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That's unnecessarily pedantic. They both measure fuel consumption, they just swap the x and y axis. It's not like the one is measuring fuel consumption and the other how cold it is outside.
MPG or L/100km
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That's unnecessarily pedantic. They both measure fuel consumption, they just swap the x and y axis. It's not like the one is measuring fuel consumption and the other how cold it is outside.
There are nuances to unit measures that many miss, and that goes back to not understanding how the unit is derived.
Same thing with ft-lb vs lb-ft, which shouldn't be used interchangeably. One measures torque, the other work.
Batteries are often rated, and sold in mAh to represent their capacity. But without considering voltage, it's an incomplete picture.
Which is "better?" BMW started putting their Econometer in instrument clusters in the 80s, calibrated to L/100km in most of the world. But in markets to suit where MPG is used, and forced to reflect that approximation, it has to use a logarithmic scale, which makes it harder to read and less useful. One could say that the former approach is better suited to an instantaneous consumption rate, which is what is being measured.
Put another way, is it a more useful, and accurate, to judge a project by the amount of money that has been spent on that project, or how far a specific amount of money can potentially go toward that project? Plenty of practical examples in real life to answer that question.
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I can’t fathom that calculation. It is out of my league.
Brilliant! Glad to have primed the pump, as it were.
These are some really good examples!
Please enlighten me about torque vs. work - I have always expressed torque in ft-lbs. (Yeah, I'm mostly metric, but am not yet onboard with Newton-Metres.)
I understand that work involves moving a given mass a given distance, whereas torque is applying a given rotational force at a given distance from the centre.
What I don't understand is which is which - does 80 ft-lbs involve applying 80 lbs of force to a lever 1' away from the axis (or 20 lbs to a lever 4' away, etc.); or does it involve moving an 80-lb mass 1' (or 1 lb 80', etc.)
That is, is torque properly expressed as lb-feet, or as foot-lbs?
Thanks!
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I think lb-ft is more correct just like N-meter but mostly we say ft-lb. Tomato tomatoBrilliant! Glad to have primed the pump, as it were.
These are some really good examples!
Please enlighten me about torque vs. work - I have always expressed torque in ft-lbs. (Yeah, I'm mostly metric, but am not yet onboard with Newton-Metres.)
I understand that work involves moving a given mass a given distance, whereas torque is applying a given rotational force at a given distance from the centre.
What I don't understand is which is which - does 80 ft-lbs involve applying 80 lbs of force to a lever 1' away from the axis (or 20 lbs to a lever 4' away, etc.); or does it involve moving an 80-lb mass 1' (or 1 lb 80', etc.)
That is, is torque properly expressed as lb-feet, or as foot-lbs?
Thanks!
Brilliant! Glad to have primed the pump, as it were.
These are some really good examples!
Please enlighten me about torque vs. work - I have always expressed torque in ft-lbs. (Yeah, I'm mostly metric, but am not yet onboard with Newton-Metres.)
I understand that work involves moving a given mass a given distance, whereas torque is applying a given rotational force at a given distance from the centre.
What I don't understand is which is which - does 80 ft-lbs involve applying 80 lbs of force to a lever 1' away from the axis (or 20 lbs to a lever 4' away, etc.); or does it involve moving an 80-lb mass 1' (or 1 lb 80', etc.)
That is, is torque properly expressed as lb-feet, or as foot-lbs?
Thanks!
Your understanding is correct.
Ft-lb is the measure of torque, or twisting force, which is also translated into horsepower using the 5252 conversion factor which a car guy has probably come across at some time in their lives.
Lb-ft is a measure of work, in a linear vector, of the amount of force applied over a distance.
Torque = F(orce) x r (position), so you can see what trying to break that stubborn bolt loose with a 1-ft breaker bar suddenly turns into a piece of cake when you stick a cheater pipe on, and push from the end of it, using your same body weight. Also explains why pipe wrenches are commonly sold in different lengths.
TBH, it's been a long time since I've sat in a physics class, high school, or even college, where the formulas are more complex and looked even more like gibberish to me, but I survived it…and decided that wasn't my strength.
Suffice it to say, each unit measure isn't pulled out of thin air, and has specific meanings as to what they represent, even if many of them sound very similar, and enough to be confused with each other.
At least with these units, they're easy to relate to, or demonstrate. With the units that relate to things like light, they're more abstract, and complex. Lumens, candela, candlepower, color temperature, etc. Those relationships aren't as straightforward, and there are more misconceptions, esp. when trying to relate color temperature to brightness, as is often done in headlight bulb marketing. Human vision is also a complex subject, which adds to the potential for confusion.
Not in europe, If I switch to MPG (did it when I drove in the UK) it shows miles per imperial gallon.
Patman
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As a European, I can chime in on where the mpg measurements eat your brain for breakfast and spit it out:
The issue is comparing mileage between different vehicles.
When shopping for a car, comparing mpg ratings, you get tricked by mpg ratings way more easily than by l/100km (or gallons per 100 miles, or ounces per mile - you name it).
For most people, the brain sees things in a linear way. Apples for apples. So an mpg is an mpg. You end up treating it as a unit, rather than as a result.
Let's say you're shopping for a car and you want to see what it will cost you in gas (or how much gas you'll need, if your gas is raining free from the sky).
- Car A gets 50mpg. Car B gets 48mpg. Difference: 2mpg.
- Car C gets 20mpg. Car D gets 18mpg. Difference: 2mpg.
- Truck E gets 12mpg. Truck F gets 10mpg. Difference: 2mpg.
- Machinery G gets 3mpg. Machinery H gets 1mpg. Difference: 2mpg.
Now, let's put those in L/100km (again, it can be any units - it's just about putting it into "Quantity needed to go a preset distance"), and apply that to a 100 miles trip (160 kilometers):
- Car A does 4.7L/100km (50mpg). Car B does 4.9L/100km (48mpg). The difference is 200 grams, or 7oz. Which absolutely negligible.
On a 100 miles trip, Car B will need 11oz more gas than Car A. I think we can agree that this is no big deal.
- Car C does 11.76L/100km (20mpg). Car D does 13.7L/100km (18mpg). The difference is now 2 liters. Not to torture anyone - thats more than half a gallon. On a 100 miles trip, Car D will need 3.2 liters more gas. Which is not quite, but quite close to, a gallon.
- Truck E does 19.6L/100km (12mpg). Truck F does 23.5L/100km (10mpg). Difference: 4.1 liters. That about a gallon and a quart.
On a 100 miles trip, Truck F will need 6.56 liters more gas. That's close to two gallons.
- Machinery G gets 78.4L/100km (3mpg). Machinery H gets 235L/100km (1mpg). Difference: 157 liters, or about 43 gallons.
On a 100 miles trip, Machinery G will need 251 liters more gas. Which is about 70 gallons.
Yes, 3mpg and 1mpg is caricatural.
However, the meat of most comparisons is (or at least has been, for decades), in the 12-18mpg range (trucks). This is a range where a 2mpg difference is substantial.
While there is technically no trickery (the mpg measurement is clearly about how far one can go on a given amount of fuel, not about how much fuel one needs for a set distance), the brain will most of the time iron it into a comparison of apples to apples. "Oh, it's just 2mpg less. Oh, a difference of 2mpg is no big deal"
US clients might have some immunity to this when shopping for a vehicle, but for anyone coming from the outside - the first time shopping for a vehicle here we're in full-blown Alice in Wonderland world. Oh, 2mpg difference. No big deal. Oh, the difference between 72mpg and 70mpg ? The same as between 12mpg and 10mpg. Two mpg.
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As a Canadian I totally get the L/100 KM. But MPG has a similar thing, you just have to remember the denominator.
8 vs 10 mpg, you're doing 2 mpg worse but the denominator is 10... 2/10 is huge.
38 vs 40 mpg, you're doing 2 mpg worse but the denominator is 40... 2/40 is peanuts.
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Eh, you were all up there converting grams, ounces, and liters, doesn't need to get that fancy. Pretty easy to see that 2 out of 10 is a large number but 2 out of 40 is peanuts. Nothing to remember
Have you checked to see if the measurements are really close? Few years ago Honda owners in Canada (maybe the USA) found that flipping from mi to km weren't showing the same amount. Being from the usa The MPG sounds better than L/100k.
Patman
Staff member
That’s what happens in my Civic, when I switch from metric to imperial and look at the odometer the calculation that Honda is using is wrong. Right now my Civic is in the body shop so I can’t double check it but if I recall, when I calculate properly the mileage in miles, based off what it shows in kilometers, Hondas calculation is off by about 500 miles right now (I’m at 287,000 km) It should be using the conversion rate of 0.6213712 to convert from km to miles but I suspect it’s not calculating it that precisely. My Corvette on the other hand is bang on when you flip it from metric to imperial.
In the UK distances are in miles and fuel is sold in Litres but no one use miles per litre which would be the logical unit of fuel consumption. The conversion from litres to gallons is simple enough so MPG is still king.
A figure given in L/100km means absolutely nothing to me and as it would require a double conversion I'd never be able to do it in my head.
A figure given in L/100km means absolutely nothing to me and as it would require a double conversion I'd never be able to do it in my head.
Honda has a recall and fix for the odometer being off in Km vs Miles. Check your local dealership.
That could vary due to temperature, driving terrain, and even how aggressive someone drives.
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Just as mpg ratings would. Nothing different there.
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