Minimum radius for Kato SD-70MAC

Discussion in 'N Scale' started by Matt Burris, Nov 28, 2007.

  1. Matt Burris

    Matt Burris TrainBoard Member

    I have been looking at the Kato SD-70MAC and was wondering what the minimum radius it would run well on. Have not decided on N scale yet, but looking at my options. I would be running Kato Unitrack and #6 power routing turnouts. Most likely 13-3/4 radius curves, but possibility of a 12-3/8 inner loop.

  2. sandro schaer

    sandro schaer TrainBoard Member

    i assume this will work for the loco. but because of the overhang you might encounter lots of derailments of the first car. i'm sure others with more experience with sd70 and tight curves will chime in.
  3. jlbos83

    jlbos83 TrainBoard Member

    The AC4400 comes with a set of long shank couplers you can install. I would expect this to, as well. I'll think it will make it, might not look great. You might end up restricting it to the outer loop.

  4. BarstowRick

    BarstowRick TrainBoard Member TrainBoard Supporter

    You can choose to make the same mistake many of us have made with tight, unsightly radius curves.

    Instead of looking at a minimum radius that a piece of equipment will negotiate, try looking at your layout with an eye on the widest curves. Most N scale is made to negotiate a 11" radius curves...but...they don't like it or look pretty and frequently derail. Adding longer couplers will work against you as they don't look realistic. In time you will get sick and tired of those tight radius curves and you'll find yourself wishing you had listened to well founded advice. The same would apply to HO. It's all about...what do you want? Toy like...9 or 11 inch radius curves or a Model Railroad with realistic rail curves.

    Hey, are you preparing some sort of college psychology paper and you're polling us for ideas. Perhaps, "Why big boys still play with toy trains". Or is this a study in economics? I know you are writing an article for one of the Model Railroad wig wags (magazines)...right? Grin! This just flashed through my suspicious brain.

    Keeping bringing your questions here.
  5. David R

    David R TrainBoard Member

    While we're on this topic, I'm toying with layout design with the atlas RTS software, using C55 track, and I've been trying to aim for a minimum of 16.25" radius fixed curves (or the flexi-track equivalent) for the main line, and maybe a bit tighter on the switches. I'd like to run some decent length trains with up to 2-4 engine lash-ups of 6-axle diesels. Will this work (well more than just work, I want the trains to look semi-realistic on the curves) or should I try to make them bigger?
  6. jpohl

    jpohl New Member

    Been a while since I said anything on this board… I took a small hiatus from N Scale for about a year and a half after we moved in to a new home, and focused on a larger O Scale Layout (which is in a stop work status do to the fact we want to move to a more convenient location for my wife).

    So now, I am planning on my next larger layout to be in N, with a around the ceiling O layout. When the new permanent layout is built my minimum will be 15” (using Unitrack that I am starting to acquire for down the road).

    Well, this year my wife said she does not want the train around the tree (always done with the O equipment), but she still wanted a Christmas Train display… Well my wheels started turning on places to put it! O would be too large for anywhere except under the tree, so I saw this as the perfect opportunity to do something in N. I immediately spotted out the built in cabinets in our family room that would work, and my wife agreed.

    On to the question… Due to space limitations, I could only make the layout 28” wide, limiting the max curve for Unitrack to the 12 3/8”. I wanted a double main, so the inner would have to be 11”. I have #6’s off of the main, and 1 #4 in one of the spurs, plus the crossover connecting the two mains together. I have a shot of the layout under construction attached.


    In my inventory are some Kato SD80’s, Kato SD70’s, and Atlas SD50’s that all run on the 11” fine. I would prefer them to be on a wider radius for esthetics, but I just can’t right now. I have been running them on this layout now for a few weeks once the track was down, and have not had one derailment. This is also running them with some Atlas Auto Racks, Kato Double Stacks, etc. On Unitrack, you should be fine with those curves.

    Hope this helps…

    Last edited by a moderator: Nov 28, 2007
  7. jlbos83

    jlbos83 TrainBoard Member

    I think you'll be fine. The best thing you can do is use easements going into the curves. You are better off to use slightly sharper curves with easments than the wideset curve that will fit.

  8. BarstowRick

    BarstowRick TrainBoard Member TrainBoard Supporter

    Radius Curves

    Hi David,

    The 16.25" radius curve will work nicely. I use a 18" radius minimum, on the main line and a 15' radius minimum, in my yards.

    I was just looking at Jeff's 28" wide layout and I feel for anyone who has those kind of restraints. I've built layouts in both HO and N scale on narrow doors and the likes. It just isn't practicle to expect large six axle diesels to ply the rails or full length passenger cars, and look realistic. The one trick I used, was to cover the curves Ie., A tunnel through the mountain. It worked until I wanted to see my trains arcing around the curve.

    The thing is you can have all kinds of fun with narrow layouts and you can run 4 axle diesels with short 40 foot cars and look realistic. If I may point to the Los Angeles, PE railroads of yesterday as examples of what you can do. Any take off from that perspective would be appropriate.

    There are ways to widen the curves even on Jeff's layout and judging from the room around the layout he could probably do that.

    It's all about fun and you don't want to miss out just because you don't have the room.

    Last edited by a moderator: Nov 28, 2007
  9. HemiAdda2d

    HemiAdda2d Staff Staff Member TrainBoard Supporter

    I'll echo the pervious comments about widest curves possible. 15" is my min, and there's only about 3 feet of that on my helix. The rest is 16" or better, and min of 18" on the mainline. Not all of us have that sort of space, but the wider the curves, the better! I had a 28" rad. curve on a layout 7 years ago, it was so graceful and worked beautifully.;)
  10. atsf_arizona

    atsf_arizona TrainBoard Member TrainBoard Supporter

    I'll second jlbos83's recommendation - the major problem with big locos is the overhanging couplers knocking the trailing cars off the rails - easements can often largely mitigate that issue.

    Easements look a whole heck of a lot better too.

    Additional point #1: my Kato C44-9W's with stock Kato couplers (which are stiffer in side to side swing) can knock certain cars off the rails entering my non-easemented 12.75" radius curve that is hidden inside a tunnel. Replacing the stock short shank Kato coupler with Micro-Trains short shank 2004s can solve that in some cases, as long as the following car also has MTs - because the MT's are much free-er in side-to-side swing.
  11. jpohl

    jpohl New Member

    Unfortunately, I only have the space that you see of the actual layout. In the background you will notice a built in cabinet with A/V equipment and a computer monitor. This layout slides onto an identical shelf on the other side of the fireplace. At 28” wide, it overhangs the countertop by 3” (one of those where I asked for my wife’s forgiveness after the fact, she was not crazy about the overhang), I am not sure how I could have squeezed larger curves than I did without taking the track to the outer edge of the layout, as is now the fron track is only about 1.5” from the edge of death for a derailment.

    See Plan:


    I hid one side of the curves in an accessible tunnel. The other side will have some factories, trees, and other elements to help distract from the curves. I like the Uitrack, and intend on using that for a more permanent layout once we are in a new house. I do like six axle diesels, and would rather the larger curves ( I have a bunch already for Unitrack, for the future), but for now this will have to do, and I will have to live with the overhang issues. Fortunately, I have not had any derails, even with the SD80 on 11” radius.

  12. Matt Burris

    Matt Burris TrainBoard Member

    Hi rick, you kinda lost me on this part of your post? Are you trying to say I ask too many questions? I know I do, LOL :) I was asking a buddy of mine who also happens to be a trainboard member this question and he wasn't sure, so he recommended I ask here. From what I gathered from the responces, I probably won't mess with the 6 axle engine unless I decide to go with 15" minimum. Being new to the hobby I haven't even asked a fraction of the questions that I really have. I'm half ready to take up something less challenging, like rocket science LOL :)

    Thanks to all who responded.
  13. CofGa_Fan

    CofGa_Fan TrainBoard Member

    I have a Kato SD70M Norfolk Southern and I also have a 2'3" X 5'3" coffee table layout with 11" radius curves and Atlas Custom turnout (not for this big gun, it's my CofG layout) and have run the loco on it and through the turnout. No derailments of either the loco of the any of the cars in tow. As previously stated, it doesn't look great, but it WILL negotiate it.
    Hope this helps.
  14. BarstowRick

    BarstowRick TrainBoard Member TrainBoard Supporter

    Radius Curves...what to do?

    LOL Speedy,

    You may be asking a lot of questions and have a whole lot more to ask. We want you to bring your questions here. You won't get a one sided opinion from this group of rail junkies.

    I was thinking (and that always gets me in trouble) You're asking questions as though you know the subject well. I was thinking this guy is putting together either an article for one of our Model wig wags or you are doing a college paper. It don't matter. It just struck me as a possibility. May I suggest you have material here for either one. Grin!

    Rocket Science? Actually in many ways that would be easier. I ran with a group of guys who spent Sundays down on the desert shooting off their mouths...ahhh....I mean rockets.

    Keep bringing your questions here. We will do our best to answer them and then duck and run for cover.

    Have fun! LOL
    Last edited by a moderator: Nov 29, 2007
  15. BarstowRick

    BarstowRick TrainBoard Member TrainBoard Supporter

    Those darn curves!

    Jeff and all tuned in,

    I like your layout and see that you can have hours of fun with it. You are right and I stand corrected...you really don't have any more room.

    Now is the time to build what you can, preparing for tomorrow. The time will come when you will have a room dedicated to your layout. Look out! You will widen the curves and add to the layout. Eventually, you will have what you want or at least come close. Most of us have managed to do that. But, don't wait until your health fails...that will slow you down.

    Have fun!
  16. Matt Burris

    Matt Burris TrainBoard Member

    "I was thinking (and that always gets me in trouble) You're asking questions as though you know the subject well."

    I can honestly say I know nothing about trains, or college either for that matter. Lucky I graduated high school. :)

    I'm learning a little everyday. I owe most of what I do know about trains to this board and especially a couple of members who shall remain nameless who have helped me behind the scenes so to speak.

    I've actually purchased a little bit of N scale stuff and a little bit of HO because I simply could not make up my mind. I'm feeling more and more like I may do a little of both. For me and a few special situations I am in different than most people, both scales have some pluses and minuses for me personally.

    I can tell you this.... I enjoy trains a great deal, and more and more by the day. I think somewhere along the line, the 19 years I spent in R/C is going to benefit me in one way or the other, even if it is just soldering ability and stuff like that. For the most part this is all new and fresh, and exciting to me and I learn something new every day. Thanks to all for your help! :)
  17. BarstowRick

    BarstowRick TrainBoard Member TrainBoard Supporter

    Speedythecat and all tuned in,

    I would encourage you to work with both N scale and HO. I don't know of a rule that limits you to just one scale...unless it's economics. My home layout is N scale and that gives me hours of satisfaction with a layout almost as complicated as a club layout. I also belong to a club of great guys who operate their HO equipment on one of the San Diego Railroad Museums layouts. We have hours of fun and it gives us time to compare notes.

    R/C I suspect, it won't be long before you see R/C moving into the model railroad world. We may be asking you questions.

    So, we aren't writing a paper for publication? Well that's disappointing...grin! Actually no big deal.

    It sounds like you have a number of good friends to help you and a great resource to get others opinions or how to information right here on TB.

    Edumacation and degrees...doesn't matter when it comes to model railroading. It's all about fun and enjoying your hobby. Your hobby needs to be an escape from the everyday world a place where you are in charge and you make the rules. "First and foremost have fun", Jim 157 a TB participant.

    Have fun!~ YES!!
  18. Matt Burris

    Matt Burris TrainBoard Member

    Thanks for the kind words Rick, I am very fortunate to have found this place and the 2 or 3 "train buddies" I have made through it. I haven't made any train enemies yet, but I suspect with each question one grows closer, LOL :)

    I'm an inquisitive little rascal when I'm interested in something. Despite the fact that the search function works well, and I'm well aware how to use it, I still end up with questions. this is a pretty deep hobby.
  19. jlbos83

    jlbos83 TrainBoard Member

    There's some truth in that. I don't know of very many hobbies that combine as many and as varied disciplines as model railroading. All the way from art to electronics, and pretty much everything in between. No wonder it is such a challenge!


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