Hypno Toad

Right, I'm not making excuses for anybody, I'm defining the difference from ice and black ice. Black ice is not easily seen, you need to know the conditions that cause it and be cautious, like you said.

Hypno Toad

You are talking about re-freeze. I'm talking about the ice that forms from the auto exhaust in sub-zero (F) temps. See my YouTube clip back on page 3, that was refreeze, not black ice. All forms of ice have the same effect on road surfaces (refreeze or black ice or ice ice), it make is slippery.

You can ride icy conditions with good tires (studded). I have years of experience riding through the winter in Minneapolis, I see tons of ice, snow, cold, etc. I'm happy to help and share my experience, but sorry, I need to be done with this endless conversation about which kinda ice is which ice. It's pointless and tiresome.

Sixty Fiver

Research seems to suggest that at the molecular level, the topmost layer of ice crystals is more active / reactive at warmer temperatures and that the forces of friction from boots and tyres can liquify the ice which is what makes ice more slippery at temperatures around freezing, but less slippery at more extreme low temperatures.

When you are dealing with a vehicle's weight and momentum any ice is a bad thing, a bicycle with studded tyres has a fairly high contact pressure, lower mass, and a fairly low rpm engine and can get much better traction than a vehicle in really icy conditions.

Daniel4

If it's ice you can't see, it's black ice regardless of how it's formed.

"Black" a generic term used to describe either the unknown or non-visible: Black Hole (light can't escape), dark matter, dark energy (unknown matter or energy causing un-explained behaviour of the universe), black box (a device where data goes in and information comes out).

TransitBiker

Black ice here forms from melting snow in sunlight then the sun sets. It doesn't really get cold enough for vapor to freeze here, though it can happen on bridges (hence the signs).

- Andy

cyccommute 

Yes, lots of bridges ice without being over water but it's not "car exhaust"

Yes, some water from car exhaust will condense out but it's a minor component. Let's say you have a city that is 30 km square (19 miles). Now, go up 60 m (200 ft), that a volume of 5.4 x10^10 cubic meters. Let's assume that the air is at-18°C (0°F). It can carry 1.2 g per cubic meter or the total amount of water available is 64,800,000 kg assuming complete saturation of the air.

Now let's stuff 44,000 cars into that volume. Let's make each one burn 1 gallon of gasoline. That 167,000 kg of water that those 44,000 cars put out. The cars contribute 0.25% of the total water in the air. It's, almost literally, a drop in the bucket.

Now let's look at the ice that could form over that 30 km area. Let's assume 3 mm so that the ice is actually completely covering the craggy surface of the pavement. I'm also going to assume that the entire area is covered with 3mm of ice including all horizontal surfaces of the buildings. The total volume of a 900,000,000 square m x 3mm object is 270,000,000 mL. Water weighs in at just around 1g per mL which means that you have 270,000 kg of ice covering the area. You are about 100,000 kg short of the amount of water you need if every single car combusts one gallon of gas. And you'd have to wring every drop out of the exhaust.

There's an ocean of moisture laden air above the cars and even the 270,000 kg of ice is but a drop in that ocean. What I contest is the statement that car exhaust is the major contributor. It's a minor contributor at best.

[QUOTE=tjspiel;17587939]The water comes from the 65 million kg of it floating around in the air. Again, some of it is from car exhaust but the atmosphere contributes more than enough on its own.

Rime ice can be crystalline or it can be thick glaze ice.

I did. All I get is something that has all the hallmarks of an urban legend.

Exactly what I've been saying. Like I said above, black ice is a convenient excuse. "I was just driving along and skidded on a patch of invisible ice." It JRA for motorists.

Hypno Toad

In Minnesota we define ice differently (already talked about this on page 4, page 5 and again on page 6). I would suggest that Minnesota has different terms because we can have both re-freeze and exhaust ice (we call black ice). These form in different conditions and in different locations; therefore, it is helpful to use different terms. This helps a rider (or driver) be attentive to the conditions and locations they need to be aware of icy conditions that may be hard to see. This is only for Minnesotans, the rest of you may use the term "black ice" however you'd like:

Re-freeze happens with temps are near freezing, snow melts and refreeze in shady areas (i.e. under bridges)

Black ice happens when temps are below 0F, ice forms from auto exhaust of idling cars (i.e. stop lights)

This is helpful the next time you are talking with a Minnesotan, doncha know, like we have hotdishes, drink pop, and kids play "duck, duck, grey duck".

Hypno Toad

Wait... WHAT!?!? Troll much??

Black ice - Wikipedia, the free encyclopedia

scroca

You guys think black ice is bad? Sheesh, that's nothing. Try hitting Vanilla Ice on your bike. Not even foot retention will help you!

tjspiel

Wait, wait, hold on. I'm not saying that ice formed from car exhaust completely covers the city. Black ice from car exhaust is very localized, - typically at intersections or areas where you have many cars stopped for periods of time or moving slowly. It doesn't take that much water.
And because it's localized and not covering everything, it is more dangerous because it's unexpected.

I should have left the whole topic of bridges alone because while they do ice up quicker, I agree that it's not usually from car exhaust but typically melted snow/ice, fog, or whatever. You can get black ice from exhaust on them as well if traffic is backed up and sitting there (and it's really cold) but usually when we get warnings about slippery bridges it's when temps drop below freezing after warmer days.

cyccommute 

Not clever at all because it's not true. Smaller engines, hybrids and electrics are made for economy not because icing of roads is a problem. Icing of roads is still a problem.

Semi-truck exhaust pipes have been pointing up since shortly after they were invented. It's not because they cause icing during winter time. And a truck passing under a wide 4 lane overpass is going to put out, roughly, 0.1g of water. There are 50 of those in a teaspoon. Not a major contributor to a bridge icing.

Discovery Channel. So much promise, so little delivery.

Not unlike living above 5000 feet. I would hazard a guess, however, that your nighttime lows are lower than your daytime highs...probably by several degrees. Let's say you warm up to freezing. At the freezing point, every cubic meter of air can hold 4.9g of water. Night falls and the temperature starts to drop. Let's say it bottoms out at -20°C. Air at that temperature can only hold 1 g of water per cubic meter. That 3.9g of water has to go somewhere, so it settles on any surface it can. In the woods and fields, it settles on to the trees and the ground but you seldom see it. It's transparent and the underlying surface is likely to be white. It is "white" ice.

We clever little monkeys like to make machines and be busy so we make roads. Then we cover them with a black tar residue that we can't find anything else to do with and the ice precipitates out on those surfaces. We can't see the ice on top because it is still transparent but the underlying surface is black. So we call it "black" ice. The ice isn't "black" anymore than it is "white" when it is not on the road.

I'm not saying that it is a myth. I'm saying that "you can't see it" is a myth. Any ice covered surface has a different look to it than a non-ice covered surface. Yes, ice is transparent but it doesn't have optical transparency. Even something that is optically transparent isn't "invisible". Light is refracted by it.

So it isn't "invisible" and "impossible to see". That's my point. Anyone who says that they "unexpectedly" slipped or skidded their car or bike on black ice wasn't paying attention to the conditions.

It is also where cars sit and wait for the light. Cars are heavy and the foot print of the tires is small. That's a lot of pressure. Pressure changes the melt point of ice and snow...think of an ice skater. The pressure causes the ice to melt a little which puts a layer of water between the tire and the ice. We do know what makes material slippery when wet and that little layer of water lubricates the tire/snow interface. Putting power to the wheels causes a little slippage which increase friction and melts some more water. When the weight is gone, the water layer refreezes and the patch is a little more slippery. Each car contributes to polishing the ice and reducing the traction.

Again, it's not the car exhaust that causes the ice nor the intersections to be more slippery. There's just not enough water in the car exhaust at an intersection to cause the problem. If each car sat at the intersection and burn and entire gallon of gas, maybe, but that isn't what happens. A car burns around 0.1 gallons per hour idling. A car waiting for 2 minutes for a typical stoplight would burn 0.003 gallons or about 7g of gas. Through the magic of chemistry, I know that 9g of water is going to be produced per car. That's a minuscule amount of water.

alan s 

Slick move, Robert Van Winkle.

Vanilla Ice on Burglary Arrest: "It's a Mess; I'm Dealing With It" - Hollywood Reporter

Hypno Toad

cyccommute 

No and I resent the implication. Nothing I have said is inflammatory nor off-topic nor extraneous. The math and chemistry I've presented is very germane to the discussion and fairly simple stuff...high school chemistry would cover it.

I've read that article and it's not convincing. The salient quote is this

Some guy on the internet isn't a credible source. Doing a google search, I can find all kinds of pages with almost the same sentence as the first sentence. But I can't find a single journal article on the topic.

And the above certainly doesn't fit with the quote from Wikipedia

At that temperature there are lots of other, more reasonable mechanisms for ice formation.

But it takes more water than you have even from many cars. I do agree with the straight dope guy about one thing, water is going to condense in the tailpipe and dribble out. You can see it from just about any tailpipe of any car. But as he said, the water is going to freeze in a blob and it will likely be outside the tire track which won't cause problems.

But if you condense water in the tailpipe, it's not helping the "freezing car exhaust fog" argument. You would need water vapor to freeze on the road surface in a uniform layer. For a typical stoplight duration and the burn rate of gasoline, you only have 9 g of water to work with. Since you aren't Canadian, I'll convert...that's a bit under 2 teaspoons. If you remove half of the water due to condensation...not a bad estimate but only a guess...you have 5 g (1 tsp) of water to work with. Let's say you have a 3 lane road with 5 cars in each lane. That's 15 cars or 75 ml (15 tsp or about 1/3 cup) to work with.

But goes into the volume that those 15 cars are contained in. That volume is, roughly, 504 cubic meters. 75 g of water (density of 1g/ml) spread throughout that volume would give you 0.15g/cubic meter. If the air isn't saturated it will absorb the water from the tailpipe easily. Minneapolis is currently (like right now) at 75% RH. That means that each cubic meter of air contains 75% of the possible 1.0g of water it can carry at your current temperature (just about 0°F) or 0.75g/cubic meter. Adding 0.15g/cubic meter of water won't cause water to precipitate out. Perhaps a very tiny amount will but not enough to cause the roads to ice.

Ice may have formed overnight but the cars would just polish that ice resulting in a slicker intersection.

cyccommute 

Pot. Kettle. Black.

Hypno Toad

Come to the Twin Cities and we will give you a real-life demonstration (-10f this morning) - absent that, this conversation is pointless, you don't believe the people that live in these conditions or the documentation that proves our point. You don't believe anything but yourself... cool, bye.

Hypno Toad

Name just one source of liquid water in the over night hours when ambient temps are below 0f, besides car exhaust, that would cause ice to form at intersections?? Without another source of liquid water, you have nothing to create ice on the road surface.

and damnit hypno toad, quit getting sucked into this idiotic and pointless thread... I'm such a moron.

cyccommute 

I have named a source of liquid water. See post 161. Depending on the starting and ending temperature, the amount of water that air can carry varies widely and in a nonlinear fashion. Air at the freezing point can hold 4 g/cubic meter. Air at 0°F can hold 1g/ cubic meter. The water has to go somewhere.

You can see where I live. We are no strangers to winter weather. I've seen real-life demonstration of winter for many years. You can't show me a "real life" demonstration of car exhaust freezing on a road way at an intersection because it can not happen. Something else is happening but the car exhaust isn't causing it.

The conversation with you is indeed pointless because it is devolving into insults made only by you. If you don't agree with my calculations, do you own. Show me where I am wrong. Otherwise, at this point, you are doing what you accused me of...being a troll.

Sixty Fiver

I am gonna go and ride my bike on the snow and ice today.... I should get the full meal deal of hard snow pack (my preferred winter riding surface), polished ice, and sections where you can't put a foot down despite it appearing to be clear, and where those studded tyres rule. I might even find some puddles where the concentration of road salt has kept things from freezing.

All this happens within a km of our house too.

Real world testing is where it's at, if I make it home without having crashed or being run over then the experiment will have been considered a success.

Hypno Toad

Insults, not really, just talking with somebody that doesn't want believe the facts and testimony of multiple posters. Calculations are fine in the classroom, but real-world life experience is what I'm talking about.

I know Denver has winter, however, the Twin Cities are unique in the US (last winter):



Climate of the Twin Cities - Wikipedia, the free encyclopedia

Therefore, we have more experience with sub-zero temps that most places in the US. With temps staying below 0F for days-on-end, there is very little moisture in the air (the air is drier than a dessert). There is far less moisture in the air than what is coming from the tailpipe of hundreds of cars. It would be very odd that the tiny amount of moisture left in the air would only form ice at places where cars are stopped, idling. Wouldn't that ice would form on sidewalks and trees and other surfaces? But it does not, it only forms on roadways where cars are stopped idling. The source of the moisture that is forming ice on the road surface is the cars exhaust. There are dozens of source that state the exact same thing I'm saying. It's OK to say you don't have a calculation to explain this, we won't judge you, just stop saying we are wrong - that is insulting.

tjspiel

Perhaps a very miserly car under ideal conditions burn that little gas in an hour. A typical car will burn 1/4 to half gallon of gas in an hour. Maybe even 3/4 of a gallon for something large. A school bus could burn as much as gallon. And as your chemistry magic showed burning a gallon of gas produces more than a gallon of water !

Of course an individual car doesn't sit at intersection for an hour but you have many cars idling at busy intersections all throughout the day. Of course they don't just idle either, they accelerate as they move on, burning more gas and producing more water than they would if they were idling.

You were convinced that any water vapor immediately rises up and out of the way. I showed you a picture that shows that is simply not the case. As they say, a picture is worth a thousand words and that same picture shows plenty enough water to cause problems.

alan s 

The exhaust appears roughly equivalent to ground fog, and would most certainly cause black ice under the right conditions (low wind, mainly). Add to this the water condensate that comes out of tailpipes, and you have plenty of water to form black ice.

scroca

Not all ice is invisible.

https://abcnews.go.com/GMA/video/ice-tsunami-video-photos-wall-ice-rises-lake-19166280

PaulRivers

People talk about having different wheelsets, but unless I have a whole second bike I know that personally the time it takes to change them means I'm not going to ride much.

Have you seen the 45nrth Xerces? If you're interested in using a skinny tire, it seems like the kind of tire you just leave on your bike all the time it's remotely winter at all as the studs don't come into contact with the road when going straight if you have the tire at high pressure -
45NRTH



Their Gravdal is like what you men by "slightly knobby tires", just with studs. Unfortunately you do end up with some studs down the middle no matter what:
45NRTH



If you're going for a fatter studded tire, the Kendra Klondike you mentioned does look interesting:
Klondike Standard

In that it's wide and knobby but no studs down the middle:


I wonder if the same thing would apply about using a high pressure keeping the side studs off the ground when going straight.

I personally haven't found much use for knobby tires in winter...when I tried them skinnies either cut through the snow, or there was to much snow for wider knobbies to be terribly useful. But that's personal experience and opinion of course.

I keep being interested in the Xerces, but here in Minnesota there's so much snow and ice they're not useful to me - I use a Schwalbe Marathon supreme than can handle the small ponds of ice we get on the paths sometimes lol. The Xerces seemed like a great tire for a "probably don't need studs but want to have something for the very rare ice I'll run across" kind of riding.

cyccommute 

I have seen no "facts" from any posters. My calculations are based on facts...real ones of known principles. If you have a different set of "facts", present them.

The amount of moisture in your air is probably higher than that here in Colorado. Our air can't carry as much water due to its lower pressure and our relative humidity...the ratio of water in the air to what the air could carry at any given temperature...is lower than many places in the US. We have cold temperatures and our tailpipes put out just as much water as yours do but we don't have this urban legend of the water condensing on the roads. We should be able to condense the water at much higher temperatures due to the lower carrying capacity of our air.

The dryness of your air doesn't help your argument either. As I've said above, if the air isn't saturated, the air can absorb the water vapor that is put out by the cars. Yes, the cars are going to have clouds of vapor around them while sitting still but those clouds will quickly evaporate into the air. The water won't go crashing out on the ground in any appreciable amount...largely because there isn't that much water in the fog.

Therein lies the problem. If the cars are the source of your ice, you'd expect the sidewalks and buildings at any given intersection to have a thicker coating of ice than elsewhere. There is nothing that would keep the water from condensing on every surface around the intersection. It wouldn't condense preferentially on the roadways.

There are hundreds of sources that state the same thing you do. All of them state it the same way that the Wikidpedia article state it. That's not a creditable source. Like I've said before it has all the hallmarks of an urban legend. I can't find a single scientific article with data that backs up the claim.

It's not insulting to say you are wrong if you are wrong. You are wrong. There's just not enough gas burned nor is there enough water produced to do what you guys are saying happens.

Got anything to back up the claim of that high a gasoline consumption? It's not hard to do the calculations yourself.

Yes, the cars aren't going to idle for an hour. They are going to idle for a couple of minutes, as I've pointed out above. A thousand cars passing a point and idling for 2 minutes each are going to produce about 7 liters of water...a bit over a gallon and a half. That's still not much water.

Let's look at that picture. Yes, there's fog around the cars from exhaust. But there is also a lot of snow on the ground in the picture. The cars moving on the snow, compacting it and sliding on it are going to do far more to make the intersection slick than the car exhaust will.

The "right conditions" is what is important. A moving car isn't a situation where there is low wind. The air around each one of those cars in tjspiel's picture is going to become turbulent the minute the cars start to move. That will stir the air, bringing low moisture air into the mix and move high moisture (warmer) air further up. the conditions would not be "right" for the formation of "black" ice.