Tom - MOA #156706, Hayward, CA
2006 BMW R1200GS Adventure, aka "Gretel"
1983 Honda V65 Magna - SOLD
Hopefully I can get some tire temperature explanations from the tire makers. Maybe they can explain that weird temperature differential from the surface, air temp and tire surface temp. I would think that being black, the tire would naturally have the same or even slightly higher temperature than the air temp.
Next time I'm in the shop I'll point that same infrared temp reader at the underside of my tongue and see if it calibrates to 98.6 degrees. I should have done that before checking any other values just to see if the gauge was accurate to begin with.
I'm a product of the Tennessee public school system, so this could be all wrong.
Could the temperature differences between surface, air and tire be due to wind chill?
At an ambient air temp of 35 degrees with a 60 mph wind (or for a tire travelling down the road at 60 mph), the wind chill is 17. So, the tire surface is cooled from the "wind chill" affect. The tread in contact with the road (middle) starts to warm first from the friction, but the tread on the side could still be cold from the wind speed.
Just a guess.
'61 John Deere 3010 LP
Windchill factor is what the skin feels.
If you take a temp. reading of a piece of machinery in calm air at -10 deg. the reading will be -10 deg.
If the wind is blowing and the temp. is -10 deg. the temp. of the piece of equipment is still -10 deg.
Lee 2011 K1300S
MOA # 30878
Past BMW Bikes, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT
Right, Wind Chill is what humans and mammals feel due to the cooling effect of the moisture in the air, on our skin, and how the wind has the ability to strip away the boundary layer of warm air just off our skin, of trapped in our clothing.
But it still baffles me that my tires were considerably cooler than the air temp. Even after sitting for maybe 45 minutes after my low-side ride. Assuming my tires had warmed (on the surface at least) to about 55 or 60 degrees, within those 45 minutes the front tire surface had cooled to less than air temp. That leads me to think the air in the tire, was never as warm as the tread surface aven after 20 miles of riding. After the ride, the thin heated layer on the tread surface was quickly displaced through conduction of the colder temperature inside the tire.
Plus the cooler air volume/tire surface area inside the tire is much greater than the much smaller surface area on the center of the tread. The more I think of this, the more I think it takes much longer than we think to totally warm up cold tires. The other correlation the tire makers may help with is how long it takes for the tire pressure to increase a few degrees as the tire totally warms up.
Andy, thanks for being willing to share your experience for the benefit of others.
As for the temperature discrepancy, it will be interesting to see how your tests of the thermometer turn out. The specific heat of air is very low compared to rubber so I doubt if the air in the tire was much, if any, cooler than the rubber....unless the rubber wasn't heated all the way through. Still, that wouldn't explain a tire temp less than the ambient air and pavement around it.
Anyway, thanks again for sharing and I agree with the posters who'd like to see this in the News.
I'm inclined to agree with piperjim (post #21) and disagree with Lee (post #22.)
Certainly, if you took a reading of anything inanimate which isn't being heated, the temperature should be the same standing still and moving 60 mph. But cold weather or hot, tires ARE warmed up by friction with the road and also flexing as they respond to a less than perfectly smooth road surface.
So it makes sense to me (assuming you started with the same "cold" tire pressure at both 40 degrees and 80 degrees) that the friction with the road and flexing should be very similar. The reason tires are slower to warm up in cold weather - and I would guess NEVER reach the same rubber temperature as in summer - is due to both the cold surface of the road AND that cold air moving past the tires. I don't think we should be too quick to dismiss "wind chill" as a factor. And then, another disturbing thought occured to me.
In Canada there has been a lot of publicity encouraging people to get winter tires for their vehicles, even in areas where snow is rarely a problem. (US too?) The reason given is that "all-season" tires have much reduced traction, even on bare dry roads, when the temp gets to about 40 F. The tread gets too hard and doesn't have enough "squirm" to give you nearly the control you had for stopping or turning in higher temperatures. "Winter" tires not only have the lugs for gripping snow; they also grip the road better in wet and/or cold or icy conditions.
Could this apply to bikes too, especially "rounders" who do not fear rain or cold?
To the OP - thank you. You have opened up a much wider discussion than you could possibly have imagined. There is clearly a lot to be learned about cold weather traction. Maybe your submission - and all the responses it has and will receive - will help a number of riders avoid an accident. And I agree you should write a motosafe article for the ON. Get more reaction to this thread first before you write a column.
Then do it!
I found this posting on a Suzuki forum, and it was credited to a police bikers forum.
"By Lt. L.P. Walker
This is a notice to all motor officers, and especially those who may not have experienced much cold-weather riding. Motorcycle tires and pavement interact differently at colder temperatures giving a rider less traction than he would have in warmer weather. ItÔÇÖs good to remember that riding in cold weather is roughly the same as riding in wet weather.
Colder temperatures affect the rubber compounds in motorcycle tires by making them more rigid and less flexible than they are in warmer weather. This means that the tire has a weaker grip on the roadway surface. Of course the center part of the tire will heat up after a few minutes of riding and give more adhesion, but the edges of the tire that do not contact the surface during normal straight-ahead riding remain colder than the rest of the tire. During tight turns, these cold edges contact the pavement and can lose traction against the cold pavement and cause a front wheel slip that can be disastrous to the rider. In temperatures in the 30ÔÇÖs and below, this becomes much more pronounced.
ItÔÇÖs good to remember that cold tires against cold pavement can cause a situation similar to riding on wet pavement. So treat colder weather the same as you would wet weather, and remember to ride safe."
And, from a moderator on a physics forum:
"Cold tires are stiffer. Thus they do not flex as much as they would when the weather is hot. Less flex when rolling in a straight line means less heat generated in the core of the tire and thus less heat on the edges. So edges remain colder in cold weather not simply because of convective cooling from the cold air, but also due to lack of flexing of the carcass, which is one of the primary causes of tire heating. every time the tire rolls into its contact patch, the tire flattens, and this bends the tire shape from round to flat at that point and causes tire heating. Added to the cold tire stiffness causing lack of flexing is the cold tread temp having much less grip. This will depend on the compound of the tire, with summer tires providing much less grip at cold temps than tires with a more all-temperature compound."
I'm suspect that we could keep a few physicists and chemists busy on this question for the rest of the winter!!!
Indeed, fertile ground for a future ON article!!!
'61 John Deere 3010 LP
Bottom line: there is a point especially in cold weather (<3C) where there is no snow on the road to give you traction that sand, chemicals, black ice, frost, debris etc when one is taking a risk on two wheels. We all have a different tolerance to that risk but it is real. As someone who has not gone down in one of these situations on a street bike - I make a decision each season when to stop riding because there are far more uncontrollable things than controllable things. I find the science helpful and interesting to know why and how but when certain conditions exist on pavement - one will go down - no matter how expert. I know this may be controversial but cold conditions on pavement and the extreme variablity of weather and road surface issues (most of which canNOT be seen) is truly treacherous and unpredictable.
Cold weather riding on dirt and gravel with a bike tires made for it (including studs) extends the season right through winter most places in the world.
[2008 R1200RT (Biarritz Blue) - Mine]
[2007 R1200RT (Sand Biege) - Hers]
And let's not get started on the roads that are shaded and those that are warmed up by the sun. In cold temps this can prove quite "exciting" especially if there is some water run-off.
2008 R12RT (Blue)
1986 R80RT (Silver)
Member of the Loonie-Tics. MOA 292.
A friend a long time ago told me that in the old days of motorcycle racing they lowered their air pressure in order to allow the tire pressure to come up to working temperatures and expanding the air inside without risk of decreasing rolling resistance due to having an over inflated tire.
I ride in the GA mtns during the winter and what I do is just that. I ride an '05 GS according to BMW recommended tire pressure is 32 front 36 rear so I lower them 2-3 lbs and find that my bike/tires grip better.
Just my two cents but then it could only be one.