Boost gas mileage with LRR tires

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Photo courtesy of Negaro UK at Flickr.com.

For years, auto designers have been using wind tunnels to improve car designs. Wind tunnels make it easy to see how different features affect aerodynamics. Hoods, spoilers, and even mirrors have been engineered and re-engineered due to wind tunnel testing. This is because friction consumes roughly 80% of all gasoline that’s used while driving. By reducing friction, wind tunnel tests improve gas mileage and boost performance.

There’s one thing that wind tunnels miss though – the friction between a car’s tires and the road. This overlooked detail has gained new attention recently. Due to tightened CAFE standards, many cars now come standard with tires that improve gas mileage.

Expected improvements are in the 1-2mpg range in highway driving, depending on the vehicle and the previously specified factory tire. The gains aren’t enormous, but as Scott Miller, GM’s vehicle performance manager for full-size hybrid trucks said, “Every bit helps.”

Unfortunately, these factory issue tires are often replaced with gas hogging aftermarket tires. What makes some tires get better mileage than others? It’s all about friction, or “rolling resistance”. Rolling resistance is a measurement of how much friction a tire produces. Tires with low rolling resistance (LRR) convert less energy into heat and noise.

So, what’s the trade off?
In the automotive world, there’s never a free lunch, and low rolling resistance tires are no exception. There are certain trade-offs that come with reduced rolling resistance. In order to minimize rolling resistance, LRR tires are designed with less surface area in contact with the road. That saves gas, but it also reduces traction and increases stopping distances.

Tires with low rolling resistance are stiffer and flex less. This means LRR tires can feel uncomfortable because they provide less cushion on rough roads. Some LRR tires are also less durable and wear out after 30,000-40,000 miles. They are also slightly more expensive than other tires, but they can save money over the life of the tire (the savings can be substantial on cars with low MPG ratings).

How do you actually find tires with low rolling resistance?

This is where things get tricky. Tire companies have been slow to report the rolling resistance ratings on their tires. Rolling resistance values vary based on the testing situations (different cars produce different rolling resistance values), so a raw number isn’t meaningful to all customers. Also, the testing process can be time consuming. Here’s how Bridgestone responded when we inquired about why rolling resistance is not listed on their website (emphasis added):

Rolling resistance has traditionally been measured thru SAE (Society of Automotive Engineers) test procedure called J1269. It measures the force required to roll a tire against a dynamometer at a fixed speed of 50 mph. Within Bridgestone/Firestone, we have over 1,300 passenger and light truck products in the Bridgestone line alone and, conceivably, each one could have a different rolling resistance. The tread compound is a major factor, but construction, size, and even tread pattern can have an influence. At least 3 tires must be run in each configuration to get a good average. At approximately 1 hour per rolling resistance test, this amounts to 3,900 hours or over 6 months just to run the Bridgestone brand.

This explains why these values are estimated. We have some data, however it frequently does not line up with those sizes or patterns requested. Therefore, estimation is required.

The weight of the tire will have some affect on gas mileage. What is more of a factor, though, is the tire “footprint”. This term refers to the actual area where the “rubber meets the road”. The same size tires may have different contact areas and therefore different gas mileage implications. More rubber coming in contact with the road can create increased rolling resistance. Generally, taller, narrower tires are better for fuel economy, if you retain your current wheels. Increasing the tire aspect ratio, for instance from 70 to 75, will provide additional load carrying capacity.

Your local mechanic may be slightly more helpful, but don’t count on it. Right now, the best way to find a tire with low rolling resistance is to find a chat board dedicated to your car and surf the wisdom of the crowds. There are also several non-comprehensive lists of LRR tires, but they may not be available in your area and the lists quickly become outdated as new models are introduced.

Hopefully, this situation will change soon. A California law went into effect in 2008 that requires all companies to list RR ratings for replacement tires sold in the state. As more people become aware of green tires, there will be rising demand. This demand will drive innovation and may also bring prices down. In the near future, we may even see a Green Seal on tires with Low Rolling Resistance, just like the Energy Star label on appliances.

The spike in gas prices in 2008 has focused attention on several ways to improve mileage without adopting radical technologies, and low rolling resistance tires are only one of several inexpensive ways to get significant improvements.

Before you go out and buy new tires, there are several ways to reduce the rolling resistance of your current set. Start by removing any excess weight from your car – all that junk in the trunk is pressing the tires down against the road and increasing the contact area. Also, check the air pressure on your current wheels:

The easiest way to reduce rolling resistance… is to make certain that the tires are properly inflated. A vehicle that requires its tires to be inflated to 35 psi (based on the vehicle’s tire placard) will have an increase in rolling resistance of approximately 12.5% if the tires are allowed to become underinflated to just 28 psi.

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Photo courtesy of Tamaki at Flickr.com.

The latest news on carbon credits

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Photo courtesy of Azure Bleu at Flickr.com.

The Kyoto treaty is in the news again as the Obama administration considers implementing a cap and trade system for carbon dioxide. It turns out that a lot of participating countries have fallen short of their Kyoto commitments, and are now required to purchase approximately $46 Billion of carbon credits to make-up for surplus CO2 production. This could mean that the price of carbon credits is about to spike upwards from their current low levels.

So, what exactly is a cap-and-trade system?
Cap and trade is a regulatory framework for controlling the emission of carbon dioxide and other pollutants that affect the climate. It is one of several proposed systems, with the largest alternative being a carbon tax. The cap in cap-and-trade refers to a limit set on the level of emissions. This cap can be company specific, region specific, national, or international. When participants spend more than their allotment, they can trade credit with other participants who haven’t produced as much as their allowed.

What are carbon credits?
Carbon credits are warrants that represent carbon neutralizing behavior (ie; maintaining a forest, sequestering carbon underground, or breaking down greenhouse gases). In some countries, factories and power plants are required to purchase carbon credits that offset their pollution. These vouchers are used to fund the development of clean technology and conservation, and they also make green business practices more competitive by putting a price tag on externalities. A cap and trade system promotes land conservation by placing a value on pristine wilderness areas. In turn, this reduces carbon emissions by deterring development.

Many different companies offer carbon credits and carbon offsets. If you’re interested in purchasing some for your personal use, there are plans that you can use to neutralize the impact of a plane trip, counterbalance your home’s expenditures, or to offset your daily commute. Here’s a price survey of various companies that offer carbon credits.

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Photo courtesy of Dianne Pike at Flickr.com.

There are concerns with how carbon credits are computed. Critics argue that carbon credits are often miscalculated, that they’re rewarded for projects that were going to be built anyway, or that the expense is not justified by the results. A recent report by the US General Accounting Office offers some support to these criticisms. Projects that have applied for carbon accreditation under the UN Clean Development Mechanism (CDM) were found to have serious problems. Several of these projects involved displacing Chinese farmers to build hydroelectric dams, and construction on some of the dams had even been underway before the project managers asked for carbon credits.

The end users of carbon credits are increasingly demanding third-party validation. In order for carbon credits to be more than modern-day indulgences, there are some important stipulations that need to be met. The carbon savings must be measurable, unique, and independently verifiable. This prevents unscrupulous carbon dealers from selling non-existent credits or selling the same credits over and over again. In the terminology of the Clean Development Mechanism, only actions that provide “additionality” are eligible for carbon credits:

If I buy carbon offsets, I make the implicit claim that I forgo reducing my own emissions (i.e. I still fly) but in exchange I pay someone to reduce their emission in my stead. If I buy carbon offsets to “neutralize” the emissions I caused during air travel from someone who would have reduced their emissions anyway, regardless of my payment, I, in effect, have not only wasted my money, but I also have not neutralized my emissions.

Currently, the majority of projects applying for CDM accreditation involve hydroelectricity. There are only a finite number of suitable rivers in the world though, so future savings will have to come from new techniques and green technologies. Microturbines fueled by waste are one of the largest areas of potential growth, and US companies are spearheading development in that area.

San Antonio recently became the first city to deploy a power plant that uses methane from sewage to generate power. Burning this renewable resource is a clean solution, because methane has more than 20 times the impact on climate change that carbon dioxide does. There’s no word yet on whether San Antonio is applying for carbon credits on this project, but it’s certainly more useful than methane flare projects that are already cashing in.

Several states are pursuing a different tactic to reduce their carbon footprint; they’re attempting to reduce overall power use. A California law is now in effect that requires all state facilities to reduce their energy use by 20%. There have been some unexpected results. In addition to new systems at government offices and service centers, Corrections facilities around the state have also been forced to go green. California’s not alone; many prison facilities nationwide are adapting energy saving technology. From prison gardens that use compost to water boilers that burn wood waste, cleantech is saving thousands of dollars and introducing prison populations to some innovations that were originally developed for the Hollywood elite. With state budgets feeling a pinch, how long do you think it will be before San Quentin starts selling carbon offsets?

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Photo courtesy of MrGluSniffer at Flickr.com.