The tightest curve radius in N and what it means for your baseboard
Benjamin | TrackDrawer.com · published 8 November 2026
The tightest curve in N in our catalogue is 192 mm (Fleischmann piccolo and Arnold R1), closely followed by Minitrix R1 at 194.6 mm. A full circle at that radius is about 40 to 41 cm wide across the sleepers, so a closed loop with a 5 cm margin fits on a baseboard 50 to 55 cm deep. That tight curve is fine for short trains and goods wagons, but long coaches look cramped and can touch each other on double track.
The smallest radius per system
The table shows the tightest curve in our catalogue for six N systems, the width of the track seen from above, and how wide a full circle becomes. The last column gives the diverging radius of the standard turnout: the curve a train follows when it takes the turnout's diverging road.
| System | Tightest curve | Track width | Circle outside width | With 2 x 5 cm margin | Standard turnout diverges at |
|---|---|---|---|---|---|
| Fleischmann piccolo R1 | 192 mm | 27 mm | 411 mm | 51.1 cm | 430 mm, 15 degrees |
| Arnold R1 | 192 mm | 16 mm | 400 mm | 50.0 cm | 430 mm, 15 degrees |
| Minitrix R1 | 194.6 mm | 16 mm | 405.2 mm | 50.5 cm | 194.6 mm, 24 degrees |
| Kato Unitrack N R216 | 216 mm | 25 mm | 457 mm | 55.7 cm | 481 mm, 15 degrees |
| Peco Setrack N R1 | 228 mm | 24 mm | 480 mm | 58.0 cm | 228 mm, 22.5 degrees |
| Tomix Fine Track C243 | 243 mm | 18.5 mm | 504.5 mm | 60.5 cm | 541 mm, 15 degrees |
The outside width is twice the radius plus the width of the track. That is the minimum depth for any layout with a loop, because an oval is a circle cut open in the middle and lengthened with straights.
Measured with the TrackDrawer Auto-designer, in 5 cm steps and with a 5 cm margin, that comes to a 55 x 55 cm baseboard for Minitrix and piccolo and 60 x 60 cm for Kato. How that compares with H0, TT and Z is covered in H0, N, TT or Z.
Every larger radius costs depth
A wider curve looks calmer and is kinder to long rolling stock. But every centimetre of radius counts twice in the depth of your baseboard. On systems whose radii follow the track spacing, such as Minitrix (33.6 mm) and piccolo from R1 to R2 (also 33.6 mm), each step outwards costs 6.7 cm of extra depth.
A few examples for Minitrix, measured across the sleepers:
| Minitrix | Radius | Circle outside width |
|---|---|---|
| R1 | 194.6 mm | 405.2 mm |
| R2 | 228.2 mm | 472.4 mm |
| R3 | 329 mm | 674 mm |
| R4 | 362.6 mm | 741.2 mm |
| R5 | 492.6 mm | 1001.2 mm |
So R3 already needs almost 70 cm of depth, R5 more than a metre. If you want an N oval with generous curves, you end up at the depth of a small H0 layout; see an H0 layout on 180 x 90 cm.
The turnout matters too
On most N systems the standard turnout diverges on a much wider curve than the tightest radius: 430 mm on piccolo and Arnold, 481 mm on Kato, 541 mm on Tomix. A train taking the diverging road therefore runs through a gentler curve than on the oval itself.
Minitrix is the exception. The standard turnout 14951/14953 is 104.2 mm long and diverges on R1 over 24 degrees, and its matching curve 14914 is a 24 degree R1 curve. That is very compact, but a long train then runs through the tightest curve twice in the turnout ladder, in opposite directions. Minitrix therefore also has a slimmer turnout, 14954/14939, which diverges on R4 (362.6 mm) over 15 degrees.
Peco Setrack N also diverges on its R1 of 228 mm, over 22.5 degrees. Besides its 15 degree turnout, Tomix has a compact version that diverges at 280 mm over 30 degrees.
Long coaches in a tight curve
A bogie vehicle sits in a curve like a chord between two points on the arc. The middle of the body moves inwards, the ends swing outwards. The tighter the curve, the more it happens.
A worked example with an N coach 165 mm long (a 26.4 m coach at 1:160) with its bogie centres 119 mm apart:
| Radius | Middle moves inwards | Ends swing outwards |
|---|---|---|
| 192 mm | about 9 mm | about 8.5 mm |
| 228.2 mm | about 8 mm | about 7 mm |
| 329 mm | about 5.5 mm | about 5 mm |
On a single oval this is mostly about looks. On double track it gets tight. With Minitrix R1 inside and R2 outside, 33.6 mm apart, the ends of the inner coach swing out 8.4 mm and the middle of the outer coach moves in 7.8 mm. With a body width of about 18 mm (2.8 m at 1:160) nothing is left on paper: two long coaches can touch in the curve. Short wagons and four-wheelers do not have this problem.
Then there is the S-curve: two opposite curves with no straight in between. That is where the couplings of two long vehicles are offset the most. TrackDrawer gives a tip when there is less straight between two opposite curves than one standard wagon; for N the app uses 136 mm. How far apart tracks should be in general is covered in track spacing.
Rules of thumb for your baseboard
- 50 to 60 cm deep: one loop on the tightest radius, with short trains. Pick the system with the tightest curve if every centimetre counts.
- Double track on R1 and R2: allow about 47 cm outside width with Minitrix, but keep long coaches off the inner track, or space the tracks further apart in the curve.
- Long express trains and a calm look: use R3 or larger as the outer curve and allow 70 cm of depth or more.
- Passing loops and stations: watch the diverging radius of your turnouts; the slim turnout costs length but runs more smoothly.
Frequently asked questions
What radius can my N rolling stock handle?
The maker of your locomotive or coach specifies it. Much short rolling stock runs through the tightest curve of every system; long coaches and some locomotives need more. Add your rolling stock to your plan in TrackDrawer and the checks will warn you at every curve that is tighter.
Can I mix curves from different brands?
Not straight away: radii, angles and joiners differ per system. Plan with one system if you can, and put a transition on a straight if you do combine.
Try it on your own baseboard
Enter your baseboard size and your N track and let the Auto-designer show which loops, stations and double tracks fit. You can set a minimum radius so the plan never gets tighter than your trains can handle.