# Turn radius???



## G1-L Tech (Dec 7, 2016)

Ok, like I said before I've done HO and had to deal with the infamous turn radius, whatever that is, I was told/ advised not to go smaller than a 36" radius, so how does that work for N scale, do I just half it?, or is there some complex formula involving quantum physics and the space time continuum?
And, what exactly does it mean, 'turn radius'?
I understand the radius part, and I think I sort of get the concept, but a,little help and explanation would be wonderful!
Thanks.
Trev


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## fulsom56 (Sep 18, 2015)

G1-L Tech said:


> Ok, like I said before I've done HO and had to deal with the infamous turn radius, whatever that is, I was told/ advised not to go smaller than a 36" radius, so how does that work for N scale, do I just half it?, or is there some complex formula involving quantum physics and the space time continuum?
> And, what exactly does it mean, 'turn radius'?
> I understand the radius part, and I think I sort of get the concept, but a,little help and explanation would be wonderful!
> Thanks.
> Trev


By "turn radius" I believe your talking about minimum turn radius & for N scale the absolute minimum would be 9.750" although I would never go that small. On my layout the minimum is 15" but I have enough room to do that. If you look at any MR magazine the layouts will give you there minimum radius or just google N scale minimum turn radius.


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## powersteamguy1790 (Mar 26, 2012)

G1-L Tech said:


> Ok, like I said before I've done HO and had to deal with the infamous turn radius, whatever that is, I was told/ advised not to go smaller than a 36" radius, so how does that work for N scale, do I just half it?, or is there some complex formula involving quantum physics and the space time continuum?
> And, what exactly does it mean, 'turn radius'?
> I understand the radius part, and I think I sort of get the concept, but a,little help and explanation would be wonderful!
> Thanks.
> Trev


Yes, you just half the 56 inch radius in HO to get N scale radius. On my large around the room layout, Iuse radii of 28-30 inches and 23-25 inches in N scale.


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## kevinh (Jan 26, 2015)

An example: Draw a circle with a radius of 10". Lay track around that circle. (The centreline of the track lies on the circle you drew.) Now, cut out an arc of track from the circle (any arc, of any length). The "radius of curvature" or "turn radius" for any piece that you cut out - as long it keeps the same shape - is going to be the same as the radius of the complete circle: 10". Doesn't matter if it's a 45-degree curve or a 180-degree U-turn, they're all 10"-radius curves. Of course, the centerlines of the two ends of that U-turn are going to be 20" apart (one diameter equals twice the radius).

Shorter locomotives and rolling stock will often work down to 9.75" radius curves (that's the smallest-radius curve that Atlas sells in its N-scale sectional track) or even below; longer locos and cars may need 11" or even larger curves to work without binding or derailing.

And the fact that you can make a particular car or loco fit around a curve doesn't mean it will look good doing it. Larger, longer rolling stock can demand 15" to 22" curves in order to not look silly. Bigger curves are almost always more graceful--not to mention closer to prototype. Your choice of curve radius will be a compromise between prototypical yards-in-N-scale radius curves and what will actually fit on your bench.

The NMRA RP-11 standard provides a table of recommended minimum radii:

http://www.nmra.org/rp-11-curvature-rolling-stock


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## traction fan (Oct 5, 2014)

*minimum radius*



G1-L Tech said:


> Ok, like I said before I've done HO and had to deal with the infamous turn radius, whatever that is, I was told/ advised not to go smaller than a 36" radius, so how does that work for N scale, do I just half it?, or is there some complex formula involving quantum physics and the space time continuum?
> And, what exactly does it mean, 'turn radius'?
> I understand the radius part, and I think I sort of get the concept, but a,little help and explanation would be wonderful!
> Thanks.
> Trev


 As others have said, the "turn radius" is just basic geometry. The radius is 1/2 the diameter of a circle. For track planning purposes, it's good to use the largest radius you can fit. Remember,when planning , that the track radius is measured from the center of the ties, right where those holes for track nails are. You will need additional table width to accommodate the outer 1/2 of the track on each side, plus room for overhang of cars and locomotives. How tight a radius you can get away with, varies with what equipment you plan to run. If your preference is for big steam (or six axle diesels) and long,85' cars; then you'll need a large radius. With shorter cars and locos you can use a tighter radius curve. Still, bigger is better; both for reliable operation, and appearance. 
I started using 12" radius curves as my N-scale railroad's minimum. When I bought two 2-8-2 Mikado steamers, I had to increase to a 16" minimum radius. I would not recommend going smaller than 16" unless you are forced to by available space. If that's the case, then stick to small locos and shorter cars.

Regards;

Traction Fan:smilie_daumenpos:


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