Re: Ho Scale Curvature

48" less 2" setback from the table edge on both sides leaves 44" or 22" radius. With the speed restriction you mention, this should be fine for both 4 and 6 axle diesels and most freight cars. 22" radius is probably too tight for 85' passenger cars, and 86' Trailer Train flats, auto racks, and Hi-cube auto parts box cars. Body mounted couplers on these long cars would definitely be a problem and I have found that most of the manufacturers' own (particularly Athearn) wide swing coupler mounts take a lot of work to work smoothly enough for good operation on curves this sharp. Take a look at the NMRA recommended practice of curvature at

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I am desiging a modern era ho scale layout & am wondering if the track can > be turned 180' on a 4ft wide peninsular. That particular bit of track runs > around a rocky ledge beside a river so would be on a speed restriction > anyway. Would it be realistic (for a model), any ideas would be much > appreciated. > > Cheers > >

Of course "realistic" curvature in HO model railroading is a rarely achieved objective. Certainly 22" radius is a jillion miles away from that. I suspect that with the length of typical modern equipment you would find that trains on a curve like that would not look "realistic." A layout operating only four axle diesels or small steam with 40' cars would be a much better choice for realism at that radius.

One possible layout technique is to bury this part of your track plan in a tunnel or deep cut so that trains are not actually seen there. If this is a scenic highlight of your layout then you would be well rewarded to find a different way of laying out your benchwork to achieve a much larger curvature there.

I remember seeing an article in one of the mags arguing that shorty passenger cars such as the Athearn are actually more realistic on most HO layouts because they mitigate the silly appearance of long cars running on too tight radius as most of us have. You might want to consider modern to not include 89' flat cars and 86' autoparts cars, and, of course, Amtrak will not run in your world.

22" is too tight to operate a significant fraction of HO equipment. If your choice of equipment is limited appropriately you could get away with it. Modern equipment might actually just work at that radius because you won't have passenger cars (Amtrak?) and you won't have steam. Many of the long modern cars are set up with devices such as swinging coupler pockets (Walthers in partiucular) to get around even 18" radius. Those devices don't work so well when backing long trains, etc. and I typically disable them. Most of the plastic diesels will run as well although I'm not sure about something like a Kato SD90. It's a shame to have to throw ugly long shank couplers on a locomotive just so it can get around some limiting radius on your layout. If you have ambitions to own and run brass someday, those items tend to be less forgiving as well.

By the way, the problem is not speed. The problem is one of geometry. Certain combinations of overhang, limited motion of couplers, limited swing of trucks, etc. will result in wheels forced off the track at any speed. Also the transition from straight to curve at the beginning causes more severe aligment problems than negotiating the constant radius. Reducing the radius further to allow easement into the curve might or might not optimize the operation of certain equipment.