Automatics In Winter Question?

when the wheels are spinning that is loss of traction and when you apply power to the wheels you lose more traction....the less wheel spin there is the better to regain that traction

A loss of traction comes from asking the tires to do more work than they can do with the amount of traction that's currently available. That doesn't just mean you're trying to put too much throttle to the drive tires. It can also mean putting too much braking force to the drive tires.

Say you're at half throttle moving forward at 40 mph on snow covered roads and the drive tires break loose under power. If you let off the gas completely the engine compression is going to try to slow the drive tires even without the jake brake on. So the wheels may have broken loose originally because you were putting too much throttle to the ground but you can make the situation worse by letting off the gas completely and putting too much braking force to the wheels. That braking force isn't much of a concern in 4 wheelers because you don't have the compression from a gigantic diesel engine applying that braking force to the wheels the way you do with a big rig. Letting off the gas in a 4 wheeler is more gentle than letting off the gas on a big rig. So lightly feathering the throttle properly will prevent too much power from going to the wheels and it will also prevent too much braking force from going to the wheels.

Now kicking it into neutral or pushing in the clutch would also prevent any engine braking force from going to the wheels. That's a good thing. But if you've shifted into neutral you're now out of gear completely and you're not going to get it back into gear while you're skidding to put power to the ground if need be. If you kicked in the clutch instead of shifting into neutral you would have to have fantastic precision to let off the clutch at the proper RPM and with just a little throttle so that you don't apply too much power or too much engine braking force to the drives if you re-engage during the skid. It's incredibly unlikely you're going to pull that off under such extreme circumstances.

The two biggest differences between a big rig and a four wheeler in a skid is that the big rig bends in the middle and it also has the momentum from the weight of the trailer pushing forward against the tractor when you're off the throttle. So when you're trying to regain control with a big rig you're not going to get the same results from your reactions as you would with a 4-wheeler. A tractor trailer behaves like two different vehicles hooked together. You have to manage the tractor itself, which would behave somewhat like a 4 wheeler would if you were bobtailing, and also the trailer which is anywhere from 15,000-60,000 pounds with all that momentum pushing you down the road if you let off the gas.

I'll say this though.......kicking in the clutch or putting the shifter into neutral is not the worst thing you could do in a skid. It isn't what I would do but I have a ton of experience in big rigs on slick roads. The worst thing you can do most of the time is to overreact and either hit the brakes pretty hard or start sawing on the wheel. You want smooth, gentle reactions. If someone had little or no experience on slick roads and little or no experience in a big rig I would say you might be better off just kicking it into neutral in a skid and hoping you can gently steer your way out of it. That might be a good newbie emergency technique.

Thanks Brett, tgat what I was getting at with the drive tires. Any power to the wheels, fuel, or braking, is still power to the wheels. I just couldn't seem to explain that right. I was told never to take it out of gear but just use the clutch, but I guess it all depends on the specific situation, and the best thing is to keep cool and not over react. About the bend - when you start focusing on the trailer you do yourself no good up front, except make matters worse. I was told always get your cab under control and forget about the trailer for now, if you can control of your can, the trailer will eventually follow suit. I know that's a perfect situation and we don't live in a perfect world, but this is all a starting point. I was also told slow and gentle steering movements when sliding g. We tend to over steer and make things worse.

I read through all of the replies on this subject, specifically the posts about running in neutral. Unless I am mistakin' (feel free to check me on this), coasting in neutral (automatic or manual trans) more than a full length of the tractor and trailer is illegal. Granted, I think it would be a rather rare circumstance to receive a citation for this, however I do know if this occurs during the road skills portion of the CDL test, it might prompt a failing grade requiring a re-test.

Fact is regardless of the legality of "coasting", "freewheeling", or "Georgia Overdrive", it totally compromises traction and control. If I am trying to manage a slide event, putting the truck in neutral is the furthest thing from my mind at that moment. To me the fall back is common sense; leave it in gear.

I read through all of the replies on this subject, specifically the posts about running in neutral. Unless I am mistakin' (feel free to check me on this), coasting in neutral (automatic or manual trans) more than a full length of the tractor and trailer is illegal. Granted, I think it would be a rather rare circumstance to receive a citation for this, however I do know if this occurs during the road skills portion of the CDL test, it might prompt a failing grade requiring a re-test.

Fact is regardless of the legality of "coasting", "freewheeling", or "Georgia Overdrive", it totally compromises traction and control. If I am trying to manage a slide event, putting the truck in neutral is the furthest thing from my mind at that moment. To me the fall back is common sense; leave it in gear.

Your right you cannot coast more then 100 feet. We're talking about a cdl test though. Your also right you should never take it out of gear. Here is the science: when you loose control and are skidding or sliding in ice your tired spin at different rates of speed that is why your sliding or slipping. If you take your foot of the accelerator....good thing, however, all your doing is trying to manipulate the tires to match speed, and most times you make the situation worse. Braking, not good at all, your compound the slide, and loosing more control of your tractor. The idea is when you leave your truck in gear and press the clutch in your cutting power to the drive tires, thus allowing the wheels to catch up to each other to go the same speed, and regaining as much control as you can, gently steering. In an automatic, I don't know how this is done except flick it to neutral - your right to be that seems dangerous. My original question was do you do cut power to drive tires to regain control in an auto Because it's different.

Schneider has us hit the skid pad, and I can tell you first hand, leaving the 10 speed in gear and depressing the clutch helped regain control a lot faster then just taking your foot of the fuel, and the brake, just made matters worse.

Second Chance wrote:

The idea is when you leave your truck in gear and press the clutch in your cutting power to the drive tires, thus allowing the wheels to catch up to each other to go the same speed, and regaining as much control as you can, gently steering. In an automatic, I don't know how this is done except flick it to neutral - your right to be that seems dangerous. My original question was do you do cut power to drive tires to regain control in an auto Because it's different.

It's my first winter in an automatic (truck) so I have no real-time experience to fall back on (a disclaimer, LOL). Except to say, common sense would tell me to leave it in drive. Depressing the clutch for an instant is far different than taking the truck completely out of gear, agreed. As this pertains to students, I don't want to mislead them into thinking that running a CMV in neutral is an acceptable and legal practice. TT is all about helping the newbies pass their CDL.

I'd love to test your question on the skid-pad before traversing a snow-covered I-81 (roller coaster) through the Scranton PA area. unfortunately not in the cards. Maybe Schneider will let you run an automatic on the skid-pad to test this out. If I had my druthers I'd prefer to drive in snow using a 10-speed only because I have 2 full winters worth of experience with it. Admittedly I am a tad apprehensive, so the first couple of snowfalls I will move at a slower speed than if I had a 10-pack. I have a call into one of the Swift safety directors who is a friend of mine. It may take a couple of days to hear back from him, but hopefully I'll have something to post eventually.

Schneider has us hit the skid pad, and I can tell you first hand, leaving the 10 speed in gear and depressing the clutch helped regain control a lot faster then just taking your foot of the fuel

What maneuver were you guys doing on the skid pad?

I just watched a video on Schneider crossroads as they are getting their drivers ready for winter descents in bad weather. This is for the D-12 automated transmission. When you are about descend a mountain get to the speed you want to safely descend. They say 20mph is a safe speed to keep slight constant brake pressure without over heating the brakes. Chou flip the switch to lick the trans in the gear so it doesn't upshift. If you start to slide, the abs will automatically disengage the engine from the drive wheels, just like if you were to press the clutch in on a manual.