What is the minimum curve to use with a HO SD45 and 85' cars ? Is 22 degrees enough or do I need to go bigger?
Degrees? Do you mean inches? If so, 22" radius is fine. That's what you would find on a 4'x8' layout on each end. In fact, you can go a bit tighter than that. Probably around 20". I'm not an HO modeler, but I've seen large engines tackle similar curves. Hope I helped, Alex
I'm not mister popular when I answer questions like this...but here goes. In HO I would push your curves out to 28 or wider. The six axle HO diesels don't much appreciate the tighter 22 radius curves. Keep in mind the wider the curve the better your six axle equipment will perform or negotiate it. I had to tear out an 18" radius curved layout when I got my first six axled Athearn SD 45's. Even at 22" radius they crawled up and out of the curves. Just one of those things. Best of luck to you.
An old table from the LDSIG about the ratio between the length of your longest car or engine and an appropriate minimum radius: 1:2 is called pushing against technical possibilities. 1:3 (or 1:2,5) nice but still looking toy-like. 1:4 good looking and flawless operation 1:5 needed for handsfree (un)coupling. The coaches you are talking about are about one foot long in HO, so 24" would be the required minimum radius. BTW when building a flatland race track you should apply different standards then building a railroad through the mountains. Radii might differ too depending on speed. Switching empty coaches in a yard is not the same as running a fully loaded passenger train through curves with speeds up to 100 miles an hour. Degrees of curvature are used when building real railroads. Imagine finding the centrepoint of a curve 500 yards away and using a very long yardstick to "draw" the curve; all done in a landscape with rivers, mountains or roads and houses. They are just looking for the next point of the line 100 feet away. The angle between what is built and the straight towards the next point is what they are looking at. Paul
Here's a link to Degrees of Curve to Radius in real feet & HO scale in inches: http://www.trainweb.org/freemoslo/Modules/Tips-and-Techniques/degrees_of_curve_to_radius.htm For other scales use that ratio e.g 1:48, 1:64, 1:160, 1:220, etc to figure inches in that scale. The narrow gauge Uintah Ry had 12.8" HO equivalent radius on a 7.5% grade & the LAJ has a 10.2" w/ a #3 switch. So small radius curves are known on the prototype so why not on model RRs IF that's what your modeling!. Laid down a temporary 10"R curve and was able to get an Athearn CF7 & Atlas S-2 + 40' box car thru many times w/ no derailments. Couldn't do it w/ a 50' box & didn't even try it w/ a 6 axle.
Especially if you have a parallel track you could have issues on tight corners. If someone asked me about any of the 85'/89' cars I'd tell them not to run them unless they had at least 30" curves. Nor would I use them myself unless I could manage those requirements. Frankly, we don't sell very many of them at the store at all because of the curves they require. I don't order them for in-store inventory anymore.
Yeah, for 85-footers and six-axle diesels I wouldn't go a hare under 24". With my HO Unitrack I only own R730 and R790 which is 28.75" and 31" respectively. One thing to note, if you ever stumble across degree of curvature in reference to roads, us highway guys use a different definition. For railroads, it's the degree between two 100' straight lines that just touch the curve at either end (i.e. the "chord"). For highways, it's the number of degrees turned by a 100' arc. This gets progressively more divergent as you get smaller. 1 degree railway is 5729.65' where 1 degree highway is 5729.58'; 20 degrees railway is 287.94' where 20 degrees highway 286.48'.
