How Smooth is “Smooth”?

Some people say, “Everything is relative.” Here’s a case where that’s certainly true. These pictures were made using a scanning electron microscope. The first is a section of tire tread near a groove, at 50X magnification. If the whole tire were that size, it would be about 167 feet in diameter, and the tread would be about 35 feet wide.

Even though the tread features of a new tire look smooth and sharp-edged, at the microscopic level, there are considerable variations in smoothness.

Bridgestone tire tread, 50X magnification

The second photo is of the same tread surface, but at 2000X magnification. Again, if the whole tire were magnified to that size, it would be a mile-and-a-quarter in diameter, and the tread would be a quarter mile wide.

Same tread surface, but at 2000X magnification

Now, the surface looks almost like boiling, molten lava. So how smooth something is, clearly depends on your point of view.

Return To TOC