[Glideslope]

So my wife's 2008 X3 always beeps when the outside temp reaches and drops below 37 degrees F. When driving up/down to the ski hill, it gets annoying really fast.

A few years later, I added my F30 to the mix... and it also barks at me (thru the HUD) that the outside temp is 37 degrees.

OK, got it.

Curious about this value, I read in the manual that the ASS disables below 37ºF but what else magically happens at this temp?



Thanks!

[jdong]

It seems like 37 degrees F is some sort of car industry standard for the temp at which frost on the road becomes a risk. The Prius does the same thing.

A frost warning does seem kind of silly. It's as amusing as those "Bridge may be ICY" signs year round, but I'm sure some day, that warning chime will get the last laugh when I end up in a ditch.

Audi also puts a snowflake up on the ambient temp display when it reaches 37.

[Glideslope]

Thanks JD! I figured it was something due to cold rubber vs wet road traction... maybe max rubber hardness and increased slipperyness (sp).

[steve111]

I've found that other European cars I've had (eg Alfa, GTI) always give you a warning for icy roads at 3C. 37F is the closest equivalent.

[Fazerfahrer]

Hi,

as discibed, in europe nearly all cars give a warning at 3*C to take attention of the risk of icy roads as from 0*C. The 37F is nearby 3*C.

[HighlandPete]

Originally Posted by Glideslope

Thanks JD! I figured it was something due to cold rubber vs wet road traction... maybe max rubber hardness and increased slipperyness (sp).

More the ice risk.

I'm in the Highlands of Scotland and very common to have black ice when the air temperature is 1- 2 degrees Centigrade, so the frost warning at 3C is just about right.

Plus temperatures can regularly drop out very quickly up here, so a warning is a good reminder that temperatures can be falling fast.

HighlandPete

[glangford]

The freezing point of water 0 degrees C is for bulk liquid. The freezing point can be lowered when water takes the form of small droplets (hence stable fog at temperatures as low as -5 C) It is raised slightly in the form of sheets, such as on a road. All this is due to the effects of surface tension on the free energy of the system. (consult p chem book for details).

[BavarianFanatic]

The surface temperature can be low enough to allow icing at that air temp. It's just a warning to be aware that there's a possibility of ice.

[mikew2069]

Good post. I've wondered the same thing. Good thing it only gets to 37 once a year in Houston!

[DrivenByE30]

Water freezes at around 0 degrees Celsius, which is the equivalent to around 37 degrees F.
The car is giving you warning to pay attention, since it is sufficiently cold outside, there may be black ice on the road, and therefore to drive more carefully...

Ass is off to keep the heater on so your ass may stay warm...

[tturedraider]

Originally Posted by steve111

I've found that other European cars I've had (eg Alfa, GTI) always give you a warning for icy roads at 3C. 37F is the closest equivalent.

^^ this

[CHCCubs]

Originally Posted by Glideslope

Curious about this value, I read in the manual that the ASS disables below 37ºF but what else magically happens at this temp?

Not sure if the ASS feature works differently in certain markets, but the ASS on my car does not disable below 3C (37F), there doesn't seem to be any limit as I've had it engage at temps as low as -20C (-4F).

[34.50]

Originally Posted by CHCCubs

Not sure if the ASS feature works differently in certain markets, but the ASS on my car does not disable below 3C (37F), there doesn't seem to be any limit as I've had it engage at temps as low as -20C (-4F).

According to the manual, ASS is disabled below approx. 37 degrees F (3 degrees C). I haven't had to disable ASS because it's been below 35 here, but today at 38 degrees, ASS finally kicked in.

[EHDEN]

good to know! will never experience this being in south beach...but very interesting! goodluck with you all in the snow! the beach looks great in December

[infinitigor]

Originally Posted by DrivenByE30

Water freezes at around 0 degrees Celsius, which is the equivalent to around 37 degrees F.
The car is giving you warning to pay attention, since it is sufficiently cold outside, there may be black ice on the road, and therefore to drive more carefully...

Ass is off to keep the heater on so your ass may stay warm...

0 degrees ceclius is 32degrees F. People in the thread are stating that road can get icy at above 0 degrees celcius

[Lost Horizon]

Originally Posted by HighlandPete

More the ice risk.
.... so the frost warning at 3C is just about right..

HighlandPete

The Scotsman is right... black ice is the big deal around our parts also.. hit it once on a curve @ 37F, and you'll understand why... it can form at 37 ambient air temp, where the clear sky radiation lowers the road temp to 32-... but that's the nerd part...

The slip slidin' away part we can all understand in the moment.. really bad ASS.. lordie, please forgive me on such a bad pun.

[Glideslope]

Thanks Guys,
I figured that... I know water changes state at 0ºC/32ºF at sea level per my Thermodynamics and Chemistry uni courses.

But, I was interested in the 37ºF figure used to trigger alerts. I realize it is due to a rule of thumb ºC figure the Europeans use translated to ºF and obviously know it is related to traction due to cold weather (it's not like airplane carb ice that can form at high temperatures).

Just wondering the BMW science behind the number 37... and I think I've read about the frost, black ice thing... and am satisfied.

[ben_e71]

http://en.wikipedia.org/wiki/Black_ice

3 deg spot on here in the UK and it appears Black Ice has a slightly different definition either side of the Atlantic ...