Low temps = lower traction, and a low side!

[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

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/in...sg1321#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/e...ter-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.