Thanks
Good point, although I wonder if there are examples of light snow conditions where other effects are seen – like where a dusting of snow is displaced (or pressure melted) by tire traffic and then the small amount of liquid is heat evaporated rather than displaced.
If I may ask, what surface were in contact with the test tires and did that surface get hot?
Thanks – and it makes me think of the reverse condition: as conditions warm up, do the tire traffic tracks in light snow or a little ice melt faster than the adjacent areas not in the tracks?
Your condition probably happens a lot in some places as the sun sets and temperatures cool while the reverse happens after sun rise and as temperatures increase.
Yes of course, where salt has been applied, the tracks are usually the first to melt leaving snow or ice in the center and sides for a while. I don’t think it’s got much to do with tire heat though.
The test station looked similar to this
https://chantengineering.com/products/testing-machinery/tire-testing/
and the contact surface was similar in texture to crocus cloth but with years of use there was a heavy coat of rubber at the center.
So here’s a whitepaper I found that contains information related to heat conduction to the road surface. Granted it is related to race tires but it outlines the major paths and their relative contribution:
http://www.izzeracing.com/products/ewExternalFiles/Izze_Racing_White_Paper_Tire_Temperature.pdf
The majority of a race tire’s heat is lost at the tire-road and tire-air (external)
interfaces. Assuming the tire is hotter than the ambient, heat is lost at the
tire-road interface from conduction into the ground, and at the tire-air
interface from forced convection with the ambient air. Heat losses from
radiation are only significant for temperatures > 100˚C and are often ignored.
However, heat to and from the tire can also be managed at the wheel-tire
interface; brakes feed temperature into the wheels & tires but wheels can
also be used to cool & thermally manage the tire.
Given the significant heat losses at the tire-road interface and transient heat
generation at the surface (surface heat generation is highly dependent on slip
ratio, slip angle, and load), a race tire’s surface temperature fluctuates rapidly
with dynamic loading.
EDIT:
Here’s another source of info: https://www.researchgate.net/publication/266341564_Effects_of_Vehicle_Heat_on_Road_Surface_Temperature_of_Dry_Condition
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760007024.pdf
Wow! Thanks very much!
[edit: interesting that tires with less tread (and/or less load) apparently generate less heat, and so would have less heat to transfer to the road surface or to the air ]
Thanks for that!
I always hate saying, "don’t know, don’t care, but…"
Running through the changes going through the stages
Coming round the corners in my life
Leaving doubt to fate staying out too late
Waiting for the moon to say goodniiiigh-hi-hi-hite
And I could cry for the time I’ve wasted
But that’s a waste of time and tears
And I know just what I’d change
If I went back in time somehow
But there’s nothing I can do about it now
Lyrics by Beth Nielsen Chapman, performed………… by Willie Nelson
CSA
My experience with light snow is the tires compact the snow into ice. Light snow is sometimes worse than a heavier snow.
Light snow means colder temps…so it can quickly turn to ice and make for slick driving conditions. When my middle child was new to driving…one morning it snowed about 1/2" and the temps were below 20. I told my son as he drove off to school to be careful because the roads were going to be slick. Luckily he heeded my warning. Said he saw many cars off the road and a 5 car crash on the way to school.
Better explained by the fact that tires are designed to fling the water out to the sides and therefore out of the “tracks.”
The tire does briefly heat the road under it, which is why you slide on ice. The tire melts the top layer of ice, and that water makes it easy to slide around on ice. The same mechanism is what causes you to slip while walking on ice. When it’s extremely cold, ice actually isn’t very slippery when you walk on it because the pressure of your weight can’t melt it before you’ve taken your next step.
The heating is more from compression due to the weight than from the tire being warm. Any time you change something’s shape, you end up with heat as a byproduct (which is why it’s always so funny in movies when they want to show someone is strong, so they have him bend a steel bar. Thing would be red hot if you bent it that fast). You’re pressing down on the road with a 3,000 pound plus vehicle - that’s gonna heat it up too. But unless you’re driving something like NASA’s crawler transporter, the heating isn’t going to be all that significant, especially since you’re probably moving over any given section of road at a pretty good clip.
It’s got to be a somewhat measurable amount. During light snowfall, there is always snow accumulation on the shoulder before the plow comes through, but the snow landing in the lanes melts instantly. I don’t think it is solely because of the salt use but maybe I’m wrong about that.
There has probably been research on this. State highway or transportation departments, or the US DOT may have employees who could direct you. Maybe the IIHS - Insurance Institute for Highway Safety, too. Someone somewhere has taken this question beyond the barstool.
I already posted several references to technical discussions on it. It’s always amusing to see speculative, qualitative assessments based on preconceived notions. We all do it. Even professional engineers tend to make conclusions based on what they think may be happening. It’s always fun to see those notions proven wrong…
Tracks on the road way are probably a result of the sum total combinations of all the things mentioned. There is heat from tires (it’s not a single car going by), pressure displacement (the surface is permeable as well), pickup and flinging of the water, convective effects of the vehicle motion moving the surrounding air etc etc etc. To say, without any data to back it up, that heat from tires is inconsequential is funny especially given some of the scientific study put into that topic stating it is significant. The tire gets heated by flexing and so does the tire to road interface due to squirming. Our tires wouldn’t wear away so fast if they weren’t constantly being scrubbed even when traveling mostly straight. Heat is heat, it doesn’t magically disappear…
I didn’t say it was inconsequential, I said it wasn’t all that significant, and I stand by that statement.
The tire wearing from its own heating was not the subject of discussion and is irrelevant to the question asked. The tire is in constant contact with itself and therefore the heat generated by the tire is significant to the tire. Not so much the things the tire very briefly rolls over.
Even if the tire heats up to 120 degrees, which would be a pretty good trick for a normal street car in the winter on ice, you generally have less than 40 square inches worth of contact patch, which means, especially at the kinds of speeds required to heat the tire that much even in the summer, the heated tire is in contact with any given section of road for a small fraction of a second before it’s gone.
In the same vein as the fact that you can wave your fingers through a flame without setting yourself on fire, the heat transfer just isn’t going to be very high because of the very brief time span of contact between the “hot” tire and the road. It will still be there, but other factors will be far more significant.
I do realize that a a 3.2 degree increase in temperature is statistically significant, but I also realize that 3 of those 3.2 degrees are heating the tire track up to the temperature of the rest of the road because the tire tracks, according to your linked study, are colder than the surrounding road when cars aren’t passing over them. This means the tire tracks during times of heavy vehicle passage, are all of 0.2 degrees hotter than the surrounding pavement. While that is definitely non-zero and may even be considered significant for the purposes of the study, as far as it being enough to melt snow? Only if the rest of the road is already within less than 1 degree of being able to melt the snow un-aided by tires.
I bet (especially in places like Texas) it’s the road that heats the tire, rather than the reverse.
Off topic again. When I was a kid I spent 25 cents or so on a mail order book “Feats of Strength”. Kinda fun. How to impress your friends. Talked about how to pull a railroad car, bending a bar etc. However I did have a guy that worked for me that could rip a Minneapolis phone book in half (about 4"). It was no trick like in the pamphlet. I didn’t believe him and he did about three in a row. Don’t make him mad.
I’ll weigh in a little here just based off of my best educated guess.
the tracks from rain or snow are more likely due to excess moisture not being allowed to sit on the road surface. each time a tire rolls over it again, it will pick up some moisture and dissipate it in the form of mist or evaporation etc.
thinner layer of moisture + minimal surface heat from tires/friction + larger internal heat from absorbing the sun/atmospheric temps = clears quicker than standing moisture next to it.
a little side reading for you: An interesting report of this was done by NASA for landing performance on a runway
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760007024.pdf
page 13 or so goes into the dissipation. which seems pretty fast especially considering the much larger friction forces/heat from airplane impact vs automobiles.
In addition to what the tires do, there is also the effect of radiant heat from the exhaust system. And all the while, moisture in exhaust gasses goes somewhere: downward to the pavement fairly quickly in very cold conditions, dissipated to some extent by air movement.
Tomato, tomahtoe…
Think what you will, the linked analysis pretty much defines how much heat is transferred using fairly sophisticated analysis tools. The other links I supplied back it up, one being from NASA. I guess I place more trust in those articles than what you surmise to be true.