How do I determine my bike's fork width? I have a Breezer Liberty 2.3. I am trying to determine whether it would work with the CycleOps Hammer trainer. The trainer says it is "Quick-release compatible for bike frames with fork widths of 130mm and 135 mm.", 
However, I am not sure how to measure that on my bike, and I can't figure it out by looking at the specs page for the bike.
This refers to the interior distance between the rear wheel dropouts on the frame. The rear triangle is sometimes referred to as the frame 'fork', not to be confused with the front wheel fork.

The vast majority of modern bikes with quick release hubs have 100mm spaced front wheel dropouts and either 130 or 135mm rear wheel dropouts. If you measure the distance with the wheel out it may be a few mm off of 130 or 135mm as frames flex a bit when the quick release is undone.