Rules of Thumb Put to The Test
August 24th, 2006 | by Brian Carr |A lot of times on Daily Fuel Economy Tip, I write about various rules of thumb. For example:
- For every extra 100 pounds you carry in your car, you decrease your gas mileage by up to 2%
- For every 5 miles per hour you drive above 55 mph, you reduce your gas mileage by up to 10%
- You save more gas by turning off and restarting your car than you do by idling for a minute.
The list goes on and on.
Well, it looks like someone has decided to put many of these rules of thumb to the test.
By hooking up a laptop to his 2006 Jeep Wrangler, Matthew Vea was able to get a pretty good feel for how accurate many of these rules of thumb really are. I’d go into the details regarding how Vea actually collected the data but you can read the article for yourself (this is actually a nice way of me saying the technical stuff in his article is way over my head).
Not surprisingly, Vea was able to confirm what you have read here many, many times - you can increase your vehicle’s gas mileage though:
- Moderate acceleration
- Watching your speed
- Properly inflating your tires
- Reducing excess weight
- Reducing drag
I highly recommend going back through Vea’s article to find out exactly how he was able to perform all these tests, and what sort of affect (or is it effect - I can never really tell) each of these items had on his gas mileage.
The best part is, all he did was confirm what you already know thanks to Daily Fuel Economy Tip (insert shameless self promotion here).
28 Responses to “Rules of Thumb Put to The Test”
By MarkFarker on Sep 28, 2006 | Reply
6. Riding a motorcycle
By Nick G on Sep 28, 2006 | Reply
How about - “don’t drive a huge gas guzzling lump of metal” ? Its a great way to save money and the environment !
By Dominic Ebacher on Sep 28, 2006 | Reply
Too many ad’s asshat.
Are you trying to feed a starving family of 7 - give us a break!
By Brian Carr on Sep 28, 2006 | Reply
Mark - I’ve actually looked into getting a Vespa because I don’t do much highway driving and I’ve heard they can get up to 80 miles per gallon.
Nick - Agreed.
Dominic - It’s just AdSense, it’s not like I’m running a milllion banner ads in addition to AdSense. Relax.
By your mom on Sep 28, 2006 | Reply
affect is a verb. always.
By Reasonable American on Sep 28, 2006 | Reply
Just don’t forget, for every 5 miles per hour you slow down, on a 100 mile trip, you waste over 9 minutes of your life driving. If you’re not driving for the pleasure of driving, that waste of your life adds up. Drive 12,000 miles a year? You’ve wasted over 20 hours of your life for each 5mph you slow down.
And by turning off and restarting your car, you are shortening its lifespan. Don’t forget, it takes energy to build a car, a lot of energy. One study actually showed that the total lifetime energy used by a Hummer is actually less than the total energy used by a Prius - that’s counter-intuitive, but the combination of the energy required to construct the Prius with more exotic materials, the significantly longer useful lifespan of the Hummer, and the significantly higher energy cost of recycling the exotic materials in the Prius resulted in a Hummer being a more responsible vehicle to drive than a Prius. Now, by shorting the lifespan of your car, you’ll have to replace it sooner, and the build energy of a new one, and the recycling energy of the one you destroyed before its time, will significantly outweigh any energy savings you got by shutting it off, and will likely outweigh the cost savings as well.
So, keep your tires properly inflated, reduce drag when you can, don’t carry excess weight unless you expect snow, and don’t drive a hybrid.
By your dad on Sep 28, 2006 | Reply
“Affect” is both a noun and a verb. So is “effect.” Total of four distinct meanings. Check dictionary.com.
By no one important on Sep 28, 2006 | Reply
Reasonable American: That study also presumed that the Prius only lived for 100k miles while the Hummer drove for 300k. Gee, I can’t imagine why someone would skew the assumptions like that, unless that was the only way to prove a point. I wonder what the numbers would look like if the Prius lived just as long as the Hummer.
By fred cooper on Sep 28, 2006 | Reply
your mom: affect is a verb. always.
Except when it is a noun. An affect is a feeling or mood.
By TK on Sep 28, 2006 | Reply
Not all things hold true, however. My car gets better mileage at 80 to 85 mph than it does from 55 to 65 mph. I’ve tested that too, believe me. All depends on gearing, tires, aerodynamic (coefficient of drag) of the car, and weight distribution.
By proHybrid on Sep 28, 2006 | Reply
Hummers are built of lower quality materials with lower tolerances than toyotas. Why do you think they have a longer useful lifespan than higher rated vehicles? This is entirely counter-intuiitive. I think the post by ‘reasonable american’ is incorrect.
By hmmm... on Sep 28, 2006 | Reply
whoever: thing.
whoever, I disagree with you. I base my disagreement upon a different study from you, which is just as un-verifiable and untrustworthy as the one you quoted. Now I feel better about myself for vanquishing you and your idiot that believes , which I disagree with.
Man, I feel better about myself now!
By jack alexander on Sep 28, 2006 | Reply
what ads?
walk, ride a bus…
stay home and geek…..
By hmmm... on Sep 28, 2006 | Reply
that should read you and your idiot (insert group) that believes (insert belief). Who knew that angle brackets wouldn’t show up? Silly HTML…
By ralph on Sep 28, 2006 | Reply
Maybe the mechanics of the hybrid car will go to 300K miles, but has anyone come up with an idea for what we’re going to do with all those batteries after they croak in a few years or 100K miles? Hybrid? No thanks. I’ll stick with my V8 Jeep Grand Cherokee and my 6 cyl Chevy truck. My 6′ 4″ frame doesn’t fit well in cars, nor do they tow or haul a cord of firewood on the weekend.
By Amskeptic on Sep 28, 2006 | Reply
The economic analysis of hybrids to WTF?! Hummers? er… conventionally powered cars usually fails to consider unequal economies of scale and unequal levels of maturity in the technologies affecting them.
Since the market is demonstrating that there are consumers willing to purchase hybrids, two things will happen if it persists. We can be reasonably sure the market will introduce efficiencies that will bring prices down. And we will have enough of a track record over a large enough statistical sample to compare the two.
In the meantime, we can wonder the lengths that naysayers are compelled, inspite of the lack of sufficient evidence.
And we can practice
-1. Riding bicycles
0. Riding Motorcycles
1. Moderate acceleration
2. Watching your speed
3. Properly inflating your tires
4. Reducing excess weight
5. Reducing drag
By zordinance on Sep 28, 2006 | Reply
http://www.planetoid.org/grammar_for_geeks/effect_vs_affect.html
Cause and effect… or act directly upon (thereby affect) something.
By ShabbaDoo on Sep 28, 2006 | Reply
Not all things hold true, however. My car gets better mileage at 80 to 85 mph than it does from 55 to 65 mph. I’ve tested that too, believe me. All depends on gearing, tires, aerodynamic (coefficient of drag) of the car, and weight distribution.
THANK YOU for pointing this out! The 55 MPH figure is usually stated as cold hard physics, rather than a “rule of thumb” - many people don’t realize effieciency doesn’t start dropping off at the same speed for every vehicle - exactly where this point lies depends cheifly on weight, aerodynamics, and on where the “power band” exists for a particular driveline configuration (which includes not only the engine, but also (as you pointed out) things like final drive ratio, tires, etc). All three of these factors vary widely between vehicles. My big old Chevy Caprice did indeed top out around 55-60 MPH , but each of the four cars I’ve owned since then (more aerodynamic FWD’s) really did get better mileage around 70-75 (I’ve always paid close attention to mileage, this isn’t just skewed recollection…)
By Fast Driver on Sep 28, 2006 | Reply
The 10% loss for every 5 miles over 55 has obviously come from the bureau of statistics pulled out of ones arse. I can see the rest, but why would you make up an arbitrary value like this. I drive on the highway all the time around(80) and i do not see a 50% drop in gas millage as your statistics would show. (and even if you take 10% off at every 5mile mark it still comes out to be a rediculously high percentage(41% at 30mpg base))
I’ve tried driving at 55-65 and have seen almost no appreciable difference in gas mileage. however in a recent trip upstate driving around 90-95 i did notice a loss of approximately 8%. I was surprised i thought i would get better doing all highway.
By T-Bird Fan on Sep 28, 2006 | Reply
I have to say that the keep the mileage to 55-65 rule is not really applicable in my case.
Car: T-Bird SC
Drive 302 miles to friends in SD, generally at 60 average with spurts up to 70, and I have to refuel immediately upon arrival, if not just before.
Drive 303 miles to Las Vegas, average 95 with spurts up to 105, and arrive with 1/8 to 1/4 of a tank left.
Car: Merc Grand Marquie
Drive 310 mile loop to Palm Springs and back average 65 with spurts up to 75, need to refill on the way back.
Drive 302 miles to Vegas, average 85 with spurts up to 95, and arrive with over 1/4 tank.
In all cases, no stops involved, save for the stopover in Palm Springs.
In a small car, with not enough hp to move it, yeah, I can see 55 saving gas. But in a well-engineered car, with enough power to move it, it has been my experience that the best mileage speed is significantly higher.
By Temp on Sep 28, 2006 | Reply
I think some heavier cars would get better mileage going faster.. You’ve got more momentum, and ur going faster.. so the gas you use keeps you going.. Some cars dont require too much more power in good conditions to maintrain 90 than it does 70. Not true for every car.. but it makes sense to me.
By Scooterman on Sep 28, 2006 | Reply
Unless you are one of those people that value style over function, I’d skip the Vespa. They cost about twice as much as other scooters, simply based on name recognition and image.
I bought a Kymco People 50 scooter (http://www.bigkidtoys.com/HTML/scootPPL50.html) a little over a year ago for my work commute. It gets about 75 MPG on that route, which involves a few hills, and some inevitable time idling in traffic. I bet it would get as high as 85 MPG under ideal conditions. The scooter is very reliable, and cheep to own, maintain and insure. Not to mention, it’s fun to ride…
…and against my pickup truck, pays for itself! Dig the math:
cost of gas: $2.50/GAL
MPG scooter: 75 MPG
MPG truck: 15 MPG
Commute round trip: 18 miles
Work Days a year: 240
per year gas cost to “truck it” = $720
per year gas cost to “scoot” = $144
savings of $576 a year, which will pay for the scooter in about 5 years.
I’m not going to give up my truck, because sometimes I need to haul stuff, but using it as a commuter vehicle doesn’t make much sense. Now if I could only get a vehicle that is powered by my smug sense of self-satisfaction!
By JoeB on Sep 28, 2006 | Reply
Temp: Not true. While heavier cars might have more momentum, that has almost no actual affect on maintaining a constant speed. Moreover, heavier cars tend to have increases in all the factors that cause a car to have lower mileage: more power required for acceleration due to higher air resistance and higher mechanical loss throughout the drivetrain and wheels/axles.
By chaositect on Sep 28, 2006 | Reply
Mass of the car takes energy to get up to speed. The exact same as it will impart with momentum (minus friction). JoeB is right there.
Way too many variables and unsubstantiated claims here, to say nothing of the grammar pedants. Good point on the energy to make / recycle cars, even if it is based on false facts. I’m thinking a Prius will last longer than a Hummer myself even if it does cost more energy to make / recycle.
I’m not saying you should give up your truck (though I’m sure that’s just what many other people ARE saying). Especially if you use it for it’s intended pupose. I’m not saying to save the environment either. The planet will survive, we’re just ousting ourselves out of a place to live. Bequething it to the cockroaches. Do what you want. I just want the facts presented properly. Grandstanding is no proper way to present or sway an argument, and it seems the human race has lost the faculty for a logical debate. It has me rather depressed.
Where can I go for intelligent internet nowadays? Anyone?
By anon. on Sep 29, 2006 | Reply
Before this is all over I’m going to end up naked in the middle of a feild and still wondering if my weight on the ground is disturbing some cockroach ecosystem.
Save the earth! Kill yourself!
By fred cooper on Sep 30, 2006 | Reply
intelligent internet = oxymoron
By Casey on Oct 1, 2006 | Reply
I’m operating under the assumption that as speed increases, So does air resistance on an exponential scale. Depending on the vehicle, More energy(fuel) is required to as the speed goes up. You may see small decreases in mileage up to a certian speed range but after that it starts falling off very quickly. It’s an accepted truth in the world of land speed record cars that it takes huge amounts of power to increase speed percentage-wise. So I find it funny to hear people talk about how their Shoebox shaped family truckster gets better mileage at 90 than 55… Of course there is also engine RPM to deal with, The lower the RPM the lower the frictional losses. so it’s plausible to get better mileage at say 4th gear and 2200rpm than at 3rd gear and 3500rpm. Possible But unlikely. There is the psychological factor also, People often try real hard to justify bad habbits when they don’t want to change those habbits.
By Adriel on Apr 11, 2007 | Reply
Well, casey, there’s also engine design to deal with…many cars can be more efficiant at higher speeds due to the engine being more efficiant at higher revs