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Re: black ice

Posted: 21 Jan 2019, 2:22pm
by Airsporter1st
Every car I’ve driven which had an outside temperature warning device, alarmed at 4 degC. I assume there is good reason for choosing that figure. The problem for a cyclist is that in the manjority of cases, they don’t monitor outside temperature continuously, although that is possible with a smartphone, at least.

Re: black ice

Posted: 21 Jan 2019, 4:43pm
by fastpedaller
Airsporter1st wrote:Every car I’ve driven which had an outside temperature warning device, alarmed at 4 degC. I assume there is good reason for choosing that figure. The problem for a cyclist is that in the manjority of cases, they don’t monitor outside temperature continuously, although that is possible with a smartphone, at least.


All (to me anyway) newer cars. Even if we had that facility, what to do... get off?

Re: black ice

Posted: 21 Jan 2019, 5:12pm
by Grandad
Unfortunately unless you change out the standard tyres a trike just stops you falling over sideways and not sliding onto the wrong side of the road on a bend or sliding straight through a junction.


Another problem is with ungritted roads that have had enough traffic to clear the two tracks taken by the motor vehicles. With a bit of luck 2 of the trike wheels will fit in one of these but the third one has to go on the central snow and guarantees a very bumpy ride.

One year the Birmingham-Llangollen - Birmingham 150 mile reliability trial was when an unusually heavy snowfall had thawed as far as Chirk, but the A5 after that was just 2 clear tracks in each direction. Not ideal for my trike. :( (In 1966 the A5 didn't have much traffic on a late winter Sunday)

Re: black ice

Posted: 21 Jan 2019, 5:25pm
by robing
It's the ground temperature that is relevant to black ice formation, which can be lower than the air temperature - hence that figure.

Re: black ice

Posted: 21 Jan 2019, 5:54pm
by Phileas
I believe the forecast air temperature is usually for 2m above the ground, hence the air next to the ground could be lower unless the wind keeps the air mixed.

Often, gritted roads are damp when ungritted roads are dry which confuses the issue somewhat.

Re: black ice

Posted: 21 Jan 2019, 6:33pm
by Airsporter1st
fastpedaller wrote:
Airsporter1st wrote:Every car I’ve driven which had an outside temperature warning device, alarmed at 4 degC. I assume there is good reason for choosing that figure. The problem for a cyclist is that in the manjority of cases, they don’t monitor outside temperature continuously, although that is possible with a smartphone, at least.


All (to me anyway) newer cars. Even if we had that facility, what to do... get off?


I think you misunderstand me - I was simply trying to answer the O.P. with a a definitive figure and then pointing out why that figure may not be valid for cyclists.

Re: black ice

Posted: 21 Jan 2019, 6:42pm
by fastpedaller
Airsporter1st wrote:
fastpedaller wrote:
Airsporter1st wrote:Every car I’ve driven which had an outside temperature warning device, alarmed at 4 degC. I assume there is good reason for choosing that figure. The problem for a cyclist is that in the manjority of cases, they don’t monitor outside temperature continuously, although that is possible with a smartphone, at least.


All (to me anyway) newer cars. Even if we had that facility, what to do... get off?


I think you misunderstand me - I was simply trying to answer the O.P. with a a definitive figure and then pointing out why that figure may not be valid for cyclists.


My apologies if I sounded confrontational - certainly was intended to be.
I recall about 12 years ago (crikey time flies) leaving home to go to Blakeney (N Norfolk coast resort) and stop in the tea room. In the depths of the tea room, away from any windows, I had a lovely bowl of soup etc, and having paid I headed towards to door and encountered snow! On 25mm tyres and over an hour's ride I set off not knowing what I'd encounter! Luckily after heading a couple of miles inland there was no more snow on my route home.

Re: black ice

Posted: 22 Jan 2019, 9:52am
by pwa
New snow is generally okay to cycle on. Cautiously.

Re: black ice

Posted: 22 Jan 2019, 10:13am
by CliveyT
Rain overnight and then clearing up meant I went out this morning to check before setting off. Ice just crusting the tops of the puddles so I decided to go on the spiked tyres.
Back inside to swap all my work stuff into the bag for the other bike.
This bike of course was hanging furthest from the door so had to get three bikes out of the garage so I could get to it.
It only had spiked tyre on the rear so I had to swap the front wheel around
The 'spare' wheel was hanging up on the far side of the van so had to push the van out of the way to get to it (and then go to the front door of the garage to push it back in again).
This wheel hadn't been touched since I built it in July so needed pumping up.

By now the sun has come up above the hedgeline and all the ice had melte, and I didn't come across any all trip.
But at least I was safe :lol:

Re: black ice

Posted: 23 Jan 2019, 7:54am
by bogmyrtle
Ice can be more problematic under thawing conditions. A road can appear ok on the whole but parts that are sheltered or where the ice was thicker can be slower to thaw. Hit one of those patches when you are bowling along its virtually impossible to stay upright.

Re: black ice

Posted: 23 Jan 2019, 8:43am
by foxyrider
bogmyrtle wrote:Ice can be more problematic under thawing conditions. A road can appear ok on the whole but parts that are sheltered or where the ice was thicker can be slower to thaw. Hit one of those patches when you are bowling along its virtually impossible to stay upright.


Pretty much what happened to me in December!

Re: black ice

Posted: 23 Jan 2019, 8:45am
by Scunnered
MGrant74 wrote:I really don't like cycling when there is a possibility of black ice. Is there a temperature below which I shouldn't go out?

If the sky is clear of clouds then before the sun is up, black ice can form when the air temperature is +3 to +4C. The clear sky allows radiation from the ground to escape so the ground/road surface temperature can be 0C.
Another condition to be aware of is when the night starts off freezing but warmer air moves in in the early hours. The air temperature may be +3C or more but the ground remains at 0 or +1C. Black ice with a thin layer of water on top is impossible to see and slipiest of all.

Re: black ice

Posted: 23 Jan 2019, 9:13am
by fastpedaller
fastpedaller wrote:
Airsporter1st wrote:
fastpedaller wrote:
All (to me anyway) newer cars. Even if we had that facility, what to do... get off?


I think you misunderstand me - I was simply trying to answer the O.P. with a a definitive figure and then pointing out why that figure may not be valid for cyclists.


My apologies if I sounded confrontational - certainly was intended to be.
I recall about 12 years ago (crikey time flies) leaving home to go to Blakeney (N Norfolk coast resort) and stop in the tea room. In the depths of the tea room, away from any windows, I had a lovely bowl of soup etc, and having paid I headed towards to door and encountered snow! On 25mm tyres and over an hour's ride I set off not knowing what I'd encounter! Luckily after heading a couple of miles inland there was no more snow on my route home.


I do apologise. Everyone must think I'm a real grouch! I of course meant to type "certainly WASN'T intended to be" :oops: :oops:

Re: black ice

Posted: 23 Jan 2019, 1:15pm
by Airsporter1st
fastpedaller wrote:
fastpedaller wrote:
Airsporter1st wrote:
I think you misunderstand me - I was simply trying to answer the O.P. with a a definitive figure and then pointing out why that figure may not be valid for cyclists.


My apologies if I sounded confrontational - certainly was intended to be.
I recall about 12 years ago (crikey time flies) leaving home to go to Blakeney (N Norfolk coast resort) and stop in the tea room. In the depths of the tea room, away from any windows, I had a lovely bowl of soup etc, and having paid I headed towards to door and encountered snow! On 25mm tyres and over an hour's ride I set off not knowing what I'd encounter! Luckily after heading a couple of miles inland there was no more snow on my route home.


I do apologise. Everyone must think I'm a real grouch! I of course meant to type "certainly WASN'T intended to be" :oops: :oops:


No apologies needed in any case and I, for one, fully understood that it was a typo first time around. :D

Re: black ice

Posted: 23 Jan 2019, 4:10pm
by flatout
In answer to the OP – No. And it is not the temperature at your departure time that is the criteria.

The best guide still remains the application of your own ‘common sense’ based on knowledge of your own cycling manor, habits and routes (gritted, hills and dips, water run-off, tree overhangs, urban or countryside, burst water mains, tyre selection, weight of bike and rider, overnight lows, recent rainfall, time of day, sunshine or overcast, vehicular traffic density, etc. etc.).

If in doubt leave it out.