Measuring Breakaway Gaps

[El Pistolero]

No, they use the time difference between motors these days...

If both would increase their speed at the same time the time difference would stay exactly the same...

 

[Waterloo Sunrise]

No, they use the time difference between motors these days...

If both would increase their speed at the same time the time difference would stay exactly the same...

Time = distance/speed

If speed increases and time remains the same, distance must increase in proportion to speed.

So you are arguing that two objects can move closer or further apart when they are always moving in the same direction at the same speed?

 

[Caruut]

The thought experiment is much purer if you think of an infinite length race, but if you want to introduce distance I can happily argue the other way.

After the instantaneous speed change occurs, the time to complete the race has halved. The measured time gap as halved. No real difference.

If however I start to conflate the 2 measures as you do, I could argue...

The time to complete has halved. The distance between is the same. Therefore my gap for racing purposes has doubled.

More gibberish.

As I have said time and again, the reason the time gap drops if they accelerate at the same time, then the group behind races the section between the two faster.

Let me give you another example.

The break goes past the 100km mark at 12:00 (going 20km/h, though this is totally irrelevant). As soon as they pass it, they increase speed to 40km/h. Then they must complete the next 20km in 30 minutes, so they pass 120km at 12:30.

Now suppose the peloton does the exact same thing, and is 10 minutes behind at 100km - that is they pass it at 12:10 (at 20km/h again, though this is entirely redundant). They also increase to 40km/h as they go past 100km. Then they will also take half an hour to go over the next 20km, so they will pass 120km at 12:40. Still 10 minutes behind.

 

[Caruut]

Two objects a fixed distance apart and always moving at the same speed are never more or less likely to catch each other, regardless of their shared speed.

No they aren't, but that neither refutes anything I said nor has an other relevance to this discussion.

 

[Waterloo Sunrise]

More gibberish.

As I have said time and again, the reason the time gap drops if they accelerate at the same time, then the group behind races the section between the two faster.

Let me give you another example.

The break goes past the 100km mark at 12:00 (going 20km/h, though this is totally irrelevant). As soon as they pass it, they increase speed to 40km/h. Then they must complete the next 20km in 30 minutes, so they pass 120km at 12:30.

Now suppose the peloton does the exact same thing, and is 10 minutes behind at 100km - that is they pass it at 12:10 (at 20km/h again, though this is entirely redundant). They also increase to 40km/h as they go past 100km. Then they will also take half an hour to go over the next 20km, so they will pass 120km at 12:40. Still 10 minutes behind.

You don't need to give more examples, I understand what you are saying, but I disagree and unfortunately you (, you freely admit) don't understand what I am saying.

Your new example is not a parallel, as the speed change is not instantaneous.

Your example simple illustrates the concertina effect of two objects change speed at a fixed point, but not at a fixed time.

 

[Waterloo Sunrise]

No they aren't, but that neither refutes anything I said nor has an other relevance to this discussion.

If you think it doesn't have relevance then you haven't remotely understood what I am saying, and there's very little point in us each reply to each other.

What I wrote in that post demonstrates that an instantaneous shared speed change leads to a change in the measured time gap between 2 objects, which was how this discussion has started.

You have now started giving examples of how if the change is not instantaneous then the effect does not hold. No ****. If I was less kind I would almost suggest you are deliberately trying to change the example.

 

[Caruut]

It's not my fault that what you're saying has nothing to do with physics. The time gap between two things is purely the time that has passed since the first object was where the second object now is.

Think about the finish line - the gap at the finish is simply the time difference between one finisher and another finisher. Suppose the first guy goes over at 17:00, and the second at 17:10. Whether the second finisher goes over the line at 1km/h or 100km/h does not change the fact that he is 10 minutes behind. Time splits are just like having an imaginary moving finish line on the front wheel of the peloton and measuring how far behind the peloton finishes.

 

[Libertine Seguros]

If you are arguing for consistency of metrics aiding comprehensibility, why do we judge the race left to run in distance but the gap in time?

Because:

If you run a race to last a certain amount of time, then comparing time between contestants is totally irrelevant, because at the end everybody will have competed for the same amount of time.

If you run a race to last a certain amount of distance, then comparing the distance between contestants is totally irrelevant, because at the end everybody will have covered the same distance.

Racing, not just in cycling, but in all forms, works to two formats:

1) There is a set distance, and whoever completes that distance in the fastest time wins. Therefore the metrics should be "distance covered/distance remaining" and "time between contestants", because that tells you where they are in the event (distance) and where the competitors are relative to one another (time). This is how Formula 1, MotoGP, road cycling, most track cycling, swimming, triathlon, most athletic (track) events, XC skiing, all work.

2) There is a set amount of time that is competed for, and whoever has covered the most distance in that time period wins. Therefore the metrics should be "time remaining" and "distance between contestants", because that tells you where they are in the event (time) and where the competitors are relative to one another (distance). This is how the hour record and endurance motor racing work.

For cycling, distance remaining and time between contestants is the only logical way to go.
Time remaining is impossible to judge, as the contestants race from point to point, so we can't say when a rider is going to get there, therefore distance remaining is the only logical way.
Distance between groups is totally irrelevant to the metric the event is judged on (it's judged on time taken to complete the course), therefore it is only logical to provide the gap in terms of time taken, for ease of clarity.

 

[Caruut]

If you think it doesn't have relevance then you haven't remotely understood what I am saying, and there's very little point in us each reply to each other.

What I wrote in that post demonstrates that an instantaneous shared speed change leads to a change in the measured time gap between 2 objects, which was how this discussion has started.

You have now started giving examples of how if the change is not instantaneous then the effect does not hold. No ****. If I was less kind I would almost suggest you are deliberately trying to change the example.

Or perhaps I understand it, and it is you that does not.

What you wrote does not demonstrate that, the counter proof is quite simply that it doesn't happen.

I gave a different example because I'd already given my first example. How about you use maths and physics to demonstrate your point.

 

[Waterloo Sunrise]

It's not my fault that what you're saying has nothing to do with physics. The time gap between two things is purely the time that has passed since the first object was where the second object now is.

Think about the finish line - the gap at the finish is simply the time difference between one finisher and another finisher. Suppose the first guy goes over at 17:00, and the second at 17:10. Whether the second finisher goes over the line at 1km/h or 100km/h does not change the fact that he is 10 minutes behind. Time splits are just like having an imaginary moving finish line on the front wheel of the peloton and measuring how far behind the peloton finishes.

As I've already said, I don't question measuring gaps in time is the easiest way in practice.

However, I have explained perfectly clearly (in response to El P above) why an instant change in speed in both moving objects will lead to a halving of the gap as measured in time, but no change in the gap as measured in distance.

You then went on to argue that the halving of the time gap was in some sense valid, as their position has worsened. I argued to the contrary that their position is no better or worse. It only appears better (or worse) if you begin mixing up the two metrics (distance and time). In practice they are 2 objects a fixed distance apart and always moving in the same direction at the same speed, so regardless of the speed the 2nd object is no more or less likely to catch the first object until the condition of equal speed is breached.

You then seemed to switch round to arguing that the time gap does not change by using an example where the speed change does not occur at the same time. Your example was completely correct, but not on the point - you are more than welcome to try to argue that the time gap does not change given the speed change occurs at the same time, but that would require the denial of either statement in my reply to El P.

 

[Waterloo Sunrise]

I gave a different example because I'd already given my first example. How about you use maths and physics to demonstrate your point.

As explained, your example is not on the topic as the speed change does not occur at the same time.

To re-iterate, and you can let me know which premise, or point of logic you disagree with....

Premise A - Time = distance/speed

Where -

Time = measured time gap
Distance = distance between 2 objects
Speed = speed of 2nd object

Premise B - 2 objects travelling at the same speed in the same direction have a constant distance between them.

Premise C - 2 objects which begin travelling at the same speed in the same direction, and then change their speed at exactly the same moment, will always be the same distance apart.

Argument -

As per Premise B & C, the distance between 2 objects will not change when they both change speed at the same time.

Thus with speed doubled and distance constant, time must halve, following Premise A.

 

[richtea]

Or perhaps I understand it, and it is you that does not.

What you wrote does not demonstrate that, the counter proof is quite simply that it doesn't happen.

I gave a different example because I'd already given my first example. How about you use maths and physics to demonstrate your point.

I'm not sure why this is going over your head. Imagine the peleton doubling their speed at the point the break crosses the line, 5 minutes down. Since it will only take them 2.30 to get there, the time gap has instantly halved.

 

[cineteq]

Re-calculating.....

 

[El Pistolero]

What's wrong with the time gap going down when someone increases their speed? That's the point you know.

 

[Caruut]

As I've already said, I don't question measuring gaps in time is the easiest way in practice.

However, I have explained perfectly clearly (in response to El P above) why an instant change in speed in both moving objects will lead to a halving of the gap as measured in time, but no change in the gap as measured in distance.

You then went on to argue that the halving of the time gap was in some sense valid, as their position has worsened. I argued to the contrary that their position is no better or worse. It only appears better (or worse) if you begin mixing up the two metrics (distance and time). In practice they are 2 objects a fixed distance apart and always moving in the same direction at the same speed, so regardless of the speed the 2nd object is no more or less likely to catch the first object until the condition of equal speed is breached.

You then seemed to switch round to arguing that the time gap does not change by using an example where the speed change does not occur at the same time. Your example was completely correct, but not on the point - you are more than welcome to try to argue that the time gap does not change given the speed change occurs at the same time, but that would require the denial of either statement in my reply to El P.

Well, it wouldn't necessarily halve - that depends entirely on how much they accelerate and how big the initial gap was.

Okay - let's extend my previous example to say that the race is flat and 200km long. A break comes out and both the groups are racing at 20km/h, so it takes 30 minutes to do 10km. At 12:00, group 1 passes 90km. 30 minutes later, group 2 passes the 90km mark, giving the break a lead of 30 minutes.

At this point, the group 1 is at 100km. Both groups increase their speed to 40km/h. Now each 10km is raced in 15 minutes.

Now consider the time taken for each group to race the final 110km from 90 where we start to the race finish at 200. Group 1 takes 30 minutes to get ride from 90 to 100, and then 10*15=150 minutes to ride from 100 to 200. Then 30+150=180m=3h.

Group 2 takes 15 minutes for every 10km, so 11*15=165m. Since they race the final 110 kilometres 15 minutes faster, it is entirely correct that they gain 15 minutes on the break. Note that I am not arguing they gain these 15 minutes as soon as they increase speed. The time gap gradually decreases between 90km and 100km.

 

[Caruut]

I'm not sure why this is going over your head. Imagine the peleton doubling their speed at the point the break crosses the line, 5 minutes down. Since it will only take them 2.30 to get there, the time gap has instantly halved.

It doesn't instantly halve - it continuously falls from 5m to 2m30s.

 

[Sidbike]

Time is more constant metric that tells how one racer/group is doing relative to another.

For example, If I were in a leadout train chasing down a break the distance between me and the break would oscalate significantly. One moment I might be 400M behind and 5 seconds later I might be 200M behind, then the next moment back to 400M. Time on the other hand will tell me if I need to speed up for the catch or slow down to let the break dangle. Same logic applies as a fan watching the race.

 

[richtea]

I don't there is a problem with it, but the point being made is analytically sound.

 

[Caruut]

As explained, your example is not on the topic as the speed change does not occur at the same time.

To re-iterate, and you can let me know which premise, or point of logic you disagree with....

Premise A - Time = distance/speed

Where -

Time = measured time gap
Distance = distance between 2 objects
Speed = speed of 2nd object

Premise B - 2 objects travelling at the same speed in the same direction have a constant distance between them.

Premise C - 2 objects which begin travelling at the same speed in the same direction, and then change their speed at exactly the same moment, will always be the same distance apart.

Argument -

As per Premise B & C, the distance between 2 objects will not change when they both change speed at the same time.

Thus with speed doubled and distance constant, time must halve, following Premise A.

You cannot use the time gap in the equation speed=distance/time. That is a separate measure of time - namely the time a given object has taken to complete said distance.

The time gap does halve, but that is because a given section is raced twice as fast. It goes down continuously during that section.

 

[Waterloo Sunrise]

It doesn't instantly halve - it continuously falls from 5m to 2m30s.

Ok, so you're disputing the method of calculating the time gap - now makes a bit more sense. Not sure its an argument worth having however, and doesn't really change the point.

The reason I started this was because when the peloton speeds up midway through a sprint stage, the measured time gap displays an artificially large and quick fall in the gap. I hope now we've discussed at this length people can now see that it is the case, and why it is the case. I simply added as an extra point that the performance of the breakaway is irrelevant in the time period during which that fall happens (instant or over the course of the time gap depending on how you measure the time gap, with a hat tip to your point above).

 

[Caruut]

Ok, so you're disputing the method of calculating the time gap - now makes a bit more sense. Not sure its an argument worth having however, and doesn't really change the point.

The reason I started this was because when the peloton speeds up midway through a sprint stage, the measured time gap displays an artificially large and quick fall in the gap. I hope now we've discussed at this length people can now see that it is the case, and why it is the case. I simply added as an extra point that the performance of the breakaway is irrelevant in the time period during which that fall happens (instant or over the course of the time gap depending on how you measure the time gap, with a hat tip to your point above).

I still disagree with this point, though. I don't think that is artificially large. The change in gap (not instantaneous) is due to racing a given section faster than the group ahead. Your point was that a fundamental problem with time gaps is that changes in speed change them. Yes, they do, but only if maintained. Perhaps a predicted time gap might fluctuate, but the actual time gap does not.

 

[Waterloo Sunrise]

If the speed of both groups doubles at the same time, then the time gap halves, either instantly, or (using your method) in (distance/new-speed) amount of time.

Either way the time gap makes the break look like it has halved its gap, when the reality is the peloton is no more likely to catch it, still travelling the same distance behind and never going faster.

If you think that is a valid representation of what is going on, when interpretted in the way people actually interpret time gaps ("wow, it's really falling the last few minutes"), then that's your look out.

 

[Lanark]

If the speed of both groups doubles at the same time, then the time gap halves, either instantly, or (using your method) in (distance/new-speed) amount of time.

Either way the time gap makes the break look like it has halved its gap, when the reality is the peloton is no more likely to catch it, still travelling the same distance behind and never going faster.

If you think that is a valid representation of what is going on, when interpretted in the way people actually interpret time gaps ("wow, it's really falling the last few minutes"), then that's your look out.

What do you mean with 'at the same time'? If the front group starts riding 40kph at 20km to go, and the peloton is 10km behind and start speeding up at the same time (so, when they have 30km to go), they'll surely ride the part between 30km and 20km a lot faster, the peloton are going 40kph there, while the lead group only did 20kph. The gap won't drop after that (if they both continue to ride 40kph from 20 kilometers on), but the first drop is a real drop in time.

 

[Buffalo Soldier]

Time is a perfect measurement. Distance doesn't say a lot.

What I want to know is: how long ago did the previous group passed this point? And that's what time gap gives me.

They can say there's a 800m gap. That's something I don't care about, since 800m on the Mortirolo, is something completely different as 800m when riding 50km/h

 

[gerundium]

breakaway 1KM ahead of peloton, both doing 20KPH, the time gap is 3 minutes.

Then both breakaway and peloton increase speed to 40kph. The time measured gap is halved, which should mean the breakaway is now in a much worse position. Except they clearly aren't.

That's not how it works imo.

Moto 1 follows breakaway. Every 5 seconds the GPS pings the location and time.
Moto 2 follows peloton, Measure time difference between the two groups on every measuring point created by moto 1.

No relative speed crap.