Specification for Track Radius

[Joel Seckar]

I have an N PRR K4 4-6-2 STEAM LOCO (DCC SOUND VALUE) PRE-WAR W/SLAT PILOT -#5448 ITEM NO: 52853.  I just started experimenting with Kato Unitrack and I am having problems with the engine negotiating curves.  The question is what radius curve should this engine we capable of negotiating?

Joel

[Len]

According to the Bachmann on-line store description: Performs best on 11.25" radius curves or greater.
http://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=265_372_1019&products_id=6168

Bigger is better when it comes to steam and curves.

Len

[sumfred]

Mine runs on 9 3/4" without any problems
Fred

[brokemoto]

The thing might run on a nine and three quarter curve, but it does run better on thirteen inches, or better.  It also looks better.

Nine and three quarters is about equivalent to an eighteen inch radius curve in HO
Thirteen is about equivalent to a twenty four inch radius curve in HO
Sixteen is about equivalent to a thirty inch radius curve in HO.

The way that I learned steam in my HO days was:

Anything eighteen inches or less and you were restricted to six drivers or smaller, but no Pacifics (4-6-2) or Hudsons (4-6-4).  The more under eighteen inches that you went, the more restricted it got.

Eighteen inches (nine and three quarter) allowed six wheel switchers and smaller; Prairies (2-6-2) or smaller; ten wheelers (4-6-0) or smaller, although some really high drivered ten wheelers might not run.

Between twenty four and thirty (thirteen to sixteen), you could run Pacifics and Hudsons, as well as consolidateds (2-8-0) and mikados (2-8-2).  You might get away with smaller drivered Santa Fe s (2-10-2) and decapods (2-10-0) as well as smaller drivered Berkshires, such as some ATSF or P&LE types. Any articulated up to a USRA 2-6-6-2, likely would operate.  Any larger articulated required something over thirty inches (sixteen inches).

Over thirty inches, (sixteen), you could run almost anything, although Big Boys, Challengers and Baldwin Centipede diesels looked better on thirty six inches (nineteen and one half) or greater.

For the sharper curves, (nine and three quarter), B-mann sells a USRA 0-6-0, a mogul (2-6-0) and a ten wheeler (4-6-0).  There is also an 1870s eight wheeler.  The 0-6-0 also has a Prairie version, but it is really a USRA 0-6-0 with pilot and trailing  trucks added; it is not a "true" Prairie type.  The mogul and ten wheeler are excellent locomotives.  If you get a later issue of the eight wheeler, it is pretty good.  The switcher can be made into a winner by swapping out the stock tender and substituting a B-mann SPECTRUM tender.

For something between thirteen and sixteen, B-mann sells the Pacific that you have, as well as consolidated, and a
USRA 2-6-6-2.  The consolidated will operate fine on eleven inch curves.  Some  have stated that the consolidated will operate on nine and three quarter, but mine are all inconsistent on that radius curve.  Some of them will climb and derail.  I do not have the Pacific,  I have the consolidated and it is excellent.  In fact, the B-mann consolidated is STILL one of the yardsticks against which all N scale steam is measured.  The other is the Kato mikado.  I have a first issue 2-6-6-2.  There were problems with the first run of these things, but I understand that B-mann has addressed those problems in subsequent issues of this one.  I do not run anything that large, any more, so I have not bought any subsequent issues.

B-mann has a B&O 2-8-8-4 and a Van SWeringen Berkshire for the larger curves.  I have the 2-8-8-4 but not the Berkshire (2-8-4).  I bought the 2-8-8-4 only because it IS B&O specific.  It is an excellent locomotive.

I might have omitted one or two.

[Len]

The rule of thumb they used for figuring minimum curve size at the club is:

3 times the overall length of the prototyp, in inches, divided by the scale ratio.

The K-4 was 48' 2-5/8" overall.
Converting that to inches gives: 578.675"
578.675 * 3 = 1736.025"

For N scale: 1736.025/160 = 10.85", call it 11" minimum for a round number. Just like the description said.

For HO scale: 1736.025/87 = 19.95", call it 20" minimum for a round number. So 18" curves are out.

Remember, these a minimum size curves. The K-4 will look, and operate, a lot better on larger curves.

Len