OO GAUGE ยท CURVES
Track radius explained: which radius do you need?
Radius is how tight a curve is: the distance from the centre of the circle to the middle of the track. Hornby setrack comes in four radii, called 1st to 4th radius. Tighter curves take less space, but not every loco or coach will run round them.
Hornby setrack radii
| Radius | Radius | Full circle needs | Part numbers |
|---|---|---|---|
| 1st radius (R1) | 371mm | 771mm | R604, R605 |
| 2nd radius (R2) | 438mm | 905mm | R606, R607, R643 |
| 3rd radius (R3) | 505mm | 1039mm | R608, R609 |
| 4th radius (R4) | 572mm | 1173mm | R8261, R8262 |
Which radius do you need?
- 1st radius (371mm) is the tightest and the one most train sets use. It suits small tank engines, short wagons and most locos sold in sets.
- 2nd radius (438mm) suits a much wider range of locos and longer coaches, and looks noticeably more natural.
- 3rd and 4th radius suit larger locos and long coaches best, and look the most realistic, but need a lot more space.
The only reliable answer for a particular model is its instructions, or the manufacturer's website, which usually state a minimum radius. Check before you buy track.
Long coaches on tight curves
Long coaches swing out on tight curves: the middle cuts in and the ends hang out. On double track, two long coaches passing on 1st and 2nd radius curves can touch. If you plan to run long coaches, use the gentler curves, or leave extra room between tracks on the bends.
Mixing radii
Because each radius is exactly 67mm wider than the last, a 1st radius loop inside a 2nd radius loop makes neat double track. See the Double oval for two trains plan. As a rule of thumb, use the largest radius your space allows.