I know this is pretty basic, but are there any general rules about what kinds of locomotives will negotiate a given track radius? If I build a layout with 18" curves, am I limited to 4-wheel trucks rather than 6-wheel? For steam, would a 2-6-0 Pacific work? I guess long passenger cars are out?
There is no general rule. There are two concerns:
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Will the engine even make it around the curve. I have a 2-8-8-2 that does my 18" and had a Hudson that would not. I have a brass 2-6-6-2 that does. You have to check each engine to make sure. With the newer engines, the manufacturer ussually gives a minimum radius, but that is not always dependable. I sometimes wish I would have stayed at a 22" minimum, but then the plan would not have fit my space. I had to add shelf couplers to keep my long passanger cars coupled.
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Does it look good? You get a lot of different opinions here. I like the look of the big over hang, but some are GREATLY troubled by it.
I think you find that almost everyone will agree that you plan for the maximum radius you can. In this case, more is better. A 22" radius is better than an 18", an 18" is better than a 15", and so on…
I can say that my Spectrum 2-8-0 will do just fine on my 18" radius, but looks better on my 22" and 26". I handlaid all my radius to get the most possible in the space provided. Generally the smaller the radius, the small loco’s that will travel it. Pay attention to the factory recommendations. It’s only their suggestion, but it’s there for a reason. As far as your diesel question, someone with more knowledge will have to help you there. I’m only running small steam!
Best of luck.
Most model four and 6 coupled engines will make it around 18’ radius. 6 axle engines will normally make it around 18" radius.
Other engines it varies by how the manufacturer has built the engine, how much slop, err, sideplay is in the axles, whether the center drivers are “blind” (flangeless), how much the traucks, driver set can swing or rotate. The majority of plastic engines will negoiate a 18" radius curve.
Having said that, as the size of the engine increases and radius decreases, you approach the boundry where things won’t work. So if you are running large engines on small radii, then the quality of the trackwork (no kinks, no place unlevel, joints smooth, etc) becomes more important. In addition the longer the piece of equipments the more overhand on the ends, the longer the couplers have to be, the more likely that pushing forces (buff) will cause a derailment. So your couplers have to be well tuned. Speed also comes into play because higher speed on sharp radii can be a problem.
Lastly, there is the visual appeal. Does the large overhang bother you? Does a train on the main at track speed zooming around a “hairpin” turn look toylike? Only you can decide.
By the way, a Pacific is a 4-6-2, a Mogul is a 2-6-0. Very different engines. the Mogul tended to be a freight engine and the Pacific tended to be a passenger engine. Typically a Pacific will be larger than a Mogul by 25-50% (longer boiler, larger tender).
Dave H.
18" is generally the “minimum minimum radius” for HO. Early in HO’s development people used sharper curves to try to squeeze in as much track as possible, but in recent decades 18"R has been about as small as you’d want to go unless you’re modelling something unusual like a crowded industrial area or a logging line using small engines and cars exclusively.
BTW, one problem with minumum radius is you have to look at both each individual engine and car’s minimum radius, and how they operate together in a train. A big SD-70 six-axle diesel and a modern 60’ boxcar or tank car might each be able to take an 18" radius curve, but might derail when going thru the 18" radius curve when coupled to each other in a train.
So, you might have to do a little trial-and-error if you want to use big equipment. Generally any four-axle diesel should be fine, and six-axle ones that aren’t too long (say an SD-9). Freight cars of 40’-50’ length with body-mounted trucks should work fine, but for passenger cars you’ll probably need to use ones with truck-mounted couplers. Athearn or Con-Cor 72’ cars would be a good choice.
For locomotives, it completely depends on the make and type of locomotive. There is no rule of thumb. There are exceptions everywhere.
For rolling stock, I use the 3X rule. The radius should be 3x the length of your longest rolling stock. For example, if you want to run a 6" box car, you will need a min radius of 18". For a 85’ passenger car, you will be looking at 36" radius (85’ is about a foot long). There are exceptions to the rule, but if you want RELIABLE operation, it is a great rule to have.
David B
As you can already tell from the prior posts the short answer is no. However, maybe the question is not will something negotiate a sharp curve but should it be forced to?
No you aren’t limited to those things, but you might want to limit yourself to them. If one really wants to operate larger equipment and has not built the track yet, why not just design with the larger curves to begin with.
I actually like your rule of thumb - 18" limits one to: 4-wheel truck diesels, 2-8-2 fixed or 2-6-6-2 articulated steamers, 60’ cars (freight and passenger). As another poster already pointed out, in reall life the exceptions are numerous just because manufacturer’s have been working around the 18" curve for years. The first one that comes to mind is the AHM/Rivarossi 80’ passenger cars. They have an offset bolstered truck wth the couplers mounted on the truck that allows them to negotiate 18" curves. Once again they look stupid but they can do it. Bachmann & AHM has many larger steamers that will run on an 18". Even Athearn’s new 4-6-6-4 is supposed to. I haven’t tried subjecting mine to that torture, so I can’t give a 1st hand account.
Passenger cars kinda bring us back to the earlier comments about appearance vs. operation. For full-length passenger cars with body mounted couplers, 26" radius is probably the bare miminum (like the Walthers cars); with operating diaphragms 30" might be better…and the bigger the curve, the better they’ll look and operate.
However, a couple of companies make 80’-85’ passenger cars that can go around 18"-22" radius curves, largely because they use truck-mounted couplers. (IHC and the old Rivarossi cars - not the newer 60’ Rivarossi cars with body-mounted couplers.) To many folks, the overhang on the sharp curves destroys the illusion of realism for them, other people only care that they run well even if they don’t look great doing so.
When recently shopping for a steam loco, I contacted Walthers to inquire regarding minimum radius and turnout their locos will run through. Following is the exact reply.
We [Walthers] design all HO-Scale, Life-Like Proto 1000, Life-Like Proto 2000, and Life-Like Heritage Steam locomotive models to negotiate an 18-inch radius curve and smoothly go through a #4 turnout.
I purchased a Proto2000 Heritage 2-10-2 steam with QSI sound, it run and sounds great, no problems staying on the track and goes through #4 turnouts fine.
Most of the newer plastic articulated steamers are ‘double-jointed’, enabling them to go around tight radii. A prototype (and brass model) articulated is only hinged from the front set of drivers, the rear set is rigid (or the reverse in a Cab-Forward). So it’s possible to run a 2-8-8-2 (and even a big Rivarossi 2-6-6-6) around 18" radii without the severe boiler overhang of the prototype, because both sets of drivers are hinged. The problem can come from whether or not the tender is close-coupled to the locomotive enough that it hits the cab and ‘lifts’ from the track on the radius.
With a prototypically hinged articulated like a brass model, of course, you run into a whole other set of problems on 18" radius. Possibly a 2-6-6-0 or, as Art Hill says, a 2-6-6-2, but I wouldn’t want to chance anything larger.
And even on my own MR, which has a 34" minimum radius, my largest brass articulateds will slide around a curve that can give a long-wheelbased rigid frame loco (like a 2-10-4) fits. So it all pretty much depends on the loco you’re using. Best bet is to check out the mfgr’s recommended minimum radius for the particular locomotive. Unless, of course, like me, you’re willing to re-lay all of your curves because you WANT that particular locomotive.
Tom [:)]
Tom
The absolutely, positively best way to find out what radii your rollling stock will take is to lay a test spiral (not helix) and run it. Mine starts at 36 inches and reduces 1" each 60 degrees. Check each loco coupled to the kind of car you expect it to pull.
I have a NYC Niagara that will, if coaxed, crawl down to 18" radius before the lead truck climbs over the rail. OTOH, a 40 foot box car coupled to that overhanging 4-10 tender will be snatched sideways off the track at about 27" radius. It’s not just the loco that has to take the curve, it’s the whole train.
Chuck (modeling Central Japan in September, 1964)
Let me add on to that phrase…
Best bet is to check out the mfgr’s recommended minimum radius for the particular locomotive and add 4. (Why 4? Because it is typically ‘doo-able’)
If a MFG says 18" (for example the Athearn Big Boy), then add 4 and play with 22" radius. I am not saying that adding 4" will cure all ills, but rather a stance that MFGrs tend to design locomotives to the smallest possible radius possible. So, if you want a Big Boy to run on 18" radius, you have to make major design changes to the actual locomotive to do so, as well as push it to it’s operating limits. If a MFG says that it will run on 18" radius, that doenst have to mean that it will do it comfortably.
David B
The new Rivarossi/Hornby 60’ coaches come with two couplers, one for use on 18" radius curves and the other for larger curves. These coaches track well. They are hard to find though.
I have several sets of the older Rivarossi 60’ coaches and have had no problems with running them on 18" radius curves.
The only problem I encountered was the weak factory mounted couplers, a quick change to Kadee solved that. Yes they do have an overhang and do look better on larger curves but they run well.
Another set of passenger cars to consider is the Roundhouse Overland car sets, providing they fit your era. These coaches are in somewhat short supply but are being re-released by Roundhouse in the near future.
Thanks to all of your for your excellent suggestions. To sum up, I guess I can run more than I thought I could on 18" curves, but have to beware of appearance, how the rest of the train performs on the track and through the turnouts, and to be safe, make trial runs. Yes, I meant to say 2-6-0 Mogul, not Pacific, guess that got some laughs.