What are bustle wheels?

First some background: Bustle wheels are used in offset printing. When a paper web goes through several units in order to create full, or process, color; the paper web takes on water from each printing unit. This in turn causes the paper web to stretch along with the printed image. This in turn causes problems with registration, or lining up of the colors, from printing unit to printing unit. Enter bustle wheels. There are several types of bustle wheels: standard, air assist, mechanical, and several combinations of the first three. They all serve the same purpose. Printers using bustle wheels will use anywhere from one to three wheels to get the desired effect. One wheel is mounted in the middle of the web, creating pressure against it and drawing it inward. This is where the word bustle comes in. You are pulling the paper inward, or bustling it, to compensate for the web growth of the previous units. Sometimes this is enough to compensate for the web growth that caused the fan out. Other times three wheels will be used if one isn't enough. One will be in the middle, the other two will be near the extreme ends.

Chris Kempf - 2009