-2C or -12C...What's the difference?

[crr003]

OK - 10

Water freezes at 0C (something about atmospheric pressure and supercooling on google though.....)

So, at -2 or -12, wetness is solid? So would you change your driving because the temperature was lower?

What would be different? Tyres less flexible/grippy? Tarmac/concrete capabilities different?

I ask as I've seen people driving down perfectly clean/dry (looking) motorways doing 45/50 in the last couple of days when the temperature has been probably the lowest the majority of Brits have seen. Other days at around freezing- minus 2 and they quite happily drive quicker.

[faboka]

I see what you saying and am doing a similar thing regarding driving slower. However my reason is more down to me expecting parts of the road to still have some snow/ice left.

Could the performance of the tyre be effected between -2 to -12?

[Mr Cholmondeley-Warner]

Perhaps they're scared by the sight of your van

Have you two been out for a drive together yet?

[ScoobyChris]

I recall reading somewhere recently (although I forget where!) that grit is only effective down to -5 degrees C. Not sure how true that is, but from what I remember of my school Chemistry it makes sense...

Chris

[GJD]

What would be different? Tyres less flexible/grippy? Tarmac/concrete capabilities different?

Freezing point reduced by the addition of the salt spread on the road? I'm not sure by how much though. Maybe -2 is actually above freezing and -12 is below?

Gavin

[crr003]

Perhaps they're scared by the sight of your van

Not any more...........
And it's not a "van"......
the Disco in snow mode is great

Have you two been out for a drive together yet?

Nope

[Big Err]

I recall reading somewhere recently (although I forget where!) that grit is only effective down to -5 degrees C.

Between -5 and -7 before the salt freezes is the word on the streets here (no pun intended ) and that's if you're roads authority has any salt left.

[mitchr]

OK - 10

Water freezes at 0C (something about atmospheric pressure and supercooling on google though.....)

So, at -2 or -12, wetness is solid? So would you change your driving because the temperature was lower?

What would be different? Tyres less flexible/grippy? Tarmac/concrete capabilities different?

I ask as I've seen people driving down perfectly clean/dry (looking) motorways doing 45/50 in the last couple of days when the temperature has been probably the lowest the majority of Brits have seen. Other days at around freezing- minus 2 and they quite happily drive quicker.

I've changed my driving as there are still bits off snow and slush on the roads. Also I'm still a newbie to driving in general let alone these conditions. However I have wondered what the average speed should be. I know it will depend on the condition of a particular road and the driver but interested in opinions. I've been changing my speed to take into consideration that the road is likely to be iced over but it seems that others haven't. I had two vans overtake me yesterday on a NSL road one of whom tooted at me as he passed. I was going at 30 as there were still patches of slush on the road. Maybe I'm being overcautious but due to my lack of driving experience I felt that 30 was adequate.

Mitch

[Horse]

So would you change your driving because the temperature was lower?

I ask as I've seen people driving down perfectly clean/dry (looking) motorways doing 45/50 in the last couple of days when the temperature has been probably the lowest the majority of Brits have seen. Other days at around freezing- minus 2 and they quite happily drive quicker.

I'd adjust speed dependant on the surface damp/dry] more than ambient temperature - although that would involve being able to see, and significantly and effectively - change speed if the surface deteriorates. I've happily [motor] biked in -6C IIRC - but on dry roads.

But I also keep a wary eye on the car's ext. temp. gauge - it's often a useful warning of weather changes let alone frost.

[x-Sonia-x]

I've been changing my speed to take into consideration that the road is likely to be iced over but it seems that others haven't. I had two vans overtake me yesterday on a NSL road one of whom tooted at me as he passed. I was going at 30 as there were still patches of slush on the road. Maybe I'm being overcautious but due to my lack of driving experience I felt that 30 was adequate.

Hi Mitch

Thats exactly how i feel. The first time I drove alone in snow was few weeks ago and it was really icy then. I drove home early hours of morning and was doing 25ish on NSL road...bearing in mind it was snowing hard and roads were icy...I felt quite safe at this speed, however I did have someone right up my backside who obviously wanted to drive faster. I personally dont think there are any hard and fast rules...only what feels comfortable and sensible for you. Someone did mention to me the other day that stopping distances in this sort of bad weather could be up to 100 times more, so I dont think you can be over cautious

[michael769]

Between -5 and -7 before the salt freezes is the word on the streets here (no pun intended ) and that's if you're roads authority has any salt left.

According to Transport Scotland salt starts to become less efficient below -6 (presumably it takes longer to melt snow and ice), at -9 and below it will not melt ice or snow but will still stop frost forming, and at somewhere between -12 and -15 depending on the concentration it stops working altogether.

[MGF]

Tonight my screenwash froze on my windscreen while I was driving. It was undiluted as well.

[michael769]

Tonight my screenwash froze on my windscreen while I was driving. It was undiluted as well.

In 1995 it hit -22 in Paisley. I was working a nightshift, and a fair number of cars broke down that night due to ice building up in the carburettor jets. When I came out in the morning the trigger spray de-icer in my boot had started to freeze.

This morning I noticed that the bottle of car shampoo in my garage was frozen solid.

[mitchr]

According to Transport Scotland salt starts to become less efficient below -6 (presumably it takes longer to melt snow and ice), at -9 and below it will not melt ice or snow but will still stop frost forming, and at somewhere between -12 and -15 depending on the concentration it stops working altogether.

Thanks for the info Michael. I just always assumed that salt melts ice no matter the temperature.

Mitch

[c8 sdd]

Bear in mind the weather forcast gives "air temperatures in the shade at 1.5 meters from the ground".

Ground/road temperatures are always lower. Typically grass that is growing in sandy soil starts to get frost
on it when the air temperature is 4 degrees.

The average modern car (and my oldey below) which has a display that shows the outside temperature normally
has its sensor up front near the bumper, this will show a different temperature from what the weatherman says,
beacuse its near the ground.

The most useful temperature sensor in a car would be one that uses an infra-red system to measure the
temperature of the road, thus alerting the driver to ice forming conditions ... i have a hand held infrared
contactless thermometer and this works quite well if i stick my arm out the window and aim it at the floor
(not ideal when you're driving though!)