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Big Shoes to Fill

Posted: August 1, 2014 by Rolf Lockwood

Forever was about how long it took, but after almost four years of public comments we finally have revised stopping-distance regulations for new tractors. Except don’t hold your breath.

The new regulations, launched with a proposed rulemaking in late 2005, don’t come into effect until 2012-model-year trucks, in 2011 at the earliest.

The U.S. National Highway Traffic Safety Administration (NHTSA) has created a standard for new-truck brakes (they’ll be mirrored in Canada, as brake rules always are) that requires a typical loaded-to-maximum GVW tractor-trailer traveling at 60 mph to reach a complete stop in 30-percent less distance than now.

That will bring them to 250 ft, down from 355. That’s for a standard three-axle tractor and a tandem trailer grossing 59,600 lb or less.
For a "small number" of what NHTSA calls "severe service" tractors, the stopping distance requirement is reduced by a smaller amount, namely 13 percent, which translates to 310 ft.

When they say "small number" in the U.S., they actually mean just one percent of the total fleet; specifically those units grossing over 70,000 lb on three axles or 85,000 lb on four axles. But hold on. Here in Canada even a five-axle rig is allowed 87,100 lb nationally, and as much as 102,500 lb in some jurisdictions.

The implication is that the 30-percent rule really only applies to a minority of Canadian tractor-trailers, though almost all of those in cross-border service, of course. And while meeting that challenge is relatively easy, NHTSA allows that heavier trucks present some difficulties in order to become compliant. Many will need air disc brakes, it seems clear, and even then a lot of them couldn’t meet the 250-ft demand.

Here’s exactly what the rule says:

The reduction applies to service-brake stopping distance but does not, however, apply to emergency braking distances. For heavy trucks in the loaded-to-GVWR condition, the stopping distance requirements from an initial speed of 60 mph are as follows:

A tractor with two or three axles and a GVWR of 70,000 lb or less must stop within 250 ft.

A tractor with three axles and a GVWR greater than 70,000 lb must stop within 310 ft.

A tractor with four or more axles and a GVWR of 85,000 lb or less must stop within 250 ft.

A tractor with four or more axles and a GVWR greater than 85,000 lb must stop within 310 ft. 

For heavy trucks in the unloaded condition, the agency is reducing the specified stopping distance from 60 mph by 30 percent to a 235-ft requirement [down from 335 ft]. This requirement applies to all tractors, including those severe-service tractors for which the loaded-to-GVWR stopping distance requirement has been set at 310 ft.

The new rule applies only to new truck tractors, and does not yet include straight trucks, trailers, or buses.

Incidentally, air-braked straight trucks must stop within 310 ft as things stand now. That won’t change in 2011.

The new rule will be phased in over the next four years beginning with 2012 models. More specifically, NHTSA requires implementation on typical three-axle tractors to be completed by Aug. 1, 2011.

Manufacturers get an extra two years to work on two-axle and so-called "severe service" tractors, the new mandate having to be met by Aug. 1, 2013.

As noted, the present NHTSA rule demands that an air-braked three-axle tractor pulling an unbraked trailer (for testing purposes only, not as an attempt to mimic real highway life) must be able to stop in 355 ft from 60 mph.

In fact, truck makers now test for stops in about 280 ft. In practice, OEMs will likely aim for — and reach — 220 ft, which is getting very, very near to car territory. Cars presently have to stop in 216 ft.

WHAT TO DO

So what does a 30-percent reduction actually mean? How will 2012 and later trucks meet the new rule? By adding brake torque, possibly even on the steer axle alone.

That could simply mean bigger cam brakes, maybe a combination of cam and disc brakes, or possibly disc brakes all round, depending on the size of the truck and its application. Meritor WABCO says you can gain 20-percent brake torque with bigger cam brakes, 28 percent with discs up front and S-cams out back, or 38 percent with air discs at all tractor wheel positions.

Bendix Spicer says that a standard five-axle rig equipped with air disc brakes all round the tractor and grossing 56,470 lb can actually stop in 213 ft from 60 mph. Meritor WABCO tests showed 204 ft. Amazingly, those numbers are below the present NHTSA car threshold. Think about that.

Key question: Will you need air disc brakes when you buy a truck post-2012?

Some claim that a truck equipped with air-discs all
around the tractor and grossing 56K lbs will stop in
213 ft. from 60 mph, which is below the car threshold.
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