"Crr vs Temperature, p.1
""Did you know that Crr [Coefficient of Rolling Resistance] changes drastically with temperature changes? I didn’t. And I don’t remember seeing any data to this effect in any of the bicycle literature. I believe I have sufficient data to show that indeed it does change.""
http://www.recumbents.com/mars/pages/proj/tetz/other/Crr.html
[I can't get past the first paragraph, but it's now my official excuse thru March.]"
Slower in the cold? Yes, it's true! Now it can be told.
Tue, 11/29/2005 - 12:30pm
Tue, 11/29/2005 - 12:52pm
#1
I am slower too for probably several reasons
With best intentions, I left Stamford, CT on my bike for the Sunday Hogwich ride. Got there at 8:40am. Missed the ride by 10 minutes along with six other people. Ended up doing my usual Bear Mountain bridge loop - albeit at a slow 18mph on the flats versus 21mph on the flats.
I checked the temperature affect using: http://www.kreuzotter.de/english/espeed.htm
and that only turned up a .5 mph impact. My guess is the other factors included the additional aerodynamic drag of winter clothing and the added leg muscle resistance of long winter pants.
Tue, 11/29/2005 - 2:04pm
#2
Stamford to the GWB
Bob, how long does it take you to ride from Stamford to the GWB, assuming you take Route 1?
Tue, 11/29/2005 - 2:09pm
#3
Stamford, CT to GWB
On the warmer days I can get to the NJ side of the GWB in under 2 hours - mostly going down route 1, across Gun Hill Road, left on webster, right on Fordham, left on Nagle, and up Broadway. A total of 33 miles with one brief stop for a powerbar and several stop lights.
The colder weather and GWB north side stairs slowed me down by 10 minutes - just enough to miss the Hogwich ride. Bummer.
Tue, 11/29/2005 - 2:15pm
#4
That's about 30 miles to the bridge, right?
I give you a lot of credit!
Tue, 11/29/2005 - 4:42pm
#5
sorry
sorry you missed the ride, although we still have a whole winter of hogwich rides.
the best thing about leading rides is that you can try to rectify things about other rides (that you don't lead) that irk you. my biggest pet peeve about nycc rides is that they always leave 10 to 20 minutes late for some reason. i might wait for 5 minutes, but only if i'm expecting somebody i know is coming but isn't there yet. otherwise, maybe i wait 2 or 3 minutes.
todd
Tue, 11/29/2005 - 3:22pm
#6
?
This guy's methodology and conclusions, while detailed, are flawed. Tire compounds tend to become more rigid as temperature decreases, which decreases rolling resistance. As Bob pointed out, there are several reasons why its harder to ride in the cold, increased air resistance being one reason and the primary reason.
It may also be the reason for missed field goals as the football season progresses...
Tue, 11/29/2005 - 6:00pm
#7
Article on air density and aero drag...
While maybe not totally scientific, this article was interesting and supports the drag from air density in cold weather.
http://www.icebike.org/Articles/SlowerWinter.htm
Tue, 12/13/2005 - 6:24pm
#8
Bob Shay wrote;
>While maybe not totally scientific
Ok what do you think was missing to make my tests so called scientific?
john Tetz
Wed, 12/14/2005 - 5:04am
#9
My comment...
"My comment refers to the www.icebike.org link, not your test. However, I am interested in understanding the factors that might affect my speed on a bicycle - including rolling resistance.
""High Tech Cycling"" by Ed Burke(2003)has been the most informative work that I have seen on the subject of riding faster. On page 5 he says - ""On level road with no wind at speeds below 8 mph, tire and bearing rolling resistance are the dominant retarding forces. However, wind resistance increases as the square of bicycle speed, while rolling resistance increases only slightly with speed. Above 8 mph, air resistance overshadows rolling resistance. In fact, at speeds over 25 mph, wind resistance is responsible for over 90% of the retarding force on a traditional road racing bike.""
He talks a lot about how to minimize tire and bearing rolling resistance. But, he doesn't touch on the impact of temperature change. So, I read your article with interest.
If my speed on flat road is reduced to 18mph when the temperature is 30 degrees F versus 21 mph when the temperature is 75 degrees F, how much of that decrease in speed can be attributed to tire and bearing rolling resistance?
Bob
P.S. my current understanding is that in the cold, cycling speed is reduced primarily as a result of increased air density and air drag from larger mass winter clothing."
Wed, 12/14/2005 - 6:45am
#10
bearing rolling resistance? seeing the forest through trees
Changes in rolling and air resistance due to cold weather are inconsequential in relation to the impact it has on the performance of the engine. For an aerobically demanding activity, the colder weather impacts the performance of the rider of much greater significance. For instance, it takes allot of energy to warm and moisten the cold, dry air you breath in.
Wed, 12/14/2005 - 7:51am
#11
From www.naturalstrength.com
Peter:
Here is some information I found on the web to support your point, but I don't believe the calorie expense is significant enough to significantly reduce cycling speed. Do you know of any other support?
Do I burn more calories when I exercise in the cold?
Cold weather itself does not increase calorie needs. (And remember: the weather can actually be tropical inside your ski outfit or running suit!) Your body does use a considerable amount of energy to warm and humidify the air you breathe when you exercise in the cold. (For example, if you were to burn 600 calories while cross-country skiing for an hour in 0 degree weather, you may use an estimated 23 percent of those calories to warm the inspired air.) But you use the heat you generate with exercise to warm the air you breathe and prevent your lungs from getting chilled. Hence, you might not sweat as much. But, you don't burn extra calories--unless your body temperature drops and you start to shiver. In the summer, you would have dissipated this heat via sweat
from: http://www.naturalstrength.com/nutrition/detail.asp?ArticleID=227
Wed, 12/14/2005 - 8:30am
#12
sure
I think it's easier to understand, if first you treat energy expenditure as a constant. That energy used to warm and humidify the air you breathe is not being used to propel you forward, e.g. it's diminishing the efficiency of your power output. Conceptually, it's analagous to running the air conditioning on high in an econobox car while driving on the highway. It really cuts down noticeably the speed (acceleration) abilities of the car.
Wed, 12/14/2005 - 11:40am
#13
effort
Or, if you were not using the 23% energy to warm the air, that energy would be available to increase your speed. So, only 462 calories (and the resulting wattage) are being put into speed. If you weren't warming the air, you would have extra effort available to go into moving you faster.
As to the original question: Based on my coasting speeds downhill being much slower this time of year, I am still a big believer of wind resistance being the culprit.
Wed, 12/14/2005 - 11:43am
#14
coasting speeds downhill being much slower
Winter clothing, like windbreakers will do that.
Thu, 12/15/2005 - 9:05pm
#15
Crr vs temp
"Roberty Shay wrote;
>In fact, at speeds over 25 mph, wind resistance is responsible for over 90% of the retarding force on a traditional road racing bike.""
....Robert got to the following URL which has much of what I and a couple of learned friends put together with a few spreadsheets and associated texts to help teach people about this subject and how to make the measurements.
http://www.ihpva.org/tools/index.html
Go to the SS PDGus1 and plug in some numbers (only in underlined cells). Your CdA for an up right will be around 2.9 Your Crr will be around .004 to .005.
A recumbent CdA is more like 2.3
In this SS is a power distribution chart so you can see where the power is going. Change your speed and see what happens.
This is a good SS to play ""what if games""
John Tetz"
Sun, 12/11/2005 - 6:04pm
#16
Actually, no. Tetz has it right.
Most of Crr (rolling resistance) comes not from friction with the road... but hysteresis loss as the casing is repeatedly deformed as the contact patch moves arount the tire. Like a spring, you get most of that energy back, but some is lost to heat. Running an undernflated motor vehicle tire can generate so much hysteresis heat the components of the tire melt and the carcass flys apart.
The casing is a nylon and 'rubber' sandwich...both of which get harder to deform as they get cold. Road friction probably does go down too but that effect is dwarfed by the increased casing hysteresis.
The property of the casing are the key. That's why racing tires have the thinnest most 'supple' possible casings. (the compounds are virtually, if not actually identical) That's also why proper inflation matters a ton. Higher pressure = less hysteresis = less contact patch deformation = faster. An underinflated tire can rase Crr to the point where we actually notice it. A properly inflated training tire is faster than an under-inflated racing tire.
Mon, 12/12/2005 - 6:05am
#17
More
A while back on another message board there was a big discussion on which has lower rolling resistance, tubular tire or clincher tires, with lots of discussion back and forth until Tour magazine did a fairly comprehensive test showing that under the conditions of there test, clinchers in general had lower rolling resistance than tubulars, with the best clinchers having 20% lower rolling resistance than the best tubulars, under the stated conditions. Before this test, data seemed equivocal and some still believe it to be so.
While this test did not address temperature, ancillary discussions briefly covered this topic, with several sources indicating that a stiffer sidewall reduces rolling resistance and with cold temperature generally resulting in lower rolling resistance, with one manufacturer warning of significantly reduced grip at 7 degree C. Regarding bicycle tires, one well known and oft quoted source made a comment that one could pick out a low-rolling resistance tire based upon sidewall stiftness. Missed was any actual test data to support these various claims.
My concern with Tetz' test was that there where key measurements affecting his test that he did not have the proper equipment to measure. However, when calculating the standard deviations of some of his test results, the spread is fairly tight. Moreover, I did find an SAE paper that does refute the sidewall stiffness and general cold rolling resistance claims of other sources. Interestingly, this paper's data indicates a cold temperature rolling resistance trend similar to Tetz.
Why the differences? Its possible that laboratory tests, done on a smooth cylinder provide one set of data while road test provide another. This is because pneumatic tires roll over road imperfections through deformation. OTOH its also possible that different tire construction may behave differently.
Tue, 12/13/2005 - 6:26pm
#18
John Z wrote;
>My concern with Tetz' test was that there where key measurements affecting his test that he did not have the proper equipment to measure.
Ok what equipment was missing ???
John Tetz
Tue, 12/13/2005 - 7:23pm
#19
Electronic Timer
An electronic timer for start/stop, but only to add to precision. You should send Tom Compton an email, because your measured change in rolling resistance is quite significant.
Thu, 12/15/2005 - 9:13pm
#20
Crr vs temp
Hello John Z;
>An electronic timer for start/stop, but only to add to precision. You should send Tom Compton an email, because your measured change in rolling resistance is quite significant.
.....I would love to have a data logger to record a more accurate initial speed coming into the coastdown trap and time coasting over the measured distance (although clicking a stop watch over the time distance is good enough). But I dont have the electronic background anymore. Got any ideas?
My measrements although not as dead on are sufficient enough to show significant trends.
Who is this Tom Compton person?
John Tetz
