Dirt bike tire selection

Choosing the correct tires for your dirt bike is a simple matter of educating yourself on the available tires. Each tire model, generally, is made to suit specific conditions. To get the best performance from your tires, you should choose tires that match the conditions in which you will be riding. In some cases, a wise selection may be a compromise to suit a variety of riding conditions.

Tires generally fall into three basic categories, referring to the terrain type they are intended for:

  • Soft terrain
  • Intermediate terrain
  • Hard terrain

Tires are either tailored to the extremes of these terrain types or to a wider range of terrains. Tires intended specifically for soft terrain will not perform well on hard pack and tires for hard pack will not perform well in soft terrain. For those that find the need for compromise due to a mix of conditions, intermediate terrain tires attempt to bridge the gap between hard pack and soft terrain. Obviously, the end goal is traction. But what is traction?

According to Wikipedia.org, traction is defined as follows:

Traction is defined as a physical process in which a tangential force is transmitted across an interface between two bodies through dry friction or an intervening fluid film resulting in motion, stoppage or the transmission of power (Copyright: "Mechanical Wear Fundamentals and Testing" by Raymond George Bayer) In vehicle dynamics, tractive force is closely related to the terms tractive effort and drawbar pull, though all three terms have different definitions.

Traction is a misunderstood concept to some degree. Digging in to the fancy definition above, it is apparent that traction may or may not involve friction between two surfaces. Using a street tire as an example, traction is accomplished primarily by means of friction between the rubber tire and the asphalt. Common sense tells us that knobby tires are useless on a smooth hard surface.

In the world of dirt, however, traction may not always be possible by means of friction as with a street tire. Loose, deep soil can behave somewhat like a fluid in that grains of dirt are free to move around. Without containment, the grains flow and settle to some level. Naturally, using a street tire in dirt such as this would have very little benefit. To get traction in dirt like this, knobs are required that can contain and push against quantities of dirt. This concept of traction is far different from the street tire example.

In the real world of the dirt we love, there can be little uniformity however. Terrain varies in all kinds of ways and with many combinations thereof:

  • Watery mud
  • Pasty mud
  • Wet sand
  • Dry sand
  • Dry hard clay
  • Wet, slimy clay
  • Dirt clods
  • Rocks
  • Roots
  • Gravel
  • Other ???

Fortunately, tire manufacturers have been hard at work developing tires that are capable of dealing with the many terrains we ride in. Your challenge as a rider is to select what is most appropriate for you, considering all that has been discussed so far. More about dirt tires will further be helpful in selecting the right ones.

Soft terrain tires

Soft terrain tires tend to have larger more widely spaced knobs. The more fluid a soil becomes, the more it is necessary to progress towards a paddle design. Because surface to surface friction is less a factor regarding traction in soft dirt, tire compounds can be harder. A harder tire compound results in a stiffer knob structure that will deflect less under load thus providing maximum push. Knobs of soft terrain compounds, more so than hard terrain compounds, will tend to tear or chunk off when used in rocky conditions.

Hard terrain tires

Hard terrain tires will tend to have shorter more closely spaced knobs than soft terrain tires. As riding surfaces tend to get harder with less floating soil, having large knobs becomes less important and surface to surface friction comes in to play. This means that hard terrain tires will tend to have softer more sticky rubber compounds compared to soft terrain tires. Because the knobs flex and conform more than their soft terrain counter parts, the knobs are much less likely to tear or chunk off.

Intermediate terrain tires

Intermediate terrain tires are a compromise between soft and hard terrain. Some intermediate tires have a very wide range of terrain capabilies, but will not perform superbly in most conditions. Tires such as this will likely have average to good performance in most of their target conditions. Fortunately, there are many intermediate tires that tend to focus on one side or the other of the intermediate range. Some designs are better suited for soft to intermediate conditions and others more for intermediate to hard conditions.

There are many design characteristics that can further tailor tires to specific conditions:

  • Knob size
  • Knob shape
  • Knob arrangement
  • Stiffening ribs
  • Grooves
  • Recesses

Dirt biking generally exposes many challenges regarding traction because conditions vary significantly. In some cases, riding conditions may not be predictable, but in other cases they can, so this in and of it self is a consideration. Regardless, understanding your needs and educating yourself on the available dirt bike tires is the only solution to choosing tires wisely.

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