Technology: Everything you need to know about tires
Most tire manufacturers have three types of motocross tires in their range. They design tires for soft, intermediate and hard terrain conditions. Soft terrain tires are made to work in loose sand and mud. Medium tires are suitable for most standard motocross tracks with good traction and a mix of soft and hard surfaces.
Hard terrain tires are made for tougher conditions with less traction. The stud patterns differ depending on the terrain the tire is made for. The ratio between the surface with studs and that without studs is crucial for the operation. A tire with more studs has more rubber in contact with the ground with each revolution of the tire. The pattern in which the studs are placed is also designed specifically for the purpose of each tire.
The rubber compound, the number of studs and the size and shape of the studs determine how stiff or soft the tire is. A stiffer rubber compound is more durable and offers less flexibility, which is good for soft conditions, while a soft compound offers more flexibility and more traction on intermediate and hard terrain. The slope at the back of the studs contributes to the degree of flexibility of the knob. Strips have also been added to connect the base of the studs, which provides more stiffness. The Dunlop MX12 has all the obvious properties of a soft terrain tire.
A tire made for sand or mud, and has fewer knobs and more open space. With this type, the studs are shaped more like a spoon or V-shaped pattern, which allows them to penetrate deeper into the ground and grab more soil with each revolution, giving the dirt bike more traction. The spaced stud pattern on soft all-terrain tires prevents the tire from filling with mud. The rubber used for these tires has a higher durometer, a measure that indicates the hardness of rubber. The stiffer tire digs into the soft surface and provides maximum traction.
With a tire for hard surfaces, the ratio between studs and the surface without studs is just the other way around. Hard terrain tires have more studs, which means more rubber touches the ground, giving the tire more grip on the hard surface. The rubber compound is also softer, allowing the studs to flex more. Hard terrain tires have lower stud heights for increased durability and traction.
Intermediate or medium tires are designed as a happy medium between soft and hard all-terrain tires. The stud sizes and stud spacing are optimized to work well in different conditions. The studs are high enough and spaced enough to dig into soft ground, but they're not too high or too far apart for riding on hard-pack circuits. The rubber compound is neither too hard nor too soft.
Lighter tires make a big difference in motocross. They ensure that the suspension responds more quickly to bumps. Tires are part of the unsprung weight of a motorcycle. Unsprung weight is any weight that is under the suspension. It is called “unsprung” because it is not supported by the springs. Heavier tires reduce engine power and braking capacity because they require more energy to start moving and therefore also require more energy to stop. Lighter tires reduce the gyroscopic effect of the spinning wheels. With less gyroscope, the bike steers lighter, steers better and accelerates faster.
If the tire pressure is too low, the tire is more susceptible to punctures and you will lose stability if the tire bends and rolls over. If the tire pressure is too high, it can affect traction and the tire's ability to follow the ground. Tire pressure increases when your tires warm up while driving or when the sun shines.
There are three numbers that describe the size of the tire. Take a 120/80-19 for example. The first number is the width of the tire in millimeters. The second number is the height of the tire as a percentage of the width. It is not 80 mm high, but 80 percent of the width, so 96 mm high. The third number is the size of the rim in inches. The most popular front tires are 80/100-21, but there are more options when it comes to rear tire sizes. Most Japanese 125 cc two-strokes and 250 cc four-strokes use 100/90-19 tires (KTM and Husqvarna use 110-wide rear tires). On more powerful bikes, riders usually choose between the 110/90-19 and wider 120/80-19 and taller 120/90-19 models.
Photos: Gino Maes and archive
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