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What is the Minimum Radius for Trains?
Allan asks readers:
“Hi I am starting an HO layout on 4×8 or 5×9 board and want 2 levels but my problem is I want the track to climb 100mm (4 inch) in a complete circle. What I want to know is what is the minimum radius that I can climb to achieve this please? I am using strong engines and only about 5-6 wagons so won’t have much weight to pull up incline. Thanks for any help on this please.”
6 Responses to What is the Minimum Radius for Trains?
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A lot depends on the rolling stock you wish to run. My layout is HO scale and is designed to fit in a trundle bed (twin size) drawer so the layout size is about 38″ x 77″. I have heard the layout style called a “folded dog bone” (resembles a figure eight with a few short spurs). The minimum track radius is about 15.5″ (Maximum track radius is 18″). There is approximately 32′ of track and the maximum rise is 5-1.2″ ( the track rises 5-1/2″ is about 16′ then returns to the lower level in another 16′. The maximum grade (slope) is slightly less than 4% – a fairly steep grade. With the 15.5″ radius, virtually all steam era model locomiotives are eliminated and virtually all cars (wagons) must be 50′ scale length or shorter. I am running four axle diesels (GP30 for example) and all cars (wagons) are typically 40′ scale length (layout is simulating 1950’s era rolling stock). This layout with these restrictions works well.
cool thanks david so according to your reply if I use a 22′ radius circle for the incline and 18’for the decline then I should be sweet with my 4 axle diesels and a few wagons to climb ok I only have short rolling stock but because I have several locos I can always add one for climbing thanks again
Hi,
Good answer David. My response would have been not so much how big a radius, but how small. I personally would not go below 16 inches because of the wheelbase of my locos, but BIGGER is better if you have the space.
If this is a new layout being built think more in terms of where your layout is in the real world (stations/buildings/locos/rolling stock) than the space you have available. Look at LDEs (layout design elements) that represent your chosen location and era, place them in logical order and then work out how you’ll get trains from A to B. Doing it this way is not only a great intellectual exercise, it’s actually fun.
thanks for the help and yes I have space to go up to 9×5 feet so as im not really modelling any specific area but wish to include a mountain area for forest harvesting and a freezing works/meat processor and dairy at lower level to be serviced by yards I needed to know about single helix to fit layout as I plan on using an outer separate controlled track for passenger service with my old (read child hood Bachmann intercity train I,m now 49) and an internal track with yards on another controller so my two boys 7&8 can run a train each and it all needs to fit either 8×4 or 9×5 so thanks for all your help and comments as I have been kinda stalled until now the other thing is I am limited in funds so am going dc only and using isolators for tracks to facilitate switching and as I’m pretty good at wiring I don’t see any real problems there so I will keep you posted on progress and now to final design thanks again allan
For the particular locomotives you intend to use, first check: what is the manufacturer’s stated minimum radius ?
This is mainly an issue with multiple axle steam locos, which have a long fixed wheelbase, so there is a limit on how tight curves can be. (The wheels tend to jam between the rails if the radius is too small.)
Frank B. is right: If you need to learn the minimum curve radius for a particular locomotive either (1) check the specifications that came with the Locomotive or (2) check a forum online for that information.
I have a 2-8-4 Berkshire by Bachmann. The forum says that the minimum curve radius is 22″. There was nothing in the packaging with the locomotive specifying the minimum curve radius.
I tried the 2-8-4 on my layout with 18″ radius and the leading driver wheel on the outside of the curve tries to climb over the rail. Of course when that happens the power circuit is opened and the 2-8-4 comes to an immediate stop.