A quick question. Does the number of wheels a Loco have on it determine what radius track it can manipulate?.. for example a Loco that has 3 sets of wheels on front and back, can it take a 15"radius curve or does it have to have all 18"radius. HO scale, by the way.? I want to know what loco to get but i may have 18"radius and 15"radius on the layout. I havent built it yet, just still planning. Any help would be great. thanks
HackSaw
The true question depends on a few factors…
If you are talking diesels, then more wheels (eg. a 6 axle diesel) will need larger turns than a 4 axle… This also depends somewhat on the distance between the trucks…
If you are talking about steam engines, it is MUCH more complicated. Really what determines the turning radius is the rigidity of the frame which depends upon number of driver wheels… (e.g. in a 4-6-2, the drivers are the middle 6, the 4 is the pilot and the last 2 are the cab trucks). This becommes more complicated when you think of articulated engines, e.g. a 4-6-6-4 where both the middle 6’s are drivers, BUT the frame is articulated (hinged) and this improves the turning radius… In effect, each section acts like a 4-6-0 rather than the huge 4-12-4!!! Much better (thanks to Mallet!).
I am sure the others here can definitely say this better than me, but I hope this gives you an idea…
Brian
I will be using diesel engines and hope they go around the 18" radius turns i am planning. I was laso told that I can straighten the turn a little by putting a smaller 18"raduis in there. I don’t have much room, but i was as many sidings as i can get and still use a big Union Pacific Engine that has the 12 wheels in all. I’m sorry if i’m not making any sense, just trying to explain as well as i can…lol
HackSaw
What you describe sounds like a 6 axle diesel, and 18" is the bare minimum for these engines, and 15" is probably out of the question. If you’re determined to have 15" curves, I would stick with smaller 4 axle units, and six coupled drive wheels if you run steam, e.g. 0-6-0’s, 2-6-0’s, etc.
If the 15" radii are confined to a yard or spur, a small switcher will have no problem with them, but it would prevent your larger power from entering those areas. I would recommend rethinking your track plan, since you’re just in the planning stage anyway. Much easier to revise it now and widen your curves at this point than when it’s a nuts-and-bolts reality.
Very good suggestion. I think i may just go with 18" to be safe and have smoother curves anyway. Luckely i havent bought a whol;e lot of track yet, so i can still change my mind again…lol… No matter how old you are, this stuff is still FUN!!..Thanks
How big is your layout going to be? If it’s a 4x8, you can fit 22" and 18" on it. I would still recommend using 4 axle diesels and the 6 driver steam arrangements that SteamFreak recommended.
18" radius and ‘safe’ should NOT be in the same sentence.
Go with 4 axel units and be ‘safe’.
David B
I’ve been wondering lately what radius I should use to prepare for future 6 axel EMD SD45’s. Would 20" be safe?
The bigger the better with 6 axles. My Dash 8 will run on 18’s but looks like crap. I wouldn’t go smaller than 22" if I were you.
I think the number of wheels per truck isn’t as important as the distance between trucks. A SD-9 might have no problems on curves that would stymie a psgr diesel or one of the newer 4400 HP frt diesels. Let’s also not forget that a single unit might be able to get around a curve that 2 units clpd together can’t due to excess overhang
You may run into another problem. If you’re wanting to run some very modern 6 axled diesels, like an AC4400 etc, you may be able to run the loco but with nothing coupled to it. The overhang on short curves will force the couplers to the outside of rail on the longer locos and may cause derailments, especially if you want to run longer, modern rolling stock. If you cannot go larger on the curves, then, as others have said, go with 4 axle locos. Put the 6 axle beasts on the shelf for now until you have more space. When I was a teenager, just had to have the big U-Boats (okay, big at that time!) but they didn’t run reliably on my small radius curves. So I opted for some GPs and F units until I had more space.
Rick
Yes, 18" radius is mininum for shorter 6 axle diesels such as EMD SD-7’s, 9’s, Alco RSD’s, etc. larger 6 axle diesels such as EMD SD-40’s, 70’s, 90’s, GE U28/30-C’s, or modern AC super power like Rick mentions should have 22" radius.
Like Loather said, they can run on it, but they REALLY do look like crap. There is also another side affect on a sharper curve. The locomotive will lift up a little. I’m not sure really how to explain it, but the locomoitve only has so much room for turning. Once you get pass that the trucks have to go farther which inturn “lifts” the loco a little off the track. This is why I can’t run my SD45 on one of my Sharpest curve very slow.
I’ve run Athearn SD40-2’s, SD45’s, F45’s and Bachmann Spectrum SD45’s on 18" curves. The SD40-2 and SD45 (in real life) shared the same frame (which is why the SD40-2’s had the “porches”). Anything longer than these on an 18" curve is probably not going to like it. Personally, I’d stick with older (and shorter) 6 axle power or 4 axle power for 18" curves. Using those longer engines, you’ll have to be mindful of the coupler swing especially with shorter cars, and they will overhang the track a good bit both in the middle, and on the ends.
WCfan, what brand of SD45 are you referring to and how sharp is the curve in question?
Brad
Well to put it in perspective, a real SD45 couldn’t go thru anything sharper than a 28 degree curve, which would be about 30" radius in HO scale - and it would be limited to 20 MPH speed doing that. So the bigger curve you can get, the closer to prototype you’re going to be.
It’s P2K, and it’s a 18" radius. It doesn’t lift up that much. Hardly noticable. But I have noticed in some places while going slow the first weel of the front truck pops out. But this is rare.
Why Torture your 6-axle diesels? I’d go with a larger radius and it won’t take that much extra space to get a 24-inch or bigger curve! Seriously. The 4x8 is a straight jacket we need to lose.
Not to get off the topic off the thread, but 4X8s have been a natural choice simply because plywood, and now many other building materials, come in this size. It was no so much a problem when only small steam engines and 4 axle diesels were the main things being sold in train sets and only those that had big layouts could afford the large steam or big diesels anyway. If we really want to “lose the straight jacket”, then lets see the model railroad press start publishing more 5X9 articles. Whether or not its prototypical or “operational” isn’t relevant, most newcomers want to see trains go around, and some of us old timers like that too.
Just my [2c]
Rick
My absolute minimum radius is 22". That’s only used on the restricted speed summit of my pass. The rest is over 22" I don’t even use 18" except on a few industrial sidings where absalutly needed.
Well I have a 4x8 because of space limitations. If I could I would make a 5x9 but then I would have no room to walk. Also, my layout is in a weird shape, a “L.” So it makes certainty curves sharper. I have basically broadened to most of my curves to around 20-24 inches. But there still is that one curve that is 18".