# Simple formula for determining curve size?



## jerryemt2001 (Mar 27, 2013)

I am thinking of suspending a G scale track in my enclosed porch. I just want a simple oval track above the porch with most likely the track on some simple run of cut plywood attached to walls of enclosed porch. The largest engine I have requires a minimum of R2 curve but everything I've read thus far says the bigger the curve the better. I am reluctant to sink $ into buying curved track that forms, say, an 8' diameter circle only to find that the diameter is so big I will not have much in straight runs. My porch is 11.5' x 15'. So here is my question. Is there a simple math formula that I use to determine the largest curve for the porch?


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## Totalwrecker (Feb 26, 2009)

Manufacturers use Minimum to sell more units, not because they look good doing so. 
Track is measured center to center so depnding on your equipment you'll need 3-5" on each side. Most track is based on an millimeter equivilant, not exact feet. 
I'd suggest 8' diameter which will leave some tangents, but not much. About 3' on ends and 7' on the sides. 

Mostly it depends on what you run and the clearances needed. 

I'm on the ground and looking down I see the tightness of the curves as my trains traverse them. I run smaller 1 :24 models and 10'D is now my smallest diameter, by choice. 

John


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## Garratt (Sep 15, 2012)

Just add the true radius of the track (centerline) plus the clearance required (from the centerline) in each corner. Then you can work out how long the straights are in between. 
Or, add the true diameter of the track (centerline) and the total clearance for each side of the room. The remainder will be the straight.

The clearance is more critical on the inside of curves because of long cars unless there is plenty of overhang from the wheels on the ends. Depending on the models you are running. You may not need as much clearance on the outside of curves which can make the right of way excessively wider than needed considering it is mounted on a wall. Do some tests with what will run up there and maybe allow a bit more just in case. 

Andrew.


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## BigRedOne (Dec 13, 2012)

In general, I would use the manufacturer's parallel track spacing as the "right of way" width for a single track. For example, the distance between R1 and R2 (in LGB) is about 7 inches, and I assume that LGB makes equipment such that parallel track on curves can be occupied simultaneously (plus usually more clearance for catenary masts, etc.) 

Therefore I add 3.5" from the centerline of the track to the closest permissible obstruction. So, you have 10.8' of theoretical maximum diameter (11.5' - 2 x 3.5") 

I like the appearance of larger curves, and even my smallish equipment runs better on R3 than R2. R3 is about 8'. That said, larger curves will also protrude further, so you have to decide if that's worth the improved running.


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## Greg Elmassian (Jan 3, 2008)

7 inches is not enough for 1:20.3 on those curves, or long locos or cars in 1:29. 

I think it would help to hear from the OP what locos and cars he intends to run, if the goal is to make the curves as tight as possible. 

Greg


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## chuck n (Jan 2, 2008)

The minimum curve recommended by a manufacturer is the minimum that the engine will go around with out derailing. It says nothing about the added wear and tear caused the the friction of forcing the engine through the curve. All LGB engines are designed to go through R1 curves, some like the Stanz (0-4-0) don't have any problems, but the mogul (2-6-0) will go through, but are not happy campers. They will slow down upon entering the curve and speed up upon leaving the curve. In that case the gears in that engine will wear out relatively quickly. Tight curves will also lead to loss of rail head on the inside of the outside rail on the curves, not to mention occasional squeaking. 

I agree with Greg. For us to really help you what kind of rolling stock (engines and cars are you planning to use? Another question, are you planning to run it all the time (every day for several hours a day) or occasionally (one or two times a week for an hour or so)?

LGB R3 or Aristo 10' diameter will increase the life of your engines, unless you are planning on running only short 2 axle cars and engines.

Chuck


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## jerryemt2001 (Mar 27, 2013)

Thanks so much for all your kind advice. I know for sure I will be running trolleys (Aristocraft). I think they are 19". I read on hear that many run them on 4'-5' diameter with no issues and they look good doing so. I am willing to operate only those size cars and save my 28" engine (the one that requires a min of R2) for display or maybe an outside track someday.


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## jerryemt2001 (Mar 27, 2013)

I forgot to add it will be run for occasional use...perhaps 20 mins a day at most.


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## Greg Elmassian (Jan 3, 2008)

The Aristo PCC car (I assume you are meaning this one) will run on quite sharp curves, sharper than 4'... so your 28" engine (what is it?) seems to be the limiting case. 

If you are ok with limiting yourself to small locos, you should be fine on the 4' stuff, but my experience says that people almost always regret going to small. 

That said, there would be a big difference int the "inside corner" overhang between an 8' diameter curve and a 4' one. You just need to be sure you leave enough clearance to the walls so the locos don't hit it. 

There's no formula, you put the locos on the track and measure how much overhang there is. 

Greg


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## Garratt (Sep 15, 2012)

I think Greg and Chuck's points are spot on. It is a very specific situation. The wider the better rule does not necessarily apply as a train around a square room's walls soon becomes just a boring circle not hugging the walls. What you will run and how frequently is important because if you want a train running a lot of the time, it will soon wear on less than optimal circumferences. If infrequent or if just particular models are run infrequently it maybe more convenient as a 'home modification' to go with some model's more minimal recommendations. 
What and how often are key points. 

Andrew


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## jerryemt2001 (Mar 27, 2013)

The 28" engine is the MTH GG-1 I have. But right now I will keep that as a nice display in my train room. I plan to put sound boards and people in the trolleys as well. I realize a circle is boring but I have to work with the space and budget I have. Boring as a circle may be to you and me visitors, on the other hand, will still find it fascinating as it is not everyday someone has a suspended train track. I prefer larger diameter. If it doesnt fit the room then I will keep for a future outside track or sell it on ebay. It certainly wont be the worse thing that ever happens to me.


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## Garratt (Sep 15, 2012)

My point was that wide curves in a square room become a circle with no straights. You then miss out on seeing the train or trolley at different angles going around through the corners. Straight sections as well as curves are good for aesthetic reasons. 

Andrew


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## mbendebba (Jan 22, 2011)

Jerry: 

I think you should go with R2 which will give you a bit over 8-foot straight runs on the long sides and a bit over 4-foot straight runs on the short sides . And, based on what you have already said, It will look fine. 

Mohammed 
http://www.allaboutLGB.com


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## jerryemt2001 (Mar 27, 2013)

I agree Garrett. My purpose in asking was how much curve can I get in that room that will allow me to keep the longest straight track. It's a balancing act. I don't want a circle which is what too wide a diameter will give me. R2 might be fine for my purposes.


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## Garratt (Sep 15, 2012)

Jerry, 

Yes, I thought perhaps you misunderstood what I meant about going around in a boring circle. I meant a geometric 'circle'. We are thinking the same. An R2 would work well. With R1 the track will be about 13" from the corner, R2 will be 15" and R3 will be about 22". Sounds like a plan!










Andrew


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