Harpers Tate
Established Member
- Joined
- 10 May 2013
- Messages
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Those sound like figures you've just plucked out of thin air
I am trying (and evidently failing) to illustrate why top speed alone isn't sufficient a basis on which to make a judgement. Yet you appear to persist with this fallacy.These numbers are made up. I don't know what they really are.....
So in what is probably a forlorn attempt to get this over:
Suppose we have two parallel, unencumbered bits of track, and we place
- on one, train A which (let's suppose) has a good acceleration curve (because it has electric transmission) and a top speed of 60mph. Let's suppose it also has good braking characteristics because it has a lot of braked wheels.
- on the other, train B which (let's suppose) has a worse acceleration curve due to it having a lossy torque converter transmission and a top speed of 75mph. Let's suppose it has less effective braking characteristics than train A because it has fewer braked wheels.
We set them off both together, to race between two points; stop to stop.
It ought to be clear that
-1- at first, train A will be ahead.
-2- at some further point, train B will overtake train A - unless the distance is sufficiently short that there isn't time for it to do so before event 3 begins
-3- at some further point, train B will begin to brake for a stop
-4- if train B is ahead of train A, then again depending on distance, there is the potential that train A may be able to overtake B again before....
-5- at some further point, train B begins to brake for a stop.
In a different situation, with the same two trains on the same track (B after A), Train B will only be restricted by train A's slower top speed IF the "unless" in point 2 arises.
There is a calculation to be done here that will determine what distance of unencumbered running is required to ensure that train A will in fact take longer than train B. That calculation involves every factor that contributes to a train journey; doors, people on and off; acceleration, top speed, braking distance; all of it.
I'll repeat - I don't know all of the characteristics of D-Trains vs. Pacers (etc). I said that at the outset. I'll say it again. As far as the evidence of this thread is concerned, nobody does.
Until we all know how these characteristics compare it is completely flawed to judge it on top speed alone and therefore to assume that there is a real issue on any given bit of track whether it's a Main Line or not.
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