Trailer Talk

On Slick Pavement, ‘The Sliding Wheel Wants to Lead’

Whichever wheels are skidding on a tractor-trailer will want to get in front and take the rest of the rig with it.

February 24, 2017

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When encountering fresh snow, wise drivers sit up, take notice and slow down. Photos: Screenshots from CBS TV newscasts. 
When encountering fresh snow, wise drivers sit up, take notice and slow down. Photos: Screenshots from CBS TV newscasts.

Here in the northern tier of states, we’ve had spring-like weather in January and February. Today as I write this, it’s supposed to go to 74 degrees, about 30 higher than normal for the season. Tomorrow it’ll turn colder, the forecasters say, and farther north and west, a snow storm is already sweeping across the land, marking an assertive return of winter.

Driving in snow doesn’t bother me because I grew up in Wisconsin in a time when winters were rough. Among other things, I learned to pump the brakes when trying to stop short on slick surfaces. It worked well on snow but not so well on ice, where going slow or staying home was the best tactic.

Pumping the brakes is what modern electronic anti-lock braking does, and it helps control a vehicle on slippery pavement. Suppliers have long said that there’s no need to pump the brake pedal with ABS aboard, and that’s correct if the systems are working properly. I say “systems,” plural, because with a combination vehicle, there’s one system on a tractor and another on the trailer (more if it’s a set of doubles or triples). Each system works independently, but if all are set up right, the vehicle will act as if the systems are linked.

I drove straight trucks while working my way through college and 10 years later I went to a very good school to learn how to drive semis. That was the Fox Valley Technical Institute (now College) in Appleton, Wis. Ten or 12 years after that, while a staffer at Heavy Duty Trucking, I returned to the school for a refresher on winter driving.  

The instructor’s main point, and the one I try to remember, was, “The sliding wheel wants to lead.” On a tractor-trailer, whichever wheels are skidding will want to get in front and take the rest of the rig with it. If it’s the steer axle’s wheels, it’s not so bad except steering control is gone and the tractor will continue traveling in the direction that momentum is pushing it. Get off the brakes, the wheels should turn again and steering control will return.

If the tractor’s drive wheels begin skidding, they can pull the tractor’s rear one way or the other, especially if there’s a crown in the road, and you’ve got the start of a nice jackknife. If the trailer’s wheels lock up, the trailer’s rear can begin to swing out – another type of jackknife. Get off the brake pedal and the wheels should resume turning and the vehicle will come back in line.  

ABS is supposed to prevent jackknifes, but somestimes can't when pavement's icy, as on this freeway in the Northeast a few weeks ago. 
ABS is supposed to prevent jackknifes, but somestimes can't when pavement's icy, as on this freeway in the Northeast a few weeks ago.

ABS should prevent all this because it lets the wheels turn briefly before applying the brakes again. It’ll do this quickly, on-off-on-off, several times a second, if the systems are operating correctly and the brakes are properly adjusted. That’s not always the case. So when encountering a slick road, it’s a real good idea to test the brakes to see how the rig behaves. Do it when there’s plenty of room between you and other traffic.

Do they all function like they should, or do brakes on one or more wheels stick? That way you’ll know what to expect when you need to use the brakes for a normal or sudden stop. An even better idea in a severe storm is to hole up until weather clears. Either way, remember that sliding wheels will carry you to grief.  

Comments

  1. 1. Dennis O Taylor [ February 28, 2017 @ 01:16PM ]

    Wouldn't it be easier to say that - when a wheel or axle starts to slide- the momentum of the vehicle will try to continue in the same direction it was going just before the slide started? Sir Isaac Newton said it that way.

  2. 2. Brian J Libby [ May 20, 2017 @ 05:02AM ]

    It's all about controlling the traction

  3. 3. Brian J Libby [ May 20, 2017 @ 05:05AM ]

    It's all about controlling the traction, hydroplaning can start at speeds as slow as 30-35 mph..

  4. 4. Brian J Libby [ May 20, 2017 @ 05:05AM ]

    Traction required!!!

 

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Author Bio

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Tom Berg

Senior Contributing Editor

Journalist since 1965, truck writer and editor since 1978. CDL-qualified; conducts road tests on new heavy-, medium- and light-duty tractors and trucks. Specializes in vocational and hybrid vehicles.

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