provide the car with enough grip in most weather conditions such as dry weather, rain, and even slippery conditions. In addition, if the conditions are severe, drivers can reduce their speed accordingly. But speed is key in all forms of racing, no less in rallying.
Dry Weather
Dry weather may seem straightforward, but temperature and humidity can still affect the tires. Dry weather will offer the maximum amount of grip for the tires, but in hotter weather the tires can overheat and wear out quicker.
Wet Weather
In rainy conditions the tires can lose traction completely. Depending on the severity of the rain, the car may experience some light sliding or loss of traction. In more severe cases, aquaplaning is common, along with spinning off the track completely.
High Temperatures
Higher ambient temperatures will naturally cause the tarmac itself to become hotter. This will cause the tire temperatures to be higher as well. This means that tires will heat up quicker, but they will also overheat quicker, resulting in extreme tire wear and loss of grip. Drivers will need to utilize harder compound tires in order to compensate for this.
Low Temperatures
Low ambient temperatures will have the opposite effect. Tires will struggle to heat up and if they are not at a certain temperature, they will not offer enough grip. The tires will also be difficult to keep warm once they are in their operating window. Drivers will use the grippier soft compound tires in this case.
Tarmac
Tarmac will offer the most grip of all surfaces. However, the condition of the tarmac can make a huge difference. Potholes and loose tarmac can cause a loss of grip and can also cause punctures on the tires. Thus, the tire choice here will really depend on the track itself and what the driver and team deems to be the best choice on the day.
Sand
Sand is an extremely soft and loose road surface, and it can be difficult for the tires to find any traction at all. Loose sand will normally just give way and cause the tires to spin without gaining any grip to move the car from its place. For this reason, special sand tires are used for these kinds of surfaces, and the driver will look to avoid going into any sandy parts of other tracks.
Gravel
Gravel is a harder form of sand and has more substance to it. It can sometimes be mixed with rocks, pebbles and other forms of small debris. This will offer more grip than sand, however there will still be a loss of traction at times. Debris and rocks can also cause punctures in the tires, so tougher tires are usually used on gravel tracks.
Mud
Mud can become extremely slippery for a car’s tires. Like sand, the tires will struggle to find any form of traction in the slippery conditions offered by muddy tracks. Mud can also splash up onto the car which can reduce the driver’s visibility.
Snow
Snow is soft and tends to give way quickly when weight is put down on it. This means that tires will lose traction and will also need to work harder in order to push through thicker snow. Special snow tires are used in these conditions.
Ice
Ice is extremely slippery and will cause an instant loss of traction. Tires are unable to find any amount of grip on ice. Cars will be unable to accelerate, brake or even turn on an icy road, making this one of the toughest road surfaces to drive on.
Different Types Of Rally Tires
Rally tires are designed differently to road car tires. There are a lot of different variables to consider. Rally tires are built using various different compounds, which vary from soft, medium and hard. They also have different types of tires such as those for tarmac, gravel, rain, ice and snow.
These different options have different types of tread, as discussed above, in order to create enough grip for the car in the various conditions. The tread blocks are also different sizes based on the type of road surface that the stage is taking place on.
Hard vs Soft
For example, if a stage has extremely hard and abrasive gravel the driver will opt for hard compound gravel tires as opposed to soft compound gravel tires. The hard compounds are able to take more of a beating and will last through the entire stage.
In addition, temperatures will also affect which tires need to be used. Higher temperatures are harder on the tires and therefore a harder compound tire is needed. However, in colder conditions, the tires need to be warmed up quickly and need to maintain their heat, therefore they will opt to use a softer compound of tire.
Tire Compounds
Tires are designed in different compounds. In WRC these vary from supersoft, soft, medium and hard. In some cases, there can be some compounds in between as well.
The softest tires will offer the most grip, however they will wear out the quickest. The hardest compound tires on the other hand will offer the least amount of grip, but they will be the most durable.
The challenge for drivers is to decide which tire compounds will be fast enough for them to be a serious contender in each stage. However, they will need to bear in mind that they still need the tires to have enough life in them by the end of the stage as well.
The other risk with softer tires is that they are more prone to failures and punctures. Excessive wear on the tires could potentially cause a tire blow out. An unexpected sharp object could also cause a puncture, but there is no real defense against things like this.
Tarmac
The first type of tire to consider is the dry tarmac tire. These look like your standard road tires with different types of grooves. They are built in 4 different compounds (supersoft, soft, medium and hard).
These tires will be used on stages which predominantly feature tarmac roads. These will offer maximum grip on tarmac and the specific grip levels are determined by the compound of tire used. Softer tires offer more grip, however harder tires last longer, as mentioned previously.
These tires will struggle for grip on dirt roads as they are not reinforced like gravel compound tires. They will also lose grip in wet weather as the grooves are not deep enough to expel enough water from under the tires.
Rain
Rain tires are designed with deeper grooves in the tread. The grooves also point outwards as opposed to being in a straight line (as with dry tarmac tires). This helps the tires to push water out from underneath the tires, giving the tires more grip.
The grooves act like channels which move the water out to the sides of the tires rather than keeping it underneath the tire. When water builds up underneath the tire it causes a loss of grip. This is due to the water breaking the contact between the rubber and the surface of the road. The grooves help to solve this problem.
These tires are made of a much softer compound, which means they heat up quickly and work well in colder temperatures. This means they will work most effectively in medium to heavy rain conditions. In drier weather, however, the tires tend to overheat and begin to lose grip and break apart quite easily.
Gravel
Gravel tires are designed for rally stages which are mostly run on dirt roads. They also offer different compounds such as soft, medium and hard. These different compounds are chosen based on the type of gravel that the stage is run on.
For example, soft and loose sand such as that of a desert will require the drivers to use a softer compound tire as they tend to offer more grip. Whereas if the stage were to be on a rough gravel road, the drivers will opt for a harder compound which is more durable.
Gravel tires are also built with reinforced sidewalls which offer better puncture resistance, which is necessary to protect against rocks and debris found on gravel tracks. These do make the tires heavier and harder, which is a disadvantage on tarmac surfaces and in rainy conditions.
The tread blocks on these tires also stand out much higher than other tires. This allows the tires to dig deeper under the soft top layer of gravel and find grip on the harder surface below.
Snow
Snow tires are specially designed with tread blocks that have deep grooves. These tread blocks allow the tire to grip on the soft snow and in slippery conditions by having each tread positioned differently.
Snow tires are also much thinner than normal tires. This is to reduce the surface area of the tire, which in slippery conditions will actually increase the amount of grip. This is the opposite of what happens in dry conditions, where you want a larger surface area for more grip.
Ice
Ice tires are very similar to snow tires with the addition of studs. The studs help the tires grip into the harder ice surface and give it the traction needed to provide the car with enough grip to move forwards. The studs essentially act as claws that push into the surface of the ice for leverage.
How Long Do Rally Tires Last?
Drivers are allowed between 4 and 8 sets of tires during a rally stage. Drivers are also allowed 2 spare tires. This means that the tires need to last a set amount of time in order for them to complete the full stage. However, this is no easy task.
Driving On The Limit
In order to win you need to drive on the limit and as fast as possible. However, the faster you drive the more pressure you put on your tires. The higher speeds will cause the tires to wear out quicker.
In addition, there is the risk of damaging the tires too much to the point where you need to change them. There could be an object in the road that causes a puncture, or you could hit a curb at the wrong angle and blow a tire. Not only will this cost time, but it will also subtract from your allocated number of tires for that stage.
Final Thoughts
Rally tires are completely different to the ones you would find on your road car. The biggest difference is that rally tires are built to be more robust in order to withstand the extreme conditions offered by rally stages.
Another factor that makes them so different is that they use different compounds in order to improve their levels of grip and durability. They are also built indifferent ways for specific road surfaces and weather conditions.
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