T his summer, Burnaby, B. C.-based Drexan Corporation released results of what could be the biggest comparison of nitrogen-and air-filled tires in normal fleet operations in Canada. Based on data coll...
This summer, Burnaby, B. C.-based Drexan Corporation released results of what could be the biggest comparison of nitrogen-and air-filled tires in normal fleet operations in Canada. Based on data collected from 1,988 wheel positions and 9.8 million tractor kilometres driven over six months in 2006, Drexan reported an 86% increase in tread life and 3.3% better fuel economy for the nitrogen inflation tractor/trailer group.
Additional findings Drexan presented to support nitrogen inflation came from comparing the trial data with fuel consumption data outside of the study: In 2004 the subject fleet, Winnipegbased Harris Transport, had used a driver inflation maintenance program and in 2005 it used a third-party inflation maintenance program. In short, Drexan calculated, a good air inflation maintenance program gives better fuel mileage (4.67 mpg) than a poor one (4.58 mpg), but a good program with nitrogen-inflated tires gives even better mileage (4.79 mpg).
Drexan is, among other things, the Canadian supplier for Parker Tire$aver nitrogen-generators. Drexan put up $140,000 to do the experiment, half of which Transport Canada agreed to refund under its Freight Sustainability Demonstration Program. Drexan designed and managed the study’s execution and led the analysis of the data. (Copies of the study can be obtained from Drexan).
In as much as the result of the experiment exceeded the more conservative expectations of some in the trucking and tire industry, they cut two ways: Harris Transport accepted the results as a validation of a nitrogen program. “I use nitrogen and I believe it is good and beneficial. For us it took doing a study and taking the data and showing it to us [to convince us],” says Kyle Harris director of operations with Harris Transport.
On the other hand are reactions such as that of Guy Walenga, director of engineering for commercial products for North America, Bridgestone/Firestone. “Some people in the industry raise their eyebrows over the fuel economy, and the 86% increase in tread life just ain’t right. We have never seen that magnitude of tread life increase in any of our field studies.
“The Bridgestone/Firestone policy [on nitrogen inflation] hasn’t changed in years. For commercial purposes Bridgestone/ Firestone has not seen enough benefits using nitrogen to pay for any benefits that might accrue from it.”
The results will find varying levels of support and the study design, assumptions, execution, data analysis and interpretation, especially surrounding the tire tread methodology, must be critiqued by those familiar with the strict rules of empirical methodology drummed into career experimental scientists. But any arguments aside, the Harris study will certainly take the discussion of nitrogen inflation to a new level. This is healthy from a scientific point of view and will hopefully inspire new studies and discussion about how they should be carried out. The Harris study also gives fleets more to chew on as they grapple with high fuel costs and try to choose among technologies, all of which, naturally, promise improved fuel economy.
One finding surprised Drexan: the two-tenths of a mile improvement in fuel economy of the trucks in the nitrogen inflation group over the air inflation group. Keep in mind that West End Tire was responsible for weekly tire inspections and topping up of the tire pressures in an aggressive tire maintenance program during the study.
“What surprised us is that we were assuming that if air-inflated tires are properly inflated, than the difference in mileage would be minimal. But it was not minimal. The two-tenths difference [in fuel consumption] says that there is a distinct advantage of nitrogen even if you have an aggressive tire pressure maintenance program [for air]. Something is going on, something is contributing,” says Drexan vicepresident Konrad Mech. “There is something else going on than just reduced rolling resistance. I think it is because nitrogen-inflated tires stay closer to the recommended tire pressure sweet spot.”
Other Fleets In May 2006 Normandin Transit in Napierville, Que. began switching its entire fleet to nitrogen. “In France nitrogen has been used for 23 years, but I had never seen it here,” recalls fleet manager Gilles Guillard. As soon as Guillard could buy a machine with sufficient capacity to serve the fleet, the company spent $20,000 for a nitrogen generator and dedicated lines to the shop’s truck bays.
The result was a radical shift in the yard’s inflation management schedule and considerable savings in tire inflation maintenance across the fleet’s 246 tractors and 500 trailers. “Before, with air, [we] did inflation checks before every trip. Now an inflation inspection is done on the nitrogen-filled tires every three months. There is no more need to have someone driving around the yard checking tire pressures,” says Guillard.
Guillard has seen at least a 15% reduction in blowouts and a minimum 15% decrease in the cost of road repairs. As well, he reports getting from 51,000 to 55,000 kilometres per 1/32 inch from the nitrogen-inflated tires, and the wear is more even; tire wear in the air-filled tires was running at 1/32 inch every 42,000 to 46,000 kilometre. The improvement in wear is about 21%. Guillard has not noticed improved fuel consumption.
Albert Chaisson, the maintenance team leader with Air Liquide, Moncton, explains that the tires on all of the company’s 250 units in Canada, mostly cryogenic trailers, are nitrogen inflated, a company practice for over 25 years.
“We use nitrogen because there is no moisture in it. Dry gas in your tires will not build up pressure under high heat. Our trailers are under heavy load. If you can keep the tires from leaking -your tires wear even. Air causes premature corrosion of the steel belts and premature aging of the tires. The tire life span is 10% longer. Some people say it is 15%,” says Chaisson. He does stress that in order to reap these benefits, nitrogen inflation has to be accompanied by tire matching, new valves when changing tires and good truck suspension.
He makes another interesting point: “In the winter the air is full of moisture. The worst thing you can do is open a valve. It can freeze and start leaking. But if you have nitrogen in the tire, you can take a chance, and add nitrogen. The valve won’t freeze on you.”
Back in Manitoba, Winnipeg Motor Express discontinued its nitrogen inflation program last year when it switched to a tire management program with Kal Tire, which does not have nitrogen inflation equipment. “We decided to give up nitrogen for other advantages,” says Winnipeg Motor Express maintenance manager Peter Kay. “I do believe in nitrogen, because anything that could help the tires run cooler could save the tires somewhat. But it won’t help if you don’t have a good tire inflation program. If people don’t check their tire pressures, the benefits of nitrogen will be nullified.” Nitrogen inflation proponents have this to say: Air-filled tires lose about two pounds of pressure a month, so fleets with lax tire management programs likely have chronically under-inflated tires. This increases fuel consumption, tire wear and the risk of blowouts. Moisture-laden air causes tire pressures to increase by 10-15% by the time they reach operating temperature, contributing to reduced tire life. Oxygen causes tire rubber to chemically degrade and the oxygen-moisture mix rusts steel belts and rims.
The Nitrogen Debate
Nitrogen-filled tires, on the other hand, lose pressure at perhaps at a third of the rate of air-filled tires, ergo better mileage, less wear and fewer failures. Nitrogen is dry, so there are no rust problems. The pressure in nitrogen- filled tires does not increase as much as tires reach operating temperatures, reducing tire wear. Nitrogen stops the chemical aging of rubber. Nitrogen-inflated tires can be recapped more times. Aircraft and racing cars fill their tires with nitrogen, so it has to be good for trucks too.
Those cool to nitrogen inflation say: Save your money (a third party charges around $10 to inflate a tire with nitrogen) and invest in a good tire management program; you need one anyway. Air is already 78% nitrogen, so how can 17% more nitrogen (a nitrogen- inflated tire has about 95% pure nitrogen in it) make any difference? Tires are designed to run at higher pressures at operating temperatures. Nitrogen may stop chemical aging, but since many fleets err on the side of caution and toss their tires after six years, aging is a non-issue. Even if you can get another retread out of your casing, it does not outweigh the cost of nitrogen inflation. Planes and racing cars work in far different operating envelopes than trucks, so comparisons with trucks are overcooked.
Some skeptics concede that nitrogen- filled tires lose pressure more slowly, they inflate less as they heat up and internal corrosion may be less. However, they are reluctant to attribute any operational significance to these effects, which are nothing that a good tire management program and air dryers cannot fix.