Western Railroad Discussion > Wheel size and radius question

Hi,

Can someone tell me please what is the as new (un-turned) diameter of a freight truck wheel and, what is the typical minimum radius curve used on the main line of class 1 railroads.

Thank you

Trevor Heath

A new wheel is either 33-inches for the 263,000 cars or 36-inches for the 286,000 (considered 100-ton) cars.

As to curve radius, that is dependent upon how much room the railroad has to work with and the speeds under which they operate, but a 1 degree 30-minute curve to three-degree would be the maximum for any kind of mainline traffic, but the exception supports the rule.

FRA specifies the speed which can be operated over the various degrees of curve as well as the superelevation and cross-level paramaters which must be adhered to.

Pick a point at random on a US main line--
travel a thousand miles in any direction,
staying on main lines-- what's the sharpest
curve you'll traverse? I'd say it will
almost always be 6 degrees or sharper--
i.e. 955 ft radius or less. In any
halfway mountainous area it will be
hard to avoid a 10-degree curve (573 ft
radius) somewhere in that distance.

Signalling and track quality permitting,
a passenger train will do 25-30 mph around
a 10-deg curve, around 40 mph on a 6-deg,
70-80 mph on a 2-deg and 100-110 on a 1-degree.

a 1 degree curve means the track curves 1 degree from tangent (straight) per 100 feet. A 10 degree curve means the track bends 10 degrees in 100 feet and, well, you get the idea. An 18" radius curve in HO works out to about a 45 degree curve. Whether the 100 feet is along the arc or the chord, I don't know. I have heard it explained both ways and at this scale it doesn't matter too much except to civil engineers.

So what is the minimum curvature of Tehachapi Loop? Couldn't find it on Wiki or other sites.

TIA,
Roust out

> So what is the minimum curvature of Tehachapi
> Loop? Couldn't find it on Wiki or other sites.

According to my 1974 Santa Fe Valley Division Track Chart, the maximum degree of curvature at Walong is 10 degrees, 05 minutes.

It is my experience and understanding that most mainline railroads in the west do not exceed a 10-degree curve by much. For example, a quick glance at a 1952 Track Chart for Cajon that I found online shows Curve #84, which I believe is "Sullivan's Curve," as 10 degrees, 1 minute, 43.5 seconds, and the curve at the west end of old Summit as 10 degrees, 20 minutes. A 10 degree curve has about a 570-foot radius, which scales to about a 78-inch radius in HO.

D F W

I will have to verify on my track charts (it's 0320am and the wife is sleeping) but I swear I saw many 12-15 degree curves on the Moffat and Tennessee main lines in CO.

pmack Wrote:
-------------------------------------------------------
> a 1 degree curve means the track curves 1 degree
> from tangent (straight) per 100 feet. A 10 degree
> curve means the track bends 10 degrees in 100 feet
> and, well, you get the idea. An 18" radius curve
> in HO works out to about a 45 degree curve.
> Whether the 100 feet is along the arc or the
> chord, I don't know. I have heard it explained
> both ways and at this scale it doesn't matter too
> much except to civil engineers.

Traditionally, it was along the chord for railroads and along the arc for highways. I assume that's still true, but don't know for sure.

Nathan Beauheim
(Yes, I am a Civil Engineer...)

Both 263K (100-ton) and 286K (120-ton) wheels are 36 inches in diameter. It's the smaller ones--177K and 220K, 50-ton and 70-ton, respectively--that are 33 inches across. I believe the 125-ton wheels (315K) are 38 inches, and there are special 70-ton wheels that are 28 inches in diameter, for installation under low-deck auto rack cars.

Confirm, CShave. Both 263K and 286K cars use 36 inch wheels. 33-inch wheels have pretty much passed out of use. Still find some 28-inch wheels on TTX flats (under auto racks and such).

One of the reasons 315K cars haven't proved economic is the cost of the 38 inch wheels, plus heavier side frames, larger bearings, heavier brake rigging, etc.

Diesel locos use 38 inch or 40 inch wheels.

As for curvature, the sharpest curve I've personally seen was a 39 degree curve on the West Virginia Northern out of Tunnelton, WV (now abandoned). The former Western Maryland (now West VA Central tourist line) had a 33 degree curve at High Falls.

Tennessee Pass did have some 12 degree curves, and so does the climb to the Cascade Tunnel out of Skykomish, WA. That's about a practical maximum for mainline routes, and requires the use of helpers to avoid "stringlining" the curve due to drawbar forces.

The C&O's sharpest mainline curve, near Hawk's Nest, West Virginia, was definitely double-digit--forget now whether it was 10 or 12 degrees.

Newer locomotives have 42-inch wheels. 40 inches was the norm for many, many years; the E units' A1A trucks rode on 36-inch wheels.

Hawks Nest is just under 10 degrees,
if we can believe the track chart.

DRGW has at least one 15-degree on
the main thru... forget whether it's
Byers Canyon or Gore Canyon. Again,
assuming the track chart is right.

Clinchfield had several 14-degree
on their main line; presumably they
still do? And of course Cantara on
SP's main line to Oregon is 14 deg,
and for that one we don't have to
rely on the track chart.

You can convert curvature in degrees to radius in feet by dividing the constant 5730 by the curve radius in degrees. Conversely, 5730 divided by radius in feet gives curvature in degrees. So a 10 degree curve is 573 feet radius. For track, the curvature is based on a 100 foot chord.

Locomotive wheels were traditionally 40" diameter new, 37" fully worn since the FT. As noted, the E units rode on 36" new wheels. At EMD, the SD70 required 42" wheels that wear to 39" minimum to maintain adequate gearcase clearance. SD60MAC and SD70MAC also use teh same 42" new wheels. The SD80MAC and SD90MAC all require 44" new wheels wearing to 41" minimum but most if not all were delivered with 45" wheels wearing to the same minimum. Many railroads are using 41 or 43" new wheels to replace 40 and 42" respectively, that wear to 37 or 39" to get some extra wheel life.

Dave