Pretty much like the title asks.
With regards to tire/road contact, does a wet road become more slippery as the temperature of the pavement approaches the point at which the water will freeze (but doesn’t)?
IOW, at 80 degrees does the pavement have more tire/road friction than it does at 40 degrees?
I’m questioning this because my confidence on my motorcycle seems to go down if I drive in the rain when it’s colder verses when it’s warmer out.
Any basis to this?
My thought is that a tire becomes ‘harder’ when it’s colder and this reduces it’s flexibility thus lowering its contact friction with the wet road.
Is this sound reasoning? and what other factors are at play here (like the molecular bonding of the water molecules and the ‘hardening’ of the pavement)?
Your theory about tire “stickiness” decreasing with temperature decreasing is spot on, and in line with what every document on the matter I’ve ever read says.
As far as water’s behavior at near-but-above-freezing temperatures, I’m dead ignorant.
Incidentally, there are rubber compounds intended for use below 45 degrees fahrenheit, and these are used in snow tires. There’s even a “police use” snow tire out there, with a 149 MPH speed rating and snow tire tread…
I believe it’s definitely tire temperature that (rightfully) decreases your confidence on the bike (versus a tire working inside its temp range).
Tires like warmth (up to a point of course).
This is a general observation and has little to do with road surface condition. A very wet and cold road is probably more slippery than a very wet and warm one (for reasons such as cold water being denser has more inertia and resists being pushed away by the tire treads more, or lower temps increasing the water viscosity) but I’m pretty sure you couldn’t tell the difference during normal riding (without accounting for the behaviour of the tires with temperature).
Note that a tire running on a wet road is itself quite wet, and effectivly cooled to the road temperature by effecient water cooling, at the point it leaves the road surface that is.
That tire is in a 50 mph wind blast. (or, however fast are you riding in the rain.) In low humiditity it is possible to lose about 20 deg. F through evaporative cooling. In the rain (high RH) it is probably still possible to lose a few deg. F.
So if you are very near freezing, it might be possible to form a thin film of ice or slush on the tire before it comes around to the road again.
OK speculation to be sure, but I have suggested a mechanism through which the OP’s concern might indeed be possible.
Wouldn’t all of that interaction cause some heat? Water drag and tire contact with road would cause heat while the other elements you propose would cool the tire. I wonder if it’s more of a wash in the end.
When cars drive through snow the snow tends to melt over time, while the rest of the snow on the road remains frozen.
Yes - heat from rolling resistance more than outweighs the evaporative cooling - for proof, put your hand on the tyre after making a journey in the wet. See, it’s warm.
But yes, in cold conditions it takes longer for the tyre to warm up, and cold tyres don’t grip so well. It’s not to do with the road surface, just the tyre. When starting from cold I often notice a bit of wheelspin on wet days; once the tyres are warm they grip much better.
I asked a similar question a while back, wondering why mud seems stickiest just above freezing, and I feel I should win a prize for generating the least interest in an OP that month, scoring a handful of views and 0 posts.
Luckily a kind scientist on daughterboard Nads suggested that it might be because water is at its densest at 4 deg C, and also surface tension increases as the temperature drops.
Water has some very odd and often unique properties. Here are 41 anomalies to be getting on with.