# USA Trains - Min Curve Radius for Intermodal Cars



## Trainguy McGee (Dec 18, 2020)

Does anybody know what the minimum curve radius is for the USA Trains Intermodal cars? I've looked everywhere and can't seem to find the answer to this.


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## Greg Elmassian (Jan 3, 2008)

Hah!

Let me give you some wisdom, although I am sure you won't take it that way:
If you have to ask, you should not consider this car.

More polite and informative response:
The minimum radius is not "real", basically the minimum curve it will go around on a perfectly flat curve is NOT what will work consistently in a train outside.

Best educated and experienced advice, based in actual experience:
5' radius minimum.... you could modify the car and reliable operation on 4.5' radius.... the specification of 4' radius is crap...

Add more cars in the train, grades, etc. and the radius increases.

I've spent some hours with a dremel grinding more clearance for the wheels, I know about this.

Of course someone will come on the thread and swear on a stack of bibles that he can run 100 of them on tighter curves pulled by a tiny loco...






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## Trainguy McGee (Dec 18, 2020)

Thanks Greg. Most of my planned layout in the yard is R5. I do however have 1 corner that will be R3 (8' Diameter). Hopefully it will still work.


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## Greg Elmassian (Jan 3, 2008)

I would not get the car if that 8' diameter is on your main line... if you go ahead, then do the modifications I showed.

You will find out for yourself, the car will really drag on the train and probably derail all cars between it and the loco.

Greg


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## John 842 (Oct 1, 2015)

Another solution might be to use a DPU (Distributed Power Unit)


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## Greg Elmassian (Jan 3, 2008)

I'm curious, how would DPU help the minimum curvature requirement of the cars? Clearly it would not shorten the wheelbase. In fact a shorter piece of rolling stock coupled to it will cause even more problems. 

(hint: coupler overhang of coupled cars very different = derailment)


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## John 842 (Oct 1, 2015)

The introduction of a DPU in the center of the train would reduce the problem of 'bowstringing' by splitting the length of the theoretical bowspring into two half length bowsprings with consequent lessening of the angle between the bowspring and the axis of the unpowered cars.

The smaller this angle is, the less is the sideways derailing force and when taken to the limit - where every car is replaced by a DPU - the angle becomes zero with consequent no sideways derailing force at all.

Therefore, with the introduction of a DPU (all other factors being equal) the benefit can be taken as - a longer train - a higher speed - *a reduced minimum curvature* - or a combination of all three.


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## Trainguy McGee (Dec 18, 2020)

Thanks all for the advice/tips. I have decided to scrap the 8' diamter corner and increase it to 10'. This should allow me to run the intermodal cars without issue (hopefully). Also, in a few months, I'll be filling in my Koi pond and relocating its position. This will allow me to increase the curve to R5 (16' diameter). Bigger is better.


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## John 842 (Oct 1, 2015)

Absolutely 'Bigger is better' - not only will it improve the aesthetics of your layout, but it will increase the ability to run a greater range of rolling stock that you, or your visitors, may want to run in the future ....

BTW - If you ever might want to run G1 in the future, 16' diameter is a little tight. I see many people regreting not 'future proofing' their tracks with 10ft. radius curves.


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## Trainguy McGee (Dec 18, 2020)

John - I'd really like to run the 20' diameter curves. Unfortunately, it just wouldn't look right in my yard due to space constraints. I also have to bend around some trees, shrubs etc.. But yes, I completely agree that the 20's would be really, really nice to have; but for now, the 16's will have to do.

I'm only 1 week away from "finishing" the layout out back. Once I'm done, I'll post some pics. It's my first G scale venture so I'm pretty excited.


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## Greg Elmassian (Jan 3, 2008)

John 842 said:


> The introduction of a DPU in the center of the train would reduce the problem of 'bowstringing' by splitting the length of the theoretical bowspring into two half length bowsprings with consequent lessening of the angle between the bowspring and the axis of the unpowered cars.
> 
> The smaller this angle is, the less is the sideways derailing force and when taken to the limit - where every car is replaced by a DPU - the angle becomes zero with consequent no sideways derailing force at all.
> 
> Therefore, with the introduction of a DPU (all other factors being equal) the benefit can be taken as - a longer train - a higher speed - *a reduced minimum curvature* - or a combination of all three.


So, the term is "stringlining"...

DPU does indeed help stringlining (of course getting the power units all running the same speed is problematic)

This is because you are effectively pulling a shorter train, thus less force (as drag) force on the cars, which helps minimize derailments.

There is unfortunately no logic that I can see that explains why a car would be able to take a tighter radius by using DPU... the issue here is actually clearance underneath the car for the wheels as they turn... this has NOTHING to do with anything else, the car by itself has an issue.

Greg


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