Curve Radius Calculator — Minimum Track Curves

The absolute minimum for OO gauge is about 371mm (1st radius Hornby/Peco), but this looks very sharp. 438mm (2nd radius) is better for most locos. 610mm or larger is recommended for coaches, and 762mm+ for long coaches like HST sets.

Longer vehicles overhang on curves — the body swings out while the bogies follow the track. On tight curves, this can cause derailments, uncoupling, and unrealistic appearance. Larger radii keep the vehicle body aligned with the track.

Peco Setrack for OO uses 371mm (1st radius) and 438mm (2nd radius). Streamline track can be bent to any radius. Hornby uses similar radii. For realistic running, use the largest radius your space allows.

Yes. Real railways use transition curves (easements) where the radius gradually changes from straight to full curve. You can replicate this with flex track by gradually increasing the curve. It looks more realistic and reduces derailment risk.