On30 or On3?

Discussion in 'On30 Forum' started by segraves1, Dec 8, 2010.

1. segraves1New Member

So basically, it sounds like:

sloppy/factory equipment = tight turns
true-scale/close tolerance equipment = wide turns
2. pgandwActive Member

In a way, yes. It really depends on the market the model was designed for. Big Boys have been built to do 18" radius or less in HO. It required pivoting of both engines (the prototype only pivots the front engine) and substantial clearance around leading and trailing trucks. And the overhang is tremendous. But Rivarossi HO Big Boys would/will do 18" radius. Marklin makes large engines that will do 15" radius in HO - their train set track radius.

But if you look at O and On3 as slightly less than double HO and HOn3, then the outlier for curve radius is On30 and not On3. 14" or 15" radius is the minimum practical radius in HOn3 using smaller locomotives. The larger C class and the K class are just too big for such a small radius, as are most 50ft passenger cars. The 14" or 15" radius in HO/HOn3 translates into 27" to 30" radius in O/On3.

Another way to look at the radius issue is the Layout Design Special Interest Group's rule of thumb (http://www.macrodyn.com/ldsig/wiki/index.php?title=Curve_radius_rule-of-thumb). The radius rule of thumb for reliable operation of virtually all models is the three times the physical length of the car regardless of track gauge. A 32ft car (dimensions are usually inside dimensions on the prototype) in O is approximately 9" long - which by the rule indicates a 27" radius to avoid underbody detail interference. For most plastic commercial cars, a 2.5X multiplier is pretty safe - except for stringlining on long trains or on a helix.

If you read the observations, I found that Lionel operated at radius of less than 1.5X times the length. However to make that work, all underbody detail was removed and the car body was mounted artificially high so that trucks could rotate freely underneath. Couplers were truck mounted. Stringlining is still common in long trains. Rolling resistance of the cars increases dramatically on curves.

Bachmann uses some of those "tricks" to make their On30 rolling stock go around 18" radius curves. And they model short prototypes - typically 28ft or less. As a result, Bachmann is operating at a radius of about 2.25X; perhaps 2X for their passenger cars when on 18" radius track. Other On30 manufacturers who want their cars to work on tight radius use very short prototypes - 18ft and 22ft. With these cars and the Bachmann Porter engines, you can use 15" radius in On30.