I’ve had an inbox full of suggestions for inexpensive streamlining of MAX, our 100-mpg, DIY car. Some of them are good, some are not so good, and a fair number of them are (to quote the Magic 8 Ball of my youth) “Reply Hazy, Ask Again Later.” I won’t call automotive aerodynamics a black art, but when you get to a specific car, you won’t find all the answers in the textbooks. 

The problem is every part of the body influences every other part of the body. Like the parable of a butterfly flapping in Barcelona causing a hurricane in Costa Rica, a small difference here can make a large difference there. A small change in the radiator intake might generate a mild change in how air flows over the hood, which could make a moderate change in airflow over the windshield, leading to a significant change of airflow over the roof, causing complete flow separation at the rear window and a huge turbulent wake behind the car. The textbooks can guide you, but the only way you’ll really know what you’re getting is to test. 

As you regular MAX Update readers know, we got an involuntary do-over on body design about a month ago and we don’t have much time to fool around. We’re doing rapid prototyping and rapid testing and going back to the basics, back to how aerodynamic testing was done in ye goode olde days.

Now I hate to oversimplify, but as a general rule of aerodynamic drag, turbulence = bad; smooth flow = good. One way to observe the flow of air close to the body is to tape tufts of yarn on the car and watch which way they blow. It sounds a bit like the old “weather string” joke (if it’s wet it’s raining, if it’s moving around it’s windy, if you can’t see it it’s dark) but tuft testing has a long and legitimate history. In the nautical world, a tuft of yarn has been called a “telltale” since about the time yarn was invented. In our case, the problem is with tufts on a car body, how do you watch them? 

In a wind tunnel, you just stand there and look, but with a moving car it's not that easy. You can’t drive alongside in another car because the wake of your observation car voids the test. So I asked myself, what would Wonder Woman do? She had an clear airplane. Why not a clear car? 

I've taken out the passenger’s seat and paneled MAX’s right side in $10 worth of one-eighth-inch Vivak, which is transparent, thermoplastic sheeting and is clear, tough, and easy to work with. You can saw it, drill it, rivet it, bend it … and tape tufts of orange yarn to it. I’ll watch the tufts from the driver’s seat and see how changes in the front of the car (different fenders in particular) influence airflow in the middle of the car, and maybe I'll learn something.

Photo by Jack McCornack

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This is more of a “downdate” than an update, but I thought you’d like to know what happened. We suffered a thrilling daylight burglary on Friday morning, October 9. OK, it wasn’t all that thrilling — we left Kinetic for breakfast at 9, came back at 10, and the door was open with the lock broken off. “Golly,” I said to my secretary, although not in those words, “I wonder if anything’s missing.”

Not much, actually: two laptop computers, two briefcases, and one external hard drive. It doesn’t sound too bad, does it? Well it was bad, because Friday is Backup Day, in which we back up our laptops with each other, and back them both up with a hard drive we keep at a secret location 10 miles from the shop ... except during work hours on Fridays when I watch that backup drive like a hawk and add the week’s work to its archives ... except during mealtimes, when we leave our work at the office.

So we were backed up solid, ready to restore from any computer crash, even ready to recover from any burglary, any fire less than 10 miles long (hey, we’re in the Oregon woods, we’ve seen worse) and most natural catastrophes, provided any of this didn’t happen on Friday between 9 and 10 a.m. (breakfast) or 1 and 2 p.m. (lunch). As you would guess, a whole lot of MAX data is (was) in electronic form, such as all MAX’s test results to date, and all the new body part drawings.

I’ve spent the last week looking for a silver lining to this cloud, and indeed I’ve found one: Now we get to work with a clean slate. For example, the “new” body (other than the roof) was designed over two years ago, and all the parts painstakingly rendered, ready for manufacturing. I’ve learned a bit more about automobile aerodynamics since then, but it was too much work to change the drawings if I didn’t have to. Now I have to. I may have even learned a thing or two about testing since MAX hit the road. Now I have to run those tests over again. And since I absolutely hate doing the same work over again the same way, I’m dang near guaranteed to do it better the second time.

Mind you, I’m not yet ready to send the burglars a thank you note. But chances are MAX will be slightly improved by this ordeal. And me? I’ll probably be slightly improved too, since I won’t be squandering my evenings in pool halls and movie theaters any more. I’ll be slaving away in my garret, drafting new MAX drawings on my replacement computer — the one handcuffed to my wrist, of course.

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The new MAX body is getting a new nose. Cardboard and computers are working hand in hand on this aspect of the design. Don’t worry, the finished nose won't look like this, we’re just seeing how small an air inlet we can get away with.

For drag reduction, the less air that goes through the car, the better. Properly guided, air that goes around, over and even below the car can have relatively low air resistance, but air that goes through will always be a big drag, to coin a phrase. If you assume that all the air that goes through a radiator is converted to drag, you won't be far wrong. If you go back to Update No. 16, you can see that MAX’s radiator opening is substantial — a full square foot of MAX’s frontal area. Is that enough area to be worth messing with?

Dynamic pressure (shown by the letter ‘q’ in the aerodynamics biz, for reasons shrouded in mystery) is the pressure of air in motion. For horseback calculation of car performance you can use q = 1 pound at 20 mph. Dynamic pressure (q) increases at the square of airspeed (if you double your speed, you hit twice as many air molecules and you hit them each twice as hard, etc.) so q at 40 mph (20 mph x 2) is 4 pounds per square foot (2 squared). At 60 mph (20 mph x 3) q is 9 pounds per square foot (3 squared). I’ll spare you the math, but it takes 1.5 horsepower to exert 9 pounds of force at 60 mph. If we could reduce the size of the radiator opening to one-third of a square foot (as shown in the photo), MAX’s “cooling drag” would only be 3 pounds, would only take one-half horsepower to overcome, and would save us one full horsepower at 60 miles an hour.

Testing will show how little air MAX needs for cooling, but my guess is not very much. While Kinetic Vehicles encourages even our high performance customers to build their cars with four cylinder engines, we have a few who have put Chevy V-8s in cars that look just like MAX — same nose and everything — and they cool just fine. Still, one test is worth a thousand guesses, all it takes is some cardboard zip-tied to the grill and a keen eye on the temperature gauge, and when we’re done we can recycle the cardboard!

Photo by Jack McCornack

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Escape from Berkeley II has a schedule, at last! Hopefully we can say it’s a last schedule. To quote the Escape from Berkeley website, “...while not final, our fairly firm dates are April 24 to 27, 2010.”

This time, we'll be racing to the Mexican border. Whoops, I mean rallying to Mexico — it's not a race, it's a rally. Hopefully for this rally, we'll be even closer to our goal of 100 mpg, if not already there.

There have been a number of date changes since the event was announced a year ago. I don't know how impulsive the organizers were being when they announced there would be a second Escape from Berkeley event, but the success of the first event probably was a determining factor.

Success? I'll say. For those of you just tuning in, the self-explanatory competition known as “Escape from Berkeley (by any non-petroleum means necessary)” involves getting from Berkeley, Calif., to somewhere far away, using only renewable fuels. To keep it from being too easy, you can't buy your fuel, no matter what it is. Instead of exercising your Visa card, you have to scrounge, forage and connive your way to the finish line. And this isn't some science fair contest with laps around a track under controlled conditions; it's for street-legal vehicles on real roads, in whatever conditions mother nature dishes out. Anyway, the premier event ran us from Berkeley to Las Vegas, and it couldn't have been more successful for us 'cause MAX won it! (See MAX Wins 800-mile Race, without Gas.)

We didn't stomp the competition, and the event wouldn't have been exciting if we had. The Green Machine, a truck powered by a wood gasifier, gave MAX quite a run for its money. The lead changed hands between us a couple times and it could’ve been a photo finish if they hadn't blown a tire on the last night of the three-day race. It proved there's more than one way to skin a non-petroleum cat.

But then again, MAX and the Green Machine, powered by two quite different alternative fuel technologies, did run away from the rest of the field. The pack wasn't biting at our heels because the pack wasn't quite ready. Man, there were some imaginative machines at the starting line. But as is tradition in the innovation biz, the finishing touches take longer than expected. Now, given the time to prepare for the sequel event, the organizers expect to see a lot of entrants not only ready to roll, but ready to win.

We won't know for sure until April, but Escape from Berkeley II could be quite the battle between the Smokers and the Greasers, as in gasifier technology versus waste cooking oil. Gosh, by the 10th Escape from Berkeley (we'll probably be escaping to Bangor, Maine, by then) it could be a rivalry like Ford vs. Chevy in the early days of NASCAR.

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How long has it been since you last checked the real-world gas mileage of your car? Have you ever done it?

It can be all too easy to assume your car gets 30-something mpg — or whatever the sticker said when you bought the car — and never realize that its actual gas mileage has declined over the years and now is far off what you expect. But it's important to keep tabs on your car or truck's mpg.

First and foremost, "knowing is half the battle," as they used to say in the old G.I. Joe cartoon PSAs from my childhood. In other words, the first step to increasing your car's gas mileage (and saving money) is to know what it actually gets. Also, unless you're lucky enough to have a real-time mpg display in your car, there's no better way to better understand how driving habits influence gas mileage than to check the numbers. As in, on this tank I ran the air conditioning more than usual (you would see the mpg decline), or on this tank I drove the speed limit to work rather than speeding to make up lost time (you would see improved mpg). Last but not least, regularly checking your vehicle's mpg can spot maintenance issues before they become leave-you-stranded and wicked-expensive problems.

If you're a gas mileage geek like me, you'll calculate your car's mpg after every fill up. But even just checking mpg once a month or so will give you real numbers that will make it easy to adjust your driving habits so you save gas and money. Think of it as a personal challenge and you'll find it easier to get excited about the math — can you beat last month's personal best of 36 mpg? Can you beat the official EPA fuel economy estimate for your car?

And, to top it all off, you'll probably be surprised how easy it is to calculate gas mileage. Even a mathematically disinclined journalist like myself can do it. All it takes are two numbers and simple division. How to Calculate Gas Mileage will walk you through the steps.

For what it's worth, here's my system. I write down the number of miles on my trip meter on the credit card receipt from the gas station, which lists the number of gallons I bought. I also write down the car's overall mileage, just to help me track the car's mpg over time. I then plug all those numbers into a super-simple Excel spreadsheet, which does the simple division for me and automatically fills in the mpg for each tank. I can then track the car's mpg over time and see how it changes with the seasons, my driving habits, as I put off maintenance, after I got new tires, etc.

So, do you ever check your gas mileage? If so, how do you do it? If not, why not? Share your two cents by posting a comment below.

Lots of the Auto X Prize design guidelines are worth continuing to follow as we develop our 100-mpg DIY car. If you scroll back to Update No. 19: A Roof Over our Heads, you'll see our first shot at compliance with the Auto X Prize’s no-roadsters rule. And if you scroll ahead a couple of posts from there, you'll find Update No. 21: New Motivation for an Enclosed Cabin, which pretty well speaks for itself.

I've driven a couple thousand miles with that “bikini top” and it's excellent for sun protection and decent for ordinary rain protection, but in serious rain, snow or slush storms, it's no great shakes. It didn't help streamlining either. The bikini top had five of the eight features we want in a top (it was cheap, it was light, it was simple, it was reliable, and it looked kinda cool), but it missed out on two biggies — weather protection and drag reduction, and it only gets a C- in the easy entry category.

I'm confident we can do better, and when I say “we”, I'm including you! If you'll go to the Kinetic Vehicles website and scroll down to the bottom of the page (look for “August 2009” subhead), you'll find some computer generated pix (side, front, top and rear) of the streamlined, aerodynamic body we're currently constructing, with front roll bar and split windshield added in. You have my enthusiastic permission to download those images and doodle up your own cabin ideas.

If you come up with something you think is worth sharing, follow the instructions on the Contact Us page to let me know. I'll write you back and we'll work out a way to transfer it. Use “MAX cabin kv” as your subject when you e-mail me. If you're a Rhino user (our software of choice for 3D imaging and CAM), let me know and I'll send you a Rhino file of MAX to work with. All I ask is you please don't send me any attachments — our system rejects anything with an unexpected attachment and I'll never see it. Actually, I'd rather not get any spam either, but I'm willing to risk it in the pursuit of a better roof.

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“When I gave up cigarettes, my dad called me a quitter.” — an old McCornack joke

We have officially withdrawn MAX from the Progressive Insurance Automotive X Prize competition. It was a no-hard-feelings decision by both parties.

Have no fear, this doesn't mean the end of MAX. It doesn't even mean an end to our involvement with the Auto X Prize competition. I intend to be there for their race events and cover them as a journalist. And I expect MAX will be the most fuel-efficient vehicle in the press corps.

But from a competition standpoint, it is clear that we and the X Prize Foundation are marching to the sounds of different drummers, so it’s time we take our hat out of the ring.

For the first year or so, the X Prize Foundation thought MAX was pretty neat. They didn't have many applicants yet, and we were one of the few with an actual car on the road. The MAX Project and the Auto X Prize were good for each other in the early days.

But lately, this competition has been interfering with our goal for MAX: a high-mileage car you can build on a budget. The final rules have no place for a DIY car, and preparing MAX (even on paper) for factory production — as in 10,000 cars a year — has been sucking up our resources like you wouldn't believe. In the last year I have literally spent more hours filling out X Prize Foundation paperwork than I've spent developing MAX, and MAX has suffered for it. Instead of working on streamlining to improve the car’s gas mileage, I've been writing business plans and tech documents and getting price quotes, for every single part in the car. Imagine trying to figure out the cost of 20,000 windshield wiper blades to be delivered in five years, etc., etc., etc.

So go ahead and ask: Why didn't we figure this out two years ago? Why didn't we realize we'd get drowned in paperwork before we ever sent in our entry fee? Why didn't we predict that 10,000 how-to e-books to 10,000 potential DIYers wasn't going to count as “manufacturing capability”? It's simple — we entered the competition before the X Prize Foundation wrote the rules.

Mind you, I have no bone to pick with the Auto X Prize folks about the rules. It's their $10 million dollars and they can write the rules any way they like. They've always been perfectly up front that anybody who didn't like the final rules could get their entry fee back. Rule development is a tough job —I can see why it took years to complete them.

But now that the rules are done, they left us with a simple choice: Is MAX going to be a $10,000 DIY car you can build this decade? Or a $40,000 factory-built car you can buy in 2014?

Well, we chose to stick to our DIY roots. The Auto X Prize is a fascinating competition, and I'll enjoy covering it for you ... from behind the wheel of MAX, a high-mileage car that I built with my own two hands.

Photo by Katherine Loeck

Browse previous MAX Updates.

Read the introductory MAX article, Here Comes the 100-mpg Car.

Visit the Kinetic Vehicles website for more technical details on MAX.