Black Ice | WEDGE ISSUE WARNING
 

I would like to ask ... please share where you live (or lived) to have knowledge about different ice conditions.

Not all ice is created the same.

Black ice is unique in temps below 0F (-18C): Black ice happens when motor vehicles are stopped and idling, the exhaust warm snow & ice on the road surface. When the vehicles moves on, the melt freezes quickly. Road salt is not effective at these temps and black ice is common at stop lights and on road after rush hour congestion. It is near impossible to see black ice (and the reason for the name).

Refreeze ice is commonly called black ice, but it's different. Refreeze happens on milder, sunny days; and when day temps are above freezing and nights are blow freezing. Refreeze ice isn't typically an issue on road surfaces because road salt and traffic won't let ice form. But refreeze is an issue on the shoulder of roads, bike trails, and bridge decks.

Why does it matter ... ice is ice, right? From the saddle of a bike it matters because you want to know when and where to look for ice that will be hard to see. For example, this morning it's -20F (-29C) and I'm riding to work, when riding in the traffic lane coming up to a stop light there's a good chance of ice being on the road surface. Approach the red lights with extra stopping distance and be aware of people in cars not doing the same. OTOH I'm riding to work when it's 25F (-4C), the day before was sunny and temps above freezing, I need to look for ice on shoulders and on bike only trails as well as shady areas.

Refreeze example, I was not riding winter tires, and I turned in the shady part of the road and took a fall (and a reminder to use the winter bike)



Next weeks wedge issue: different terms for snow conditions :D

how about ice under fresh powder. compacted the tread, lifted me off the studs. but as I put a foot down, I went down. silly man
https://cimg2.ibsrv.net/gimg/bikefor...bdcee8d30b.jpg

Great question ... I don't have a term for this, other than "that sucks!"

Also, been there, done that ... and I've got it on YouTube (of course I do! :lol:)


This also brings up one of the trickiest parts for studded tires: high pressure to bite into the ice vs lower pressure for a bigger contact patch on the snow. I've been on the wrong side of this equation so, so many times!

Living in the temperate zone, I'd never heard of the special <0F definition of black ice. Black ice, as I understand it, is simply ice that's difficult to see.

I'd argue that the "refreeze" ice is pretty specific. It's been a few years, but I vaguely remember from chemistry class that salt won't melt ice below a certain temperature, which was either 7 or 9 degrees (F) below freezing. So perhaps you won't see "refreeze" ice on the road on a 25F morning, but be careful if it's down to 20F, because it's possible then. (And be careful in situations like Virginia on I-95, when it was impossible to pre-treat the road surface because it was raining while it froze!)

I've got family in Williamsburg, VA, and drive I-95 getting to/from DCA to their place ... I-95 is a nightmare on a sunny summer day, I truly feel for the people that got stuck in that mess. We have the same thing happen here every year or two, rain prior to a cold front with snow. There's not much to do but sit at home for a day or two, roads are just dangerous until the salt can cut through the mess.

Funny thing here right now, we've been so cold for so long that residential streets are just snow-packed ... you can't see the pavement. Main roads and highways are clear and dry, but the less traveled roads are gonna be snow packed for a while.

I appreciate the distinction. I have called the refreeze variety "black ice", but I also call it "glare ice". We had a big problem with it on a Saturday morning back in early December, before there was much salt on the roads.

Am thinking about my tire selection for a road ride tomorrow. Studs or 43 mm gravel tires at low psi? I don't think there's much hard ice around, but lots of very hard packed snow tending toward ice. Hmmm.

I grew up ice skating, both on artificial ice in rinks and pond ice. Black ice is ice that has a very pure and strong crystal structure. Happens as undisturbed water is cooled. But as that ice goes through temperature changes, that very strong crystal structure is lost and the ice turns grey. Rink ice is grey ice. (Perhaps really cold places can make black rink ice but I never saw it in Massachusetts. 5F grey rink ice is very hard but it is not as hard as pond ice.)

Black is is so strong that very thin ice can support a person easily, even though it is so thin that it bends down a half inch or more under their weight. I've skated ice that was well under a 1/2" thick. The danger is that it is so clear it is invisible. 1/4" or 1/8" looks no different. Now, once that ice has seen a day of warmer air, it turns to grey and better be over an inch thick to skate. (And it will continue to degrade with more warm days. But if the nights mean adding thickness, the overall strength may well build. Danger comes at the end of winter as the thickness building stops and the very thick ice "rots".

So, back to ice and how it behaves under skates and bicycle tires. What makes ice so much more slippery than say glass is that under sufficient pressure it melts. Skates place a lot of weight on a thin blade. That amount of pressure melts the ice. (There is a minimum temperature at which skates work. I've skated at 5F. That works. But I am guessing -20F would be disappointing.) Also, ice hardness varies a lot. Black ice is hard. Cold black is very hard. Skates need to be a lot sharper for good skating, turns and stops on new pond ice than rink ice. Skates sharpened for cold black ice are trippers on rinks! We walked the wooden ramps aggressively to dull our skates if they were too sharp to play hockey. Good skate sharpeners know how sharp to to go. Some of us put in special requests.

And bicycle tires. Ice is all over the place. Frozen puddles may well be classic black ice. If cold enough not all that slippery because it isn't melting and relatively hard but snow on it may well be like deep dust on glass. Warmer and you may have water, either from the prevailing temps or your tire's pressure on it. Slippery! There is no rule for how hard grey ice will be. The strongest is maybe 1/3 to 1/2 that of black ice but it degrades much like wood rots, just far faster. (Think slush and that tree that came down 25 years ago.)

So - experience with your local weather and roads counts for a lot. Riding the same old roads all winter sounds boring but knowing where to expect that ice can prevent a lot of falls. Access to thermometers and reliable weather forecasts that tell you what you need to know can be invaluable.

We were snookered this year with freezing rain then an immediate light snowfall and cold weather. Kept me from riding knowing there is a perfect sheen of ice beneath the snow. If we had gotten snow first you have confidence that even though it may have ice underneath the ice will be "rough" and provide some traction.

Ponded water that freezes is super hard studs will scratch it but not get much grip. I encounter that mostly when riding on a creek and going under a bridge that keeps the ice clear of snow. Also a big problem in the spring during the nightly re-freezes.

Freezing rain is similar in its hardness to pond ice. Maybe its not so much the hardness as the uniformity. Other types of ice have a jagged texture where grip can be found.

With either of those types of ice you have to be super careful with any kind of side sloping on the road / path. Gravity pulls you to the low side, trying to steer against the pull will make the front tire slip out. Sometimes I'll just let it carry me off into the grass. Many times that isn't an option because the low side has curb, railing or pile of snow so I just come to a stop before trying to get out of the hole.


I like breaking frozen puddles, but you need be be careful doing that. If the ice is really thin it just shatters. But at a certain thickness you just carve a channel the same width as your wheel. Its like riding in a really narrow rut and the wheel will fight any attempt to steer which can throw off your balance. Not much of a problem on a short puddle, but beyond about a bicycle length you could get into trouble.

One of my fav kinds of ice is refrozen slush, grippy and makes a nice popping noise.

those are great cycling conditions, cold compacted snow. jealous!

Agreed, so nice!

https://cimg9.ibsrv.net/gimg/bikefor...9519a8494d.jpg

oh man, I can ride that all day long :thumb:

I think I might live in the worst spot in North America for ice. It gets pretty cold, but every couple of weeks we get a chinook wind that brings the daytime temperatures up as much as 20 degrees.
Once we have had a few freeze - melt - freeze cycles, the ice can be anywhere.

We are just coming out of a couple of weeks of -25C weather and the roads have been nicely packed and polished. By next week, they are predicting +5C during the day, that will be ugly.

I'm always a fan of studded tires ... but that's cause my bike-handling skills aren't great! But you're right, it's all hard-pack snow out there. And tomorrow gonna be a heatwave with temps around 30F, might be a summer kit kinda day :thumb:

There is a think about lake/pond ice, the colder it gets the harder it gets.

It was around 0F during this race, studs had a hard time biting into the ice. And to the post I made early, picking the pressure for this race was a no-win ... high pressure was good on the bare ice, but left in struggling (and wrecking) in the drifting snow.

really interesting phenomenon. for me the snow compacting into the tread is trouble
https://cimg5.ibsrv.net/gimg/bikefor...3f6ad36253.jpg

My experience is different. Maybe the number of studs is a factor?

https://cimg6.ibsrv.net/gimg/bikefor...889cf81eb0.jpg
Making a turn on hard ice. No slipping here. Tires are Nokian "Extreme 294".

IME when temps go sub-zero, the ice is harder for the studs to get a grip on. As temps get closer to freezing, it's easier for studs to grip the ice. Additionally, I've personally found that if your studs are new, they get a much better grip ... and worn down studs are gonna have a hard time biting into the ice.

You may be right. I've always thought that the resistance to sliding (sideways) is limited by the shear strength of the ice, which I believe is greater at lower temperatures. There's no doubt that the grip afforded by studs, regardless of number ("density") or wear status, is considerably less than rubber on dry pavement. You can't just lay the bike into a high-speed curve. But straight-line travel and careful turns are much more predictable with studs.
That lake in the picture is nicely frozen over with no snow cover! I'm mounting those Nokians and planning a ride tomorrow. I'll see if I can calibrate myself on the hard ice so I can compare with softer stuff when the weather warms up.

https://cimg9.ibsrv.net/gimg/bikefor...68a625f81c.png


https://cimg0.ibsrv.net/gimg/bikefor...ba9791fb6c.png

The different symbols are for different types of ice - one from a bobsled run, the other from a hockey rink. But I don't know which is which. Either way, chalk up the difference to different textural properties of the ice - different sized ice crystals, different alignment of the crystals, etc. - or possibly different impurities.

Thanks for the graphic. It doesn't say which hardness measuring system is represented (Mohs, Vickers, Brinell, etc.), but it's apparent that hardness is inversely proportional to surface temperature.
It would be interesting to see the relationship between the hardness of ice and its shear strength. The studs, whether made of steel or tungsten carbide, must be harder than the ice, so there shouldn't be issues with penetration. If the studs are worn and rounded, as Hypno Toad suggests, the studs would more easily slip up and out of whatever purchase they had. Studs with a good engagement with the ice could still slip by physically shearing the ice.
So, not being a mechanical engineer or having any particular expertise in the physical properties of ice, I set out to see how my studded tires perform. We've had sustained temperatures in the upper teens and lower twenties for a week or so, and the ice seems hard and adequately thick. Skaters and ice fishers were in evidence. Images below.
What I *can* say is that the tires (Nokian "Extreme 294") have plenty of traction. It is possible to spin the rear wheel in a lower gear, and modest brake pressure on either wheel would cause a skid. So extremes of acceleration and braking are to be avoided, but there is plenty of usable traction in between.
BTW, the Nokian studs are tungsten carbide, and each stud has a sharp point on it. This is different than the studs on my Schwalbe tires, which are also carbide, but are cylindrical with flat ends. Carbide wears very slowly, even on pavement. Some less-expensive tires have steel studs which wear much faster.

https://cimg6.ibsrv.net/gimg/bikefor...ffd9eb4252.jpg
Hard, clear ice!

https://cimg7.ibsrv.net/gimg/bikefor...57bfcefba4.jpg
It's nice not to fall!

Though the publication doesn't specify, I would assume that they are reporting Brinell hardness because the units are in MPa. Surely you recognize that that such units couldn't be Mohs hardness, for example.

Generally hardness and strength follow similar activation laws, so i assume that their temperature dependences are similar.

I don't know for certain, but I doubt that a bicycle tire stud slipping out of an indentation in ice does saw by plastic flow of the ice, as would be implied by shear strength. The time scales seem wrong. Brittle fracture seems more likely, and therefore tensile strength.

I also am not a mechanical engineer, but that's my $0.02.

just don't try to put a foot down & get off the bike! ;-)

Yes, I knew it wasn't Mohs... I was in a "listing" mood.
I'm out of my depth here. It wouldn't surprise me to learn that there's a complicated explanation which, fortunately, doesn't have to be understood to appreciate studded tires. :D