HO Minimum Track Radius

Model Railroader General Discussion (Model Railroader)
21

A clearance car such as this will determine if new equipment will work with existing tunnel, structure and sise-by-side clearances.

NYCT took an old 60’ car, cut it in half and extended the car to 75’ the new length that the wanted to buy. This told them where they needed to enlarge the tunnels or in some cases to restrict the 75’ cars from operating on that line. It also demostrated the location of the trucks and kingpins.

Most of the 75’ cars are gone or will be going away soon. New cars are all 60’ cars

The relationship of the truck and kingpin vis a vis the end of the car will determine the end overhang or the middle overhang.

On your railroad, just try the cars out and see if they work. I have some brass cars that never worked on my railroad because I never installed 60" curves. They make a very nice static display.

Subway cars of LION are 50’ long and will handle all of my curves. 85’ cars will not run on my layout. Some equipment is too tall to run in my tunnels.

22

From the instructions of the Marklin/Trix Big Boy… (Found on the internet - I do not own one.)

Important information about the operation of this locomotive: This locomotive can be used on curved track with a minimum radius of 360 mm / 14-3/16", but we recommend larger radius curves. Due to the overhang of this locomotive’s long boiler, signals, catenary masts, bridge railings, tunnel portals, etc. must be set out further from the curved track for clearance. The track must be well mounted for the high weight of the locomotive.

JW

23

Hello All,

On my 4’x8’ HO pike I have asymmetrical curves comprised of code 100 track.

The 180º curves at each end consist of 90º 15-inch radius and 90º 18-inch radius with a 2-inch straight section between the curves as an easement.

I regularly run a 4-unit consist of GP40s and a 3-unit consist of GP30s pulling Tyco 34-foot operating hoppers with no problems.

There is also a crossover made up of 4 Atlas Snap Switches that uses the short curved sections provided with the turnouts. These are placed back-to-back to form a dreaded “S” curve.

The MU’s can negotiate this “S” curve, albeit at slow speeds.

I added a modified PECO curved turnout on the 18-inch radius curve side, before the crossover to eliminate half of the “S” curve.

For the coal unloading/loading sidings I used PECO #2 turnouts.

The 4-unit GP40 consist negotiates the lower loading siding pulling 16, 34-foot Tyco operating hoppers.

A curved asymmetrical 3% grade is used to get the 3-unit GP30 consist pulling 8 loaded Tyco operation hoppers up to the unloading tracks.

This 180º asymmetrical curve consists of 90º 22-inch track to 90º 18-inch radius with a 2-inch straight easement section in the middle.

On the upper unloading siding, with #2 PECO turnouts, the loaded Tyco operating hoppers are shoved over the unloading track to the waiting empties below.

This is a slow-speed operation as the cars on the lower track are spotted under the unloading track while the loaded cars on the upper track are shoved over the unloading track mechanism.

A 15-inch radius 360º spiral trestle (helix) brings the empties back down to the mainline pulled by a single GP30 cut from the 3-unit consist.

I also have a wye for turning the 0-6-0 USRA with Vanderbilt tender used for excursion train that pulls 42-foot Olde Tyme cars up the 3% grade and down the historic spiral trestle. A 0-6

24

Thank you everyone for the advice! Much appreciated.

25

At one time Atlas made 15" radius sectional track. I would never consider it for mainline track but in a tight switching area with short locos and cars, you can get buy with it. I’ve gone as tight as 18" in my industrial switching area but an SW7 switch engine and 40 foot cars is the largest equipment that has to negotiate these.

As for mainline, make your curves as broad as possible no matter what kind of equipment you want to run. If you can do no bigger than 24" radius track, I would limit myself to 4 axle diesels. You might get by with a Consolidation steamer (2-8-0) but for the most part, 6 drivers max. If you want to run full length passenger cars, I’d suggest a minimum of 30" radius. One thing you want to take into consideration is appearance as well as performance. You might get larger equipment to take tighter turns but it won’t look good doing it due to the overhang.

26

Hello All,

They still do…HO CODE 100 15" RADIUS TRACK.

Absolutely!

Occasionally I’ll get the urge to run The Royal Gorge excursion train with four (4) 85-foot passenger cars and an F7 ABB on the head end and an F7 A on the rear, for prototypical reversing operations.

The F7 units appear OK, but the overhang of the cars looks ridiculous over my tight asymmetrical curves.

Oh, how I wish for a larger pike, but this is the lot I am dealt.

Hope this helps.

27

I’ve got some Atlas Code 83 15" radius for my whacky logging division not yet built.

I’ve got steam skidders from Bachmann.

I’ve got the weird not to scale Mantua 2-6-6-2 tank.

Kadee skeleton cars x 3 and a very odd shorty log car from decades ago.

There’s nothing in this hobby that can be described as too nutty. It all works for somebody.

28

After 50 years in the hobby and starting my last layout I view radii much differently now. Instead of what is the minimum radius I can do I try to view turns as what is the maximum radius I can use and strive to work that into the plan. I know there are people who have to use smaller radius curves but try to upgrade if at all possible. 22" opens up far more types of equipment then 18" and still fits a 4x8 sheet of plywood.

29

Hello all,

As one that is limited to a 4’x8’ space, I find this does not hold true with the advent of DCC operations.

If you only want a single oval of track to run larger motive power and rolling stock you will soon tire of watching them go round-and-round.

In the age of DC this might have been a viable solution.

However, in the age of DCC some seek more operational possibilities.

By limiting the size of motive power and rolling stock, to match the limitations of trackage, the advantages of DCC can be realized.

Of course, I would like a larger pike to run a greater variety of motive power and rolling stock but at this point I am constrained by the dreaded 4’x8’.

Railroad modeling is a series of compromises and selective compression, even on the largest pikes.

If your goal is to run 4-6-6-4s, 6-axle diesels and 85-foot passenger and well cars, then yes, a single oval of 22-inch track is desirable.

But if you want the challenge/enjoyment of DCC operations then a rethink of motive power and rolling stock versus track radii is inevitable.

Hope this helps.

30

As you have already read the anwswer is a resounding, “yes”, if the cars couplers have a fixed mount on the body of the car/loco.

I only saw one other person (dknelson) mention this, and that is the answer is a resounding, “no” if the couplers are mounted on the truck. When a coupler is mounted on the truck it follows the curve of the track. It aligns to the center of the track so there is no “swing out” that causes the problems on sharp curves. This is how Lionel gets O-gauge equipment around 15.5" radius curves (O-31). In HO all the Tyco, Marx, original LifeLike, and Bachmann equipment was like this.

Then there are the compromise cars a few people have mentioned. This is where the coupler is on a swinging arm that decreases the swingout decreasing the radius that car will work on.

Finally there is the trick of pivoting the truck toward the center of the car. AHM/Rivarossi/IHC used this (in combination with the truck mounted coupler) to get their 85’ passenger cars reliably around 18" curves.

31

here’s a thread I created in 2019 about setting up a test track for minimum radius:

https://cs.trains.com/mrr/f/88/t/276727.aspx

starting post:

I commented about my loco testing on the other two posts about small radius curves and logging locos. I expanded my test sessions and couldn’t believe how many of my HO locos do not derail running through a 15" radius curve, even at full speed.

The S curve test track consists of 3 feet Atlas straight track to build up speed, then one 18" radius Atlas curved snap track, then a reversed 15" Atlas curved snap track, then 2 feet of straight.

Here’s a list of all the locos that wouldn’t derail on this setup after several passes, even at full throttle:

Bachmann Spectrum 3 truck Shay (hit or miss, suggest 16" minimum)

Bachmann Spectrum Baldwin 10 wheeler 4-6-0

Bachmann Spectrum Decapod 2-10-0

Proto 2000 SW8 (no surprise)

Proto 2000 FA1-FB1, lashed up

Atlas Classic RS-3

Proto 2000 E8/9 six axle (!)

Athearn Genesis Mikado 2-8-2

Rivarossi Berkshire 2-8-4

IHC Santa Fe 2-10-2

The Berk and Santa Fe slow down a bit running through the 15R and of course they look silly but they would not derail!

This test might prove useful to owners of larger locos where a small section of the layout has to be 15R to fit.

50’ cars and passenger cars look laughable on a 15" curve but they do make it through.

32

If you model streete cars a 9" radius would work. In a steel mill, a 6" radius would be ok.

33

I just finished my steel mill. I am using an Atlas MP15DC and a Walthers SW7 to move the same cars plus gondolas and coil cars. I used 18" for most curves with a few being a little wider (20 to 22) and one smaller (maybe 16.). I was more concerned with S curves and clearance than actual radius. Everything I have used so far has not had any issues.

Rick

34

This is truly helpful!