What each specification tells you

Bearing type predicts longevity — sealed bearings stay quiet for years, unsealed bushings do not. Wheel material predicts noise, with polyurethane quieter than nylon. Rail material and finish predict how long the running surface stays smooth.

Carriage travel predicts who the machine fits. Together these four cover almost everything that determines how a reformer feels.

Carriage and rail specifications
SpecificationGoodConcerning
Bearing typeSealed precision bearingsUnsealed bushings, or unstated
Wheel materialPolyurethaneHard nylon
Wheel count4–8, positioned outboardFewer, positioned inboard
RailMachined, seamlessFolded or stamped section
Carriage travel40–42 inUnder 34 in for adult users

Unstated is a specification

Manufacturers who use sealed bearings say so, because it is a selling point. A listing that describes the carriage as "smooth-gliding" without naming the bearing type is usually not using sealed bearings.

The same applies to rail construction and carriage travel. Absence of a figure is information.

What you can test in person

Lateral rock at the far end of carriage travel tells you about wheel positioning and bearing quality. Noise with springs detached tells you about rail finish. Both take seconds and are more informative than the specification sheet.

If you can only do one thing before buying, rock the carriage sideways at full extension.

Why rails deserve attention

The rail is half the glide system and the half that cannot usually be replaced on cheaper machines. A scored or corroded rail permanently degrades the machine regardless of how good the wheels are.

Machined, seamless rails with no fixings in the running surface are what to look for.