Low temps = lower traction, and a low side!

[ANDYVH]

I work part time at the local BMW dealer in the Green Bay area, Nick's BMW. One of the best parts of working there is I am the main demo lead rider. When customers come in for a demo ride, I lead them on a preset route in the area around the shop. We do demo rides late into the season as long as the roads are clean. Saturday, at about 3pm a customer came in to test ride a used K1200LT. Rather than get out one of the other demo bikes to ride, I told the shop owner I'd ride my own bike since I rode in that day anyway.

The demo route I do has a few turns so the test rider can at least get some idea of how the bike ridden handles. Some of the turns are simply 90 degree county highway to county highway, others are two-lane backroads with moderate easy turns. The temps were low, about 35 degrees, and the following rider was riding slow and very cautiously, so I backed off my pace to match his. About four miles from the shop was the first 90 degree turn, one I had taken MANY times through the season, sometimes at "enthusiastic" levels because I know the turn and bikes so well. So I backed off what I thought was enough. Wrongo!!

I entered a right hand 90 degree turn, braking done, in 2nd gear and setup for the turn/steady throttle, pressed firm on the right grip to set the bike into the turn, and the front tire totally washed out into a lowside! I'm sliding briefly on the pavement, maybe rolled once, watching my bike slide and spin on the RH saddlebag and valve cover. DAMN! Everything came to a stop quickly, riding gear scuffed, bike still runnning on its side, I'm fine. It was maybe a 30mph lowside at most. I got up and ran to my bike, shut it off, then picked it up. The following rider caught up to me saying "Wow! I just saw you go down! You ok!!??" Yeah.

I briefly looked over the bike, checked myself, looked over the turn, and found nothing to cause the lowside. Got the bike started and we completed the demo ride, while in my head I am trying to figure out what I did wrong. I had taken that same turn MANY times in the past FAR more spirited than I had just done. All I could think was, cold tires. After about an hour back at the shop, I rode back out to the turn, with a infrared thermal reader with me. Before I left the shop I checked the front tire, 20 degrees (center of the tread) on 27 degree pavement (oh by the way, NO frost or moisture involved). I rode the four miles to that turn and stopped there, checked the tire again. Center of the tread was already at 55 degrees, not bad. BUT!! The RH side of tread, just 1.5" off center, that I had leaned into was ONLY 25 degrees! 30 degrees cooler!! As I suspected, cold tire with less grip. The rear tire was at 55 degrees, and 45 degrees off center.

I rode back to the shop, another four miles. Got off the bike and the front tire was already at 75 degrees in the center of the tread. But 1.5" off center it read only 54 degrees, still at least 20 degrees cooler. If I had more time I would have ridden 10 miles, then 15 miles, then 20 miles, and each time taken readings on the tread center and off center to see how the front tire builds heat. My tires are new Avon Storm sport-touring tires with maybe 2,000 miles on them. Good tires, well rated for grip, with variable compounds in the material for better grip off center. But, I did not get enough heat into the WHOLE tread to take that corner like I did. So what was learned from this?
1. If you ride in cold weather, ride conservatively for at LEAST ten miles before expecting ANY normal grip.
2. Even after ten miles, off center of your front tire may be considerably cooler than the center.
3. BACK IT OFF, until your brain is "warmed up" for the ride as much as your tires. Or perhaps, COOL your brain and actions until your tires have warmed up.

So now I have to do some ebay shopping for a used RH valve cover. New winter project also to repair the RH saddlebag. Spend some bucks on getting my scuffed jacket and riding pants repaired. Reset my ego, perhaps do a little reality check in my noggin. And say "thanks, Lord" for the protection of riding gear that let me learn from a low-side witout even a scrath or bruise. Rememer, learn from EVERY ride. good and bad.

[Omega Man]

Glad your OK. Your info is a good reminder of everything needs a warm-up. Gary

[tommcgee]

A buddy went down in NH a couple of weeks ago, frost on the road. Warm tires don't help that.

[ANDYVH]

Yeah, this is the time of year when low temps and humidity in the air can put that layer of frost on the surface. No big deal in a car for the most part, but even a small patch of frost in the wrong place can wreak havoc on a bike.

If you are a cold weather rider you have to be aware of all these factors. Even last night, in east central Wisconsin the temps got up over 40 degrees. But it was a somewhat humid day, and when the temp dropped there was a heavy layer of frost on many lighter travelled roads. I was in my car for that drive though.

[E_Page]

Good info for cold weather riding. Thanks for sharing to allow some of us to learn from your misfortune. Glad your OK.

[dbrick]

Thanks, Andy, for your careful and useful observations. Glad you weren't hurt.

It's been cold (relatively speaking!) around here the last week; 41° when I left home today, 35° when I got to work. And it wasn't ten miles, either: my bike's tires were surely not ready for anything beyond tiptoeing along.

[BCKRIDER]

Very interesting! Any explanation how the "cold" tire could register only 20 degrees when the pavement was 27 and the air temp about 35? I would have thought that tire temp, after sitting long enough, would equal the air temp.

Anyone know what "ideal" temp is for street rubber? My guess is that in cold weather we NEVER have as much traction for cornering or stopping as in summer heat because we never reach that ideal temperature, even if we drop tire pressure 2-3 psi.

Further food for thought: what is your traction equation when riding on roads which are both cold and wet? My guess, again, is that it is a LOT less than when riding on a warm wet road.

Pure conjecture on my part. I do think this thread opened up a safety issue which has not received the print discussion it deserves. If there is scientific data on these questions (and I bet there is) it deserves wider circulation.

Thanks to the OP for sharing his experience and observations. Hope this thread will garner more information on an important but often overlooked topic.

[ANDYVH]

My hope is to present my findings to Avon tire and see if they have any supporting data. But, in this lawsuit happy land of ours I bet they will be hesitant to share. I was not harmed in any way, in fact I am far more sore from raking/gathering the leaves on my 1/2 lot here in Green Bay than from my little get-off. That was three days past I feel nothing and have no bruising.

If I can get any corrobative data from Avon to go with my results then it would be good info for many riders on this forum. At first I was really ticked that I missed something and goofed on my riding. Actually I still am, but if we all can learn something from this its not all a loss.

As to your question, on wet roads I concentrate on smooth actions and limit any control input that destabilizes the bike, even on throttle, clutch, shifting and braking actions. That is one reason why this caught me, because I have ridden on wet roads in high 30's temps many times. This turn was not wet, the day and the air was dry (low humidity), there was no film of dust on the road (that I could find), no obvious debris or winter car droppings (common in these parts), the sun had been shining on the road all day. So to me that leaves cold tires as the traction limiter.

Yeah, that temperature differential was very curious. I would have assumed the tire tread surface would have been the same temp as the air or the surface it was on. Now, my bike was on the centerstand before I took off. I took a tire temp reading at the leading (front) point of the tire, not just above where it contacted the surface. I may check that again when I get another go at this.

[Evergreen]

What tire pressures were you running?

[ANDYVH]

I have been running tire pressures in the 40 front and 42 rear range for years now, with no other adverse affects prior to this event. So I won't consider tire pressure to be at fault. At the lowest, my tire pressures "may" get down to the low 30's at worst.

[PGlaves]

I entered a right hand 90 degree turn, braking done, in 2nd gear and setup for the turn/steady throttle, pressed firm on the right grip to set the bike into the turn, and the front tire totally washed out into a lowside! I'm sliding briefly on the pavement, maybe rolled once, watching my bike slide and spin on the RH saddlebag and valve cover. DAMN! Everything came to a stop quickly, riding gear scuffed, bike still runnning on its side, I'm fine. It was maybe a 30mph lowside at most. I got up and ran to my bike, shut it off, then picked it up. The following rider caught up to me saying "Wow! I just saw you go down! You ok!!??" Yeah.

That is NOT approved R1100RS riding style. 10 demerits, and go to your room. :)

[EXR911]

Does your local municipality put down liquid calcium chloride solution ahead of possible freezing/snow events? If so there can be a very slippery, although temporary (1 -2 hour) situation under certain air humidity conditions, even when the temperature is well above freezing. And this can occur several days after the stuff has been put on the road.

PT9766

[irish]

Very interesting post, I'm glad you are okay! Since I got a BMW I have been riding much later in the year and I have lately been thinking a lot about how cold weather affects traction. Thanks for the info.

[ANDYVH]

Yes, I had recently thought of the calcium chloride as a new possible danger to motorcyclists. Last week, with an expected sudden drop in temps, both Green Bay and Depere (directly south of Green Bay) road crews were wetting the streets down with the liquid calcium chloride applied behind a sprayer truck.

I came across the stuff in my car, about two blocks behind the truck. At first I thought "what the heck, they're spraying water on the streets and bridges!?" Then it dawned on me its that new application. But this instance of my recent lowside, being on a county two lane highway, it was not the case of anything that I could tell had been applied to the road. It looked clea and normal to me.

But it does bring up a new aspect of possible low traction issues when you don't expect it. The application of calcium chloride applied wet, on dry roads, on days when you would not expect a sudden decrease in traction. Something new we all have to watch for if your riding season extends into late fall/early winter in locales where road crews are trying alternatives to road salt.

[R80RTJohnny]

Very glad to hear that you are OK and providing us with all this information. This really has the makings of a good article for next fall's ON. Great stuff - tire temps, road temps etc...

[Greenwald]

Very glad to hear that you are OK and providing us with all this information. This really has the makings of a good article for next fall's ON. Great stuff - tire temps, road temps etc...


I agree! As I said in responding to your PM to me the other day on this subject, this is great material for a MotoSafe article.

Especially when you consider that right now, your information is only exposed to this subterranian world we call 'The Forum.'

After all, with around 1,700 registered users, that's less than 5% of the MOA membership; 95%+ are still waiting to hear your story.

Stop posting and start writing - I am looking forward to picking up a future issue of ON and reading about your incident and research in detail! :type

[TomDac]

Very interesting! Any explanation how the "cold" tire could register only 20 degrees when the pavement was 27 and the air temp about 35? I would have thought that tire temp, after sitting long enough, would equal the air temp.



This was exactly my thought too. Weird.

[TexanRT]

very glad to hear that you are ok and providing us with all this information. This really has the makings of a good article for next fall's on. Great stuff - tire temps, road temps etc...

+1

[ANDYVH]

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.

[Lee]

I would think that being black, the tire would naturally have the same or even slightly higher temperature than the air temp.



That's true. Our cars have TPM and when parked facing east or west on a sunny day, the tires on the south side of the cars will read several degrees higher than the north ones.

[piperjim]

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.

piperjim

[Lee]

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?



No, wind chill does not affect tires, machinery, ect.
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.

[ANDYVH]

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.

[Lee]

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.

I live approx. two miles from work and I can see a one to two PSI increase on my car tires with the TPM display.

[rx35285]

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.

[BCKRIDER]

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!

[piperjim]

I found this posting on a Suzuki forum, and it was credited to a police bikers forum.
:thumb
"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. It’s 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 30’s and below, this becomes much more pronounced.

It’s 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."
:clap

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!!!

piperjim:usa

[marchyman]

I don't think we should be too quick to dismiss "wind chill" as a factor.

Wind chill is all about perceived temperatures. Tires don't perceive! Tires may not get as warm in the wind and they will cool to ambient temperature faster in the wind, but they will not fall below ambient regardless of the amount of wind.

[bogthebasher]

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.

Ride safe.

[R80RTJohnny]

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.

Ride safe.

Very interesting point. Where I live there are two factors that I take into consideration when putting away the bikes. The first is temperature - <3C is just about right (daytime high as this would equal -5C overnight). The second is when they start with the salt and the sand on the roads.

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.

[Cal]

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.

Cal

[41077]

Wish I'd seen this post before doing the very same thing yesterday, it was cold bike had sat in the wind for two hours and I hadn't gone 100 yards when I turned too sharply at 15 maybe 20 mph. Watching your bike slide away from you as you sit on the pavement sucks. I attributed my fall to the still fairly new tires and leaning the bike over to where the contact patch was the edge (chicken strip) portion of the tire that was slick. Roadway perfectly dry, ego and finger bruised. Glad I'm not alone but word to the wise if I had taken a more normal approach (faster-smoother) to the curve I wouldn't be thinking about body work this winter.

[piperjim]

Yes, my use of the term "windchill" was incorrect. I should have used
"convective heat transfer" to describe the effect of air movement on heat loss from the tire. While similar, the two terms are not identical.

As I said, I'm a product of the public school system:cry

piperjim

[ANDYVH]

Well I'll see if Avon Tire is interested in participating in the discussion. I just sent an email to their "Contact Us" section on their Avon USA website. I'm hoping to get some relative data on cold tire grip that I could use for an article submisson to the ON.

[ANDYVH]

I did get a response from Avon Tire, though not very detailed and noncommittal (as expected). But the response did details that Avon and most tire makers recommoend 15 to 20 miles of riding until the tires are sufficiently warmed. It also said the cold air does have a cooling effect on the edges of the tire even when the center of the tire is warming up. So the edges take langer to get up to temp.

[deilenberger]

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.

Cal

The question is - what's the temperature when you set the tire pressure? Chances are - by filling to a lower pressure at lower temps, you're actually filling the tire correctly.

I recently set mine at about 45F - to 34F/38R. Next day I took a ride in mid-30's temps. I have a tire-pressure-monitoring system that allows me to monitor not only the pressure (on a real time basis - every second) but also the temperature of the air in the tire. Leaving the garage, the tire temps were low 40's.

After riding for about 45 minutes, moderate speeds (never over 50MPH - it was also very gusty out, with 30MPH gusts, so no highway..) my tire temps had risen to about 60F. Tire pressure had increased to 38F/42R - and the difference was quite noticeable as the pressure increased.

BMW's recommended pressures are at 20C (68F) - any other temperature requires some compensation for the effect of heating or cooling the air in the tire.

In any case - my rule of thumb, below 50F consider traction much less then "normal" riding temps - and ride like it's raining (smooth, conserve traction, etc.)

YMMV (but Boyles law sez it won't..)

[Cal]

Don,

What you are describing is exactly what I do. The only exception is I have not quantified with instruments, etc; just my own gut feeling.

Cal

[rx35285]

Dropping pressure 2-3 psi to increase the contact patch and, therefore, traction makes sense.

I think I will continue to keep my tires at the specified pressure and adhere to the guidelines such as riding like it's wet when the ambient temp is below 50 and knowing that it takes a good 15-20 miles to warm the tires. That said, I wouldn't hesitate to lower the pressures if I were facing a few miles of slippery roads, re-inflating when the hazard is passed.

It seems to me tires should be set at the specified pressure at the current ambient temperature in which the vehicle is operated. On airplanes and cars were are always cautioned in cold weather to check pressures and bring them back up to spec. It has to do with load capacity and energy efficiency.

Don, it looks like you got a 4 psi increase for only a 15 degree temperature rise. Charlie Boyle must be turning in his grave. :) It would be interesting to know how much the tire temp increases with all things equal except ambient temp. Your experiment showed about a 15 degree rise with a 45 degree ambient. Wonder what it would be with the same ride, wind speed, same road surface, same weight on bike, ie, all things being equal, except an ambient temp of 70. It won't be much more than 15. In fact, the inability to control the other variables might make such an experiment invalid. Or maybe what's needed is a designed experiment for a Six Sigma pro.

Good discussion - it will help me be a better rider next spring (tonight's ambient will be about zero F) and it's good mental exercise for this mechanical engineer who likes thermal science.

[Evergreen]

I have been running tire pressures in the 40 front and 42 rear range for years now, with no other adverse affects prior to this event. So I won't consider tire pressure to be at fault. At the lowest, my tire pressures "may" get down to the low 30's at worst.

I asked what pressures you are running because I have always understood that tires that are over inflated (within reason) run cooler, even in the summer. I have verified this personally by taking tire temperature readings after riding at different tire pressures to try and find the optimum pressure to run a tire long distances at high speed on my trips over the years. I also have had airhead models that due to thier age lack reliable tire pressure recommendations from BMW because today's tires aren't comparable to those made when the bikes were new. I have always found that the higher the pressure, the cooler they run.

Some of the other posts about lower pressures causing more tire flex and heating while cornering seem to also support this approach. Also, I suspect that the larger contact patch caused by a tire inflated to a lower pressure may help to warm a larger section of the tread. You may want to try lowering the pressures to 36 on the front tire (or whatever BMW has in the manual for your bike) and try the experiment again. Then, try different pressures, maybe even lower.

I suspect that you will find a much wider section of tread being heated and therefore able to get you as much traction as the center of the tire can provide.


Regards,

Greg

[pffog]

...............
Some of the other posts about lower pressures causing more tire flex and heating while cornering seem to also support this approach. Also, I suspect that the larger contact patch caused by a tire inflated to a lower pressure may help to warm a larger section of the tread. You may want to try lowering the pressures to 36 on the front tire (or whatever BMW has in the manual for your bike) and try the experiment again. Then, try different pressures, maybe even lower. .....................

Lower pressure increases traction and heat generation. Most people at track days START at 30 psi front AND rear. Some lower, certain Michelins (I believe), recommend starting at 24PSI in the rear!

[ANDYVH]

Wow, the more this post gains responses the more info and background I have to add for an article I plan to write for the ON. Anything I use in the article from this thread will give credit to the source from this thread. Thanks everyone, I didn't expect this amount of discussion when I first posted this thread.

[bobs98]

Thanks for the insights guys.

Maybe I shouldn't be as concerned about running on slightly lower tire pressure when the temps are colder. Perhaps a "cold" pressure of 36 and 40 is too high for good traction? I like to ride thru the winter as long as the roads are clear, and have been as low as 14F for the ride into work. I have wondered about the stability issue, but have not had any problems so far in the lsat 5 years of sub freezing commutes.

Lots to consider here, with safety being at the top of the list.

[UncleMark]

Don't know if this will help.... Written awhile ago...

http://www.expressoriders.org/SMF/index.php?topic=247.msg1321#msg1321

The PDF has quite a bit of info...

After pondering my cold tire crash, here are some things that I haven't figured out:

*How long does it take for the whole tire to warm up if temps are in the 30s?
*Does the tire STAY warm after it's warmed up so long as it's rolling?
*Will the WHOLE tire stay warm, or just the center?
*Will the tread portions to the outside of center warm up in due course on their own - and stay warm?
*Are there warning signs that your tires are too cold (other than the outside temp)?
*How can we know if the tire can be trusted to adhere to the best of its ability?
*Should cold weather riding be limited to shallow lean angles?
*Is riding in the cold safe, even if we can keep ourselves warm?

Most of these questions get answered in some respect in that article. Is riding in the cold safe, even if we can keep ourselves warm? Yep...

[deilenberger]

After pondering my cold tire crash, here are some things that I haven't figured out:

*How long does it take for the whole tire to warm up if temps are in the 30s?
It may never fully warm up in 30F temps. Depends on speed, road surface temperature, and tire pressure.
*Does the tire STAY warm after it's warmed up so long as it's rolling?
Unlikely - I think the closer to the bead of the rim, the colder it's going to be.
*Will the WHOLE tire stay warm, or just the center?
"Stay"? I think not since I doubt if the entire tire ever gets warm.
*Will the tread portions to the outside of center warm up in due course on their own - and stay warm?
Somewhat probably IF you ride long enough, and your tire pressure isn't too high, and the ambient temperature isn't too low.
*Are there warning signs that your tires are too cold (other than the outside temp)?
Nothing I could say "Watch for.." I am very sensitive to tire feel - and traction - and they simply don't feel as secure when cold.. the response to inputs is different then when it's a nice summer day, and the tires have warmed up nicely.
*How can we know if the tire can be trusted to adhere to the best of its ability?
You can't - so don't ride at 10/10ths. I think I suggested - in cold, ride like it's wet - ie - smooth, don't take too much of the traction pie for any one item (braking, cornering, etc.) because there is less pie there.
*Should cold weather riding be limited to shallow lean angles?
Certainly a consideration.
*Is riding in the cold safe, even if we can keep ourselves warm?
Is ANY riding "safe"? I think not - it's all relative. Is the risk/benefit ratio worth it? That's for you to answer. For me - it generally is. My mental health benefits a lot from even a short ride in mid-winter. I feel less troll-like.. :)

[lkchris]

Don's correct, I believe, and nothing more than the fact that for cars at least there are "winter" tires said to be necessary when temps fall below 40 degrees F. Seems unlikely that would be a selling point were "normal" tires able to "warm up" to the point there's no problem.

Here's an article from Germany indicating that fitting winter tires (or all-seasons) is legally required over there. Interestingly the article (it may be an error) implies this applies to motorcycles, too.

http://www.magazine-deutschland.de/en/artikel-en/article/article/fines-for-german-drivers-not-using-winter-tyres.html

[ANDYVH]

In retrospect to what happened to me almost two weeks past, if I had decreased my tire pressures to increase traction (by way of added tire flex/deflection) I may have avoided my lowside. As it is, I did back off quite a bit in entering the turn compared to what I had done on that turn many times previously.

However, what I did do that morning, even though I had adjusted my speed down, was I applied my usual delayed-apex into the turn which requires a bit more assertive press on the right grip to initiate the lean. It seems that slightly over-assertive action did me in. Had I simply flowed through the turn with a bit more gentle touch at the grips I may not have gone down.

The analogy to ride riding is a good one, smooth and easy, with all control inputs.

[Paul_F]

Wow, the more this post gains responses the more info and background I have to add for an article I plan to write for the ON. Anything I use in the article from this thread will give credit to the source from this thread. Thanks everyone, I didn't expect this amount of discussion when I first posted this thread.
No, thank you Andy for bringing this to our attention. I had a friend slide out behind me a few years ago. He didn't know what caused his front tire to slide out. It was a very cold day in early April (and wet). After your posting this thread, I'm certain we have finally come across an answer. I often ride into mid-December (not this snowy winter) and I now plan on being much more careful in the cold weather and will use lower tire pressures. Thank you again Andy! :dance :ca

[ANDYVH]

Thanks for the support and comments, all appreciated.

Going back to the initial issue of how the tire could measure colder than the surface it was on, I think "emmisivity" is the answer. Emmisivity is the variance of heat dissipation of different surfaces, think of the heat emmision of a concrete parking lot (where my measurements started) versus the heat emmision of a black tire tread compound. That could easily account for the seven to ten degree temperature difference.

Now, had I been using an actual surface contact style thermometer versus one of those trick infrared digital thermometers the difference may have been minimal.

I can forsee more analysis/data collection coming next spring when I am riding again. Ohh, exciting,...data collection.

I need a life, heh, heh.

[DaveJohns]

Thanks for the support and comments, all appreciated.

Going back to the initial issue of how the tire could measure colder than the surface it was on, I think "emmisivity" is the answer. Emmisivity is the variance of heat dissipation of different surfaces, think of the heat emmision of a concrete parking lot (where my measurements started) versus the heat emmision of a black tire tread compound. That could easily account for the seven to ten degree temperature difference.

Now, had I been using an actual surface contact style thermometer versus one of those trick infrared digital thermometers the difference may have been minimal.

I can forsee more analysis/data collection coming next spring when I am riding again. Ohh, exciting,...data collection.

I need a life, heh, heh.

(I learned of this thread through a post on the Rounders web board, I can't seem to stop my inner geek from spouting something...)

+1 on emissivity. We love to trust what our instruments tell us. IR thermometers and imaging cameras are especially susceptible to giving 'false' readings because of how IR is radiated from particular surfaces. Roughness / distance (think signal noise and 1/r^2 law) / material composition / reflectivity / and even the angle of a surface wrt the camera can all affect how an IR camera 'reads' temperature. You can even see 'reflections' of temperature in a dull but flat metalic or ceramic surface with a FLIR camera - reflections of the heat of other things 'seen' in the surface as if looking in a cloudy mirror, regardless of the temperature of the surface the camera is pointed at.

A quick sanity check:
The first law of thermodynamics says that thermal energy flows from hotter things to colder things. Therefore, the tire cannot be colder than the things around it, unless something colder than the tire (and the environment) is pulling thermal energy out of the tire; pulling it's temperature below that of the environment. That's not likely.

What makes temperature rise? The absorption of energy. What makes temperature fall? Giving up energy. Temperature (change) of a material is inversely proportional to the specific heat of a material and directly proportional to the amount of energy gained or lost. Specifically: delta-T = Q/(Cv *m)... the temperature change in a thing [delta-T] is equal to the amount of heat energy it absorbs (or loses) [Q] divided by its specific heat [Cv] and mass [m]. ...I could continue with this level of analysis if it would be helpful in this forum: to look at the sources of heat generation and heat loss and what can happen to rubber temperature as a function of the environment and the location of the rubber.

Where I run out of expertise is where the rubber meets the road, so to speak. How does the coefficient of friction change as a function of temperature / rubber durometer / ?? / ?? / what else?... Yes, it would be nice if a tire expert could provide some adult-level 'unfiltered' data. Your typical support personnel on the other end of the address 'support@wemightneveransweryou.com' are capable of only parroting back to you information from published data and legal disclaimers. It's hit-and-miss even in the high-tech arena to break through the wall of tech support to get someone who can answer real questions. "I can read the data sheet. If the answer was on the data sheet I wouldn't be calling you..."

"Not everything that counts can be counted, and not every that can be counted counts." -Einstein. Very very true. There are many things that can cause a real world system to be different from an 'ideal' analysis. But, before we can begin to understand the general behavior of a system, we must begin at grapling with first principals.

"You can't ride at 10/10ths" is also +1!! advice. You gotta ride within the evelope you're given. Hopefully this thread will help more of us be better informed of the things that CAN pull in the edges of the permissible riding envelope.

I'll shut up now. I have no life. :blush

[ANDYVH]

One thing I do have some basis in is synthetic rubber compounds (our beloved tires are NOT rubber, but a synthetic man-made rubber like product). Rubber duromerter (the amount a specific type and thickness of rubber is deflected per a specific load) is affected by temperature.

As a tire gets colder, the ability of the tire tread material to deflect/displace/and grab into/on the roughness of the road surface is decreased. One way to offest this is to reduce the air pressure in the tire, which allows the tire carcass to deflect more per load. That deflection/distortion creates the heat the tire material needs to warm up and grip better.

Most synthetic materials like neoprene and nitrile (common to tires) get harder and less flexible as they get colder. So the tread surface cannot deflect as easily to grab the road surface. Less grip = more slip unless the speed, side load and lean angle are decreased or the loading transitions are applied much more smoothly like we normally do during rain riding.

[DaveJohns]

Most synthetic materials like neoprene and nitrile (common to tires) get harder and less flexible as they get colder. So the tread surface cannot deflect as easily to grab the road surface. Less grip = more slip unless the speed, side load and lean angle are decreased or the loading transitions are applied much more smoothly like we normally do during rain riding.

Yup... and the tires will never achieve the same running temp in cold weather as they will in hot weather, no matter how long you ride. The rate of heat extraction (cooling rate) is proportional to the temperature difference between the tire and the environment. The temperature stabilizes when the rate of heat generation is equal to the rate of heat extraction. So, if your tires stabilize at 20 degrees warmer than the road in the summer, and the rubber DIDN'T get harder in the cold (the rate of heat energy does NOT change), they'd still only achieve 20 degrees warmer than the road in the winter, which is a lower temperature. But, since the rubber DOES stiffen, and heat is generated at a lower rate when cold, the delta-t is probably lower in the cold, which makes your peak tire temp even colder.

The dynamic coefficient of friction is lower than the static coefficient of friction. Therefore it takes more force to get two surfaces to slip between each other than it does to maintain the slip motion once it is started. That's why 'abrupt' changes can cause slip and a washout. What is an 'abrupt' change? Any change in speed or direction requires an acceleration. Acceleration is a change in velocity with respect to time, where velocity is defined as a vector which contains both speed and direction. So, the more 'abrupt' the change, the higher the brief acceleration. F = ma, so a brief acceleration requires an impulse force. Changing speed or direction slowly will decrease the impulse force required to make the change. But, if that impulse force is greater than the product of the mass of you and your bike multiplied by the static coefficient of friction, the tires will slide, and once they are sliding, it takes less force to remain sliding than it took to start the slide, so nature determines the slide will continue unless you can correct for it and regain static contact with the road.

Side note: In a stable turn, centripital force F = (mV^2)/r acts radially outward horizontally from the COG (this is your side load), and the gravitational force F = mg acts vertically downward from COG to the ground (this force times your static coefficient of friction must be greater than the side load, or a slide will begin). But, in the lean, the resulting vector forces normal to the centerline of the bike/rider system (proportional to Sine(angle) times side load and Cosine (angle) times force of gravity) are equal and opposite. The lean angle always adjusts to maintain that equalibrium. So, when the centripital side load is less than gravity times your mass times the static coefficient of friction, your tires are in static contact with the road (with the higher static friction force). When your side load force exceeds the friction force limit, the rubber slips, and at that moment in time, the lean angle is too acute to maintain equalibrium. The result is that gravity pulls the center of the bike downward, increasing the lean, making the situation worse. It's a positive feedback instability that tends toward the bike laying down on its side. Gravity wins. That's why low sides occur.

Many things will affect the static coefficient of friction: tire durometer, sand, water, oil, road roughness, paint, leaves, tar snakes, snow, ice... the reduction in traction due to the temperature effect on tire rubber durometer is only one variable out of many that affects how hard we can start, stop, and turn.

Side note: There is a point during a typical 'fishtail' where the sideways motion of the rear wheel stops and swings the other way. If the tire 'grabs' - that is, if it regains static contact w/ the road, the coefficient of friction takes a unit step upward in magnitude. The lean angle required to maintain equalibrium during the slide in the moment prior to the 'grab' is not correct to maintain equalibrium with the higher static friction. The result is that the bike flips forward. The centriptal force wins. That's why 'high sides' occur.

I think we know these things intuitively just from watching the way the world works from the time we're toddlers. But, it's neat to look at the underlying physics of why these things happen.

I hope this has beneficial in some regard.

[ANDYVH]

I understand this one too, as I ride dirt bikes and an ice bike:

"Side note: There is a point during a typical 'fishtail' where the sideways motion of the rear wheel stops and swings the other way. If the tire 'grabs' - that is, if it regains static contact w/ the road, the coefficient of friction takes a unit step upward in magnitude. The lean angle required to maintain equalibrium during the slide in the moment prior to the 'grab' is not correct to maintain equalibrium with the higher static friction. The result is that the bike flips forward. The centriptal force wins. That's why 'high sides' occur."

I have had occassions to get the rear tire to break loose in corners while riding a R1200GS. The rear tire slide was very predictable and easy to control. The key is to NOT chop the throttle closed if rear tire slide occurs. Doing that will cause sudden grip and the bike can high side quickly with terrible results.

[DaveJohns]

I remember the MO DMV manual for motorcycle riders cautioning to keep the rear wheel locked in a skid, and not let off the brake until the bike is stopped. I think the CA manual had the same warning...

The same thing would apply to a power slide - keep it going! It looks cool too, and feels great. Ride on!

[Terry Karney]

Wind chill is all about perceived temperatures. Tires don't perceive! Tires may not get as warm in the wind and they will cool to ambient temperature faster in the wind, but they will not fall below ambient regardless of the amount of wind.

That's not quite what wind chill is. Wind chill (and it's been modified a few times tin the past 10 years, one learns a lot as an NCO in the Army about things like this), is a function of how the wind removes heat.

If the air is still, the warmth of your body heats the surrounding air, and so less energy is needed to keep the body warm. The principle of layering is to keep that air near the body from moving so much, and so keep the radiant energy of the body in a place it can be used.

Wind, of course, removes that layer of heated air.

Tires, not being animate, don't work in the same way. They absorb energy from the surroundings, and radiate it back; because thermodynamics means they will move to stasis with their environment.

That is also why, though I'd have to see the actual conditions, the tires were colder than the ambient. By excluding incoming radiation one can make ice in the desert, merely by digging a hole, and exposing the water to the nighttime sky. It's a quirk of how things work that a the water is trying to heat the whole of the sky, and it can't.

Given the right conditions, the tires, in a colder environment than N. Africa (where I learned of this trick being done), could have been doing the same thing. If they, like water, were shedding heat in a situation where there was no source of incoming heat, to balance them out, they could have been trying to warm the surrounding atmosphere, and so gotten colder than ambient. It's counter-intuitive, but it's possible.

[BCKRIDER]

Anyone else not understand the last two paragraphs of the above post? I'm not sure if my IQ is slipping, someone can provide a clearer explanation of a real phenomenon, or this is nonsense.

I would have bet my bottom dollar (well, maybe not) that 1. a tire off the ground and out of the sun would eventually reach exactly the same temperature as the surrounding air, and 2. a tire in contact with colder ground than air temperature would be very close to air temperature.

Not sure what this has to do with scary performance of cold motorcycle tires, but it's always good to learn something new. Let the explanations continue.

[brewmeister]

Is a simpler explanation like when you take a room temperature bottle of beer and place it into a bucket of ice then spin it around while in contact with the ice thus making the beer cold in a matter of a minuet or so versus leaving it just sit in the refrigerater and the cold air in the frig makes the beer bottle cold but it takes longer?

[E_Page]

Is a simpler explanation like when you take a room temperature bottle of beer and place it into a bucket of ice then spin it around while in contact with the ice thus making the beer cold in a matter of a minuet or so versus leaving it just sit in the refrigerater and the cold air in the frig makes the beer bottle cold but it takes longer?

I think it's more like when you take a really cold bottle of beer, open it and it instantly turns to beer slush.