# Curve Radius VS Number of axles



## Aminnich (Nov 17, 2014)

Hey guys!!

Today I went to a train store on the way home from Washington DC. They were going out of business!! So i bought a whole bunch of stuff, including some engines. I got 4 axle engines, because thats what I have right now and i didn't know if the 6 axle engines would work on my layout. 

I have 18 inch radius curves, I did a quick search while in the store and found that a 6 axle engines could go on 18 inch curves, but very slowly. Is this true????

Also while I have you, what about 4 axle rolling stock that is long?? (Like long lumber cars or auto racks) I keep hearing you cant use certain things on 18" or longer radii.


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## shaygetz (Sep 23, 2007)

I run 4 axle Athearns on 14" curves with no trouble. Rivarossi made their 20" long 4-8-8-4 Big Boys to run on 18" curves, which I've done many times, yet, I have a Shay less than 4" long that needs 18" curves...it all depends on how they were designed.


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## MtRR75 (Nov 27, 2013)

Aminnich said:


> Also while I have you, what about 4 axle rolling stock that is long?? (Like long lumber cars or auto racks) I keep hearing you cant use certain things on 18" or longer radii.


The problem with long rolling stock is the with how couplers behave on tight curves. Long cars (like 70' and longer) will only run on 18" radii curves if the couplers are mounted on the trucks -- so that the coupler can swing far enough left and right to stay attached to the next car and keep the wheels on the track at the same time. If you have body-mounted couplers on these long cars, the coupler will end up so far from the center of the curved track that it can pull the car (or the one that it is attached to) off of the track.

Long cars on tight curves do not look very prototypical, but that is a matter of personal preference. Some of us tolerate it in order to be able to run the trains that we want to run on the layout that we happen to have.


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## Aminnich (Nov 17, 2014)

MtRR75 said:


> The problem with long rolling stock is the with how couplers behave on tight curves. Long cars (like 70' and longer) will only run on 18" radii curves if the couplers are mounted on the trucks -- so that the coupler can swing far enough left and right to stay attached to the next car and keep the wheels on the track at the same time. If you have body-mounted couplers on these long cars, the coupler will end up so far from the center of the curved track that it can pull the car (or the one that it is attached to) off of the track.


That makes a lot of sense, thanks. 

I also looked at the engine I had from before and it is a 6 axle engine. I also have an engine that came with the bachmann EZ command, which i havent opened yet. So now i have 3 4 axle engines and 1 6 axle engine.


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## MtRR75 (Nov 27, 2013)

Aminnich said:


> I have 18 inch radius curves, I did a quick search while in the store and found that a 6 axle engines could go on 18 inch curves, but very slowly. Is this true???


Shaygetz is correct in that it depends on the locomotive. Most manufacturers try to design their locos to run on 18" radii curves, because they know that there are lots of layouts built with these curves, and they want to sell as many locos as they can.

There are a couple of hints as to how well steam locos might run on 18" curves that you can assess when picking through used locos. Most 6-drive-wheel locos will run on 18" radii curves. The problems start when you go to 8 drive wheels (4 axils). Turn the loco over and look for two things. (1) Is there some lateral play in the drive wheels. This is one way that 8-wheel locos can stay on tight curves. (2) Do some of the axils (usually the middle ones) have no wheel flanges on them. This is another way that long locos can stay on tight curves. The unflanaged wheels are usually wider and will slide across the top of the track and not bind to it.

However, unflanged wheels can cause problems at turnouts. They are wide enough that they may make momentary contact with BOTH electrical sides at the frog of the turnout. This can lead to a momentary jerk in the running. If the train is going slowly it may short out and stop. Also, these momentary shorts can cause problems with DCC systems. How serious this problem is depends on the loco and on the type of turnout you have. So everybody's experience will be different.


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## Aminnich (Nov 17, 2014)

I wont have this problem, Im only running diesel engines. They fit into my layout better


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## CTValleyRR (Jul 26, 2014)

The only way to know for sure is to test them. Pulling cars and on grades, especially.

Often , the problem isn't so much operating them, but how unrealistic they look going around them, or whether you can couple or uncouple them in a curve.


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## CTValleyRR (Jul 26, 2014)

Also, you gave me a scare for a minute, there. MB Klein, aka modeltrainstuff.com, is conceivably on your way home from DC. I'd be really bummed if they went under, but they don't appear to be.


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## Aminnich (Nov 17, 2014)

Thanks guys!! 

I just went to Home Depot for some more foam and building materials. HOPEFULLY, the layout starts to take shape tomorrow!


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## grashley (Aug 27, 2015)

CTValleyRR said:


> The only way to know for sure is to test them. Pulling cars and on grades, especially.
> 
> Often , the problem isn't so much operating them, but how unrealistic they look going around them, or whether you can couple or uncouple them in a curve.


I AGREE. 

I have N scale with a double oval. All my locos and cars do well on the larger (11" R) oval. My 6 axle diesel refuses to run on the smaller (9.5" R) oval. It derails on the curves. Some of the longer cars also will not run on the smaller oval. They either derail or uncouple. Test all rolling stock and find out!!


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