Curve radius

railman2009 Mar 1, 2009

  1. railman2009

    railman2009 TrainBoard Member

    Hypotetically speaking:
    If I want to run a 30 to 40 car train of assorted freight cars with 2 or more engines, and some of those cars are 60 footer's, what would be the absolute minimum radius I could use without the cars binding, falling off the track or looking totally unrealistic going around these curves. This could be on a flat surface or on a standard 2% grade.
  2. BarstowRick

    BarstowRick TrainBoard Supporter

    I like the appearance of my trains on 16.5" radius. Any tighter and the cars look unrealistic.

    You can use 11" radius as a minimum and the cars won't stringline or pull off the tracks. However, that is tight and you loose some of the aesthetic value.

    OOP's This a Z scale discussion and not a N Scale one. Cut those values in half and they might work. Best you let your fellow z scale brothers redirect you. I would think the wider the better.

    Have fun!
    Last edited by a moderator: Mar 12, 2009
  3. JoeS

    JoeS TrainBoard Member

    195mm in tight. Not bad for 4 axel Deisel or small steam and 40 foot cars. I'd go with 220 if I wanted to run larger loco's and longer cars. My passenger cars work fine with 195, but do overlap a tad. I have never experienced any binding with 195.
  4. railman2009

    railman2009 TrainBoard Member


    I'm not into the metric measurements. Can you give that to me in inches? In the overlap of longer cars, on your system, can you look down from above and believe it as real? I guess what I'm asking is does the overhang detract from the appearance when looking from top and sides?
  5. JoeS

    JoeS TrainBoard Member

    Off the top of my head not sure what it is in inches. I think the best advice I can give you is to buy an oval of micro-track, about 17-19 bucks. Then buy a package of 220mm micro-track around 17 or so as well, and see for yourself what is accaptable as far as looks. (I keep an oval and track with a Zthek battery controller for testing so the track you buy shouldn't go to waste.) All I can tell you is if you have been hanging around here lately there is all sorts of opinions as to what looks right/better.

    You need to decide for yourself what is acceptable. Everybody has that one thing that gets to them. For me, I hate the open ends on MT Deisels. I have fabricated my own plows but they stink. :D I am waiting for MT to come out with the plows so I can make them look "right" to me. others do not like the MT passenger cars. I think they look great! Some people don't like the pulling power of the AZL steam. (you get the gist) :D My point is everybody has their thing. What looks right to you looks right. I'll run my passenger cars with overhang. Does not bother me. Yet I hate marklin steam loco shells cause they look toylike. To each their own.
  6. bambuko

    bambuko TrainBoard Member

    1" = 25.4mm
    divide 195mm by 25.4 and you have the answer in inches!
    Anyway, whatever measuring system you use - multiply the length of longest car you are going to run x5 to get the desired min radius. Anything below that is going to look ridiculous.

    never, unless you suspend your critical faculties :tb-biggrin:

    Yes, but as they say YMMV and it all depends on you :tb-biggrin:
  7. Glenn Woodle

    Glenn Woodle TrainBoard Member

    The 195mm & 220mm are the curves in the MTL set. I forget if they are about 7-9".

    If you get the MTL Expansion Set, you get a circle of 195mm + 1/2 circle of 220mm, along with a LH & RH set of turnouts & 2 110mm straight track. This would be a great way to start. AFAIK the 195mm is fine for most trains. The new MTL passenger cars may have been designed with the 195mm in mind.

    Marklin's tight curve is about 5". Those aren't used for American practice. They could be used if you have Marklin's 0-6-0 switcher with the 2 axle wagons.
  8. HOexplorer

    HOexplorer TrainBoard Supporter

    My new Northern Division will only use Micro Track in the 490mm size. I wouldn't run any 60foot or over car on anything less. Cheers, Jim CCRR
  9. daniele

    daniele TrainBoard Member

    I can just forward what jim wrote:

    I do only use radii that large! on my layout, the minimal radius is 18" (465mm), what is also the minimal radius of the 1:1 scale locos! No problem on 2.5% grades with up to 70 cars!

    Don't go under 13" or so; I had a layout with a 2.5% grade and a 8" radius: well, I was so badly disappointed, that I immediately sent it to the scrapers torch! Not even a train with 15 cars could make a run without any trouble...


  10. bambuko

    bambuko TrainBoard Member

    and that's in keeping with my advice :)
    60 foot = 60 x 12 = 720 inches x 25.4 = 18,288 mm
    in Z that equals to 18,288 : 220 = 83 mm

    so you are operating on 490 : 83 = 5.9 multiples of car length

    If appearance is your goal, this is the way to go !

    ps and before somebody gets their nickers in the twist - yes, I am sure, they "can" also be run on 195 mm radius - whatever rocks your boat ;-)
  11. railman2009

    railman2009 TrainBoard Member

    Turning Radius

    Thanks everyone: All of this has been very helpful. I guess it really does come down to personal preferance. I will keep this in mind. I'm running 10 radius now, on a 2.2% grade hauling only 5 cars with one GP9. I have two situations where this is in play and my tables are 2 ft. wide by 4 foot long. Since these curves are going to be hidden, it doesn't matter so much so long as the longer cars can make it around and up the grade. All other curves will be long and gentle.
  12. BNSF Dash 9

    BNSF Dash 9 TrainBoard Member

    I can throw 2 cents in. I'm building a very small layout and I thought I could get away with 145mm curves in the tunnels. I'm finding out that SD70M and Dash 9s won't make that turn. I'm also having troubles with bigger cars like double stacks. 40' & 50' cars do just fine. I have not tried my 4-8-4. Keep in mine my track is just pinned down at the moment, I'm still working out the bugs. I have 195mm and 220mm curves that look 100,000 times better. If I had the room I would go even bigger as 220mm still doesn't look right to me.

    I have not tried to pull strings of cars yet, but the better the track is laid the more cars you can pull on a grade. I learned this in HO scale.

    Also a tip I also learned in HO scale. Add a strip of .010 styrene under the outside half of ties to elevate the outside rail. I even go to .020 strip in the middle to super elevate the sharper curves. This will help alot! I'm still playing around with the idea in Z to get an exact formula, but .010 and .020 are working for now. I think I'm going to add a touch of weight in each car you help prevent roll over, but that's only if I need to as nothing has been tipped yet.

    Last tip... don't forget the run the heaviest cars up front toward the loco and put the lightest cars on the rear of the train. This also helps to prevent rollover and as some people would swear on... pull longer trains.

    Good luck! :tb-biggrin::thumbs_up:
  13. ddechamp71

    ddechamp71 TrainBoard Member

    Some data that was initially coming from Joe Fugace in Model Railroad Hobbist Magazine, whose purpose is establishing a "ratio" between curve radius and rolling stock's length. The formula is Curve Radius/Rolling stock's Length. This works for every scale.

    Ratio description:

    -2.0: the equipment is able to run but some problems are likely to occur
    -2.5: almost all equipment is able to run flawlessly
    -3.0: all equipment runs flawlessly with adequate coupler performance
    -3.5: the equipment has a good look from inside the curve (should be OK for a walk-in layout)
    -4.0: the equipment has a good look from outside the curve
    -5.0: the equipment can be coupled or uncoupled on the curve with a perfectly scaled coupler set on the car's or locomotive's chassis.

    Before even seeing this formula above, as one of my goals is my equipment having a good look from outside the curves, I came to the conclusion that on my in-progress layout whose curves are a minimum of 35 cm (14") radius, I can use equipment no more than 60'. Indeed my MU'ed Dash9s and SD70s look odd, and I prefer using my GP35s and other 4 axle engines to this prospect (and it's not a problem as this layout will show what should be a branchline in the prototype, thus mainly running 4-axle locos). And for the same reasons I ban using my double-stack cars as well as the autoracks I will order when they're available.

    My 6-axle locos and the cars described above will be at home in many years, when my main project (50 cm / 20" minimum curve radius) is a reality.

  14. East Coast Main Line

    East Coast Main Line New Member

    I look out the window at Britain's East Coast mainline (hence the screen name); looking at the TEA-Class 102 Tonne tank cars on the siding, painted on the side, it says "Minimum Curve Radius 70m"; this is for loose shunting (switching). Once coupled into a train, the minimum radius is 150 metres. Translated into English, that's (more or less) 12 1/2" for loose shunting, and 27" radius for a train.

    I think I'm going to need a bigger shelf than I thought...
  15. ddechamp71

    ddechamp71 TrainBoard Member

    I bet this 150-metre radius when coupled to a train is due to the european coupler style (ie buffers on car's side ends). On the opposite, according to the book below, an SD40-2 coupled with another is able to run on a R=262-foot (78.6 m) radius curve, and an SD40-2 coupled with a 50' boxcar on a R=359-foot (107.7 m) curve radius, thanks to their knuckle coupler.


    Attached Files:

  16. traintodd

    traintodd TrainBoard Member

    This has been on the other boards, but I'll give you my input. The largest cars I have, other than passenger cars, are 60 footers, and they run perfectly on 18" radius curves on 2% grades. Both Marklin and MTL passenger cars run fine on 18" radius, but look better on 21" and 24" radius curves.
  17. Z_thek

    Z_thek TrainBoard Member

    "Both Marklin and MTL passenger cars run fine on 18" radius"

    Of course they run (and look) fine. 18" radius is huge. Our group's (ZoCal) members fairly large end modules are 30" wide, the largest radiuses are between 13" - 14", still no problem with look and drag.

    Lajos :0)

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