Excavators are built to be able to move around on tracks. The tracks of the excavators today come in three types. You can get rubber tracks, iron or steel tracks and steel tracks with street pads installed.
Rubber tracks are most common on the small or mini class of excavator. These tracks vary in width and length and come in different tread designs also. Rubber tracks need to be adjusted like metal tracks as they will stretch somewhat over time. They only need a little of of adjustment from time to time. Rubber tracks are quite nice in the fact that you can travel almost anywhere. You can off load your little ecavator o a city street and travel around, hop a curb and travel down a sidewalk, scoot across some lawns and go and dig along a building without making a mess or breaking any concrete or leaving marks in the asphalt.
Rubber tracks are more costly though than iron or steel. They are almost twice the price of steel tracks so a lot of owners who are in need of replacement tracks will often look for a second hand pair of tracks. The fact that rubber tracks will wear out faster than steel tracks allows there to be a wide assortment of after market companies that build rubber tracks. You can find a lot of different styles of treads designs and thickness for whatever application you are using.
You can also get steel or iron tracks for most all excavators whether it be the mini or midi. Almost all heavy excavators come with steel tracks though. Dimensions such as pad thickness and pad width all play an important part in the design of the track. The heavier the excavator the heavier the tracks pads. Grouser depth and size will play an important part in traction and stabliziation while travelling or during extreme digging.
Rubber tracks do not fair so well in rocky terrain, especially if there is sharp rocks laying about. The tracks, like a tire can cut quite easy and this is what will wear the track down. Also in real loose gravels, rocks will get inside the track when turning tight corners and if the rock is large it may jam up in the rear drive hub causing the machine to come to a stop. When this happens you need to swing the house to the side and using your boom you need to put presur down there by lifting the stuck track off the ground and then roll the track fore and aft to dislodge the rock. In the case of steel tracks in a lot of case the steel will crush the rock eliminating this procedure.
For heavy excavators though that have only steel tracks, there is an option in having the track rubber. One way is to get what is called "bolt on" street pads or "Geo Grip" pads. Geo Grip pads are a bolt on pad but they are a lot thicker and larger. It is like bolting an entire rubber track over your steel track where as street pads are smaller rubber inserts that bolt onto each metal pad. These types of padded tracks are good for heavier machines in the 15 ton range where rubber tracks are not an option. In the event that you no longer need the rubber pads, you simply unbolt the pads and you're back to steel tracks.
One of the more recent inventions with excavators is the amphibious types of tracks. These systems allow the enitre excavator to float about in swampy and soft ground. They are basically a pontoon with a track that runs the circumference of it. This allow the excavator to move about by either floating or moving about on land. As the tracks turn they act like small paddles and move the excavator about. With one track going one way and the other track going the opposite the excavator can turn 360 degrees with ease. Many shallow water dredging operations will use this type of excavator.