Except there is no study that supports your claim that cruise control can save 10% on flat courses. In fact, the “studies” our there show the exact opposite. If you do some googling, as suggested by someone in this thread, for ultra-distance economy with a Honda Insight, you’ll see that manual speed control ALWAYS yields the best results for a driver with any experience. You cannot, in any way, infer that it is “well accepted” that cruise control offers the 10% savings you are claiming. That isn’t at all the conclusion of the edmunds “study.” Basically, you are pulling a number out of your ass and then claiming it is a “well accepted fact,” when nothing could be further from the truth. Nothing new there…
Gee, I thought I gave a reference to an article that tested the “myth” and proved that cruise control saved between 7 aned 14%. But, I guess you are right, it wasn’t a study. Anyhow, why don’t you read the original question. Such claims are common knowledge and “seemingly true”. The math we did before suggests there should be some improvement. Why is it so large in the case of cruise control compared to cycling? What is the difference?
Except there is no study that supports your claim that cruise control can save 10% on flat courses. In fact, the “studies” our there show the exact opposite. If you do some googling, as suggested by someone in this thread, for ultra-distance economy with a Honda Insight, you’ll see that manual speed control ALWAYS yields the best results for a driver with any experience. You cannot, in any way, infer that it is “well accepted” that cruise control offers the 10% savings you are claiming. That isn’t at all the conclusion of the edmunds “study.” Basically, you are pulling a number out of your ass and then claiming it is a “well accepted fact,” when nothing could be further from the truth. Nothing new there…
Gee, I thought I gave a reference to an article that tested the “myth” and proved that cruise control saved between 7 aned 14%. But, I guess you are right, it wasn’t a study. Anyhow, why don’t you read the original question. Such claims are common knowledge and “seemingly true”. The math we did before suggests there should be some improvement. Why is it so large in the case of cruise control compared to cycling? What is the difference?
The magnitude of the speed variance (assuming we’re talking about intra-pedal stroke variations)… Haven’t we been over this?
However, it is also the case that there’s also a substantial amount of energy to be saved (from both physics and physiology) if one maintains a constant speed while cycling (assuming a flat course), rather than letting it drift about.
But, a skilled driver can always beat cruise control for MPG, because the driver can see changes in terrain and “preempt” the worst fuel economy situations.
Agreed. However, you actually see few drivers driving this way - it’s either jamming on the accelerator or slamming on the brakes. My sense of this is that very few drivers look further down the road than the 40 - 50 ft or less in front of their cars. Beyond that, they don’t have a clue that is going on. I can’t say this for sure, but my sense is significant fuel efficiency gains could be made by many drivers, by gradually accelerating/braking, looking far down the road and adjusting speed to the traffic conditions, but I am sure that many would not like this.
Here’s some tests, to gauge where we are at with this:
Try running down a road, into traffic on the edge of the road( as you should be) and notice how many cars don’t see you until the last minute. Or, try coasting gradually to a stop at a light and watch how many cars will do a massive acceleration just to get around you only to have to slam their brakes on at the light. Or when pulling away from the light gradually, how many cars will honk, then undergo a massive acceleration( maybe even give you the finger!!) to get around you and one car ahead!!
Except there is no study that supports your claim that cruise control can save 10% on flat courses. In fact, the “studies” our there show the exact opposite. If you do some googling, as suggested by someone in this thread, for ultra-distance economy with a Honda Insight, you’ll see that manual speed control ALWAYS yields the best results for a driver with any experience. You cannot, in any way, infer that it is “well accepted” that cruise control offers the 10% savings you are claiming. That isn’t at all the conclusion of the edmunds “study.” Basically, you are pulling a number out of your ass and then claiming it is a “well accepted fact,” when nothing could be further from the truth. Nothing new there…
Gee, I thought I gave a reference to an article that tested the “myth” and proved that cruise control saved between 7 aned 14%. But, I guess you are right, it wasn’t a study. Anyhow, why don’t you read the original question. Such claims are common knowledge and “seemingly true”. The math we did before suggests there should be some improvement. Why is it so large in the case of cruise control compared to cycling? What is the difference?
The magnitude of the speed variance (assuming we’re talking about intra-pedal stroke variations)… Haven’t we been over this?
However, it is also the case that there’s also a substantial amount of energy to be saved (from both physics and physiology) if one maintains a constant speed while cycling (assuming a flat course), rather than letting it drift about.
Yes we have been over this before which is why I am asking this follow-up question as to the size of the difference. I don’t see it as being simply the magnitude of the variation as the small magnitude comes about because of the high frequency and the math should be the same.
You got me thinking about this and I think it has to do with the frequency, as a rapid frequency (bike) never allows the object to ever come close to the terminal velocity at either the high or low end whereas a slow frequency allows the object to approach or reach the final velocity of that power. The effects would be exaggerated if the object spent more time at speed where the effects of the non-linear forces were “maximum” instead of just accelerating towards these values in a “close to linear” relationship.
I ran some numbers at analytic cycling to test the theory. Their standard 75 kg person averaging 300 watts on the flat would go 12.00 m/s. But the same person riding at 500 watts for an hour and 100 watts for an hour would average only 11.17 m/s even though he avaraged the same 300 watts. He would average 11.17 m/s if he rode steadily at about 246.5 watts. This speed variation cost him over 50 watts out of 300 or about 15%. There may be other losses in the car also as there could be variable drive train losses, especially with an automatic transmission where there can be substantial “slip” associated with accelerating. Even varying between just 350 and 250 watts has an overall lowering effect of over a watt.
Anyhow, I think this question is now answered for me unless someone sees a flaw in what I have said above.
Cycling is to** Driving as Pedaling** is to the** Firing of Pistons as Gasoline** is to Glycogen.
It seems like you are comparing Driving to Pedaling
Wouldn’t this be a better way to us “cruise control” to compare an Automobile to a Bicycle? :
**Cruise Control(Driving) on a flat road is efficient b/c you aren’t switching gears and are not accelerating.
------------So------------------
**Cycling on a flat road at a constant wattage, not switching gears, would also be efficient.
It’s the variance, not the frequency that drives the difference (although as you say, a lower frequency permits a bigger variance.)
.
Cycling is to** Driving as Pedaling** is to the** Firing of Pistons as Gasoline** is to Glycogen.
It seems like you are comparing Driving to Pedaling
Wouldn’t this be a better way to us “cruise control” to compare an Automobile to a Bicycle? :
**Cruise Control(Driving) on a flat road is efficient b/c you aren’t switching gears and are not accelerating.
------------So------------------
**Cycling on a flat road at a constant wattage, not switching gears, would also be efficient.
There’s another significant tautological flaw in Frank’s argument: gasoline efficiency is about going as far as possible on a given amount of fuel, whereas cycling efficiency is about producing as much power as possible for a given rate of oxygen consumption.
But nobody rides that way. Nobody rides for 350 watts for an hour and 250 watts for an hour, unless they are doing a specific workout. Nobody races that way…
But nobody rides that way. Nobody rides for 350 watts for an hour and 250 watts for an hour, unless they are doing a specific workout. Nobody races that way…
It is a way of analyzing the problem to see what the important aspects are and to see what the maximum “worst case” effect would be. Two people never leave two stations at two different constant speeds and wonder when they will meet either but it is a good problem to illustrate problem solving techniques.
You are right. You have just proven that it is a bad idea to vary your power by 17% if you are trying to achieve maximum efficiency. However, this has been shown time and again by a lot of the knowledgeable folks on this forum, who have shown that a Variability Index of ~1.06 (Ashburn or Tom A., feel free to chime in if I’m off a bit on this) or so will result in the fastest time for a typical triathlon bike course. Now, VI is not exactly the same as your 350/250 problem, but it is MUCH more applicable. Interestingly, a VI of 1.06 is FASTER than a VI of 1.00. So some variability is still important to achieving the fastest time. This is for generally “rolling” courses that don’t net any altitude gain or loss. And VI is a measurement of power variability. Dr. Coggan can explain it more thoroughly. VI is where you should be focusing your attention, as it is MUCH, MUCH more relevant to this problem.
You are right. You have just proven that it is a bad idea to vary your power by 17% if you are trying to achieve maximum efficiency. However, this has been shown time and again by a lot of the knowledgeable folks on this forum, who have shown that a Variability Index of ~1.06 (Ashburn or Tom A., feel free to chime in if I’m off a bit on this) or so will result in the fastest time for a typical triathlon bike course. Now, VI is not exactly the same as your 350/250 problem, but it is MUCH more applicable. Interestingly, a VI of 1.06 is FASTER than a VI of 1.00. So some variability is still important to achieving the fastest time. This is for generally “rolling” courses that don’t net any altitude gain or loss. And VI is a measurement of power variability. Dr. Coggan can explain it more thoroughly. VI is where you should be focusing your attention, as it is MUCH, MUCH more relevant to this problem.
I suspect the variability index for optimum performance will probably vary based upon the course. The hillier the course, the more variable the power for optimum performance I suspect. We had a thread on this awhile back where I thought there might actually be an advantage to varying power. (Search for the “. . . thinking outside the box” thread). Of course, the difference is in the engine. A gasoline engine will never get tired and efficiency can be well defined and is repeatable. The human, not so. The body might do better over the long run in having periods of light load to allow for recovery to allow periods of higher load when they are most important, climbing for instance. So, one is willing to negatively affect one efficiency to positively affect another one of bigger importance.
I guess it is possible that constant power for 1 or 5 hours might optimize time trial performance if the course were perfectly flat and there were zero wind (indoors on a track perhaps) but I am not sure that has been “proven”. If it is optimum it certainly is hard to do.