# New Member - Track Diameter Question



## southside78 (Jan 30, 2012)

I'm a new member of the forum here from Chicago and have recently become interested in building an indoor layout. This website has been a great resource of information and I’ve spent some time reading through prior topics, but still have a couple questions. 

Regarding track diameter, I realize that using "the biggest your space allows" is the best way to go from both an operating and aesthetic perspective. However, the space I have will accommodate 10 ft diameter track, but I'd prefer the layout options available if I were to use 8 ft diameter track. My question is what is the maximum length modern engine and rolling stock that I can use on 8 ft diameter curves? I am not concerned about overhang or how unrealistic they would look on the 8ft diameter, but rather what is the maximum length threshold that can run on 8ft diameter turns without derailing? The USA Trains website says that their 30.5 inch long SD70 MAC will run on 8ft, but what about something as long as their 36.75 inch Bi-level Auto Carrier or their 33 inch passenger cars? 

Also, how long of a straight track is needed in between the two curves of an S-curve given a certain car length and does it matter if the two curves are 8ft or 10ft in diameter? For example, if I have a 28.5 inch intermodal container car, would 2 feet of straight track be enough in the S-curve to prevent derailments and is the answer the same for 8ft or 10ft diameter curves on either side?

Thanks everyone
Jason


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## chuck n (Jan 2, 2008)

I'll answer you last and easiest question first. I have always been told the the length of straight between two curves in an "S" curve should be equal to the length of your longest car or engine. That is the longest piece of rolling stock.

There are many ideas and thoughts on minimum radius. If a manufacturer says that his engine will go through a minimum radius of 4' it will. Whether or not it will pull a car through with out a problem is something else. That all depends upon the couplers and the car. 

There is more than just cosmetics when using the minimum radius. The engine is going to work harder pulling itself and a train through tight curves. This will lead to wear and tare on the wheels, motor, gears and track. Ask anyone who has run their new starter set around a Christmas tree on a light colored carpet. Black dust comes down from the track. That is brass from the track that is being worn away. The wider the radius the longer everything will last.


We don't just recommend using the widest radium you can because it looks good. There are other valid reasons as well.

All of the curves on my layout are Aristo 5' wide radius. My switches are LGB (18000 series) which are about 8' radius.

Here are some pictures of my USAt SD70 and some USAt streamliners entering and leaving the curves.

Over head of SD70, note the centerline of the coupler is outside the outer rail. 











SD70 entering a curve pulling a 40' box car. The coupler on the engine is swung about as far to the top of the picture as it can go. The coupler on the box car is also swung way out.














Two USAt streamliners entering curve.










USAt streamliner in curve showing underhang (?).




















SD70 leaving curve, note the centerline of the couplers is outside the outside rail. Not a lot of room for error. 


















I had a lot to trouble getting the couplers correct so that I could pull a box car (40') through these curves with a USAt GG1. I tried truck mounted and body mounted Kadees. No luck, the box car always came of the track. The only way to solve the problem was to use an extra long shank USAt coupler and not tighten it up completely, so that there was some additional swing.



If you really want to use 4' radius, try to find a layout with 4' curves and run the engine and cars you want to use on it. That is the only way to know for sure. 


Chuck


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## blueregal (Jan 3, 2008)

Don't go with anything less than 10ft diameter 5ft radius, you will thank yourself later when you want to run some bigger steam engines and or sd70 macs usa, I had a retailer tell me this in the 90's when I got into g-scale, and have never looked back and wished I would have went 16 or 20 but then I'm outdoors if you have limited space I would at least not go any less than the 10ft. if possible. Regal


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## livesteam53 (Jan 4, 2008)

You are correct 10' is the smallest I would ever go. I have had 8' once and it is just to tight. Go as large as you can you'll never be sorry.


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## southside78 (Jan 30, 2012)

Thank you for the replies. Chuck, I appreciate the pictures you uploaded - they were very helpful with your comments. My gut was to go with the 5' radius, but it's driven home by these responses. 

Jason


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## Greg Elmassian (Jan 3, 2008)

Actually, the absolute minimum is a straight the length of your longest car.... but that barely helps. you really need double the length of your longest car. Lay out an "S" curve with different lengths of straights and run the cars through and watch your couplers, especially body mounted ones. 

I don't want to and won't argue this, try it yourself and you will see. 

Greg


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## chuck n (Jan 2, 2008)

There is a difference between body mounted couplers and truck mounted couplers. The truck mounted couplers will stay centered on the track, while the body mounts will swing further out. My guess, and it is only a guess is that hook and loop is the most forgiving type of coupler when you are nearing the minimum permissible radius.

Chuck 

Edit: I'm talking about truck mounted hook and loops. Body mounted H&L, as in the Bachmann Thomas series, pose special problems in 2' radius curves.


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## avlisk (Apr 27, 2012)

Chuck N, I'm at the same place as the original poster of the original question. Your description, information, and pictures that are worth 1,000 words are greatly appreciated from this newbie. You've done good. Thanks. I'm going to order the 10 footers. 
Ken Silva 
Phoenix, AZ


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## Randy Stone (Jan 2, 2008)

Well I'm going to buck the trend here and say 8 foot is doable if that is what you need to use. 
I have run my Dash 9 with Kaydee couplers around my kidney shaped layout that has 8 foot diameter curves. 
I've used the Dash 9 to pull my USAT 33 inch long passenger cars. 
I've pulled over 40 coal cars with the Dash 9. 
While doing this, the caboose was only 6 foot infront of the Dash 9. 
I've even backed the 4 passenger cars into a siding. 

Yes the Dash 9 needed work so the couplers would swing far enough to allow it to pull cars around the 8 foot diameter curves. 

Is 8 foot has good as 10 foot? No but then 10 foot diameter isn't as good as 12. 
Can you run a Mallet on 8 foot? Probably not. But most other steam engines will run on 8 foot dia 
Will running modern passenger cars on 8 foot look relistic? No, but it won't on 10 foot either. 

I don't have room to run 10 foot curve even if someone gave me a box of it. So I make do with what I can use. 

If using 10 foot curves keeps you from running the track layout you want, then are you really going to be happy? 

http://www.youtube.com/watch?v=A1HNrB5cPqo 

Here is a video of my Dash 9 pulling 4 USAT Passenger cars around my kidney shaped layout using 8 foot diameter curve track. 

http://s541.photobucket.com/albums/...I_2600.mp4


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## avlisk (Apr 27, 2012)

Good to know, rivette. I have room for 10, so that's what I'll get. While we are on the topic of track, and because rail joiners doesn't seem to me to deserve its own thread, I ask: does any of the 45mm track come with rail joiners or must they be purchased separately? 
Ken Silva


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## Randy Stone (Jan 2, 2008)

Hi Ken 

The Aristo Craft that I have bought new comes with rail joiners and the little screws to secure them all together. 

Can't say about the other brands.


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