Speed for short-tie ratins depends on gear-ratio. E-units were geared for higher speed and less starting tracteve effort than freight units in general.
Rock Island also used some of its E's in freight service. RI had few major grades so that minimized the issues with short term ratings.
In the cases of Erie Lackawanna and Rock Island, financial considerations may have also been a factor. With the decline of passenger service, E's became surplus power, using them in freight service may have postponed the need for new power.
E units 'short time ratings' would kick in in the neighborhood of 25-27 MPH, versus freight units getting into their short time rating at approximately 11 MPH.
Short time ratings are the denote speed at which Maximum Amperage can be fed to traction motors continuously without damage. If speeds drop below the Short Time rating speed, then the resulting INCREASING AMPERAGE being sent to the traction motors can only be withstood for increasingly shorter times.
In the late 1950's the B&O assigned all their F3 passenger geared engines to the Chicago Division to operate between Willard and Chicago, with the passenger gearing intact. The maximum grade on this route was 3 tenths of one percent - ie. 4 inches of elevation change over a 100 foot span.
Never too old to have a happy childhood!
If a RR is looking for new units to pull its freights, why would they even consider E-units? What advantage would they have over Fs or GPs?
After the "Lake Cities" was discontinued and the Jersey suburban service was re-equipped, EL made regular use of their E's in general freight service. Admittedly, they used 3 or 4 at a time on the front end.
Later in their lives some were used successfully for freight service. Perhaps the most notable were the Bangor and Aroostook's pair of E7's that were rebuilt for freight service with EMD assistance.
I'll leave most of the reasons why they weren't desireable for freight service and why their limitations had to be respected when put to use in those duties, to others to explain better than I can. But reason #1 in my eyes comes down to the limitations of their gearing.
The BAR had to modify the trucks to enable the use of 38" wheels (Edit: Some references say 40"), enabling re-gearing to 62:15. With the factory 36" wheels the minimum gearing possible was 57:20 with a maximum speed of 85 mph, which obviously isn't too well suited for freight service (and one reason why some of the notable users of them in freight service put them at the head end of short, fast, and relatively light trains that often looked overpowered in order to protect the motors).
The results as publicized by the road were very successful. It gave them a unit that performed as well as a F3 at speeds below 25 mph (albeit more expensively than a F3, such as 24 cylinders to maintain versus 16). And at speeds above, the full 2,000 horsepower could be put to use to outpace a F3.
For a cost of less than the half the trade-in allowance that they would've got for them from La Grange, they were able to get half a decade more out of them before going in trade for new GP38's in I think 1966.
The F series locomotives were used for both freight and passenger interchangably... why were the Es used almost exclusively for passenger?
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