 Today you will learn about Tired Tread and Tired Track Evidence. So you may be wondering, what's the difference between Tired Treads and Tired Tracks? Well, it's really pretty simple. Tired Tread Evidence deals with the design and dimensions of an individual tire on a vehicle. Tired Treads are a form of Impression Evidence where an object is pressed against a soft surface so that the surface is stamped with the shape and details of the object. Tired Tread Impressions can be analyzed very closely. For example, a tread from an accident or crime scene can be compared with a Tired Tread from a suspect vehicle to try to identify a match. Tired Tracks, on the other hand, refer to all of the tire patterns created by the car as a whole rather than analyzing the tread pattern of one tire specifically. Tired Track Evidence deals with the spatial relationships between two or more tires which can be helpful when trying to determine the dimensions of the suspect car. This is an example of Tired Tread Evidence where you are able to analyze the design features of an individual tire. This is an example of Tired Track Evidence. As you can see here, you can look at the spatial relationships between two or more tires. So let's talk about some of the things you can analyze and learn from Tired Treads. This is a list of some of the main pieces of information that forensic investigators can learn from analyzing Tired Treads. You can determine tread design, the type of noise treatment the tire has, tread wear features, and any other individualizing characteristics the Tired Tread may have. When I say tread design, I'm talking about the design features that make up the pattern of the tire. These design elements are separated by grooves in the rubber that run across the tire. These grooves have a few names including slots or transverse grooves. You can also analyze a Tired Tread to look at tread wear indicators which are raised bars of rubber that indicate how much a tread has worn down. These can be some great points of comparison when trying to match Tired Tread marks. One other thing that you can look at with Tired Treads is the type of noise treatment the tire has. In order to talk about this, we have to have a little bit of background info first. When a car is moving, the tires rotate and undergo stress from the load or weight of the vehicle. This stress causes the Tired Treads to vibrate and produce different pitches or noise. So noise treatment refers to specific Tired Tread designs created by tire companies that incorporate differently sized tread blocks, meaning sections of tire. The different sizes of tread blocks will create a variety of pitches which will reduce noise. If a tire's tread blocks were all the same size, they would all produce the same pitch creating a lot of noise. This image shows you how sections of tread or tread blocks come in different sizes, small, medium, and large, which are also called pitch lengths. As you can see here, noise treatment designs can be complex involving various combinations of differently sized Tired Tread blocks. The pattern of noise treatment can be really helpful for finding characteristics to help match a Tired Tread impression from an accident or crime scene with a tire from a suspect vehicle. The image here represents a whole tire tread, and you can definitely see the complex arrangement of tread block sizes, numbering 1 through 4, which can be really helpful in matching tread patterns. When analyzing tire treads, you want to make sure you look for tread wear indicators. These indicators, called wear bars, are raised rubber bars that wear down as a tire is used. Wear bars can sometimes be seen in Tired Tread impressions, and when you identify the wear bar along with a noise treatment, this information can allow a forensic investigator to pinpoint the exact section of tire tread that made the impression. This can be really helpful when trying to match accident or crime scene impressions with suspect treads. Now, let's move on to Tired Track Evidence. If you remember, Tired Track Evidence involves the patterns made by two or more tires so that you can look at dimensional characteristics, among other things. Some of the most important things you can analyze with tire tracks are measurements such as Tired Track Width or Stance, wheel-based dimensions, turning diameter, and the relative positions of tracks when a vehicle turns. Track Width or Stance is the measurement made from the center of one wheel to the center of the opposite wheel. One thing you have to keep in mind with this measurement is that Front Track Width and Rear Track Width will usually be different. In a front-wheel drive car, the front wheels provide inaccurate measurements when they turn. So you'll want to rely on the Rear Track Width, meaning the rear wheel dimensions. Another important measurement to take from tire tracks when available is the wheel base. This measurement is taken from the center of the hubs from the front wheels to the center of the hubs of the rear wheels. Unfortunately, all of the points needed to make this measurement are rarely available at an accident or crime scene. The times when this might be available are when the car is parked in snow or rain where you could clearly see where the bottoms of all four tires were. If you have a circular tire track pattern, you can determine the vehicle's turning diameter. This is the diameter of the circle that the vehicle makes when the steering wheel is fully turned. The turning diameter can be calculated using the equation B squared divided by A plus A, where B is the distance between two points on the turn circle, and A is the distance between the outer margin of the circle and a midpoint between those two points on the circle. The last important thing to document from tire track evidence is tire positions. Tire positions can only be documented for turning vehicles because that's when you'll see all four tire tracks. When a vehicle moves in a straight path, only the rear tire tracks are available. When a vehicle turns, the rear and front tires track separately. Here is another image of tire positions from a turning vehicle. You can clearly see that all four tire tracks are visible when a vehicle is turning. It's really important to document this and understand how tire tracks are made and which tires are being represented by specific tire tracks. All of this information is critical in order to interpret the sequence of events of an accident or crime scene and also to help match evidence to suspect vehicles.