HO curve radius

[Anonymous]

Hello again, i just wanted to know what the smallest possible curve radius is for a basic HO diesel engine. Just so you know im not quite sure what a radius is, in train terms, lol, so please make it basic. thanks in advance, Daniel Cassidy.

[Anonymous]

The radius is the distance from the center of the circle to anywhere on the circumference, in this case, the track. I have had no trouble with four-axle diesels on 18" radius curves. I tried 15" once, but I had a lot of derailments.
Reed

[Anonymous]

>>Just so you know im not quite sure what a radius is, in train terms

Basic geometry. The radius is 1/2 the diameter of a circle. If you lay a circle of track, and measure from the center of the circle to the centerline of the track, you will get the radius of the circle, and thus the curve of the track. On railroads, you don't normally see a full circle, so the radius would be measured as if the curve continued into a full circle. Railroads use a spiral easement to gradually curve the track from straight to the curve radius. This easement does not have a fixed radius, as it changes from one point to another.

>>i just wanted to know what the smallest possible curve radius is for a basic >>HO diesel engine.

Most HO equipment will operate around the 18 inch radius curved sectional track that comes with train sets. Not all equipment will look correct rounding a sharp curve, as long cars and locos will have unrealisticly large overhangs (not to mention the difficulty of keeping body mounted couplers coupled). I have seen 15 inch radius curved sectional track for sale. Locomotives such as 4-wheeled switchers can operate around even tighter curves as might be needed in tight clearances of an industrial district of a city. The sharper the curve, the slower the speed required to go around it.

It is usually best to use as large a curve diameter as you have room for. It looks more realistic, and you will have less of a problem with trains navigating it. My current layout I am using 36 inch radius on the mainline, although I will have tighter 28 inch radius curves in other places.

Dale B.

[SteelMonsters]

I've packed in as much track on my 4x8" layout as I could. It' has two oval mainlines. The outer has a 22" radius while the inner oval has a 16 inch radius. There is another u turn inside of the ovals that has a slightly less than 12" radius. One side is conneted to the inner oval, the other enters a 12" radius teardrop reverse section.

My three locos make the 12" radus as well as all my rolling stock which are 50' Scaled or less. I have to take it at a slow to moderate speed but I'm not complaining.

When I have the space to build a larger layout, I will use large radius turns..

[Big_Boy_4005]

BNlover is correct. Standard minimum is 18" radius. Most manufacturers design their products to operate on that curve. 15" radius is the absolute minimum for short wheelbase equipment.

Traction (streetcars) can handle even tighter curves, as small as 9" or 10" radius.

Of course large equipment may look strange going around tight curves. An 80' car will overhang so badly on 18" radius, that you will almost be able to see both rails if you look straight down from above.

Standard spacing for parallel tracks is 2" centers for straight track, but it is a good idea to widen that to 2 1/2" for curves, especially tight ones, to prevent sideswiping.

[Jetrock]

Some streetcars can handle a 5-6" radius--typically one-truck Birneys or other short trolley stuff.

Typically the tightest radius that can be handled for conventional eqipment is about 12", which will permit 40-foot boxcars and small diesels to turn at slow speeds--typically the only place you'd find such tight curves is in close-quarters industrial trackage where speeds seldom went over 10-15 mph anyhow. 80' cars and modern three-truck equipment is right out of the question for such tight curves, though. Since off-the-shelf 12" curves is pretty much impossible to find you'd have to use flextrack, which is better because on tight trackage you want few or no gaps in the rail (as you get when you stick two pieces of track together) to cause derailments.

I've run my GP9's over 12" radius curves with 50' boxcars with no problems--but I'm careful about my trackwork and run them slow. At high speeds they'll jump right off the track. 40' cars and things like 44-70 ton GE switchers have more margin for error but should still be run slowly. I suppose that even smaller switchers (23-25 ton GE switchers, 0-4-0 tank engines, etc.) could run on even smaller radius but the 40-foot cars might have trouble going down to 9-10"--if one is running a layout set early enough to make use of 36' freight cars, though, it might work out just fine.

If you're modeling a rural setting then you want those curves as broad as possible--you WOULD NOT find super-tight curves on the plains. Even in the mountains one might find tight windy curves but unless you're modeling a narrow-gauge logging line, stick with 15-18" as a minimum, more if you plan on running anything resembling large equipment.

[Anonymous]

thank you guys so much [:D]

[BR60103]

I once made a streetcar layout on a 2'x4' board. I ran freight trains using the Roundhouse old timers - 36' boxcars and such. I usually used 4-wheel locomotives.
Curve radius is measured to the centre of the track. This lets you match up track centerlines when drawing layouts.
(Lionel measured their curve diameter over the outside of the ties!)

[Jetrock]

I'm working on a 2x4 streetcar layout myself--I made a mockup on a 3x6 board but had difficulty reaching the back. I'd be interested in hearing more about other people's small streetcar setups, actually, if you have any ideas to share!