Sunday, December 21, 2008
Science / Housekeeping Special Bonus Dear Science: Why is My Car Shit in Snow?
Posted by Jonathan Golob on Sun, Dec 21, 2008 at 4:58 PM
This just in to the Dear Science SNOWPOCALYPSE 2008 (tm) (Hannukah eve again, bitches) crisis center war room control:
Dear Science,
Do AWD or 4WD help me STOP my vehicle faster in inclement weather? I've always assumed that even with my extra weight and wider tires this was true... hence my absent mindedness when tailgating other drivers and driving 5mph above the posted speed limit (cops are too busy dealing with traffic accidents to be shooting a radar gun anyway) when it snows.Thanks Dear Science!
Your all-wheel or four-wheel drive does not help you stop or steer. It only helps you reach a speed at which you will be unable to control anything. So, stop tailgating. Stop now. Stop. Park your car and stop. Stop. Do not drive. Stop. Go home and eat soup. Have you stopped yet?
If you want the science, read on at dearscience.org.
But here's what you need to know: The amount of frictional force generated by your tires determines how fast you can change the speed of your car—up or down—and how fast you can turn. The less friction, the slower you can make your car change speed or direction. Snow and ice on the road reduce the friction.
Let's play this out. You're attempting to go up Denny Way, despite the road closed sign. Your (idiotic) strategy? Floor it, fuckers!
Just before you start, your tires are still stuck to the road; that's static friction. You press the gas all the way down, causing the tires to apply a huge force to the road, speeding you up a bit. Pretty quickly, this force exceeds the modest static frictional force your tires are producing. They start to spin. Force exceeding the static friction dumps you into kinetic friction, and that means you're slipping.
Not only is your car not going forward, now you cannot steer or stop as you slowly drift into a pole. You panic and slam on the brakes, figuring you should at least be able to stop since the brakes worked a few seconds ago. But they don't. Because the kinetic friction generated by your tires is so much less than the static friction you had to work with before, even the modest force generated by braking exceeds it.
Once your tires start slipping, it's really difficult to get them stuck to the road again. The solution? Do things slowly. Accelerate slowly. Turn slowly. Brake slowly. Go unbearably slow, slow enough that the forces you're applying to turn, accelerate or brake are less than static friction.
If you start to skid, you're told to take your feet off the gas/brakes and turn into the skid. And now you know why—because you want your tires moving at about the speed your car is moving relative to the road, which shifts you back from kinetic friction to static. Then you're back in charge and can start steering.
And this is why tailgating is such a profoundly bad idea. If you try to stop too quickly, you'll totally lose control and fuck over someone more responsible than you. Stop.
And finally:
"...Mr Plow is a loser,
and I think he is a boozer"
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1
Also please learn how to use snow shovels. Imagine if everyone were to simply take responsibility for the sidewalks on their property...
4
Unfortunately, every last snow shovel in this town is gone. Trust me. I swear we will have one for next time. Usually a broom works just fine for our one day snowstorms. Sorry! It is pretty embarrassing for an east coaster to be without the proper equipment.
5
also aren't wider tires worse in the snow? why do I think this? anyway as an ex Bostonian I agree - go SLOW. or better yet curl up with some drinks and stay home.
6
Even on a racetrack, when you should have all the friction you could dream of from your fancy tires and the well maintained tarmac, abrupt turning or braking or acceleration will send you out of control. Normal driving at moderate speed on good pavement tends to forgive some inept driving, but at high speeds or the snow, those bad habits won't cut it.
9
@5: Here's the rub with wider tires.
The wider the tire, the higher the static friction. But, tire width has no effect on kinetic friction. So, the drop in available friction when you start to skid is higher.
So, you have the double whammy of having excessive confidence from the higher static friction limit, combined with a huge loss when the tires start to spin. It's even less forgiving.
The wider the tire, the higher the static friction. But, tire width has no effect on kinetic friction. So, the drop in available friction when you start to skid is higher.
So, you have the double whammy of having excessive confidence from the higher static friction limit, combined with a huge loss when the tires start to spin. It's even less forgiving.
10
Wide tires are for heat dissipation (think F1 cars) or for floating on mud (think 4x4s). Floating is not what you want in snow.
These are WRC snow tires:
http://www.wrc.com/news/big/080204_sotto…
These are WRC snow tires:
http://www.wrc.com/news/big/080204_sotto…
11
I've been wondering about bikes. It seems like the tiny surface area (so, minimal static friction) of a bike tire should make it damn near impossible to bike on snow/ice, but I'm seeing people do it.
12
Oh, also...
Another way of looking at this question is to note that insurance is higher on 4wd vehicles, especially the high ground clearance trucks, than normal cars. If 4wd were safer, that would be reflected in a lower accident rate and lower premiums. In fact, the feeling of confidence that you get from sitting up so high with power on all the wheels makes you use a cell phone more, wear seat belts less, and drive worse.
Another way of looking at this question is to note that insurance is higher on 4wd vehicles, especially the high ground clearance trucks, than normal cars. If 4wd were safer, that would be reflected in a lower accident rate and lower premiums. In fact, the feeling of confidence that you get from sitting up so high with power on all the wheels makes you use a cell phone more, wear seat belts less, and drive worse.
14
@11 Bikes also weigh a lot less than cars. And you can get studded snow tires for your bike if you really want to get serious about winter riding in icy conditions:
http://www.peterwhitecycles.com/studdedt…
And a simpler way to put what JG is saying is that:
"Some cars have all-wheel drive, but *all* cars have all-wheel stop."
In addition, fat-ass FUV's have longer stopping distances on dry pavement than sedans do. So it only makes sense that they're even more at a disadvantage at stopping on wet/snowy/icy pavement.
http://www.peterwhitecycles.com/studdedt…
And a simpler way to put what JG is saying is that:
"Some cars have all-wheel drive, but *all* cars have all-wheel stop."
In addition, fat-ass FUV's have longer stopping distances on dry pavement than sedans do. So it only makes sense that they're even more at a disadvantage at stopping on wet/snowy/icy pavement.
16
You native northwesterners are hilarious (and dangerous) in the snow. I see many people applying the "floor it till it goes" solution and tailgating. Not 20 minutes ago, I saw someone tailgating AND honking at the person in front of him to go faster. Needless to say, I stayed away from that chump.
I come from a place in the great white north where all snow tires have cleats and all winter roads are entirely made of rock salt and sheer ice. I can four-wheel drift through turns and maintain control with the best of them, but I don't because if a) you have no idea what you're doing and b) are driving where there are actually people and things to hit, for the lovechild of Bristol Palin's sake, slow the fuck down.
I come from a place in the great white north where all snow tires have cleats and all winter roads are entirely made of rock salt and sheer ice. I can four-wheel drift through turns and maintain control with the best of them, but I don't because if a) you have no idea what you're doing and b) are driving where there are actually people and things to hit, for the lovechild of Bristol Palin's sake, slow the fuck down.
18
@13
Oh FUCK yes. I'd love to do that shit.
Hey. . . I know a boy with a Subaru along those lines. He liiiikes me.
Boy-Who-Likes-Me, do you think I could borrow your car for a minute? :D
Oh FUCK yes. I'd love to do that shit.
Hey. . . I know a boy with a Subaru along those lines. He liiiikes me.
Boy-Who-Likes-Me, do you think I could borrow your car for a minute? :D
19
@16
You are so correct. I'm an ex-Bostonian and am appalled at the unsafe driving I've seen the past few days. Slow the f*ck down, you idiots! It only takes one patch of ice to send you head-on into some innocent, careful driver.
Also, this article is an excellent explanation of the physics at play. It's all about minimizing accelerations in all directions, since F=ma, and F is not available right now...
You are so correct. I'm an ex-Bostonian and am appalled at the unsafe driving I've seen the past few days. Slow the f*ck down, you idiots! It only takes one patch of ice to send you head-on into some innocent, careful driver.
Also, this article is an excellent explanation of the physics at play. It's all about minimizing accelerations in all directions, since F=ma, and F is not available right now...
20
Jeebus, does all this really need to be explained???
Maybe some thinning of the herd is a good idea...
Maybe some thinning of the herd is a good idea...
21
MichaelPGH:
From what I and others have obaerved, yes this is neccesary. Sadly, these fools thin the wrong people, not themselves.
From what I and others have obaerved, yes this is neccesary. Sadly, these fools thin the wrong people, not themselves.
22
good explanation. sadly most of the idiots won't think to educate themselves.
on foot is best for now.
on foot is best for now.
23
ah thanks for the wide tire lesson. I'm a bio girl and friction is barely covered in my freshman sci class. I knew there was something I should be better able to explain.
24
@8:
Jonathan: On the DearScience post, you say that "the wider your tires...the higher your mu." I believe this is wrong; mu is a property of the two materials that are in contact with each other and does not depend on the surface area of contact.
In fact, all else (mu and normal force) being equal, the force of friction does not change when the surface area changes. See http://www.physlink.com/education/askexp… for an explanation of why.
As for the bike tires question, skinny bike tires are typically better in the rain (and probably light slush) because the greater pressure allows them to cut through the water better, as opposed to wider tires, which, with lower pressure, can hydroplane. When the snow is heavy enough that you're trying to stay on top of it, of course, you'd want wide bike tires (or skis).
Jonathan: On the DearScience post, you say that "the wider your tires...the higher your mu." I believe this is wrong; mu is a property of the two materials that are in contact with each other and does not depend on the surface area of contact.
In fact, all else (mu and normal force) being equal, the force of friction does not change when the surface area changes. See http://www.physlink.com/education/askexp… for an explanation of why.
As for the bike tires question, skinny bike tires are typically better in the rain (and probably light slush) because the greater pressure allows them to cut through the water better, as opposed to wider tires, which, with lower pressure, can hydroplane. When the snow is heavy enough that you're trying to stay on top of it, of course, you'd want wide bike tires (or skis).
25
@20
nice blog. i and you have some artistic commonalities:
- i've read an MFA dissertation on the "The Raft of the Medusa."
- the Seaman album looks pretty good (check out KBCS streaming on sunday nights? now? nice and medieval)
- i've spent a week in Delft
- last year i met a woman who has swum in that Hockney pool, or so she said
- and...looking out from Forbes Terrace Apt. in Pgh '92, i wrote a song based on that Lennon bloodsplattered eyeglass photo -- the corner where the squirrell hill library, the JCC, and the Squirrel Cage are. Squirrel Cage still serving drinks?
i liked living in seattle because there was little snowfall, but when it happened i was always happy, driving or not
i need to start writing songs again - "I Heard the Thinning" seems to be a title worth exploring, cheers
nice blog. i and you have some artistic commonalities:
- i've read an MFA dissertation on the "The Raft of the Medusa."
- the Seaman album looks pretty good (check out KBCS streaming on sunday nights? now? nice and medieval)
- i've spent a week in Delft
- last year i met a woman who has swum in that Hockney pool, or so she said
- and...looking out from Forbes Terrace Apt. in Pgh '92, i wrote a song based on that Lennon bloodsplattered eyeglass photo -- the corner where the squirrell hill library, the JCC, and the Squirrel Cage are. Squirrel Cage still serving drinks?
i liked living in seattle because there was little snowfall, but when it happened i was always happy, driving or not
i need to start writing songs again - "I Heard the Thinning" seems to be a title worth exploring, cheers
26
Well said, Science.
Also: try to avoid braking and turning at the same time. You may find out the hard way that you have enough traction for one or the other, but not both. Going slow helps a lot with that.
Also: try to avoid braking and turning at the same time. You may find out the hard way that you have enough traction for one or the other, but not both. Going slow helps a lot with that.
27
Dear Mr. Transplant:
If you don't like it here, maybe you should reevaluate your criteria for deciding what location would nurture you the most, and allow you to maybe spread postive energy instead of negative energy? It's a real downer when people from somewhere else make these comments and make us have to think about things. That's not blissful, you know! Also, Seattle has HILLS so it's not comparable to driving in the snow in other cities, or states, or nations, or continents. We are unique, also we are also the only place that has geology formed by glaciers, so that's why we don't have a subway system and why the underground tunnel costs for our light rail not-a-subway system are 4x higher than elsewhere.
Happy nonholy days--
If you don't like it here, maybe you should reevaluate your criteria for deciding what location would nurture you the most, and allow you to maybe spread postive energy instead of negative energy? It's a real downer when people from somewhere else make these comments and make us have to think about things. That's not blissful, you know! Also, Seattle has HILLS so it's not comparable to driving in the snow in other cities, or states, or nations, or continents. We are unique, also we are also the only place that has geology formed by glaciers, so that's why we don't have a subway system and why the underground tunnel costs for our light rail not-a-subway system are 4x higher than elsewhere.
Happy nonholy days--
28
My big outdoor push broom and some salt worked to clear my part of the sidewalk in Greenlake on Thursday, but it wasn't working this morning. As others have said, snow shovels are gone everywhere, I've been looking for a couple days. I was tempted to steal one of the five outside the Roosevelt Square Bartells. Even worse, my friends in West Seattle who are currently in Hawaii have my regular shovels. I'll try to find a snow shovel tomorrow.
29
I saw some immigrant guy driving a white subcompact with all 4 tires tiny spares. Does that define dumb?
30
Just watch Top Gear, especially the winter episode where Jeremy and James race Richard to the North Pole. Those Icelanders (?) know a thing or seven when it comes to driving in the snow.
32
@16 And I love how people from out of town always assume all bad drivers are "native northwesterners". How could you tell, did they have stickers on their car? Were they flying Washington flags and singing "Louie-Louie"?
Trust me, there are shitty drivers everywhere. If Seattle is so horrible, maybe you should try Oklahoma.
Trust me, there are shitty drivers everywhere. If Seattle is so horrible, maybe you should try Oklahoma.
33
Driving in snow is like walking on ice: you can do it, but you can't try anything sudden (start, stop, turn) or you will wipe out.
34
Most people are just complete morons, don't know how to drive, never learned, never will learn. They will always be stupid. The low temperature lowers their already rock-bottom IQs.
They will never get it. Never. They will always be idiots.
They will never get it. Never. They will always be idiots.
35
As #32 and #34 point out, a moron is still a moron when it snows.
I've lived in the Puget Sound area my entire life, driven in snow maybe twice before this year, but I did all right because I try not to be a moron. I drove to work and back on Thursday, and it sucked, but I made it all right. The reason I was able to do that was because I made sure had the right equipment with me and I drove SLOWLY and CAREFULLY. Meanwhile, morons around me slid, skidded, spun, and generally acted like automotive billiard balls.
Today I took the bus because hey, I'm not a moron.
I've lived in the Puget Sound area my entire life, driven in snow maybe twice before this year, but I did all right because I try not to be a moron. I drove to work and back on Thursday, and it sucked, but I made it all right. The reason I was able to do that was because I made sure had the right equipment with me and I drove SLOWLY and CAREFULLY. Meanwhile, morons around me slid, skidded, spun, and generally acted like automotive billiard balls.
Today I took the bus because hey, I'm not a moron.
36
I'm a native Northwesterner and I can tell you that blaming the natives makes no sense at all. Every time I go to a party, the people I meet are all like "Wow, I haven't met many people who are actually from Seattle!" If that's true, then who is it that's really driving out there? Yeah, that's right, it's YOU, transplants! Since you apparently make up the majority of the population here, one can only assume you all have rose-tinted memories of what good drivers you are. You bring your "experience" driving in the snow here to Seattle, only to find yourselves thwarted by topography and steep grades never encountered in Chicago, Boston, or New York. So slow down and stay off the hills.
37
@1 - Huh? Do you think the problem is that nobody knows how to use a snow shovel? Since we live in Seattle, and snow sticking for more than a day is a freak occurrence, I think it's more likely that nobody even owns a snow shovel.
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