Using a Hyper-Gravity Drive

When I was a kid, one of the highlights of every family trip to the mountains was when we would come over the pass, and my dad would kill the engine of our 1968 Volkswagon Bus and coast the rest of the way home. "Freewheeling," the hippies would call it, when one's wheels, presumably, turned for free, and in the days before power brakes, there was little to be lost by turning it off.

I've begun to re-employ this technique when it's possible and safe: rolling out of the driveway in the mornings. Waiting in traffic on a downhill slope. My son and his friends call it my "hyper-gravity drive," since I'm using gravity to move the car forward.

Here's the technique I use on hills: I cut the engine entirely, put the car in neutral, then turn the key back halfway on so I still have radio, power brakes, and of course, so I can watch the speedometer count the miles I get for free. If I need to start again, I pop the clutch in fourth gear and the engine purrs back into life so smoothly the car never knew it was off.

I've gotten good at this, and use it when I'm doing my errands. (Mostly when I'm driving alone.) I live in a city built on the side of a long, sloping hill, so there is rarely a reason to use my engine whenever I am heading west.

There is one long, lonely, road that has two stoplights on that sometimes turn red on me. I roll to a stop and sit there in silence, listening to the frogs sing outside. When the light changes, I take my foot off the brake and feel the thousand pounds of steel around me respond to the earth's core by inching forward, then rolling, then hitting the speed limit. I can hear the frogs as I roll away, and send them a prayer to survive the summer's heat.

Sometimes, if there is a car behind me, I pull over and let them pass. I wish I could tell them to slow down and enjoy the earth while we still can, especially if they gun their engine going downhill.

10 comments:

Larry said...

I have been doing the same thing of late! I live mid way up a long hill and I burn gas going up , but then I get it back when I go back down. The puzzled faces of people standing at the corner as a silent camry rolls to a stop is cool too.

Watts said...

Please do not turn off, your engine when the car is in motion, it is extremely dangerous.

There is a big difference in your dad's old VW bus and modern cars. I doubt your dad's bus had either power steering or power brakes. Therefore turning the engine off didn't affect them.

Both power steering and power braking systems, rely on engine power. Turning the key back to the on position with the engine shut down, does not restore power to either of these systems.

Power braking is possible with the aid of the brake booster. The booster relies on vacuum created by the engine, to operate. When you turn off the engine yet still feel the effect of the power braking system, it is not because you turned the ignition switch back on. It is because, the booster is still pressurized. One you step on the brake pedel, this vaccum is lost, but is not replaced by the engine, since it is off.

To test this, park in your driveway and crank your engine. After a few seconds turn your engine off. Turn the ignition switch on as you described. Now pump your brakes, you will only be able to push the brake pedal to the floor a couple of times before the reserve vaccum is gone and the brakes get hard.

The power assist in a power steering system, is provided by the power steering pump, which is driven by an accessory belt connected to your engine. Power steering is lost immediately when the engine shuts down; there is no reserve power left in the system. You may not notice this at highway speeds, because when the car is rolling fast there is less need for power steering. This was true in your father's bus as well. I bet it was very hard to turn the steering wheel when the bus was stopped or moving slowly, yet easy to turn it when the bus was going down the road.

Now you may be thinking, "What's the difference? It's no less safe than what my dad did."

Modern cars were designed with these power systems in mind, and they are sized to do their job appropiately when used as designed. For example, your power steering system is hydraulic. When pressure is lost to the system, not only does it revert to a manual steering system, but your input to the steering wheel must provide enough force to drag along the hydraulic fluid and cylinders in the rack and pinion system, in addition to providing enough force to steer the wheels.

Many cars have a steering lock that engages when the ignition is turned fully to the off position.
Again, in your driveway, turn you ignition switch fully off and turn the steering wheel back and forth. It will most likely, lock in place.

You mention that you are doing this in a city. There could be any number of things that you would have to react to, such as a child running into the street, or a dog in the road. The potential loss resulting from lack of control could be devastating, much outweighing the potential gas savings. Please do not propogate these suggestions.

rbhawaii said...

Turning off your car is not recommended if it has an automatic transmission. The tranny will not lubricate itself as it's pump is driven by the engine. You should instead, just put the car in neutral! Your rpms will drop by more than 50% to under 1000 rpm. My '91 Explorer normally gets only 15 mpg (Ethanol blend sucks!). When I "coast" a tank, I get 20mpg!

rbhawai said...

Oh yea, be careful when shifting into neutral. Most cars have a "detent" stopper to keep you out of reverse but you can slip right past it if you are not careful.

rbhawaii said...

If you have a manual transmission, in a fuel-injected car, good news!
When ever you are going down hill, shift into top gear and turn the key off - ONE CLICK ONLY!(steering lock)
You will have all of your power brakes, steering etc. but no gas will be used. The engine still turns and circulates it's oil, but burns no gas at all. I do this all the time!
I'm working on puting a switch on the injector wire. I plan to use a double pole, double throw switch, so that I can place a resistor in the circuit to fool the computer into thinking the injector is still there. Otherwise, it will probably throw a fault code.

mez said...

My 2007 Mazda5 is equipped with a manual transmission, so we tried doing the 'shut off' or 'pulse' driving one day to show the kids how easy it is to get good gas mileage. We were physically shutting down the engine to slow down to 55, then bump start the engine and go back up to 65 so the average is somewhere around 60.

Unfortunately, this vehicle has electric driven power steering and the wheel gets VERY VERY hard to turn when the ignition is shut off. After two 'pulse' restarts, the engine threw up a code (service engine soon light came on) and told us to service the power steering unit. Luckily, after 3 restarts, the code went away, but nonetheless, it happened. We now just 'coast' with the engine idling and still get 8 - 10% return on our gas tank.

This was VERY dangerous and a very poor way of getting good gas mileage while sacrificing the safety the car provides. Does the car you drive shoot off the airbags when the key is in the 'ACC' position? What if you hit something and the airbags didn't go off? What if a deer happens to run in front of the vehicle? There will be no options. Do not sacrifice the safety the manufacturer has built into the vehicle for fuel mileage. Pay the extra $4 and put another gallon in your tank, money well spent. Or maybe, cut down the 'extra' trips and really save some money.

No, I don't work for an oil company. I have a family I'd like to have around for a while.

Kristen Caven said...

Every car is different. I can't claim this technique to work with every car, especially new cars that do the thinking for us, but there may be situations that work for some people.

As I said, half of the recipe for a Homemade Hybrid is the mind of the driver. So absolutely, if you don't feel you are in control, DON'T DO IT! Know yourself, know your route, and know your car! My 1993 Saturn has a manual transmission, power steering and power brakes. I have learned how many minutes I have before the brakes get hard, and I pop-start the engine when they do. Please, if you try this, stay alert. ALWAYS leave more than enough stopping room (6 seconds) between yourself and any cars ahead. And only use this technique on roads you know well.

Here's a situation in which anyone could use gravity only with minimal risk: when stuck in line in a parking garage, on a downhill slope. Why use gas for that? Consider the pedestrians who have to breathe the air.

Anonymous said...

I also have a sloped driveway with a gate at the end. I roll the car out of the ddriveway and now close the gate before I start up. Thank you for the informtion! I did not know I didn't need to warm up.

Sage said...

Read your driver's handbook sometime. It is against the law (probably everywhere) to operate your vehicle while in neutral. There is a huge lack of control with no power brakes or power steering, and you will NOT be able to react in time to avoid any unanticipated disruption to your freewheeling, like the people breaking the law by driving and talking on their phone, who CANNOT pay adequate attention to either. There are safer ways to burn less fuel. As Watts said, do no propagate these suggestions.

Joshua said...

This is absolutely ludicrous. I don't care if people go out and spend their money on hybrid cars or ride bicycles or whatnot, but endorsing this sort of dangerous and illegal driving is completely absurd. If you want to have a cause, have a cause. Wear a t-shirt. Get a bumper sticker. Don't put other people at risk because you want to save one-tenth of a cent on gas today. If I found out you were driving like that with my kids in the car I would lose my mind.

I was even willing to let the "turn off your car at a red light" thing go, but now I'm going to have to speak up.

All of this is complete nonsense. Trying to change the world by turning off your engine at a stop light is like trying to empty the Pacific Ocean with a Dixie cup. For every hybrid car hitting the streets, fifty ICE cars are rolling out right behind it. If you want to get a hybrid because you like the way it looks or because you PERSONALLY want to save the gas money, then fine...but don't go around thinking that you're saving the world. Sure, someone might cut down on their contribution of pollution by one-trillionth of a percent by buying a hybrid, but I'd rather they carry piles of old tires to a bonfire in the back of a Hummer then become another "world-saving/smug" evangelist.

© 2007 Kristen Caven

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