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||Sunday, December 07 2003 @ 08:46 AM PST
|I originally wanted to have this done before this last storm, but real life got in the way, and this... grew.
This is intended to be a guide of sorts to the different factors that are involved with driving in snowy weather. Hopefully it will have some reasonably interesting information, but because I'm not too confident of that, and due to its length, I've divided it up into sections so that you, gentle reader, may decide what kind of information you want to know. An interactive table of contents, if you will.
The impetus for this was, of course, my rant the other day, and my own desire to put my money where my mouth is, or something like that. As an aside, the word count on this works out to about a tenth of a short book, so if I find nine more topics to blather on about, maybe I'll publish them together and start giving autographed copies as Christmas presents. Man, I'm overtired.
Disclaimer: This may be bad advice. It has, in general, worked for me. No lawsuits, please.
The Fundamentals (Show)
The Myth of Four Wheel DriveDriving Tips (Show)
Types of Four Wheel Drive Systems
A lot of people who buy SUVs in this region do so because they are under the mistaken belief that having four wheel drive in their vehicle somehow makes them inherently safer on slippery surfaces such as snow and ice. They are both right and wrong, but unless they understand the details of four wheel drive systems and a bit of physics, chances are they're effectively wrong.
The first thing that people have to understand is that four wheel drive or all wheel drive will make it easier to accelerate forward under just about any conditions. The problem is that in probably ninety-nine percent of the situations where there is the potential for a collision, forward acceleration has absolutely no bearing on whether or not the collision occurs.
Most collision avoidance comes in a vehicle's ability to steer and brake. Even on dry pavement in the middle of the summer, SUVs aren't generally good at this because they are massive (which has an effect on braking distance) and comparatively top heavy (which has an effect on steering). Under adverse conditions, these poor characteristics (especially the mass) are even more of a factor.
Here comes the physics. Pay attention.
Linear motion is described by a speed and a direction. These two together form what is known to physicists as velocity (a much beleaguered term in the general populace). Any change in velocity, whether it is a change in speed or direction, is known as acceleration. Acceleration requires a force, which itself has a direction component. Because, as the man said, "for every action there is an equal and opposite reaction," any force that accelerates a vehicle in a given direction must apply the same amount of force to something in the opposite direction.
Just to make sure you're really getting all of the last paragraph, here are a couple of things that don't exist in nature: deceleration and centrifugal force. What the schmucks in the journalism field call deceleration is simply acceleration in the direction opposite to the motion (or negative acceleration in the direction of motion, if that's easier to visualize). Those same schmucks talk about centrifugal force, which is actually the apparent force exerted on an object inside another object that is being accelerated around an axis, and is more properly described as centripetal acceleration. The reason that it's not a force per se is that, as I mentioned before, a force has a direction component, and centrifugal force, if there were such a thing, would have a direction component that constantly changed, depending on the relative locations of the objects in motion and the axis. This kind of system is a bit more complicated than can be accurately described solely by one basic building block of physics, so physicists (and I) don't acknowledge the shorthand (except maybe with an eye roll).
Anyway, I was supposed to be talking about cars, not indulging in scientific snobbery.
All of the acceleration that occurs while driving, whether it's positive, negative, forward, backward or side to side, happens via friction in the 200 square inches or so of the tires that are in contact with the ground at any given moment. Just so we're all keeping track, 200 square inches is just slightly larger than a standard size sheet of paper. Picture, if you will, a piece of rubber that's the size of a sheet of paper. That sheet of rubber is solely responsible for pushing between one and three tons of vehicle around. In a vehicle that's in good working order, the tires are always the weakest link in acceleration. Of course, you're going to immediatly say that the size of the sheet we're working with (to beat a metaphor within inches of its life) is going to be larger with heavier vehicles and smaller with lighter vehicles, and you'd be right. The issue is that the contact area isn't that much larger with the heavier vehicles. It's also worth pointing out that weight does come into play as a positive factor with regard to the tires creating friction.
Now, here's the question. After reading all of the above, when driving in adverse conditions, would you rather be in a Miata that weighs in near the one ton mark, or a Hummer that weighs in over the three ton mark? Most of you are going to read that question, skim the above paragraph and say, "I understand what he's saying, but I think I'd still rather be in the Hummer." That, my friends, is a direct result of one of the most successful marketing initiatives ever undertaken by the major companies that build vehicles. All evidence to the contrary, almost anyone, myself included, would rather be in a truck of some sort that has four wheel drive when driving in the snow.
Okay, so I've gone on at length about how those SUV drivers I mentioned before are wrong, but I also said that they were right, didn't I?
The way in which a four wheel drive system makes driving safer in slippery conditions is that it gives the vehicle the ability to briefly lose traction on a wheel when accelerating (again, in any direction) without having serious effects.
Notice that I said, "on a wheel". It is a common misconception that all four wheel drive systems help when traction is lost on more than one wheel. This is not the case, but to explain why, I have to get into another technical discussion, this time about different types of four wheel drive systems.
Winterize Your Vehicle
One of the biggest disservices done to the american public over the years has been the use of marketing terminology to describe drivetrain components. Because of this, it's sometimes very difficult to tell when you're buying a vehicle what kind of four wheel drive system is has. There are no set definitions on the terminology, except that anything that says it has "four wheel drive" or "all wheel drive" does, in fact, provide some motive force to all four wheels. When trying to establish the relative efficacy of a particular vehicle on a particular terrain, this knowledge alone is, at best, almost useless, and, at worst, outright misleading.
The real determining factors lie in the manner that the various axles and driveshafts are all connected to each other, so I'm going to have to get into a discussion about differential gears and transfer cases.
When a vehicle turns, its wheels are spinning at different rates. If you want to illustrate this to yourself, take two pens at once and draw a curved line on a piece of paper. One of those lines, if you were to straighten it out, is longer than the other, even though they took the same amount of time to draw, so the pen drawing that line must have been moving faster. Got that? Good.
Almost all four wheel drive vehicles use a pair of drive shafts that each connect to either the front or the rear axle. The junction where this takes place is called the differential case, which contains the differential gears. In order to keep these gears from exploding, or your wheels from skidding, when you turn your car into the Blockbuster parking lot, the differential gears are set up to turn each wheel independant of the other. If that's all that's happening, this is known as an open differential.
As was so eloquently described in the movie My Cousin Vinnie, an open differential has a drawback. If one wheel meets no resistance, whether it's due to snow, ice or mud (as it was in the movie), it will spin freely when you press the accelerator, and the other wheel on that axle will sit there uselessly as if to mock you. At some point, some clever engineer devised a way to limit the amount of power going to one wheel to something less than one hundred percent. Thus was born the limited-slip differential.
In the last few years, some manufacturers have started offering something called a locked differential. These are very handy when driving off-road because instead of the power distribution being allocated so that each wheel has at least some motive force, a locked differential ensures that each wheel has exactly half of the force provided by that drive shaft. If you've got front and rear lockers, each of your four wheels is getting a quarter of the output from your motor. The reason these aren't all that common is because they're relatively difficult and expensive to make. The problem isn't so much figuring out how to lock the two sides together, but rather how to unlock them, and lock them again ad infinitum by pushing a button on the dashboard.
So, when you're driving down the road in a blizzard, which kind of differentials do you want your vehicle to have? Perhaps surprisingly, the best type for that situation is actually the limited-slip differential. It's fairly obvious that an open differential is the least desirable, but less obvious is why the locked differential isn't the most desirable. When you're driving down the road in a blizzard, you're driving on a surface that is unpredictable in its ability to provide friction. If you're on a curve, or maybe pulling into that Blockbuster, having a locked differential requires that at least one wheel start to skid a little bit, and frankly, we'll have none of that. It's hard enough driving around in this ice rink of a parking lot as it is, you don't need to start off with the handicap of having only two wheels making good contact with the ground.
Transfer cases, like differentials, transfer power to the front and rear in either a locked, limited slip, or open manner. Those aren't the terms that the industry uses to describe their behavior, but the industry's terms are useless anyway. Also like differentials, the best one to have is the limited slip. Any self respecting SUV will also have a low gear built into the transfer case, but that's not normally useful for on-road driving so we won't get into it now.
So, to sum up, the ideal system that we're looking for is four wheel drive with limited slips in the front, rear, and center.
Here's where it gets interesting (I can see you rolling your eyes from here). Most SUVs come with something called part-time four wheel drive. The only piece of information that's guaranteed from knowing that it's part-time is that the transfer case is locked. The reason that they call it part-time is that if you were to drive it around all the time in four wheel drive on dry pavement, you'd be skidding tires around all over the place, and eventually your transfer case would tear itself apart. Don't run a part-time system on any surface that provides a lot of friction.
Generally speaking, part-time systems are comprised of a locking transfer case and open differentials. Not coincidentally, those are the cheapest to manufacture. Many manufacturers offer an option to turn the rear differential into a limited slip, which is definitely an improvement in poor weather conditions, but it's still not ideal.
The next type of system, and this is where we get into the crappy marketing terminology, is generally known as full-time four wheel drive. The only thing that you know for sure is that it doesn't have a locking transfer case. It may be comprised of any combination of open or limited-slip differentials and transfer cases, but it probably doesn't have locking differentials.
At its worst (both diffs open, transfer case open), the only thing that this system gives you is the ability to turn on four wheel drive anytime you want, regardless of the surface friction. At its best, (limited slip diffs front and rear, limited slip transfer case), it will provide you with the best possible mechanical traction control. The reason I get so tweaked at the marketing types over this is that the cheapest part-time system is superior to the cheapest full-time system (and less expensive), but the best part-time system isn't as good as the best full-time system. Basically, without getting into a technical discussion with the sales person (which will inevitably cause him or her to call in a mechanic), you might never know whether you were getting the right thing. That thing called "All Wheel Drive", incidentally, is just full-time four wheel drive without the low gear.
Okay, enough with the technical crap. You've already got something to drive, so here are some things you can do to make the most with what you've got.
The first thing you've got to do is deal with your tires. It all comes down to the tread. If you have the means, I highly recommend having a set of snow tires that you throw on each winter. If not, then make sure your tires are in good shape, and I don't mean making sure they pass a state inspection.
Just to give you an idea of what I'm talking about, the tires on my Jeep have about 36000 miles on them, and as far as the state's concerned, they're probably good for another 30000 or so. I'll be replacing them this year. Each winter, and this is only my third on these tires, I've noticed that they grip less and less in slippery conditions. The first winter they were pretty much unstoppable. I couldn't even do doughnuts in my office's snow covered parking lot because they kept gripping on me. These days they still do the job admirably (I just drove around for a couple hours in the middle of the storm), but I don't feel like I'm on rails anymore.
Don't read too much into the mileages I quoted; every vehicle is going to be different. The tires that I have on mine are specifically made to grip very well when they're new, but they don't last very long in the grand scheme of things. It's a compromise I was willing to make.
If you're looking to buy winter tires, the canadian government started a program in 1999 that sets standards for winter tires in Canada. From what I can tell, the standard is set fairly high (they take winter seriously up there, as well they should). The tires that pass will have a little pictograph on the sidewall that is a mountain with a snowflake. I haven't looked into this myself, but I'm guessing that the tire manufacturers have no reason to not put the pictograph on the ones they sell here in the US, so it's something to keep an eye out for.
Another little tidbit is to make sure that you have caps on all of your valve stems (that'd be where you hook the air pump to the tire to inflate it). When you're driving in snow and ice (and mud, for that matter), you might get some stuff packed into the top of your valve stem causing the pin to depress and in no time you're standing on the side of the road changing a flat tire in a blizzard, a problem you could've fixed yourself for less money than it costs to buy a number 6 at McDonald's.
Also, and I know that everybody in the world knows this already and blithely ignores it, check your antifreeze to make sure that you both have enough, and that the mix is balanced. If you don't already have one, go down to Autozone or whereever and pick up a coolant tester for about five bucks. Your engine will thank you.
Hitting the Road
The Road Surface
So, you're going to head out in crappy weather. First, you're going to need to get your car onto the road from whereever it is now. The very first thing you need to do when you get to your car is to make sure that your exhaust pipe(s) are cleared of snow. If they're not, you need to get them cleared before you try to start your motor. There are two basic reasons for this. The first is that if your exhaust pipe is plugged, your motor may very well not start, or not stay running for long. The second, and more important reason is that during the fifteen minutes or so that it's going to take you to dig your car out of that snow drift, your passenger compartment may be filling with exhaust fumes. This is not a good thing.
Now you can start your car and turn on the heat and defrosters. Unless there are a total of eight or so snowflakes on your windshield, you probably don't want to run the wipers just yet, as any ice that's there will degrade your wiper blades. It may not be noticable, but if you do it habitually, you're probably replacing blades twice as fast as somebody who actually does things in the right order.
The next thing you need to do is clear off your car, and I do mean clear it off. Just scraping the windows doesn't cut it. I will grant you that this is one of my pet peeves, but there is actually a reason for it. Years ago, I had the vague misfortune of driving a 1989 Ford Escort Wagon. One day, the day after a snowstorm, I was driving merrily along after not having cleared off my roof. For ten minutes or so in the city, the drive went without incident, but at one set of lights I braked a bit harder than I had previously, and I suddenly couldn't see out of my windshield. A four foot sheet of snow and ice had slid off of my roof, covering my hood and windshield with about six inches of snow in about a half second. Needless to say, the guy behind me was not amused when I had to get out and shovel off my windshield.
The other thing that happens, and in a significantly larger percentage of cases, is that the same four foot sheet of ice and snow blows off of your roof about ten seconds after you get on the highway, and lands either right in front of the guy behind you, or even worse, on his hood. This is one of those things that everybody has seen happen, but almost nobody stops to consider that, the guy in front of you that you're calling an asshole feels the same way about the guy in front of him, and guess what the guy behind you thinks?
So, to avoid being part of the problem, here's what you have to do: Start at the top. Clear off your roof first. Then do your windows. Next is the hood and trunk. I'm not saying that your car has to look like it's in a showroom, but at least give it a good once over. Don't forget your bumpers.
Now that you're mostly snow-free, make sure that all of your windows and side mirrors are scraped and brushed, and that all of your vehicle's lights and license plates are cleared off. That's it. Easy, huh?
If you need to dig your vehicle out, I've got some rules for you to memorize. Generally speaking, your car doesn't enjoy going through snow that's higher than your axle. Plan on spending twice as long to do it right, rather than digging for five minutes, spinning your tires for ten, digging for another five, rinse and repeat. Your sanity will thank you, and your boss will get over it. The added bonus is that you (or one of your neighbors, if you park on the street) will have a much easier time getting another car in later.
If you were doing any driving in the snow before, now is a good time to get rid of that black, caked on, road grime snow that's inside your fenders. If you let that crap build up enough, it will start to have more of an effect on your driving than you could reasonably want.
So, you've got the heater going, the motor warmed up, and a nice clean runway between you and the road. What's next? You just need to get in, take a quick look that your windows and mirrors are still clean, put on your seatbelt, check for oncoming traffic, and get the hell out of there.
Now that you're (finally) on the road, let's take a minute to talk about the road itself, because we should probably know what we're getting into. This stuff is pretty much straight out of the state licensing handbook, but it bears repeating because almost nobody seems to remember it until their car is sliding sideways into a ditch.
Bridges will generally freeze before the rest of the road. This will often lead to disasterous consequences for some unwary motorist. There you are, breezing along the nice clean (if damp) interstate at sixty or so, when all of the sudden the rear end of your SUV kicks out, and you get to the other side of the bridge and are suddenly confronted with the return of friction, except that now you're almost sideways. Sounds like fun, right?
Black ice is even worse because, unlike bridges, there's no markers or visual cues that you might be on a different type of surface. Generally, black ice forms when water in its liquid state freezes in place on the roadway. It's called black ice because it's nearly invisible, is indiscernable from a damp roadway if you do see it, and provides almost zero friction for your tires. It sucks, and unfortunately, the only way that most people figure out what's going on is by watching that pickup truck in front of them start spinning like a top, at which point, it's too late.
The only advice that I can give with black ice is that you have to have a much higher level of awareness the day or two after a snow storm, or on a day when it rained for a little while and then the temperature dropped. In either of those two cases, you're going to have to pay close attention if you're on what looks like a wet road. Even in areas where salt is used, if the temperature is below 20 degrees or so, and the road looks wet, you're probably dealing with black ice.
Speaking of salt, there's a pretty easy way to tell if a road has been salted, that just about everyone probably knows already. If the spray from the cars in front of you leaves white streaks from your wipers, the road is most likely salted. Here in Massachusetts (I can't speak for other states), you also need to pay attention for little orange signs that say "salt alternate in use". This is usually in areas near rivers, wetlands, or heavy agriculture, because too much salt would screw things up. From what I've seen, the only salt alternate that's used in this state is sand.
Okay, so you're on the road, and it's covered in snow. The first thing you need to remember is to slow down. You want to be moving slowly enough that if all hell breaks loose and you go into a skid or something, you've got enough room so that when you finally do run into something it's not going to hurt too much. This, I'm sure, seems fairly obvious to all but the local Darwin Awards candidates.
When I went into that whole discussion earlier about friction and velocity and acceleration, I was laying the ground work for the following sentence: Driving in snow means that your driving in a situation with a reduced amount of available friction. Seems pretty straightforward, right? Practically speaking, this means that everything you do in terms of controlling your vehicle's motion should be done gently. Take wider, slower turns than you normally would. Accelerate slowly, and start the process of slowing down well before you need to be stopped. This is all very basic stuff, but every single person that sits there fishtailing and spinning their tires while pulling into Dunkin Donuts for that all important cup of coffee is in violation of this principle. A rule of thumb is that if your tires are spinning, you screwed up.
Sometimes though, you just can't get enough friction going to get where you need to be, and tire spin is the net result. In those cases, let off the gas slowly until you start to get some kind of friction, then slowly bring it up again. Rinse and repeat. On my way out last night, I watched a guy fishtail his way up the street until he finally gave up and turned into a parking lot. He made it about two hundred yards when a calm driver gently nudging the car forward would've made it to Texas, if he or she so desired.
Gear selection is also important to help keep your tires from spinning too much. When you're accelerating forward, you want to be in the highest gear that is practical to do so. For most people with a manual transmission, that means starting in second, and working up to your top gear by the time you reach forty or so. For just about everyone with an automatic, that means leaving it in drive or overdrive. You'll never have as good a control as you would with a manual transmission, but that's the best you can do (and it's probably what you would've done anyway).
When you're slowing down, down shift instead of using the brakes. This applies to people with automatics as well. You know that shifter that has P, R, and D on it? It also has 2 and 1. Use them. That's what they're there for.
Obviously, just shifting down into first gear doesn't bring you to a stop, so some braking will have to occur. If you've got Anti-lock brakes, all you need to do is apply gently increasing pressure to the pedal. For those of us without ABS, gently pump the brakes until you've come to a stop. The goal is to use the brakes to apply friction to the wheels, but the wheels shouldn't come to a complete stop until the car does. Ironically, this can sometimes be easier to manage if your brake fluid is low, but that's not exactly recommended.
We've covered the basics of driving in snow, but so far we haven't taken into account the thousands of other people that are out there driving poorly. The short answer is to stay the hell away from them. All of them.
One of the things you've got to keep in mind is that no matter how fast or slowly you're moving, snow has a nasty tendency to make your vehicle move around side to side a bit more than it should. This also applies to all of the other vehicles. Now, I know you're not going to pay attention to this, but you shouldn't pass on the highway unless you've got about a lane between you and the person you're passing. On backroads, don't pass at all, and give oncoming traffic as much room as you can, stopping if necessary.
I talked before about accelerating, turning and stopping gently. That requires that you plan ahead, and when you're dealing with other cars on the road, you have to plan even further ahead. You don't want to be at the point where you should start moving over a lane so you can make your exit, only to find a car in that lane. You don't want to start slowing down for an intersection and find out too late that there are already eight cars waiting there, which effectively reduces your available stopping distance by about 150 feet. Basically it boils down to driving defensively, which, incidentally, is not how I normally drive on dry pavement, but driving offensively in the snow is just asking for a police report of one kind or another.
One of the things that people do that drives me nuts is turning on their high beams when a snow storm reduces visibility. Snow in the air has an almost identical effect on visibility as fog. Fog, as you learned when you were studying for your license test, is a situation where you never want to turn your high beams on, because that much more light is reflected back at you, making it more difficult to see. That's why there are such things as fog lights. Incidentally, fog lights are usually only effective if they're mounted under the bumper. Doing this increases the angle between the path of the light and the driver's eyes, thus reducing the amount of reflected light hitting the driver in the face. Lights that are mounted on the bumper or on the roof are driving lights, and when driving under normal conditions, the only effect they have is to destroy the night vision of oncoming traffic, and royally piss off the person that they're tailgating. This is also why I refuse to buy halogen headlights, but that's another rant for another time.
Driving in reverse is one of those skills that very few people have. Under normal conditions, most people can, through trial and error, make their car go where they needed it to, but it's frequently painful to watch. In snow, it can go from cynically comical to downright dangerous. Something that people fail to realize is that a front wheel drive car, when it's in reverse, is the antithesis of when it's moving forward. Your nice little Honda suddenly becomes a rear wheel drive, rear wheel steered, ergonomically challenged vehicle. I don't really have any great advice to give here, other than just pointing out that most vehicles don't just behave differently when reversing in snow, but, to their drivers, behave irrationally. Plan accordingly.
One last little bit from the "Making Your Life Easier" department, when you park your car and it's snowing, lift your wiper blades off of the windshield. This will keep them from becoming popsicles, and it'll make cleaning your windshield that much easier.
You read this whole thing and tried your best, but you still managed to screw up. Well, I've got you covered.
When a skid starts, you need to steer the wheels into the skid. This advice has been passed down from driver to driver for generations, but what the heck does it mean, really? The idea is that you want to try to keep your front tires rolling in the same direction that you're moving. Eventually, the rear tires will catch some friction and be deflected back behind you. This works best if you let off the gas so that your various wheels will straighten themselves out of their own accord. Otherwise, you run the risk of preventing your rear wheels from getting any grip because they're spinning at a speed that has no correlation to the ground beneath them. If you're driving a front wheel drive vehicle, it may be useful to add a touch of gas, but if you're in any danger of spinning your front wheels, it's probably not a good idea, since the only chance you have of pulling out of the skid requires those wheels to remain useful.
If you get to a point where the rear of the car is traveling ahead of the front, there are theoretically some things you can do, but human reaction time isn't usually fast enough and they're very case specific, so just accept the fact that you have lost control of your vehicle, and brace for impact. If you got into this mess in the first place because you were trying not to hit another vehicle, hopefully it slowed you down enough that no serious injuries will occur.
We'll assume for the sake of argument that you missed that school bus full of nuns, and ended up in a snow drift on the side of the road, and now you're stuck. Getting unstuck is much like the process of digging yourself out, except that you may no longer have the option of giving up, going back in your house and pouting. Once you've exhausted the techniques covered in the previous discussion, there are a few more you can try.
Since you've already done a bunch of digging, the problem that you're most likely having is that you've managed to put your car on what most closely resembles a skating rink of some sort. The easiest way to fix the problem is to grab the set of tire chains that are sitting in your trunk, attach them to the drive wheels (or, in the case of four wheel drive, the wheels with the most weight on them, taking into account inclines, if necessary), and pull yourself right out.
Oh, you don't have tire chains? In that case, pretty much anything other than ice will help. The idea is to try to add friction to where the tires touch the ground. Sand, rock salt, cardboard, wood, kitty litter, small rocks, and lots of other stuff can prove useful. Even snow, believe it or not, can be useful, but it's not worth trying unless all other avenues have been exhausted, because a more likely result will be the production of more ice. If you have some way to break up the ice or even chip it up a bit, that can work wonders. Crushed ice provides more friction than smooth, solid ice, and that little bit can make the difference.
The key to success for any of those methods is very gentle acceleration. If you've got an automatic, you can even try putting it in gear without hitting the gas. If you've got a few people hanging around, by all means have them push and rock your vehicle, but be careful not to hit them with stuff spinning out from under your tires. I've seen people almost lose a limb because of two by fours being shot backward at them while they were pushing.
If none of that works, and there are other cars, or even better, friendly plow truck drivers nearby, don't be afraid to ask for help. Chances are pretty good that if somebody is in a position to help you, they will at least feel guilty when they drive by. At some point, somebody will feel guilty enough that they'll stop. Tow straps come in very handy in this situation.
A tow strap is a twenty foot or so length of nylon webbing that's about three inches wide. Picture a bright yellow, twenty foot long, double thickness seatbelt. On each end, the strap is looped back on itself and securely stitched. This simple device, which will cost you a whopping fifteen bucks or so, is the single safest way for one vehicle to pull another out of a snow drift, assuming there are no professional winch operators present. Because the strap has no metal parts, or anything hard or dense in general, if it breaks, nobody gets hurt. The same cannot be said of tow chains or the very similar looking twenty foot long bright yellow webbing with big fat metal hooks on each end. Either of these can quite easily kill somebody, and, to make things even more interesting, they typically aren't rated to pull as much weight as a real tow strap (about 20000 lbs.)
On the other hand, you are stuck on the side of a road, so you can't exactly be that picky about it (unless you provide your own), so keep in mind that just about anything will help. A piece of ordinary rope might be all it takes to get you on the road again. It's important to remember that you're only looking for that last little bit of help. You don't need to be towed home or anything.
When you're hooking two cars together like this, you absolutely, positively must attach the strap/rope/chain to the frame of each vehicle, unless one or the other has a actual towing apparatus (like a trailer hitch or tow hooks), in which case, use that apparatus for that vehicle. It's important to note that the little metal rings that stick down from the bottoms of some cars are not an appropriate towing apparatus. Those are where that car can be attached to a car carrier. It typically takes four to eight of them to secure a car, and they only really have to keep the car from bouncing around too much. They are not typically strong enough to give or receive a good yank from another vehicle.
When all else fails, call a tow truck. It'll probably take a while, and, unless you're a member of an auto club or something, it'll cost you money.