Do speed limiters always mean better mileage, less emissions?
June 2, 2008
June 2, 2008
There have been many compelling arguments made both for and against Ontario’s controversial legislation that, if passed, would mechanically limit truck speeds to 105 km/h. We’ve heard them all here at Truck News. Some of them have been absurd (that the Ontario government are communists and that truckers will take up arms before allowing their trucks to be governed). Others make a lot of sense – like this one:
Doug Monahan is one of those owner/operators who meticulously tracks his fuel mileage. He spec’d his latest truck with fuel economy in mind. It has a small, 450-hp Mercedes-Benz engine which allows him to average 7.73 mpg even without an aerodynamic tractor. He gets 8.7 mpg on flat ground and about 7.3 mpg through the hills.
Doug hauls into the US where he encounters a lot of these hills, especially through Virginia. While he averages 95 km/h here in Canada, he says he needs the extra juice to get over the hills without burning up too much fuel in the process. He generally approaches the bottom of the hill at 75 mph, which allows him to increase his fuel mileage by half a mile per gallon when all is tallied on the other side, he claims. He says he needs to keep the smaller engine wound up to maximize his fuel mileage in the hills. He has experimented by running his usual 95 km/h through the hills in the US and he says he saw his fuel economy suffer significantly.
“That’s money right out of my pocket,” he insists.
He claims that his smaller engine will put out more greenhouse gases if he’s limited to 105 even through the hills in the US. That’s because it will have to work so much harder to get up the hill if he can’t build up speed at the bottom. Now, Monahan is a reasonable guy and he knows that slowing down saves fuel. That’s why he spec’d a smaller engine. However, he said his fuel savings will lost if he has to run at 105 through the hills. And he’s not happy about it. He feels the proposed law should apply only to new trucks, since he would have spec’d his truck differently had he known about the proposed law at the time.
He makes a good point. When new regulations are hoisted upon the automotive industry, existing vehicles are usually grandfathered. He’d like to see the Ontario government follow that lead in this case as well.
“Then the owner/operators and the company know what they’re getting into and they can order the truck accordingly,” he points out.
George Desjardins, an owner/operator with 30 years experience, agrees that his fuel economy will suffer in the hills if his truck is governed at 105.
“In the perfect world these pro-speed limiters live in, there mustn’t be any hills,” he wrote to Truck News. “The world I live in there are, and when you are loaded with a gross weight of 130,000 lbs, you must drop gears to climb hills, even little ones. This causes the engine to rev up even though the truck is losing speed. If you can’t increase your speed a little prior to the hill, you will be in a lower gear and running with a higher RPM that much longer, thus spewing greenhouse gases into the air that much longer.”
He adds: “Being that at the present time I can speed up prior to climbing a hill, I can in a lot of cases stay in high gear and not contribute to this problem as much.”
Desjardins spent extra money on a big engine and now feels this legislation will, in his words, “castrate it.”
It’s not easy to determine to what extent fuel mileage may be compromised in hilly regions with the proposed law, if at all. But we mustn’t underestimate the implications the proposed speed limiter law will have on how fleets and owner/ops spec’ their equipment. Perhaps the law would be more readily received if current trucks were exempted from the rule?
James Menzies is editor of Truck News magazine. He has been covering the Canadian trucking industry for more than 15 years and holds a CDL. Reach him at email@example.com or follow him on Twitter at @JamesMenzies. All posts by James Menzies