On Sep 17, 2010, at 9:11 AM, al.kresse wrote:

Does anyone have early Master Car Builder's or ARA documentation explaining the rationale for 4-wheel vs. 6-wheel trucked freight car classes?

Example: circa 1915-1920, 50-ton axle 4-wheel trucks become 100-ton 6-wheel (used for USRA class gon designs) and not (50+25) 75-ton trucks; and 70-ton axle 4-wheel trucks become 120-ton 6-wheel trucks and not (70+35) 105-ton trucks.

I believe there were only 40-, 50-, and 70-ton "standards" for cast sideframe truck designs but a full range of axle "standards" for this era.

Did the use of clasp brakes give "rationale" to classify on the upside or the journal-size ratings? Was this was before tested DIN life ratings were associated with bearing sizes and types?

Al Kresse

Al,

If I understand your question correctly, ultimately, car tonnage ratings depend on axle and bearing ratings (and car construction that can withstand the load).

From an email in 2006 by Tim Gilbert:

Between 1925 and 1962, the Maximum Total Weight Allowed on the Rail
for a car with four axles (two four wheel trucks) were (dashes are
necessary to maintain column integrity for Yahoo):

------ Journal----- Total Wgt ----Standard Nominal
Axle -- Size ------- On Rail ------- Capacity
A --- 3 3/4" x 7" --- 66,000 -------- 40,000
B --- 4 1/4" x 8" -- 103,000 -------- 60,000
C --- 5" x 9" ------ 136,000 -------- 80,000
D --- 5 1/2" x 10" - 169,000 ------- 100,000
E --- 6" x 11" ----- 210,000 ------- 140,000
F --- 6 1/2" x 12" - 251,000 ------- 200,000

Note: The last page in almost every ORER published between 1925 & 1962
has a table including the Axles, Sizes of the Axle Journals, Total
Weight on Rail and Standard Nominal Capacity.

As noted, the numbers apply to 2 4-wheel trucks. To get the number for each axle, divide by 4. Thus, a car would require 10 "A" axles to achieve the rating of car with 4 "D" axles. The ratings increases you site appear to come from both increasing the number and the diameter of the axles.

Regards
Bruce

Bruce F. Smith
Auburn, AL
http://www.vetmed.auburn.edu/index.pl/bruce_f._smith2

"Some days you are the bug, some days you are the windshield."
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