PGR derailleurs use a distinctive operating mechanism:
- The nipple of the cable is held by a fixed ferrule that is at the inside end of the tube along which the pulley cage slides. The cable is clamped at the lever.
- The end of the cable outer pushes the pulley cage along the tube.
- Unlike pull-chain mechanisms, this allows the derailleur to be top-normal.
- A single, tightly wound, helical, spring both tensions the chain and powers the sliding tube mechanism.
- Helical springs are often used in compression, but this one is used in tension. The mechanism uses washers with wings on them to engage with the first and last coils of the spring.
Other than this PGR derailleurs are decently constructed alternatives to the, say, Simplex derailleurs of the time.
This is a well-used, but presentable, example of a PGR 3 with the following features:
- The main arm is aluminium.
- It has two pulley wheels.
- The tension pulley has an off-centre bolt - allowing you to adjust the effective length of the pulley cage by plus or minus 5mm.
- The sliding tube is 49mm long, possibly indicating that this is a 4-speed system.
- The b-pivot bolt is labelled 'BREVETTI ACCORSI.', indicating that Duilio Accorsi has a patent registered somewhere.
- The outer pulley cage plate is labelled 'CAMP. ITALIANO DILETT. 1948'. This may indicate that a PGR 3 was used by the Italian Amateur Champion in 1948.
Note that I have also seen a photo of a PGR 3 with a steel main arm.
- Derailleur brands: PGR
- Country: Italy
- Date of introduction: 1948?
- Date of this example: unknown
- Model no.: unknown
- Weight: 205g
- Maximum cog: unknown - but not too large!
- Total capacity: unknown - but not too large!
- Pulley centre to centre: 44mm to 54mm (adjustable using a tension pulley with an offset bolt hole)
- Index compatibility: friction
- Chain width: unknown
- Logic: top normal
- B pivot: unsprung
- P pivot: sprung
- Materials: the main arm is aluminium, the rest is steel
