Slower In
Winter?
There is frequently much discussion as to why we cycle slower in winter than in summer.
There are several reasons put forward for this often observed phenomena, some of which are
well reasoned and some of which are pure nonsense.
Why Slower?
Some of the reasons put forth for slowness in winter are as follows:
- Cold Bearings and grease are stiffer and harder to turn
- You need your energy to keep warm
- Your tires are colder and therefore have greater rolling resistance
- You tend to ride softer tires for better control on ice
- Your clothing is bulkier, making it more difficult to push your shape though the air.
- You are dressed in heavier clothing, making that much more weight to carry
- You are dressed in heavier clothing which resists your movement making pedaling harder
- People simply don't like generating the steam-bath like atmosphere inside of winter
clothing, and therefore psychologically resist working as hard as in summer
- Air Density is greater and impedes your progress through the air
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Are
We Slower?
There is one school of thought that holds that we are not indeed slower at all, and any
difference in speed is comparing apples to oranges in that we are riding different
equipment (mountain bikes instead of road bikes) using different tires (fat tires, perhaps
with studs rather than road tires) and carrying more weight of clothing, boots, etc.
Now I won't volunteer to do a time trial on my road bike, at 5 degrees, dressed in my
summer shorts and short-sleeved jersey in winter.
And I admit, that when pressed for time, or feeling spunky, I can still achieve my
summer speeds on my road bike in winter.
But its a lot more work. I'm about 3 to 5mph slower in winter riding the same bike and
the same tires. If I switch to my studs the difference is greater still.
These numbers seem to agree with those reported by other members of the ICEBIKE mailing
list. We do indeed seem slower in winter! |
Lets examine each of these claims and attempt to weigh each as a factor in determining
winter speed differences. In some cases the data is not readily at hand, and we will have
to use intuitive measures. We will assign and estimate of overall effect to each factor.
If a factor is correctable, it gets the weight of its corrected state.
1 Cold Bearings.
 Cold bearings are
indeed slightly stiffer to turn. This can be very pronounced if you have water in your
bearings and they have frozen solid. Too heavy of a grease can cause problems in your
freewheel when you want to coast, the chain wants to keep turning the cranks. You might
also find your cranks difficult to turn in really cold temperatures. (If this is the case
you want to check our Winter Maintenance page).
But this is, in the end, a maintenance problem, like a dry chain, or a rubbing brake.
One that most ICEBIKERS take care of before they start complaining about it slowing them
down significantly. It can be fixed by the application of the proper grease.
Try this test: suspend your front tire, and give it a spin, making sure the brakes
don't rub. Time it till it stops. Try it again after the bike has sat out over night. Try
to spin it with the same amount of force. Time it till it stops. You should find a small
difference between the two times. This difference represents the degree of increased
rolling resistance attributable to cold bearings. If the spin down time is cut in half,
then the miniscule part bearing friction plays in slowing your
bike in warm weather is twice as much in cold weather.
However, two times zip is still zip. Bearing friction is never much of a factor in well
maintained bikes. It is easily swamped by tire inflation, which in turn is swamped by
aerodynamic drag.
Harder to test and more likely to be a source of increased resistance is your crank.
You just have to go by feel as you hand turn it backwards when cold. Or derail the chain
on the inside so that it is off the chain rings all together. Now give the cranks a spin
and they should whiz around freely. If not, it might be time to overhaul the Bottom
Bracket.
Correctable to Estimated Maximum Effect: 1%
2 Using Energy to Keep Warm.
If you've been ICEBIKING for more than three days you already know that you generate a
lot of heat while cycling in winter and that dressing too warm can cause problems. No
significant amount of energy is being diverted to keep you warm, you are pumping out way
more heat than you need anyway. Sorry, that dog won't hunt.
Estimated Maximum Effect: 0%
3 - 4 Cold Tires.
Cold tires can be stiffer, as anyone knows who has gotten into a car at 40
below and CLUNKED down the street on "square" tires. After a few blocks, the
heat of flexing warms the sidewalls enough that this effect disappears.
This must pertain to bicycles too, but I have no idea of how to measure
the effect. Perhaps some of the tire companies have a handle on this.
Related to this is the fact that we often run our tires at lower inflation
in winter (for better traction). This, while a real source of increased rolling
resistance, is not germane, since we are usually wise enough to take it into account.
Besides, some of us ride the same tires year around, varying only the pressure. In the
Dead of winter, on bare pavement, we will run the same pressure as in summer, and still
feel slower.
Combining these two effects, rolling resistance may be higher just due to
colder temperature air in the tires creating a lower pressure. Tires inflated in a warm
house will seem under inflated after being outside at 10 below. Again I would expect this
effect to be small.
Therefore, Items 3 and 4 are jointly attributed a rather small effect,
which for sake of argument, and until better data comes along, I will arbitrarily set at
an overall effect of 3%, which I believe is generous.
Estimated Maximum Effect 3%
5 Less Aerodynamic Shape.
Even the same rider on the same bike is bound to be less aerodynamic in
bulky winter clothing than in summer shorts and a jersey. Even baggy summer shorts and a
sloppy Tee shirt.
A rough measure of this can be obtained by measuring your width in a
jersey and comparing that to your width in your winter clothing. The width of your arms
may almost double, your torso may grow by 2 to 4 inches in width. Most likely, those
riders that are concerned about being aero in summer carry this concern over into their
winter riding. There is only so much you can do in the way of aero clothing when it gets
really cold.
On a flat road, aerodynamic
drag is by far the greatest barrier to a cyclist's speed, accounting for 70 to 90
percent of the resistance felt when pedaling. The best aero tuck of professional cyclists
still yields a constant 6 pounds of drag while riding in calm air.
A more upright MTB is closer to 10 pounds.
Jim Martin is a doctoral candidate at the University of Texas and is the
Director of Sports Science for Team EDS. He has served as a consultant for USA Cycling's
Project '96. Jim has used a mathematical model for cycling in his studies of aerodynamic
drag.
One of the interesting tidbits in Jim's data is that body size does play a
part in drag calculations as you would expect. Larger riders suffer more drag. Jim found
that this did not tend to handicap them because they also had more power, the power
increased with body size faster than drag did.
For a regular bike (no aero wheels) a 200 pound rider suffered a pound
and a half more drag than a 125 pound rider. This was due solely to body
size.
This may be comparable to the increase in drag
due to bulky clothing. It may well be that a 125 pound rider bulked out in winter gear now
suffers the drag penalty of a 200 pound rider, without the benefit of the additional
power.
If the numbers are anywhere close, this represents roughly a 15%
penalty for winter garb. I suspect it is less than that, because many winter
cyclists wear winter tights so that their lower half is still about as aero as in summer,
except for the larger boots flailing through the air.
Therefore, I think there is some evidence to attribute a fairly large
effect to the drag-ie nature of winter gear, and I will arbitrarily assign a range as
indicated below. (We can argue about later).
Estimated Maximum Effect 5 to 10%
6 More Weight.
More weight due to winter clothing is unlikely to cause the difference in
speed of the degree we notice in winter riding.
Again, Jim Martin has estimated that a 5 pound increase in weight will
only cost you an additional 30 to 50 seconds over a 40k constant climb of a 3
percent grade (70 minute run), and far less on flat ground. Weight itself is not a
significant penalty unless it includes bulk, and bulk's penalty comes from drag. On hills
weight does matter, but no more so in winter than in summer. I've assigned this a weight
equivalent to 30 to 50 seconds out of a 70 minute run.
Estimated Maximum Effect 0.8%
7 Hard to Pedal in Heavy Clothes
Anyone who has ever tried to ride in tight blue jeans knows its harder to pedal in
inappropriate clothes. This can really affect the up stroke where your leg is generating
little real work anyway.
The difficulty in finding good cold weather riding tights may necessitate use of cloths
designed for other sports, or several layers of tights and long underwear. Even when super
cold weather tights are found, they are somewhat more bulky and can add to the effort
involved.
This is really hard to quantify because there exist no measurements of how hard it is
to bend your leg. I asked a Physical Therapist if there existed such a measure. She just
laughed at me.
Many riders report increased resistance well before the need to break out the really
stiff winter tights, often beginning to be noticeable at just above freezing. So while
this is a real problem, we are going to give it a lower effect rating because we just
can't measure it.
Estimated Maximum Effect 1%
8 Discomfort Avoidance
I often find I am reluctant to work hard and generate a sweat when dressed for cold
weather. Lets face it, in spite of the claims of breathability. of modern fabrics, they
don't really start breathing until the "microclimate" inside of them is way
warmer and wetter than you would like. I imagine that a hot muggy day in Alabama might be
almost as appealing for a workout.
I will be the first to admit that this may be an indication that I am over dressed for
the conditions at hand. (And still they ask "Aren't you cold out there?")
It is a strictly a psychological barrier, and winter cyclists can do something about it
such as gauge the temperature more closely, and you can force yourself to work harder.
Still, it does present a deterrent, although I would be hard pressed to rate it or
measure it, but I don't think it is a real significant.
Estimated Maximum Effect 1%
9 Higher Winter Air Density
Air density can play a surprisingly large part in winter cycling. Winter temperatures
in the range experienced by ICEBIKERS can drive air density up significantly.
| As air gets colder, it gets more dense. There are more atoms
of the various composite gasses and water molecules occupying less space. Per unit of
volume, the air weighs more. At left is a table of air density values in Kilograms per
Cubic Meter of air. At 77 degrees (F) one cubic meter of air weighs 1.18 Kilograms. By the
time your down to Minus 40 it weighs 1.5 kg.
If your frontal area when on your bike is one square meter (probably close) and you are
moving at 25kph (15.6mph), you will move about 7 meters a second and you will push 8.26 kg
of air out of the way every second.
That's in summer. In winter, at about 5 degrees (F) (-15C) you must push 9.57 kg out of
the way every second. That's 15% more work every second.
If you are used to a level of effort sufficient to carry you comfortably along at 20mph
(32kph) you will find you have to work 15% harder, or accept a speed of 17mph (27kph).
At lower temperatures, this additional effort can amount to over 25% more work.
When combined with other factors that slow you down in winter, this can be a
significant impediment. ICEBIKING should make a great training program.
- Note: cold air can hold less water vapor than warm air. Water,
as we all know, is heavier than air, but water vapor is lighter than air. As a
consequence, moist air is lighter than dry air. These tables and graphs were calculated
for sea level and zero percent humidity. If you factor in the moisture content of
summer air, the density could well be less than 1.18kg per cubic meter. Since winter air
is usually very dry at low temperatures, the difference in air density may well be more
than this conservative analysis points out. The effect of water vapor is not great,
which is why it was factored out of these figures.
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Degrees
F |
Degrees
(C) |
Air Density
(kg/m3) |
Percent
Chg. |
77.0 |
25 |
1.184 |
0.00% |
68.0 |
20 |
1.204 |
1.71% |
59.0 |
15 |
1.225 |
3.47% |
50.0 |
10 |
1.247 |
5.30% |
41.0 |
5 |
1.269 |
7.19% |
32.0 |
0 |
1.292 |
9.16% |
23.0 |
-5 |
1.316 |
11.19% |
14.0 |
-10 |
1.341 |
13.31% |
5.0 |
-15 |
1.367 |
15.50% |
-4.0 |
-20 |
1.394 |
17.79% |
-13.0 |
-25 |
1.423 |
20.16% |
-22.0 |
-30 |
1.452 |
22.63% |
-31.0 |
-35 |
1.482 |
25.21% |
-40.0 |
-40 |
1.514 |
27.90% |
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Estimated Maximum Effect 10 to 20%
Conclusion:
If we take just the two big ticket items from the above
list, Higher Air Density, and Less Aero Shape
(drag) we have forces at work (and some numbers to back them up) that can account for 15
to 30 percent greater effort to maintain the same speed, or 15 to 30 percent reduction in
speed.
So using these numbers, a 20mph rider gets reduced to 14 to
17mph (30% and 15% reduction respectively). The 17mph rider gets knocked down to 14 or
even 12 mph.
We have therefore accounted for typical speed reductions
reported by die hard ICEBIKERS, without having to resort to use of those factors of which
we are unsure.
When you add to this an allowance for lower tire pressure,
the added rolling resistance of studs, the increased wind in winter, and the effort needed
to plow through snow or slush you will see that there is ample reason that we are indeed Slower
In Winter.
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