Tires: Tire manufacture, holly holly, writing a dissertation

Question
Hi,

I am writing a dissertation on tyre impression evidence and need to know some background as to the manufacture of tyres and how these different features may affect an impression left at a scene. Apart from the ingredients used, does the general process vary between manufacturers, and if so, at what points in the process would these differences occur? Any help would be greatly appreciated.
Thanks Holly

Answer
Holly,

As a general rule, tires are manufactured the same regardless of who makes them.  There are going to be slight variations, but that would be in the details - essentially the process is the same.  If you look at different manufacturer's web sites, you'll sometimes see the manufacturing steps and that should confirm this.

But there are differences.  As you pointed out, the ingredients would be different, and the details in how the materials are processed are different, but that has almost no effect on the tire impression left at the scene of a crime.

Also, the tire's structure - eg: the width of the belts, the angle of the belts, probably have more effect on the footprint than the materials.  But again, those are not important when confronted with a tire impression from a crime scene.

Things like inflation pressure, the amount of wear, the unevenness of the wear,  are more important than the manufacturing technique or the tire's structure,

BUT!!!

The most important thing when confronted with a tire impression from a crime scene is the cuts and missing chunks.  Those details will uniquely identify an individual tire.

Defense attorneys will try to discredit the evidence (and the expert) by pointing out that the size of the individual tread elements are different than the mold drawing (it's always a good idea to consult with the tire manufacturer to confirm the tire pattern.), but this doesn't really affect the identification.

So while it may seem that differences between tires is important, in the big scheme of things, it has little effect on the impression, and external factors - inflation pressure, wheel alignment, the surface where the impression was left - have more.

Good luck with your dissertation.