PVD Two-by-Two

What is Two-by-Two?

Some call it double-double or dos-dos.

This system consists of two single speed gearings mounted side by side. To change gears, the wheel is removed, the chain moved latterally front and rear, and the wheel is replaced. Typically, the chain needs to be re-tentioned.

What makes PVD's special

With the PVD setup, the chain does not have to be re-tentioned when the gear is changed. This is accomplished by having near identical center to center distances on the gears. This can be done by going through a bunch of calculations. see: Length Calculation