In this post, I will attempt to provide a simplistic overview of a hypermiling technique known as “Pulse and Glide” (P&G). Before we get started, you need to know that the application and technique for P&G is variable based on many factors such as the car, terrain, traffic, current speed limit, etc. For all those reasons, this will be an overview and not overly detailed. My concern is that if I provided any real details: 1) you would try to apply the details where they don’t fit, and 2) someone will argue the minutia of the details.
How Do You Pulse and Glide?
Many times, I compare hypermiling to riding a bicycle. This works because almost everyone knows how to ride a bike, which makes it a universal reference. Also, you most likely remember how tired you can become if you do not ride efficiently. Though neither you nor your car will get tired, you have to focus on the amount of effort being exerted; the goal is to travel farther with less effort.
The Pulse. Just like riding a bike, the intent of the pulse is to get up to speed. When accelerating from a dead stop, use a brisk acceleration: accelerate quickly but not stomp on the gas. Once you have reached a speed that is, perhaps, a little faster than the speed limit or average traffic speed, let up on the accelerator.
The Glide. Think about riding that bike. Once you have reached a decent speed, it requires only a minimal amount of effort to maintain it. In fact, depending on the situation, you might be able to coast for a long distance before needing to pedal again. In exactly the same way, the point of the glide is to “stop pedaling”.
The first and second generation Prius were exceptionally good at gliding because they had a “dead band”. This dead band is a spot in which there would be no power coming from the engine or batteries to drive the wheels and also no regeneration from the wheels to the batteries. A practiced driver could work the accelerator into that dead band and let the car roll.
Unfortunately, this type of “free wheeling” is nearly impossible in almost all modern hybrids. And so it is with modern hybrids that the glide is an attempt to reduce the energy flow to a point as low as possible.
Pulse Again. As you can imagine, after coasting for a while, you will start to slow down. Once you’ve slowed to a speed you are no longer comfortable with, pulse again. Unlike the dead-stop pulse, this time you want to use just enough acceleration to get back up to speed. Just like riding that bike, it’s not a sprint back up to speed but rather just enough.
And then you glide again. Then pulse, then glide, repeat.
Why Does it Work?
The concept is simple: the entire intent of P&G is to glide more than you pulse. The following image provides a sort-of representation starting from a dead stop, accelerating up slightly above the desired speed, gliding, pulsing, and then gliding again. As you can imagine, the farther you can glide the better. The black line in the following image might represent the average traffic flow, the speed limit, or simply the speed you want to average. Your situations will vary.
It works because gliding is essentially free. It’s the pulsing that costs you. Therefore, rather than paying to constantly maintain a steady speed, you allow your speed to vary. The trick comes in making sure the pulsing uses less effort than would otherwise be used maintaining a steady speed.
This week Russell, Paul, Mark and Patrick discuss…
According to FuelEconomy.gov, under-inflated tires can lower your mileage by 0.3% for every 1 psi drop of all four tires. Other sites put the figure at 0.4%. Even though it doesn’t sound like much, the point of this ongoing series of articles to make clear that all things – when taken together – can account for a significant improvement in overall efficiency.
When to take the Measurement
Hot air expands.
That’s it. Now you understand how the temperature of the tire will affect the temperature of the air and therefore the measurement of pressure. Always measure the tire pressure before driving the car. Taking the measurement after a long drive – especially at high speeds – will return a deceptively high reading.
Ideally, you should measure your tire pressure every month. First of the month? Check your pressure.
Winter versus Summer
In addition to hot air expanding, cold air constricts. Most sources put the anticipated psi drop at 1psi for every 10 degrees of temperature drop. In some locations, the difference between the hottest Summer day and the coldest Winter morning could be more than 100 degrees Fahrenheit. For tires, that’s a potential 10psi swing.
When Autumn comes, don’t be surprised if the tires start reading low. It will be necessary to add air to maintain pressure. In the Spring, – and this is important – it might be necessary to remove air to keep the tires from becoming inadvertently over-inflated.
Tires are Part of the Suspension System
Before getting into maintaining and manipulating tire pressure, it should be mentioned that the tires are an integral part of the car’s suspension system. Having shock absorbers is great and all, but it’s the pliability of the tires that cushions the car from all the bumps in the road.
Over-inflating your tires will create a rougher and bumpier ride. It does. There is no way around that. If you decide to over-inflate your tires, you must realize that you do so fully understanding the impact it will have on the smoothness of your ride.
At the Very Least: Maintain Recommended Pressure
Every car has a sticker somewhere indicating the recommended tire pressure. Usually, it’s on the driver’s door jamb but some cars have the sticker on the inside of the trunk hatch.
It is important to keep in mind that the tire pressure on the side of the tires might actually differ from the pressure recommendation on the sticker.
The reason for the potential variance is that the tire is manufactured for a wide range of cars. The tire manufacturer does not know the size and weight of the car it will be mounted on. The manufacturer of the car, on the other hand, knows all the variables and calculates their recommendation. This is why you should always refer to the sticker on the car rather than the sidewall number.
If you do nothing else, absolutely maintain the recommendation on the sticker.
The Dangers of Under-Inflated Tires
Most people who have ever ridden a bicycle have ridden on under-inflated tires. Squishy tires make controlling the bicycle very difficult because the rim is sliding from side to side. The same is true on a car except that cars travel much faster and corner much harder. An under-inflated tire could potentially create the situation in which a quick decision cannot be realized with a quick movement.
Do you remember when all those Ford Explorers were losing control and sometimes flipping over? In every case, one of the tires exploded, which make people suspect it was the fault of Firestone. After a bunch of investigating, it was found that in almost every case, the pressure of the remaining tires was low. As a result, it was determined that the exploding tires were cased by under-inflated tires overheating and rupturing resulting in sudden loss of control. Under-inflated tires create additional friction and could possibly become so hot they weaken and rupture.
It has been proven that under-inflated tires are more prone to skidding in the rain, making stopping more difficult. At the very least, braking distance is increased. Worst-case situation: braking distance is farther than the distance to the car in front of you.
Under-inflated tires do not contact the road the way they are supposed to. This affects overall handling and tire wear. Some estimates put the impact of under-inflation as high as 25% faster tire wear.
So there you have it. If you take nothing else away from this article, please check your tire pressure once a month to make sure you are safe.
Exceeding the Recommended Tire Pressure
NOTE: This is a contested concept for the reasons explained below. It is assumed you are a mature and responsible adult capable of making decisions for yourself that affect the operation of your vehicle. If any part of this bothers you, don’t do it. Just because you read about it on the internet doesn’t mean you have to do it.
There are many people on PriusChat.com working to improve their mileage. They employ many techniques and reliably report their results. I mention this because there is substantial anecdotal evidence that increasing your car’s tire pressure can return higher mileage.
The recommended tire pressure for a 2004-2009 Prius is 42psi front and 40psi rear (42/40). The 2psi difference is explained as additional support for the engine in front. Some people increase to 45/43 and report repeatable mileage improvements. Some have gone as high as 50/48 and continued to report even better overall mileage. However, above this pressure, on real significant improvements are realized.
These results – though shunned by many – seem to indicate there is a mileage improvement to over-inflating tires. To a point.
Concerns of Uneven Wear
Many opponents to over-inflating tires use the argument that the tires will develop a bulge and develop a bald stripe along the radial axis. This was true a long time ago. Modern steel-belted radial tires, however, are reinforced in such a way that over-inflating does not bulge the tire.
Concerns of the Tires Exploding
The level to which some drivers over-inflate their tires is only a few psi. Perhaps as high as 10psi. This sounds like a great amount. But the realization that it’s intentionally a fraction of the tire’s potential is not something you will ever see advertised.
I had the pleasure of meeting an actual tire engineer at a car show. I can’t mention his name or which manufacturer he works for. To be honest, it has less to do with confidentiality and more with a horrible memory.
In our discussions, I mentioned that I had inflated my tires above the recommendations and was mildly concerned. He gave a “pa-shaw” sound and rolled his eyes. He then explained that the sidewall tire recommendation is based more on the risk of litigation than the potential of the tire. This gave me a certain level of ease.
As I look over this article, it’s clear that much of it addresses arguments against over-inflating tires. It’s just that this article only addressed potential mileage gains of over-inflating tires the comments section would light up with those very arguments. So they are pre-emptively addressed in an attempt to make it clear that I’m fully aware of those arguments and am not making blanket suggestions without realizing potential consequences.
Make sure to check your tires’ pressure every month. At the very least, maintain the tire pressure recommendations listed on the sticker in your car. If you choose to over-inflate your tires, be aware that you will experience a bumpier ride because the tires are part of the car’s suspension system. Though there are concerns of damaging tires with higher pressure, the evidence simply isn’t there to support them.
Yesterday was Earth Day: a perfect time to talk about hypermiling and reduced emissions. But I’m not going to. You see, if we really try, we can do even better than hypermiling. In fact, focusing exclusively on driving more efficiently is not always the best approach. After all, it assumes that you will always be driving. Also, there are stories about people literally driving farther than necessary just to make sure their engines warm up so they can register better mile-per-gallon averages.
Today we’re going to shift our focus from driving more efficiently and focus on driving less. There are several approaches to reducing our dependence on our vehicles. This article might not get to them all but hopefully it will serve as a good start and get you thinking.
The most obvious alternative to driving is walking. OK, I know what you’re thinking: “I live too far from work” or “I have to haul things” or whatever. Yeah, I get that. I have those things too. Walking is not an all-or-nothing alternative. The point here is not to walk everywhere all the time. The point is to know your walking speed and acceptable distance. Then, when you have to get yourself from one place to another, ask yourself whether it is within your acceptable distance. If it is, seriously consider walking.
On a more personal note, we have become a sedentary society. We sit in our car, at our desk, and in front of the television. No matter who you are or what your current state of health might be, we can all benefit from taking more steps every day.
Stepping up from walking is riding a bicycle. The same concept applies: know your acceptable distance and situations. If the current need fits your parameters, ride your bike. From time to time, someone at the local fitness center will wonder why there are so many parking spots and so few bike racks. This is a perfect example of when to ride your bike.
Not only does bicycling extend the distance and shorten the time compared to walking, mountable carriers allow for light grocery shopping. If you need to run to the local store for a few things in order to complete the recipe, don’t bother firing up the vehicle; hop on your bike.
Some of us are lucky in that we have coworkers who live within a mile or two of our homes. This makes carpooling pretty convenient. Some companies have bulletin boards where people can post interest in ride sharing opportunities. Some are actual bulletin boards in a common area such as the cafeteria whereas tech savvy companies might have information on their intranet.
When it comes to driving less, any improvement is an improvement. Let’s say you have a coworker who lives halfway between you and work. Even if you drive to their house and park your car, you are not driving the entire trip. Even if the coworker lives a few miles out of your way, the fact that you are not driving every day means that you are driving less.
Of course, carpooling means taking turns. Don’t be a carpool leech! The only acceptable exception is that you do not have a car at all.
Some people have mass transportation options and don’t even realize it. Make sure to check your community’s internet site or other information to see what mass transportation options exist.
Some people place a stigma on riding the bus or train. Their belief is that not rolling up in your own set of wheels somehow makes you less of a person or they see mass transportation as a lower form then car ownership. But these people are spending money on gasoline and potentially on parking fees. They log more miles on their car, which will result in faster wear-n-tear maintenance. They aren’t aware the amount of money they are spending just because of their personal belief.
Those who ride the train and/or bus to and from work do not have to drive in the rain or snow. They save money on gasoline and potentially parking fees. Ridding as a passenger is much less stressful than driving and provides ample opportunity to get a little more work done, sit quietly, or catch up on that podcast.
Plan your routes
Have you ever been our in your car running a few errands and realize that you’ve crossed town twice already and will need to do it again? Hopefully, it occurred to you that had you planned your errands a little better, you wouldn’t have to do so much driving around.
Not only does better planning reduce the miles you log in your car, it saves you time and money. You save time because, of course, you spend less time in your car. You save money because gasoline is not cheap.
Next weekend – or whenever – when you are about to run a series of errands, consider writing them down and then numbering them based on a preferred route. You would be surprised how much time you end up saving this way and how much better you feel for having gotten through them faster.
Reducing the miles driven in your car by any amount is an improvement. Even if carpooling and mass transportation are not available in your area, you can still find other ways to drive less by biking and walking from time to time.
Here is my biggest rub. I pulled these tips from international sources. These things are tightly integrated into the very fiber of most Europeans. Trains and buses are used to capacity and many companies have as many bike racks as parking spots. Some European companies charge their own employees for parking in their garage as a way to encourage carpooling and mass transportation. Sadly, these things are usually either ignored or rebuffed by most American citizens. I shutter to think how bad things would have to get before more people here started acting more like the people over there.