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Comparison of SD70ACe tractive effort to Siemens ES64 F4


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I am wondering what "tractive effort" really means and how it relates to the horsepower of the locomotives "engine".


According to Wikipedia, the US locomotive from EMD SD70ACe has 4300 HP / 3200 kW or 4500 HP / 3400 kW (depending on version/tier) of "power".  According to the MRCE website and Wikipedia, the heavy freight electro locomotive from Siemens ES64 F4 (DB BR189) (aka EuroSprinter family) has 8600 hp / 6400 kW of "power".  To untrained and unschooled eyes, that looks to be twice as much "power".  (Which kind of makes sense since the SD70ACe has to carry a diesel engine and fuel in addition to the electro motors of the traction system).


But looking at "tractive effort", the SD70ACe has more than twice as much as the Siemens ES64 F4.


SD70ACe has continuous tractive effort of 157,000 lbf / 700 kN and a starting tractive effort of 191,000 lbf /850 kN.  Continous tractive / HP = 0.2059 kN / kW


The ES64 F4 has a continuous tractive effort of 270 kN and a starting tractive effort of 67,000 lbf / 300 kN.   Continuous tractive / HP = 0.0422 kN / kW


So the Siemens can put out less than half the "tractive effort" than the EMD SD70ACe with double the horse power.   I know these are not directly relatable as things like gearing and stuff affect the torque and other things that can be applied.  The Siemens has a slightly higher top speed of 140 km/h compare to the SD70ACe at 120 km/h, which implies a different gearing but the speed differences are not that great.


Looking at an EF 510 in Japan, according to Wikipedia, the "horse power" is 4,550 hp (3,390 kW) and only a tractive effort of 199 kN (45,000 lpf) [does not say if that is starting or continuous but I would assume continuous].  Top speed of only 110 km/h.  Continuous tractive / HP = 0.058702 kN / kW


So the US locomotive has 4-5x the "tractive effort" per unit of power (HP) compared to the Siemens or the EF 510, both electro locomotives, who get their "power" from overhead wires instead of from burning diesel fuel.


That seems like a much bigger "advantage".  What am I missing?  Being a dummy when it comes to these sorts of things.



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From what I understand, Horsepower generally refers to the power output of the motors/diesel engine while tractive effort is a more realistic indicator of how much such a locomotive can actually pull, and is affected by things like drivetrain losses, wheal gearing and diameter as well as the weight of the locomotive.  Increased tractive effort means a locomotive can pull more, while increased horsepower means the locomotive can reach a greater speed with the same train.  Its certainly a rabbit hole where the more you learn the less you feel you know!  



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bikkuri bahn

It's basically weight.  The US diesel locomotive is around twice the weight of the electric locomotives.  Axle load is a whopping 31 tons (for comparison, a DF200 has an axle load of 16t).  Each type of locomotive is designed specifically for the environment it will operate in.  In the SD70 case, that's hauling mile long drags of bulk freight on mostly exclusively freight tracks.  The European and Japanese locomotives are pulling shorter trains, and sharing those tracks with passenger trains, which will likely be more numerous and have higher priority. So apples and oranges. 

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But since the max speeds are somewhat comparable (of course that does not say what load they are carrying at that top speed), why don't the Japanese and European locomotives add weight and reduce the HP to get more tractive effort?


Btw, I did notice that the US locomotives are much much heavier and seem to be ballasted to get that weight, which would increase tractive effort.


I know this is similar to the torque vs HP on a car where higher torque allows you to either get off the line quicker or pull more off the line, while more HP allows a higher speed.


It is just that the  numbers are so different that it made me wonder what was up.


Anyway, thanks for the comments.


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55 minutes ago, chadbag said:

But since the max speeds are somewhat comparable (of course that does not say what load they are carrying at that top speed), why don't the Japanese and European locomotives add weight and reduce the HP to get more tractive effort?



Good question!  That comes down to the civil engineering of the tracks they run on.  While a heavier locomotive will have much higher tractive effort, the tracks need to be able to support this weight!  This means a lot more work in not only the rails and ties, but also the ballast, and the dirt under the ballast!  Also bridges and other structures must support this weight too.  This all adds up to a huge expense to build and is something that can't be upgraded easily.  As JR lines are narrow gauge they are often built to much lighter loading than a US class one freight line, and the benefits they'd get from heavier axle loading don't outweigh the amount of money and time it would take to have them at those standards.

This is why JNR built locomotives like the DD54, ED62, and DD51 with the center unpowered axles.  They had adjustable suspension to control how much of the locomotive weight was on the powered wheels.  When the weight was on the powered wheels the locomotives had higher tractive effort, but this limited what lines they could run on!  When the suspension was adjusted to equalize the weight over all wheels the locomotive could run on lighter built track, but had lower tractive effort.

This has been an issue in the US as well!  The Western Pacific railroad had track (over) built to much higher standards compared to most other western railroads.  Because of this they ordered mostly 4 axle power and heavily ballasted their locomotives.  This meant they needed less locomotives to haul a train over their tracks, but when the locomotives would venture onto other railroad's rails they could damage the track and right of way.   The adjacent Southern Pacific instead opted for track that was "good enough" and instead would add more locomotives when needed for heavy trains.    

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Classic case was the Ome line in Tokyo, where the 1930s era ED16s survived into the 1980s because the line wasn't suitable for heavier locos, and presumably there were no newer alternatives available. The line was finally upgraded to support F-class locos (EF15 for a short while, then EF64-0s).

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As @Kiha66noted, tracks are designed for specific axle loads. Keeping in mind that heavier axle load tracks are more expensive to build and maintain. IIRC, track maintenance standards are higher for fast passenger services than for slow freight.

From the introduction of a research paper on the effect of increasing axle load in Europe for freight operations.



it is clear that heavier axle loads shorten track component lives, increase the rate of degradation of the track structure and may increase the risk of derailments. Likewise, the wagon-maintenance costs may increase with increased wagon loading. There still is no common standpoint on what the 'optimum' heavy axle load would be. The various operators favour 25 or even 30 tonne.

Edited by disturbman
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