Comments on: AskPablo: Lighten the Load

By: V. Laxmanan

V. Laxmanan — Wed, 01 Apr 2009 14:05:34 +0000

Hi Pablo: I am very glad to see your post. Good work. I tried something similar back in June 2005 and decided that a simpler linear relationship could be used to describe the data. I have revisisted the problem and revived the calculations for 2009 vehicles. I have posted my results on the Magnesium Forum, see link below.
http://www.magnesium.com/w3//forum/read.php?thread=2772#t7093
I would very much like to use your data too, if you can share the Excel file with me. That would give us data for 2005, 2007 and 2009 and would make a good comparison of how fuel economy issue is being addressed on a year-to-year basis.
Laxmanan

By: rhett

rhett — Wed, 18 Jul 2007 17:08:16 +0000

I have a question about your excel graph. You say that it took some tricky excel work, but it seems to me that this is real data. Did you change the weight in your car and measure the fuel efficiency?

By: Pablo

Pablo — Thu, 21 Jun 2007 20:58:30 +0000

Update: The senate just voted to increase the CAFE standard to 35 MPG by 2020. This new standard now includes SUVs. Car makers are arguing that this standard is not attainable. As you can see in my column it is attainable, if the weight of cars is reduced. Smaller engines, carbon fiber car bodies, and hybrid technologies can all make this happen. Japan’s MPG standard is 45 and Europe’s is over 40. It is about time that the US shows a leadership position on global climate change…

By: costa

costa — Wed, 20 Jun 2007 14:57:21 +0000

Great post! There is a recent article examining this relationship, and adding vehicle power into the mix too (here is the GCC summary). As you said, most people don't use the space afforded by a larger vehicle on a daily (weekly?) basis. It would save the owner money by owning a smaller/lighter vehicle for most uses, and renting a larger vehicle when then needed it for hauling or recreation. Keep up the great work Pablo!

By: Pilot

Pilot — Tue, 19 Jun 2007 09:27:17 +0000

Excellent post, but note that the relationship is non-linear. The type of relationship curve represented usually suggests that constant change on the input generates disproportionate change on the output. That’s the case here too.

By: slanted tom

slanted tom — Mon, 18 Jun 2007 18:05:04 +0000

I’m glad you took the trouble to present to your readers the relationship between vehicle curb weight and gas mileage. Although there’s nothing new about this linkage (I remember it from twenty or more years ago) most Americans never see the connection, probably because the marketers don’t want them to think about it. Lighter vehicles get better gas mileage.
Just guessing, the data points above the curve are 4 cylinder cars and the ones below are 8s. Eight cylinder engines develop more power will accelerate a vehicle faster but use more gas to do it. Tires, gearing, rolling friction and aerodynamics explain the rest.
My ‘89 Corolla wagon gets 35 city (if I keep my foot out of it) and over 40 on the highway. I’ve guessed that it weighs 2500 pounds.
Then there’s this tiny 3 wheel car that weighs in at about 750 pounds and would graph in at about 80 mpg. I don’t remember the name.
Keep playing this song and maybe more Americans will learn the words and sing along. Lighten up, save gas and save money.

By: Nick

Nick — Mon, 18 Jun 2007 12:36:32 +0000

Bravo! I nominate this as one of the best Ask Pablos ever… PLEASE DIGG IT.
GM also bases their numbers on the claim to have the “most models” that are efficient. Of course, they offer identical models under different brands, so this is basically baloney too.
Finally, although I have no problem with smaller cars, we could still have larger vehicles if we found a way to improve what they’re made of – ie, the Amory Lovins hpyercar idea!