I started my plan by looking at 101 trackplans. I'm loosely basing mine off that. It has 24" radius for the inside loop and 26.25" radius for the outside loop. I guess they recommend it to prevent collisions in the curves. Most of the radius tools like ribbonrail only come in even-numbered inches. I'd much rather use 25" and 27" on my layout - because I can be more accurate with the tracklaying that way. But, I'm thinking there is a reason they recommended that extra 1/4 inch. Any thoughts? Do most of you just keep the 2 inch spacing when your double-track enters a curve?
I can't vouch for the designer, but if he followed the NMRA guidelines, I can pretty much vouch for them...and those guidelines. It depends on what you are running on the curves. On 27" outer curves, 80'+ passenger cars or autoracks will encroach on the inner curve at their centerpoints. If you also have a steamer, such as the Rivarossi H-8 Allegheny, running along the inner route, the corner of the cab roof closest to the tender sticks way out on such curves. Personally, I think that, for those radii, 2 1/4" centers is tight. Not if you are running shorties, 40-50' boxcars, Mikados, GP-38's and such, and probably not most of the larger/longer diesels in the SD70 range. Unless space really is at a premium, you would want it to be both a functional and a visually appealing and realistic separation between the two tracks. At the least, you would want to be able to get two fingers between two trains to pick up and rail a car without dislodging the other train's cars at the same time. So, long and the short of it, or the wide and narrow, is to pay close attention to the guidelines, practice fit when you can to be sure, and give your rolling items some elbow room on them curves.
Thanks for the input. I don't have any long steam engine or autoracks, but I do have some walthers passenger cars - the lightweights. I plan on running those continuously on the outter loop. Ok, so I should go with 24.75" radius for the inner loop. Keeping the outer loop at 27" will give me 2.25" separation. I have a Shinohara double crossover pretty close to where the curves starts and that is set at 2" separation. I'll move the double crossover a little farther from the curve and then build a little more easement into the inner curve to make up the extra .25". Since I don't have a radius tool for 24.75" I'll have to rely on the Mark One Eyeball. I know I can get the roadbed where I want it by drawing a line on the foam by swinging a ruler with holes in it. I've already drilled the holes in the ruler I need and marked my center point. But when it comes to laying the track on the roadbed, that'll be a bit more tricky. Thanks, Hammers
I use the 2 1/4 inch spacing throughout the layout, works for me, never have had a problem with it . Then again I am modeling the 1950's so nothing to large will be running. I f you are using cork road bed just follow the center line for your track. If using something else just redraw the center line on whatever you are using.
You can test my clearance calculater ( at my download site). It gives for 85' cars and 27'' radius 25.59'' inner clearance. With 25'' radius you get 25.75'' outer clearance. Those long cars will collide. With 24.75'' inner radius you get 25.50'' outer clearance. This will fit. If you have shorter cars you will get other values. Wolfgang
radius tool BTW, this was my radius tool for 47'' radius. More at my new yard at Westport site. Wolfgang
Wolfgang, Always helpful, as usual. Thank you very much. I will try it with 24.5" and 27". I think that will be more reasonable with the passenger cars.
It's worth mocking up a section of double track curve at those radii and testing your actual long equipment passing each other - just to be sure...
101 Track Plans was made in the 50s. Back then (at least, as far as I can tell from 50s books), "shorty" passenger cars were much more popular than now as a solution for medium and sharp curves. And, of course, there weren't 80' freight cars. 2.25" centers on medium radii are based on the assumption you won't be trying to squeeze the largest equipment around them - though, as already noted, 80'+ cars will fit. Just don't try to use the 101 Track Plans curve spacings for scales other than HO. The conversion factors given are wrong.
Thanks for your help. Yeah, I'm not using the 101 plan exclusively. If you're familiar with the Denver and Northwestern RR. plan from that book - thats where I started. It took me some time but I did a few mockups. I have several pictures attached in case anyone else stumbles across this thread and finds the information useful. The outside curve is 27". I tested the inside curve at 24.5" and 24.75". I did not bother testing 25" because of the information Wolfgang gave - thanks for saving me some time. I did my testing with the longest cars I have - the Rapido lightweight passenger cars (B&O for those wondering in the pictures). In the end I decided that 24.75" will meet my needs best. That comes out to 2.25" spacing. As you will see in the pictures, the cars clear each other and I have plenty of room to get my fingers in between the cars. Also, I will be able to (barely) use the pre-molded tunnel portals that I already purchased. With the 24.5" radius on the inner curve, the tunnel portals would not work. Also, this will make it easier to get them back down to the required 2" on the straights. I have a Shinohara double crossover near the curve and this will help make a less difficult.
The above photos were with 2.5" spacing. 27" radius and 24.5" radius. As you can see, the tunnel portal just won't work. But, there is plenty of space between the passing cars The below photos are with 2.25" spacing. 27" radius and 24.75" radius. The fit is a bit tighter, but I believe it will be ok. They pass each other nicely. I can easily get my fingers in between the cars. They pass through the tunnel portals (barely). The other point is that this is the longest equipment I have. I don't actually plan to run two passenger trains on both mainlines at the same time. It is much more likely that the passenger train will only be on the outside main and shorter freight trains will be on the inside main.
If you are going to be using a steamer, watch its rear cab roof corner on the outside on the portal in the position you show in your last image. Those cab roof extensions back over toward the tender really swing out on tighter curves, and you'll scrape both the portal and the paint on the engine's cab. It may even jam and you'll get stuck there.
According to information in John Armstrongs Track Planning for Realistic Operation, he recommended 2.0-inch minimum centers for straight track in yards, and on a 24-inch radius curve 2 1/4-inche centers - to avoid interference with passing trains that have long cars.
Everyone has posted some really good information. Hammers, you can also go to the NMRA website and download any and all of their standards, including a chart of recommended track centers for varying curve radii. I would highly recommend that for your future planning and layout construction. You might also consider laying out spirals to transition your curves from tangent track to the full body radius. This will help your equipment run much smoother in and out of curves and they will look better doing it, too. Rob Gardner
