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Post by PK on Jun 13, 2013 23:55:54 GMT
Thought the hipermiling was interesting but not sure you can really drive less than 45mph in some places. Judging from their map and the video, they went north on 101, then cut East over to the Napa Valley. Probably followed Silverado Trail up the valley, then West over the hills near Calistogo to the Santa Rosa area, then South back to the city. While they had to be on freeways for at least part of the trip (where 45 is, indeed, supposed to be the min speed), I can tell you that in those areas it's pretty unlikely they'd have received a ticket for going under 45, particularly once they were off the freeway and onto highways/county roads. Even without an escort. |
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Post by the light works on Jun 14, 2013 0:47:12 GMT
Don't really think it matters though since it was a 50 mph accident. Even though the cops in the movie were fat, I haven't seen it so were they fat or just big boned? Thought the hipermiling was interesting but not sure you can really drive less than 45mph in some places. One question though, couldn't it have hurt the engine if you turn it on then later turn it off then turn it on? I think that's just not going to work in real life because you can run into a light that is too short. a stop-stat hybrid has a starter motor that is rated for that. a standard car starter is not. - you will wear out your starter sooner by shutting the car off every time you come to a stop. |
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Post by blazerrose on Jun 14, 2013 2:04:08 GMT
I thought the lead car was the camera car, which passed Tory at one point on the highway and he waved at them. Then the CHP was the trail car. They showed Tory radioing he was running out, so it would be easy for the camera car to stop and get the camera out, then wait for Tory to pull over. I'm guessing Kari and Grant had a similar set up.
Hypermiling has a point, but really, angering every other driver on the road just isn't worth it. The way I drive I can get about 40 mpg on the highway, and about 36 in town, about 4mpg above what my car is supposed to get. It involves downshifting and accelerating gently, not punching it. On the freeway, though, I typically drive 60-62, or flow of traffic.
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Post by The Urban Mythbuster on Jun 14, 2013 4:02:59 GMT
Also, with turning the engine off at every stoplight, you're going to need a new starter every year...
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Post by OziRiS on Jun 18, 2013 13:01:03 GMT
I thought one of the tests in the hypermiling test sequence was kinda weird. I was always taught that accelerating slowly actually used MORE fuel than quickly getting up to speed and then keeping it there.
I think the team even made that point themselves when talking about easing off the accelerator and coasting when approaching red lights, slowly coasting up to it until it turns green, so you don't waste the car's momentum and have to use more fuel on accelerating from a dead stop. If you look at it the other way around, you're working against the car's inertia, trying to build up momentum. That takes energy no matter how you're going to do it, so the question is: What's better? A low amount of energy for a long period of time or a higher amount of energy for a shorter period of time?
I have a 2005 Skoda Fabia 1.9 TDi station wagon with a manual transmission. When I accelerate from a dead stop to 50 kph (about 31 mph), which is the speed limit in cities in Denmark, I can do it in two ways:
1. Slowly building up speed averages me about 35 MPG and takes me about 20-30 seconds after which I can reach up to 52 MPG when maintaining speed.
2. Quickly accelerating to 50 kph, which averages me about 21 MPG, but only takes me about 5 seconds (75-84% faster) after which I get up to the 52 MPG.
In other words, slow acceleration gives me about 68% of maximum fuel efficiency for the vehicle for 20-30 seconds, while quick acceleration gives me about 41% fuel efficiency for about 5 seconds. I'm not math savvy enough to do the remaining calculations in any coherent way, but I'm pretty certain the quick acceleration (at least with my car) makes more sense.
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Post by the light works on Jun 18, 2013 14:39:22 GMT
my understanding is you want the acceleration rate that gets you to high gear in the shortest possible DISTANCE. ont thing I have noticed is that when I do a full throttle launch, the shift points are delayed, and with minimal throttle it takes a longer distance to get to the shift points; but with moderate throttle, I can get earlier shifts, and be in high gear in a shorter distance.
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Post by The Urban Mythbuster on Jun 18, 2013 15:11:33 GMT
Decided to punch in some numbers to see how much gas is used & what I found supports your hypothesis that quicker acceleration is better.
1) Slow accel for 20-30 seconds (.0055-.0083 hours) from 0-30mph (avg = 15 mph) at 35 MPG = 0.00236-0.00356 gallons consumed
2) Quick accel for 5 seconds (.00135 hr) from 0-30 mph (avg = 15 mph) at 21 MPG = 0.00096 gallons consumed
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Post by OziRiS on Jun 18, 2013 18:36:10 GMT
Thanks TUM  I could see it in the numbers, but didn't quite know how to rack 'em up in the appropriate equation for it to make sense Much to TLW's point, I often skip gears when accelerating at full throttle, going from 1st to 3rd to 5th. Slow acceleration forces me to go through all 5 one at a time, or I'm using way too much fuel for way too long in one gear. |
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Post by The Urban Mythbuster on Jun 18, 2013 19:45:53 GMT
It's been a while since I channeled my inner Math geek...  |
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Post by OziRiS on Jun 18, 2013 20:21:19 GMT
Just out of curiosity, how'd you set it up? I kinda got stuck after the whole percentage of maximum fuel efficiancy thing and couldn't find a way to factor in time spent.
(To the mods: I know this is slightly off topic and I thought of having this talk with TUM via PM, but decided against it since I saw a possible opportunity for someone other than myself to learn/re-learn something about math from this)
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Post by Cybermortis on Jun 18, 2013 21:13:56 GMT
*Mod Hat on* This does relate to the episode, and asking to see the maths makes sense in context. So no worries  -CM |
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Post by The Urban Mythbuster on Jun 18, 2013 23:47:01 GMT
For example, accelerating to 30 mph in 5 seconds yields 21 mpg...
First, convert seconds into hours: 5 sec x (1 min/60 sec) x (1 hr/60 min) = (5/3600) hours = 0.00139 hours
Next, convert hours into miles (I took some liberty in deciding that 15 mph was a fair average for accelerating from 0-30): 0.00139 hours x (15 mi/1 hr) = 0.0208 mi
Finally, convert miles to gallons (using 21 mpg): 0.0208 mi x (1 gal / 21 mi) = 0.000992 gallons (9.92 x 10^-4 gallons)
Putting it all together yields: 5 sec x (1 min/60 sec) x (1 hr/60 min) x (15 mi/1 hr) x (1 gal / 21 mi) = 0.000992 gallons
[Repeat using 20 sec & 30 sec at 35 mpg]
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Post by the light works on Jun 19, 2013 0:20:48 GMT
Extreme case: it's about 3 miles from the south city limits to the turnoff to the highway I live on. accelerating at my preferred rate, I am in overdrive by the time I hit the 55 MPH speed limit sign (at 55 MPH) location. accelerating behind a take your time driver, I have had times I did not hit overdrive until I hit the left turn lane where I could accelerate around the take your time driver.
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Post by Cybermortis on Jun 19, 2013 13:09:27 GMT
For example, accelerating to 30 mph in 5 seconds yields 21 mpg... First, convert seconds into hours: 5 sec x (1 min/60 sec) x (1 hr/60 min) = (5/3600) hours = 0.00139 hours Next, convert hours into miles (I took some liberty in deciding that 15 mph was a fair average for accelerating from 0-30): 0.00139 hours x (15 mi/1 hr) = 0.0208 mi Finally, convert miles to gallons (using 21 mpg): 0.0208 mi x (1 gal / 21 mi) = 0.000992 gallons (9.92 x 10^-4 gallons) Putting it all together yields: 5 sec x (1 min/60 sec) x (1 hr/60 min) x (15 mi/1 hr) x (1 gal / 21 mi) = 0.000992 gallons [Repeat using 20 sec & 30 sec at 35 mpg] Your maths is good, but assumes that the engine is equally efficient at all RPM's - which is not the case in the real world. The reality is that at higher RPM you waste more fuel, as less is burned to produce energy you can use. Engines are designed to be efficient within a certain range of RPM's, rapid acceleration takes the engine above this efficient range. The principal is the same as keeping your speed low, in both cases you are keeping the RPM's within the most efficient range for the engine. If you read the MPG figures closely you'll note that when most manufacturers list the MPG for a particular vehicle they pick the figure from the most efficient speed/RPM for it - which as it turns out is usually 45mph. If you look at the figures above and below this speed (usually 30 and 60mph) they are considerably lower. The reason for this is that vehicles are more likely to be travelling at lower speeds/RPM (city streets or roads with similar speed limits). But you need to have a decent acceleration for safety (higher RPM) or in the case of larger vehicles so they can move heavier loads from a standstill. So engine designers compromise, making their engines efficient at RPM's that allow for fair acceleration and speed. |
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Post by the light works on Jun 19, 2013 13:36:05 GMT
For example, accelerating to 30 mph in 5 seconds yields 21 mpg... First, convert seconds into hours: 5 sec x (1 min/60 sec) x (1 hr/60 min) = (5/3600) hours = 0.00139 hours Next, convert hours into miles (I took some liberty in deciding that 15 mph was a fair average for accelerating from 0-30): 0.00139 hours x (15 mi/1 hr) = 0.0208 mi Finally, convert miles to gallons (using 21 mpg): 0.0208 mi x (1 gal / 21 mi) = 0.000992 gallons (9.92 x 10^-4 gallons) Putting it all together yields: 5 sec x (1 min/60 sec) x (1 hr/60 min) x (15 mi/1 hr) x (1 gal / 21 mi) = 0.000992 gallons [Repeat using 20 sec & 30 sec at 35 mpg] Your maths is good, but assumes that the engine is equally efficient at all RPM's - which is not the case in the real world. The reality is that at higher RPM you waste more fuel, as less is burned to produce energy you can use. Engines are designed to be efficient within a certain range of RPM's, rapid acceleration takes the engine above this efficient range. The principal is the same as keeping your speed low, in both cases you are keeping the RPM's within the most efficient range for the engine. If you read the MPG figures closely you'll note that when most manufacturers list the MPG for a particular vehicle they pick the figure from the most efficient speed/RPM for it - which as it turns out is usually 45mph. If you look at the figures above and below this speed (usually 30 and 60mph) they are considerably lower. The reason for this is that vehicles are more likely to be travelling at lower speeds/RPM (city streets or roads with similar speed limits). But you need to have a decent acceleration for safety (higher RPM) or in the case of larger vehicles so they can move heavier loads from a standstill. So engine designers compromise, making their engines efficient at RPM's that allow for fair acceleration and speed. not quite that straightforward. vehicles are designed for best efficiency at the speed they are expected to travel. in the case of my parents' cars, the minivan holds its efficiency (according to the onboard fuel monitor) until 65 MPH. the pickup, by fill to fill calculations, had its best efficiency, ever, driving 65 MPH down the freeway with a trailer load of polycarbonate panels for their greenhouse. and as I have pointed out on other threads, my service truck does not shift into high gear until it is going 50 MPH. the only universal rule is that normally aspirated gasoline engines are most efficient at 100% horsepower output. |
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