Hello everyone and welcome to Train Talk!
Today, we are going to talk about classifying steam locomotives into various groups, based
on the number and types of wheels they have, also called a wheel arrangement.
During the steam era, many manufacturers produced a wide variety of steam locomotives, most
of which were built specifically for a particular railroad.
To make things even more complicated, many railroads had their own systems of classifying
steam locomotives for purposes of keeping track of them.
So, one of the best ways to organize steam locomotives was based on their wheel arrangement.
Wheels are grouped into three types: pilot wheels, driving wheels, and trailing wheels.
The pilot wheels help guide the heavy locomotive around curves.
Driving wheels are the wheels that actually move the locomotive and train down the track.
These wheels are powered by taking the pressure of expanding steam and using it to move the
large connecting rods that are attached to the drive wheels.
The trailing wheels help support the weight of the fire box.
Keep in mind, not all steam locomotives have pilot wheels or trailing wheels, and some
locomotives don’t have either.
Additionally, there are some locomotives that have two different sets of driving wheels,
but we will get to that in a minute.
Ok, so we’ve grouped our basic types of wheels, now what do we do?
The most used system of designating wheel arrangements is known as the Whyte classification
system, named for its creator Frederick Whyte, a mechanical engineer employed by the New
York Central railroad.
The Whyte system denotes wheel arrangements by counting the number of a certain type of
wheel on both sides of the locomotive, starting at the front and working back with different
sets of wheels separated by a hyphen.
For instance, a locomotive with two pilot wheels, eight driving wheels, and two trailing
wheels would be called a 2-8-2.
It is important to note that when we are counting the wheels, we are counting what is on both
sids of the engine.
So, while you can only see half the wheels when looking at one side of the engine or
the other, we are counting wheels on both sides, which is why this locomotive is called
a 2-8-2 and not a 1-4-1.
This locomotive, which has 2 pilot wheels, 8 driving wheels, and no trailing wheels is
designated as a 2-8-0, the 0 indicating the lack of trailing wheels.
Well, that’s pretty much the basics of it.
In addition to these number and hyphen designations, many wheel arrangements were given names.
Let’s go through some of the most common wheel arrangements now.
The 4-4-0 was one of the most widely and longest used wheel arrangements of steam locomotives
ever produced.
It was given the name “American”, because it was really the railroads of America that
pioneered the use of this wheel arrangement.
4-4-0’s were used almost exclusively throughout the mid 1800’s and they were still being
produced as late as the 1940s.
This is really the locomotive that most people think of when they imagine the trains of the
old west, often adorned in bright and colorful paint schemes and plenty of brass.
4-4-0’s were so popular because they were quite versatile.
They could be used for either passenger or freight service.
The bigger the diameter of the driving wheels, the faster they were designed to go.
Today, there are a number of 4-4-0’s that still run in tourist and museum service, the
oldest of which was built in 1856.
The 2-8-0 wheel arrangement, named the “consolidation” was developed in the 1860s and was another
of the more common wheel arrangements of steam locomotives produced.
According to steamlocomotive.com, the name “consolidation” actually comes from the
consolidation of two different railroads into the Lehigh Valley Railroad, which happened
around the same time the wheel arrangement was first produced.
Due to their rather short drive wheels, consolidations were limited in their top speed, so they were
often used to pull heavy freight trains.
Consolidations were produced well into the first half of the 1900s and they were used
right up to the end of the steam era in the United States.
Currently, consolidations are one of the best preserved wheel arrangements of steam locomotives,
and they are among the most common seen in operation today.
The 2-8-2 wheel arrangement was developed in the late 1800’s and was named “Mikado”.
This name comes from one of the first orders of 2-8-2 locomotives being built for a railway
in Japan.
“Mikado” was the english word for the Japanese Emperor at the time.
Mikados were well balanced, multipurpose locomotives used by many different railroads throughout
the 1900’s.
While they were primarily used for freight service, they could be seen pulling passenger
trains from time to time as well.
Mikados, like consolidations, are a well preserved type of locomotive and there are several examples
that still operate today everywhere from tourist railroads to mainline excursion trains.
4-6-2 locomotives, called the Pacific, were primarily used for high speed passenger trains
from the early 1900’s through the end of steam in the mid to late 1950s.
It is believed that the name “Pacific” comes from the first operator of this type
of locomotive, the Missouri Pacific, which purchased its first Pacific locomotives in
1902.
Today, a number of Pacifics remain in preservation, but very few of them still operate.
4-8-4s were one of the most popular wheel arrangement of big steam locomotives.
They were named “Northern” because they were first built for the Northern Pacific
Railroad in 1927.
These were powerful locomotives that were built to reach speeds as high as 110 miles
per hour.
Northerns were often used as passenger locomotives, but they also saw service on high priority
fast freight trains.
There are a number of preserved northern type locomotives today, but very few of them still
operate.
Of the ones that do, they are primarily used for excursion service out on the main line.
Locomotives that did not have pilot wheels or trailing wheels were called switchers and
they were typically only used for moving cars short distances.
Switchers came with either 4, 6, or 8 driving wheels and were designated as 0-4-0, 0-6-0,
or 0-8-0.
In addition to standard tender engines, tank engines also use this same classification
system.
Tank engines are noted by putting a capital letter “T” right next to the number of
trailing wheels.
For instance, this locomotive would be classified as a 2-8-2T.
There is one final addition to the wheel arrangement naming system, and that is for locomotives
that have multiple sets of driving wheels, called “mallets” and “articulateds".
These types of locomotives are complicated enough that I want to do an entire episode
on them, so for this episode, we will just focus on the wheel arrangements.
Basically, they follow the same system of designating wheel arrangements except the
multiple sets of driving wheels are separated with a hyphen.
For example, the Union Pacific’s articulated locomotive “Big Boy” has 4 pilot wheels,
one set of 8 driving wheels, another set of 8 driving wheels, and then 4 trailing wheels,
so it would be called a “4-8-8-4”.
And this locomotive, a tank engine with 2 pilot wheels, 6 driving wheels, one more set
of 6 driving wheels, and then 2 trailing wheels would be called a “2-6-6-2T"
Well, that covers pretty much everything.
Now let’s try to figure out what these wheel arrangements are, and learn a few new names
too!
4-4-0 “American"
2-6-0 “Mogul”
2-6-2 “Prairie”
2-8-0 “Consolidation”
4-6-0 “Ten Wheeler”
2-8-2 “Mikado”
4-6-2 “Pacific”
4-6-4 “Hudson”
4-8-4 “Northern”
2-8-4 “Berkshire”
2-6-6-2T “Mallet” tank engine
4-6-6-4 “Challenger” Articulated
Well, we’ve covered a lot in this episode.
I hope you had fun!
There are some other types of steam locomotives that don’t follow the whyte classification
system at all including “geared locomotives” and cog locomotives, but we will cover those
in future episodes.
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And if you’re not already, be sure to subscribe to the channel for new videos every week.
Until next time, I’m Mike Armstrong.
I’ll see you down the line!
Thanks for watching.