| User | Comment |
|---|
Enheduanna  | | posted 16-Feb-2002 10:49am |
Isn't it around 50 MPH or so? |
| RayB | | posted 16-Feb-2002 10:51am |
I used to have a 1979 Datsun/Nissan 280ZX and I swear I got the best gas mileage the faster I went. I could go over 700 miles on a tank if I drove over 100mph but couldn't go but about 500 going 55. Boy, you cover some miles going real fast thus giving you alot of miles to each gallon |
| juliw | | posted 16-Feb-2002 10:56am |
I'd say 25-35 miles per hour |
| juliw | | (reply to RayB) posted 16-Feb-2002 10:58am |
I loved the 280 ZX. My dream used to be to own one in firethorn orange (this was in 1976) |
| RayB | | (reply to juliw) posted 16-Feb-2002 11:02am |
I have had quite a few cars since then but the 280Z was my favorite. |
| juliw | | (reply to RayB) posted 16-Feb-2002 11:05am |
I can see why. That was one sharp car! |
| Zang | | posted 16-Feb-2002 12:00pm |
I would have thought it was "as slow as possible". I picked the slowest speed 25-35. |
| confetti | | posted 16-Feb-2002 12:04pm |
*confetti stares at you and chews her gum in silence* |
| Dino | | posted 16-Feb-2002 12:22pm |
45-55 MPH? |
| Biggles | | posted 16-Feb-2002 12:39pm |
This question is gobbledegook to me! I get as far as understanding you want to know what speed needs the least petrol per mile? I think? But I have no idea! I would assume the fastest, but I really don't know. |
| mandy | | posted 16-Feb-2002 4:13pm |
55-65 |
| Oscar | | posted 16-Feb-2002 4:31pm |
55-65 |
| Oscar | | (reply to confetti) posted 16-Feb-2002 4:32pm |
you can be such an ass wipe sometimes.
If you don't have anything to say about the survey, abstain or something, but don't leave us with your "I'm bored" comments. |
| confetti | | (reply to Oscar) posted 16-Feb-2002 5:19pm |
Sheesh whatever. Ban me if you want. |
| Oscar | | (reply to confetti) posted 16-Feb-2002 8:47pm |
I've tried, but I guess we all failed. |
jettles   | | posted 16-Feb-2002 10:10pm |
35-40mph |
| confetti | | (reply to Oscar) posted 16-Feb-2002 11:06pm |
You can filter me if you want. It doesn't take a mathematical genius to figure out how. |
Kristal_Rose  | | posted 17-Feb-2002 12:45am |
I'll guess 45-55. |
| Oscar | | (reply to confetti) posted 17-Feb-2002 1:00am |
ahhh, filter, yes...ban, as you said, no. |
| justjulie | | posted 17-Feb-2002 8:31am |
JULIW & ZANG
WINS!!!! |
| confetti | | (reply to Oscar) posted 17-Feb-2002 11:36am |
So go ahead. It might improve your complexion. |
| Dino | | (reply to justjulie) posted 17-Feb-2002 12:19pm |
damn! *stomps up and down in a tantrum* |
| Cain | | posted 17-Feb-2002 12:42pm |
45-55 mph? Not sure. |
| Oscar | | (reply to confetti) posted 17-Feb-2002 1:50pm |
no thanks |
| confetti | | (reply to Oscar) posted 17-Feb-2002 4:09pm |
Fine, but then there's no excuse for you being peeved at what I say. It's your own choice to read my comments. |
| Oscar | | (reply to confetti) posted 17-Feb-2002 4:23pm |
Yep, and my choice to get peeved at them. |
| HareKrishna | | posted 17-Feb-2002 4:36pm |
|
| msgman | | posted 17-Feb-2002 4:54pm |
The best economy (ie, best gas mileage) is obtained at the slowest speed the car will go in top gear without the engine "straining". For most cars, that's usually around 30mph, but it depends a lot on the engine.
That's simple physics - I'm surprised so many people got it wrong. |
| Kristal_Rose | | (reply to msgman) posted 17-Feb-2002 9:50pm |
Hey, finally an excuse to put this baby in seventh gear.
For a given H.P. load (affected by wind resistance (which kicks in more significantly around 55), friction coefficients, viscosities) there will be an optimum RPM-mixture/timing/compression and hopefull an appropriate gear to match (not necessarily the highest). A calculus equation in five variables, no wonder there's much further to go in ignition computers. No wonder they stick to using look-up tables. Now an older car only had vaccum to control mixture, so presuming a fixed mixture/timing/compression would indeed be the lowest solidly sustainable rpm:speed ratio. 3200 in 1st at a 1/4 mixture might surpass 800 in 4th running rich for BHP output. I don't know.
What physics did you have in mind? |
| msgman |
The question of how much power is required to move a given object a given distance at different velocities is simple physics. As cars are complex machines the real-life application is somewhat harder, which is why you can't say for certain what the most economic velocity is for a specific car without knowing exactly how it's put together, what the air resistance and rolling resistance are, etc.
But the underlying principles are always the same, and thus it's possible to give an "average" figure for an "average" car under normal circumstances, which is what the question is asking us.
Moving an object faster always requires more power than moving it slower. So in a theoretically perfect system, the best economy is obtained at the slowest possible velocity. A car, however, is not a perfect system, and having an engine running is using power even when the car is stationary. So in a real-life system, the best economy is found at the point where the "wasted power" curve intersects with the "theoretical efficiency" curve.
Modern cars use a highly complex system of ignition management and applied aerodynamics in order to improve efficiency at higher speeds, but all this is doing is flattening the efficiency curve somewhat, as well as reducing wasted power. It doesn't significantly alter the actual position of intersection point, merely broadening the "acceptable efficiency" banding. |
| justjulie | | (reply to Dino) posted 18-Feb-2002 8:08am |
don't be too upset! i just made a fresh batch of cookies with your name on it!!!!  |
| Gamera | | posted 18-Feb-2002 1:05pm |
What a bizarre and meaningless question. How could those things not be a factor? How fast does the average living being travel? Species is not a factor, nor is age nor size a factor. |
| Kristal_Rose | | (reply to msgman) posted 18-Feb-2002 3:38pm |
In a frictionless environment, maintaining a higher speed should take no more power than maintaining a lower speed. Lubricated moving parts may resemble the difference between static and dynamic coefficients of friction, in which case a lower speed may be more economical to maintain (that would of course have to overcome the air resistance curve).
Of course theoretical ideal physics and applied practical results vary, otherwise tires of any width would offer the same friction. |
| bandit1cat | | posted 18-Feb-2002 4:08pm |
I've read that it is 37 mph. |
| msgman |
It isn't maintaining the speed that's relevant in a frictionless environment, it's accelerating to that speed. |
| Kristal_Rose | | (reply to msgman) posted 18-Feb-2002 6:29pm |
If one goes from San Diego, CA to Portland, OR up the I-5 that acceleration becomes negligible. Regenerative braking systems should diminish that concern as well. |
| msgman |
Not negligable, but it is low in the context of an extremely long (compared to the velocity). However, that's irrelevant - however small the acceleration component is, it's always higher at higher speeds than at low ones. And, in a frictional system, resistance (wind resistance, rolling resistance) also increases with speed. So there are two components, both of which increase power (and hence fuel) consumption with speed. In a vehicle powered by an internal combustion engine, there is also an element of "idle" power consumption, which is pretty much a flat rate. So the most economic speed is that at which the combined acceleration/friction power consumption curve intersects the idle power consumption curve.
Regenerative braking only applies to systems that can use the regenerated power - in practical terms, that means electric vehicles. But electric motors have no idle power consumption, so their "intersection point" is effectively zero - the faster an electric motor goes, the less efficient it becomes, no matter what speed it starts at. |
| Kristal_Rose | | (reply to msgman) posted 19-Feb-2002 4:35am |
I realise too (we both knew all this stuff before we started obviously) that the power involved in acceleration is somewhat logarithmic, but I still contend that a single acceleration up to speed over the course of maintining that speed constantly for a 1000 mile drive, regardless of what that reasonable speed or economy might be, is but the smallest percentage of the total trip gas consumption. But now you have given me inspirational food for thought with this absence of idle consumption - We are looking for the maximum of MPG (KPH) here. If we never start the dang thing up and give it a nudge with our pinky, we have division by zero, or infinite MPG.  (Alas, much like my car spends it's time doing  ) |
| Kristal_Rose | | posted 19-Feb-2002 4:37am |
IF YOU WANT BETTER GAS MILEAGE, DON'T START YOUR CAR! |
