Casaubon's Book

Run the Numbers on Your Ride

There’s a great post at The Oil Drum by Jeff Radtke that gives people a good way of evaluating the resource uses in their cars. Now you don’t actually have to do this to figure out that light cars are better than heavy ones – the results aren’t that difficult. But if you think it is fun to figure out smaller distinctions, it is worth doing.

This type of analysis is useful because it is easy to factor in conversion efficiencies and payload versus tare weight. Rather than use motor output power, one can use the thermal power theoretically available in the flowing fuel. EROI may be factored in, as well as GHG emissions. Analysis may be completed at the level of individual trips, vehicles, or an entire system with resource extraction, infrastructure development, manufacturing and direct fuel use.

Kinetic energy divided by required power is considered a residence time for the input energy in the utilized form. This model may provide an intuitive understanding of energy use. Residence time for anything in a container is the quantity residing divided by the flow rate. This is as true for a vehicle containing kinetic energy as it is for a mountain lake holding melted glacier, or the CO2 present in our atmosphere

I do have a bit of a quibble with Radtke’s assumption that one will continue, in the longer term, to be the standard number of car passengers – and indeed, if you want to green your ride, the single best way to green your ride is probably not to buy a brand new car, but to put more behinds in your car when you do drive. Yes, yes, I know the carpool is impossibly retro, but hey, retro is cool.



  1. #1 knutty knitter
    July 11, 2010

    Carpool is only thing available round here 🙂 We share a car with next door and carpool as well. A better bus system would help!!!

    retro9 cool viv in nz

  2. #2 Eric in KC
    July 11, 2010

    Like viv in nz, carpooling is the only “public” transportation available around here; however, with a hoard of youngsters with various activities and issues (though nothing like your son), I use a car for commuting, my wife uses a car for commuting and we both use an 8 passenger SUV for hauling our combined family around; usually, 4 kids, sometimes 5 (and periodically 6 with a friend or oldest sibling thrown in).

    Admittedly – we’re not the most efficient at using fuel, but we’re getting better at it! We will likely always need a large vehicle – not just for kids but also for building a new homestead when the resources are lined up. And, until that homestead is self-sufficient, the world ends up in a handbasket or I retire we’ll be commuting. And if the world ends up in a handbasket – I may need a large vehicle for hauling the troops around…

    So – the choices for fuel utilization depend on circumstance and the decisions that we’ve made to be where we are.

    Sharon – totally different subject. Have you read much of J. Russell Smith beyond Tree Crops? I ran across this article (published in 1914!) discussing a multi-level agriculture:

    He makes a cogent argument for living off what trees can provide. Much like what is proposed by Badgersett and Oak Watch – though Oak Watch is less developed…

  3. #3 Sharon Astyk
    July 12, 2010

    This is not intended as one-upmanship or “I’m doing it better” but just to note, with four kids, we manage to get along with everyone in a Ford Taurus ;-).

    That’s awesome, btw, about the tree crops!


  4. #4 Don
    July 12, 2010

    The table is hard to read. Why, for example, is “bicycle” listed five times, with different results each time? What is a “faired” bicycle anyway, and how can any bicycle travel at 75 mph?

  5. #5 clew
    July 12, 2010


    Because there are different kinds of bicycles, with different efficiencies; and because a bicycle ridden at 10mph has different drag and efficiency than one ridden at 30mph.

    ‘Fairing’ is a shell or oversock that streamlines the bike. Faired recumbent bicycles can certainly do 70mph; the landspeed record is something like 160mph. (Not everyone can do that, but racers already do 80mph stretches. It’s an extreme case, probably on the chart to show the range covered by bike technology.)

  6. #6 Don
    July 13, 2010

    Thanks, Clew.

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