in building my new layout (finally started today) im using a 24" radius for the minimum curve. (HO scale) im worried about the longer cars(centerbeams) sideswiping eachother. what should the outside radius be? could i get away with 26"?
Thanks
GEARHEAD426
Iffy. Probably not. I believe the NMRA suggested mins for 24" is near 2.25" (plus or minus 0.15") You could verify that by going to their website. I don’t have the link handy.
I guess it depends on how long the “longer cars” are. But, if they are full size 85’ passenger or TOFC cars I would go with 26 1/4" to 26 1/2". Why don’t you layout one curve of the size being considered and see how the specific equipment in question does?
With a min inside of 24" you would need to have 26 1/2" for the outside. Even though 2 1/4" spacing would work, it is good to have an extra bit of buffer on the turns. You don’t need to keep the track centers at 2 1/2" throughout on the straight mainlines. These can be 2" for a better look. You make the change at the easements as you bend into the turns. Just don’t go under 24" or many pices of long equipment will not run or look right.
Easements really help out here, and super elevation makes it look really good.
28" or larger would be better.
A good general rule-of-thumb promoted by the Layout Design Special Interest Group of the NMRA is to make your curve radius be 5 times the length of your longest car (coupler to coupler).
For example, an HO forty foot box car is about 6" long, coupler to coupler. For your cars to look good and to have reliable coupling on curves, you need a 30" radius. For fifty foot cars in HO, the car is about 7.5" long, so you want 7.5 x 5 or a curve radius of about 37.5".
You can cheat a bit and go perhaps 36", but you get the idea. For sixty foot passenger cars, they are about 9" long over the couplers, so you would want about a 45" radius for the cars to look good and to couple easily on curves.
Now there’s another trick you can take advantage of, too. Curves, when viewed from the inside, don’t look as sharp. So for inside curves, you can drop the radius about 10% or so (say 27" instead of 30") and the curve will still look pretty good.
But outside curves (like at the end of a peninsula) look sharp and the equipment doesn’t look as good, so the curves there should be as broad as possible. If you can manage it, you should use the 5x rule for those curves.
In yards where you do a lot of switching, you should also use the 5x rule, since that will help insure you can easily couple while switching cars.
“Get away with?” - probably 2.5 " (26.5"r) without sideswipe. 3" spacing safer.
NMRA (min r.) 44" (I use 46"r and 44"r) - fits on a 4X4 corner section
“Looks Good” (realistic) 60" -Joe Fugate
No disagreement here.