# HO track radius



## Bloomfield Station (Mar 15, 2016)

I am in process of moving and building a setup in a new room. Please help me in deciding minimum radius. What determines the minimum radius an engine or passenger car can run? I am displaying an HO setup in my fictional town of 2175; passenger only. I have developed molds for the bodies of engine and cars while using my HO scale engines and chassis. Since I am creating my own passenger car chassis with as of yet developed axle sets, I realize that current passenger cars "codes" are still based on freight cars and weight allowances. 

My fictional town will have freight on a separate run thus allowing my own "code" requirements keeping in mind weight and speed engineering issues.


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## mopac (Feb 24, 2011)

In my opinion, 2 things determine minimum radius. If a loco or cars derail from too
small of radius, it needs to be bigger. Also how the equipment looks on the curves.
A long engine or car will will hang way over the inside rail on a small radius. A bigger
radius is always better. Go as big as you can. All equipment will always look better on
bigger radius. A 4 axle loco will navigate 18" radius. 6 axle locos pretty much needs 22"
radius. These are minimum radius. Again bigger is better. Passenger cars look much better on 30" radius.


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## Bloomfield Station (Mar 15, 2016)

Thanks for the quick response. I intend to make my passenger cars articulated, short with same dual wheel axles. Is there any way to use smaller radius? What if I modify the engine wheelset to be one axle as well as the passenger cars? I could grind down one set on each axle to allow the wheel to lay on the track with no flanges. I'm not sure of this methodology. It was suggested just now from someone responding by email. But if I should use 18", I will!

Thanks again to any and all suggestions.


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## mesenteria (Oct 29, 2015)

You must listen to the voices. 

Those of your rolling stock, that is. Mock up some flex track, on a clean sheet of plywood or drywall, in a spiral between 26" and 15" radius. You'll need at least two lengths of flex for this. Mark the discrete radii at every inch with a marker or piece of tape. Then, COUPLED (!!!!!!), run them (engine and car, car and car, car and caboose) back and forth, pulling and shoving, and watch where the first axle begins to lift out of the gauge as the radius descends. That there is yer minimum radius.

Sometimes the manufacturer/importer specifies the minimum radius. Walthers notoriously used to specify a minimum radius of 24" for their heavyweights with diaphragms. Nonsense! It was much closer to 27" when the cars were shoved, not trailed. This is understandable because the draft gear bunches up the slack when the cars are shoved, and it forces the diaphragms closer. They bind and force the car ends out of the gauge. 

So, for this reason, you have to mock it up and perform trials of all your typical rolling stock..._in combination_! And why I said towing and shoving. 

Armed with this incontrovertible information, you may faithfully replicate a proven minimum radius on your new layout and know you'll never have to rerail a car because you goofed.


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## Bloomfield Station (Mar 15, 2016)

You are right! Before I good. That's a great idea. I can modify the freight cars I have now with different axles to see which offer the tightest turns. BEFORE I lay track, in all directions and speed. Thanks again for the input.


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## Bloomfield Station (Mar 15, 2016)

Before I goof, not good. Lousy word corrections.


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## mopac (Feb 24, 2011)

It sounds like you really want to go smaller radius than 18". That's fine. You will not be able to run full size passenger cars, even with a lot of modifications. I suggest you mold
40' passenger cars. Maybe 35'.


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## tooter (Feb 26, 2010)

My stuff runs on 6 inch radius curves... 





 
Greg


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## Bloomfield Station (Mar 15, 2016)

Thanks for replies. I think some of you missed the point that I am making my own chassis and thus wheelbase. I am not using any existing passenger cars. But, it seems that the shorter the wheelbase the tighter the radius. I plan to use the shortest wheel based engine chassis. Since the consist will be articulated I can make a shorter wheelbase to work the small radius curves.

Thanks for your input. Now I understand the wheelbase dictates the radius.


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## Bwells (Mar 30, 2014)

How small of a radius are you thinking about? 15, 12? Is this for a shelf layout?


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## Cycleops (Dec 6, 2014)

You might also like to consider the turnouts too. If you are using short wheelbase locos electro or live frogs might be preferable.


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## DonR (Oct 18, 2012)

As mentioned, one of the major considerations on
tight radius curves is the way the ends of locos and
cars jut outward. On a very tight radius the inside
ends of cars can actually touch. On a tight radius it's
almost mandatory to have truck mounted couplers
else the cars pull each other off the track.

Have I missed your explanation as to why you want
tight radius curves? Even on an HO 4 X 8 sheet you can
have 22" radius.

Don


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## traction fan (Oct 5, 2014)

*wheelbase*



Bloomfield Station said:


> Thanks for replies. I think some of you missed the point that I am making my own chassis and thus wheelbase. I am not using any existing passenger cars. But, it seems that the shorter the wheelbase the tighter the radius. I plan to use the shortest wheel based engine chassis. Since the consist will be articulated I can make a shorter wheelbase to work the small radius curves.
> 
> Thanks for your input. Now I understand the wheelbase dictates the radius.


Bloomfield Station;

You're right about wheelbase being a big factor in how sharp a curve a given loco or car can negotiate. Even the prototype railroads had this problem, though proportionally their curves are huge compared to what model railroaders use. Many years ago, my favorite railroad, the Milwaukee Road; tried one of it's then new "Little Joe", electric locos on their coast division. (part of which I model). The long, four axle, trucks on this loco wore out the track and wheel flanges so badly, that the railroad assigned the "Little Joes" to the rocky mountain division, which had broader curves. Other railroads had similar problems. This is the reason that some larger steam locomotives were articulated.
As long as you keep in mind the advice already given, you should be able to make your passenger trains go around some pretty tight curves.
Several of us are curious about what you have in mind that requires such sharp curves. We would like to hear from you in text,or photos. Can you share that with the forum?

Good luck with whatever you choose;

Traction Fan:smilie_daumenpos:


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## traction fan (Oct 5, 2014)

*Powererd frogs*



Cycleops said:


> You might also like to consider the turnouts too. If you are using short wheelbase locos electro or live frogs might be preferable.


Bloomfield Station;

Cycleops makes an excellent suggestion here. 0-4-0, and other short wheelbase locos, may stall on unpowered turnout frogs because they only have a very short power-collecting wheel arrangement. Using a turnout with a powered, metal frog will prevent this stalling. Peco's electrofrog, which Cycleops mentions, is one commercial turnout with this feature. 
Another thing you may want to consider regarding turnouts. Virtually all commercial turnouts have a much wider radius (or a straight track equivalent) than the tight radius curve you seem to prefer. This can be good, or bad, depending on how you decide to use it. The wider radius curve of the turnout can be used as a form of "easement" which will help your trains ease into the tighter radius curve beyond the turnout. On the other hand, if you are trying to shoehorn your track into a very narrow space; the turnout's wide curve may constitute a bulge that won't fit. Since you are planning on making your own car and loco bodies, I assume you're quite handy. In that case you might consider making your own turnouts. The advantage being that you can make them with a tighter radius than anything offered in commercial turnouts. I have built 6" radius turnouts, for a trolley layout. The short wheelbase trolley cars ran quite reliably on these turnouts.
There are many methods of making turnouts. I wrote up mine, with extensive text and photos, in an earlier post on the "General Model Train Discussion" section of this forum. If you're interested, go back a page or two, and look under "How I build my own turnouts" by "Traction Fan".

regards;

Traction Fan:smilie_daumenpos:


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## Bloomfield Station (Mar 15, 2016)

I plan to use 10" turns to navigate thru town of skyscrapers. No it's not a shelf setup. I'm going around a 10 x 12 room and I need sharp turns to allow other equipment and streetcars to run as well. I'm going to do a temporary setup to run equipment verifying the proper radius. I've already determined the math involved to determine wheelbase vs radius using info I gathered from articles and suggestions here. Thanks guys.


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## Bloomfield Station (Mar 15, 2016)

Sorry I had end prior reply sooner than I wanted. I learned my lesson for not planning ahead when I built my prior setup. This time I'm planning all aspects to make sure I build the frame work properly.

I too will be using trolleys as mentioned above. Keeping in mind this is only passenger in the future

I have no pictures as of yet but once I get my diagrams drawn of layout. I will share.

Regarding turnouts: I plan to build my own and had collected copies of numerous articles.


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## Lemonhawk (Sep 24, 2013)

Take a look at proto87 stores street rail. They inadvertently sent me someone else's street rail order and its intriguing, looks like the type of street rail I remember. I certainly plan on making street rail for trolleys in my next layout!


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## DonR (Oct 18, 2012)

Lemonhawk

What you call 'street rail' is usually called
Girder Rail. It has a flangeway, the edge of
which is designed to hold keep the flangeway
clear from pavement intrusion.
Streetcar modelers use it as do those
who have regular railroads with street running.
It comes as single rails that you must hand lay.

Here is the Proto87 girder rail link:

http://www.proto87.com/Street_track_for_trolleys_and_trams.html

There are also special tight radius turnouts available
for streetcar layouts which are shown. Streetcars had to be able
to make the same turns around city street
corners as did cars and trucks.

Don


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## Nikola (Jun 11, 2012)

OP, I see no reason why 10" curves are a problem. Your task is even easier with your custom rolling stock.

I have had HO layouts running 12", 10", 8", 6" and possibly shorter turns (streetcars with single trucks) and it can work. I was always careful with rolling stock, couplers, engines and so on. For really tight switches I made my own stub switches. Crude but effective and not out of character for some layouts.

I was not concerned about car to car spacing or overhangs. It was more useful for me to be able to have a layout in very tight quarters.

So my advice is to lay out your scenery and track plan and take it from there, knowing there is a solution for anything you come up with.


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## Nikola (Jun 11, 2012)

BTW, I have 2 - 8 - 0 locos that negotiate 15" curves no problem.


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## Bloomfield Station (Mar 15, 2016)

Since this is in the future, I assume the prototype "codes" will be replaced and eliminate the overkill on passenger. Mine will be shorter and single wheeled per axle. Now my issue is to find an engine (chassis) with a short wheelbase I can place my fabricated body.


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