Hypermiling: Results for over-inflated tires
Daniel | June 26, 2008I have to tell you right up front that writing about hypermiling is annoying. I get really excited because I know that I’m seeing gains, but by definition, the better I do with it, the longer between stops at the gas station, which means I don’t get to write about it as often as I’d like.
I bet you’re just as frustrated as I am about how seldom you get the chance to stop for gas.
Right before we left for Disney, I topped off my tank. I only needed about 4.5 gallons (I have the exact figures in my glove compartment, in my car, parked at mom’s since I’m in the truck that’s going to Atlanta tomorrow). The last time I’d filled my tank, I’d also over inflated my tires to somewhere between 42 and 45 PSI - it’s hard to tell on the little gauge I have. The mileage boost was 3.8 MPG. Over the course of a tank, that’s like getting a free gallon of gas!
Follow me inside for the review and total mileage gain from following a few simple tips…
In my original post, I talked a bit about how a lot of the driving tips were things my father has done pretty much his whole life. Things that used to make me a little crazy, really. Here they are:
1) He accelerates really, really slowly. When I was a kid, it was painful. Doesn’t matter if it takes a mile to accelerate to 45 MPH, you’ll get there.
2) He watches WAY down the road, and if he sees a red light coming up, he lets off the gas and will coast the last half mile. I took this one step farther and I put the car in neutral for the coast to the red light. Quite often it’s green when I get there because of the delay of coasting in.
3) Dad doesn’t do this, but I turn off the engine. If I get caught at a red light and I know I’ll be there for more than 10 seconds, I shut off the engine. Yes, the urban myth is that it takes more gas to start an engine than it does to leave it running. This may have been true when cars had carburetors. Today’s cars have fuel injectors that spray exactly the same amount of gas into each cylinder whether the car is running or starting. Even if you can cut the engine for 10 seconds, you’re saving gas.
4) Dad drives slow. It’s the reason I teased him for 10 years when he got his last speeding ticket. As you can see on the graph at the beginning of this article, your best gas mileage is between 30 and 60 miles per hour. 40 to 55 seems to be the sweet spot.
That’s it. Those things took my average mileage to 34.6 MPG - which was a 4.6 MPG improvement. Over inflating the tires has taken my average mileage to 38.4, which is a 3.8 MPG improvement over what I’d gained already, and a total improvement of 8.4 MPG.
When I get back from Atlanta, I’ll change my oil to a full synthetic at 0W/20 and report back on what (if any) additional mileage gains that brings, along with some analysis.
My 2008 Scion xB is listed as getting 28 mpg
Danny | June 26, 2008 | 2:56 pmMy 2008 Scion xB is listed as getting 28 mpg on the highway, but I regularly get 33 or better, using most of your Dad’s tips. I don’t usually drive slow, but I don’t speed, either.
Looking forward to seeing how the rest of this turns out.
Putting the car in neutral might not always be the
Tino Schwarze | July 23, 2008 | 7:02 pmPutting the car in neutral might not always be the best option. Sometimes, you’ll even save if you use the highest gear and let Inertia keep the motor going. A modern motor will stop injecting any gas, if inertia keeps it going. Of course, this depends on the street, whether it’s hilly and how far the red light is.
Tino.
@Tino: You always have excellent input my friend! Thank
Daniel | July 23, 2008 | 10:08 pm@Tino: You always have excellent input my friend! Thank you!
1. Over inflated tires wear out sooner. 2. Over inflated tires
Eugene B. | August 6, 2008 | 2:06 pm1. Over inflated tires wear out sooner.
2. Over inflated tires affect your cars handling. Resulting a more jarring ride. Hydroplaning on wet pavement.
3. Over inflated tires affect your ability to stop. The tires will skid more, stop less.
You cannot over inflate your tires without affecting other factors.
Enjoy your 3.8 mpg increase, buying tires more frequently, rougher ride and stability. Less stopping power could result in auto accident, injury or death. Manufacturers recommend tire pressures provide the optimum rolling resistance and safety. Avoid them at your peril and the peril of others.
@Eugene B: You make excellent points. I myself pointed
Daniel | August 6, 2008 | 2:17 pm@Eugene B: You make excellent points. I myself pointed out that you needed to change your driving habits to account for the change in handling and the change in stopping in the first post I made about hypermiling. The internet being what it is, I should have included the warning in this post as well.
Interestingly, I’ve never seen anyone point to any studies that show over inflating your tires by a modest amount shortens their life. If you have a link to one I’d love to see it!
Common sense alive and well. When you over inflate your tires
Eugene B. | August 6, 2008 | 2:53 pmCommon sense alive and well.
When you over inflate your tires (see tires for maximum pressure recommendation) you tend to balloon your tires resulting in tire wear more in the center of the tread and not uniformly across the tread. When tires wear more in the middle they wear out sooner, you have less stability, stopping power, etc. You don’t need an internet study here. Common sense will work, just think it over. Keep in mind over inflated COLD tires when driven will result in additional tire pressure when driven due to heat and friction. This will result in excessive tire pressure affecting poor handling and possible tire failure (BLOWOUT). As in the Zen world you cannot affect one without affecting the other. Let me know how pleased you would feel about the increased mpg after a tire failure, by the side of the road, in the rain, after an accident, etc. Tires rarely blow out in the driveway. Your increased tire pressure benefit pales when compared to the potential hazards. You are gambling with your safety.
@Eugene B.: Yes, I understand all of that -
Daniel | August 7, 2008 | 1:08 am@Eugene B.: Yes, I understand all of that - which is why I recommend over inflating your tires only a moderate amount (for instance, adding 6 to 8 additional pounds of pressure is not enough to cause a ballooning of a modern tire) and I suggest not doing this at all unless you are willing to adjust your driving habits (and therefore the conditions that the ties operate under) to compensate.
An additional argument can also be made that manufacturers are already leaving a margin of safety build into their recommendations. Still further argument can be made that it would be safer still to drive with under inflated tires - they would wear out faster, true, but would aid handling and braking, and slow acceleration. When you compare the recommended pressures with the potential hazards, they too become a bit pale.
My main question is where the information on “shortens the life” of tires comes from. As far as I could tell, while that is considered to be conventional wisdom, it does not seem to be what people “in the field” have been reporting on hypermiling forums and websites. If the only source of study for this information comes from the tire manufactures themselves, and people out “in the field” are reporting different results, I’m inclined to be skeptical of the corporations rather than of the regular people.
I will , of course, report my own findings here - but it looks like it’s going to be a while before I can comment on tire life. I will say this: for my car, tires are $140 for 4 40,000 mile tires. Even if they wear out 10,000 miles faster, that’s still only a difference of $140 over the course of 120,000 miles. If I gain 3mpg from the over inflation, in that same 120,000 miles, if gas is only $2.50 a gallon (and personally, I think those days are long behind us) I’ll save around $676 on gas. The amount saved only goes up as the price of gas goes up.
Okay, I went to some hypermiling sites and found the
Eugene B. | August 7, 2008 | 11:59 amOkay, I went to some hypermiling sites and found the following statements, “Gerdes also recommends filling tires to the maximum safe pressure listed by the manufacturer,” Larry Singleton….over inflates his tires by about 15-20 pounds……. however such practice could lead to uneven tire wear and worse, a loss of vehicle control,” Hmmm, sounds like they agree my points. Why don’t tire manufacturers recommend over inflation in order to save fuel? Tires would wear out faster and they would sell more tires in the process. Sounds logical, right? Except you don’t sell many tires to the injured and deceased. This will also result in reports on the news, that will lessen, not increase, tire sales. Are you aware that oil is used in the manufacture and transportation of tires? So when you over inflate tires you save gas, but replace your tires sooner, tire manufacturers make, transport and sell more tires (using more resources) but you save gas. Keep in mind it isn’t just you. If millions of drivers over inflated their tires to “save” fuel, millions of drivers will need to buy tires sooner. Life is an equation, you cannot change (A) without changing (B). Tire manufacturers have billions of dollars invested to provide the consumers with the best product possible, their reputations and your safety depend on it. U.S. tire manufacturers constantly test their product. For optimum tire life and your safety the recommended tire pressure is embossed on the sidewall of the tire. Ignoring this information can result in the compromising of your safety and the safety of others. You need to ask yourself if tire manufacturers or hypermilage enthusiasts have the best safety information. If your actions result in an accident that take you off the road that is one thing. If you damage other vehicles, injure or end the life of other drivers while in the pursuit of higher gas milage where is the savings? You may choose to ignore all of the above citing the hypermilage scripture and actually obtain a few more mpg and feel justified. However your actions may result in unintended consequences that will affect you and others. I’m guessing that your testimony about obtaining higher gas milage resulting from over inflated tires that was a contributory factor to the injury or death of another won’t do you much good. Actions have consequences! Look at this way, you can choose to go buy some economy grade tires that are cheaper to replace, over inflate them and hit the road. WAHOO, look at that MPG. Hit some oil, grease, water, sprinkler run off, rain-snow-ice (yes, winter is coming) and loose control of your vehicle. Most likely you will not be the only one affected. But hey, until that happens, enjoy that additional 3.8 mpg.
@Eugene B: I appreciate your passion on this topic, but
Daniel | August 7, 2008 | 12:41 pm@Eugene B: I appreciate your passion on this topic, but you’re no longer responding to what I’m talking about, instead choosing to pull random quotes from other sites to argue against. I agree with you that if you inflate your tires to unsafe levels and then drive normally on them, you’re asking for trouble.
This is, however, not something I’ve ever recommended here.
If you overinflate your tires a moderate amount and change the way you drive, you are not only not compromising your safety, you’re increasing it by observing safer driving habits (such as driving with buffers, accelerating more slowly, using lower maximum speeds, etc etc.)
“You need to ask yourself if tire manufacturers or hypermilage enthusiasts have the best safety information.”
Personally, I choose to not put a lot of stock into what the tire industry tells us. These are the people, after all, that chose to let people die in Ford Explorers, because it was more profitable to do so rather than fix the problem. You’ll note that the people that were dying were following the manufacturer’s recommendations. It’s a personal choice for me to gather the information from my observations, and the observations of others, and make a decision from that. Another route you might go is to talk to your mechanic - see what he or she recommends as safe for your vehicle in your area.
Reviewing information from Hypermiling sites, as you suggested, is what
Eugene B. | August 7, 2008 | 1:49 pmReviewing information from Hypermiling sites, as you suggested, is what we are talking about. You can choose not to accept the information, this does not change the information. Over inflating tires is not safe. A majority of tire manufacturers provide a safe product, if used in a safe manner. I wish you safe miles and nothing less. I have turned a wrench for over 40 years. Your site may be read by others that hopefully will stop and think before they over inflate their tires. I merely provided additional information and a word of caution.
Daniel and Eugene B. I agree with both of you. Eugene:
Jan M | August 21, 2008 | 2:41 pmDaniel and Eugene B. I agree with both of you.
Eugene: I think there is a greater risk when adding 10-15lbs over the recommendations of manufacturers however I am doing it and still get good traction dry or wet. The only thing I notice is a bit rougher ride. I think when we talk about greater risk we talk in generallities. No one that I have heard has actually quantified the risks. I’d really like to hear from an automotive engineer with facts and figures. I do agree that there is some greater risk but how much?
Daniel: I like what you had to say about the tire industry. Why haven’t they given us an option of 60psi tires yet? Semi-trucks often have 100psi in the trailer and drive wheels. The technology is there but I think the industry is fearful that they will be known as the ‘poor riding tire makler’
By the way I have 48lbs in all my vehicles and do some hypermiling when I can. I recently had my Pontiac Vibe oout for a 100 mile ride and got 50 mpg (cdn gallon). The car is rated for 40 mpg hwy (cnd gallon)
Jan
http://thesavingsletter.blogspot.com/
BTW I'll have some other saving information for you in
Jan M | August 21, 2008 | 2:43 pmBTW I’ll have some other saving information for you in a couple of weeks. It’s not all about gas. I think I’ve found a way to save on maintenance as well
Jan
Wayne Gerdes, the man who coined the word "Hypermiling" has
andy | September 11, 2008 | 4:40 amWayne Gerdes, the man who coined the word “Hypermiling” has “over” -inflated his tires on his honda accord for 100,000 miles. Guess how many times he has replaced them……NEVER! He is riding on the original factory tires. How do you explain this?
I inflate mine 35 pounds over and have seen the wear on the tires STOP! Tire manufacturers would never want you to find this out. When I used to inflate my tires so called “properly” I replaced them very often perhaps every 35000miles. Now, these tires stopped wearing immediately after inflating them at higher pressure. Many hypermilers report the same results at CLEANMPG.com (I have nothing to do with cleanmpg.com but reccomend it highly)
I have gotten as high as 77 miles per gallon on a regular 4 cylinder gas car after learning from cleanmpg.com. I never get a tank of gas that is less than 55 mpg now that i have learned from cleanmpg.com. You don’t have to buy anything. That’s the beauty of hypermiling…..