North Coast Joe

Thanks in advance for any answers! A noob with bunches of questions....

So, after about two months of riding, I'm up to 20mi/day (delighted with the weight loss already). Being a noob, I now realize that darkness and/or snow & ice conditions reduce my average speed by up to 50%. Is twenty miles at a 6mph average equal to twenty miles at a 12mph average? Mr. Nelson (my former physics teacher) says it's the same amount of work....it sure doesn't feel like it is, though!?!

Really surprized at how sure-footed my bike is on snow and ice, though I can't stress the reduced speed factor in snow. A two foot wind drift across the road brought my to an abrupt halt! My thought as I carried the bike through the remainder of the drift: "This is gonna kill my average speed!"

10 Wheels

Average speed is a personal thing that doesn't mean much to another rider in other riding conditions.

Just have fun riding untill you get in about 2,000 miles.

Then you can work on speed and up your average.

Want to compare your riding, join:

https://www.bikejournal.com/home.asp

Rowan

Practice (the real world) often trumps theory (the ideal world). Your averages are influenced by a number of things, ranging from road conditions, to how your body functions in cold compared with warmer temperatures.

For you, the rider, the work will be more difficult if you have to ride through a thin layer of snow, for example, or if the wind is blowing into your face, even at half a mile an hour.

If you are cold, your body will concentrate on keeping you warm first, and won't pay that much concern for the muscles on your limbs and extremities. That will reduce your efficiency.

Then, you are likely carrying around more clothing that (a) will weight slightly more than otherwise and (b) likely will be slightly more restrictive, so your legs in particular will be working harder to overcome that restriction.

Average speeds may be a guide to fitness in a very generalised way. But rarely are the conditions on two rides the same. I think you've already discovered that.

Bluish Green

20 miles a day is awesome, great job so far.

As far as the physics, in a lot of the scientific calculations, assumptions are made about frictionless surfaces, etc. In the real world, you have varying wind conditions (including increased wind speed due to increasing your speed), work needed against rolling resistance in tires, varying road surfaces, work lost in flex of suspensions, etc. It's a lot more work doing the same distance at higher speed.

Also, many of us have noticed that our average speeds tend to drop as the temperatures drop, due to a number of different factors - more weight carried due to clothing, more resistance in grease and lubricants on bike, higher density of air, etc.

When it's cold, I find that pre-ride stretching is more important to keep my flexibility and avoid injury. I also have learned to actually dress warmer on my legs than my torso, to keep my legs warmer at lower speeds.

Good job so far, keep it up! Snow is one thing, but ice is very dangerous if you don't have winter tires with carbide steel studs. Studs help keep you upright on ice but don't do anything in snow. Knobby rubber helps with traction in snow but does nothing on ice.

Welcome!

Bill Kapaun

Wind resistance is supposedly factored as the cube root of speed.
So, it takes more than twice as much work to go twice the speed, while it only takes 1/2 the time to get there.

I'm much slower in cold weather, but don't worry about it.

Myosmith

KE=MV2/2 *

The amount of energy required increases exponentially with velocity. While the total amount of work is the same you will have to put out significantly more watts to accomplish the same amount of work in half the time. The demand for wattage (energy) increases in an exponential, not linear, manner as you increase speed. So while you moved the same number of pounds over the same distance, the energy needed to accomplish it at 12 mph is significantly more than to do so at 6 mph.

This exponential increase is why it takes X increase in energy to double your speed, but X2/2* to double it again. You are also dealing with increased friction and aerodynamic drag.

* sorry but I can't superscript the exponential notation here so assume the small two is the exponent.

North Coast Joe

So, the total kinetic energy equals (mass X velo) squared then divided by two? A great answer to why going slowly in the dark feels easier than the same route in dry daylight conditions.

Thanks to all for the answers....especially those who convinced me to forget it and just have fun. I'm so fat it's a benefit to be out there at any speed, and it's such a delight to move so quickly and quietly. Nice machines, these bicycles!

10 Wheels

Hey Joe,

Night ridng is so fun.

Do you have a tail and head lights?

TwoFourOne

(mass * velocity squared) / 2.

Myosmith

TwoFourOne cleared it up nicely. You only square the velocity, not the mass as mass' effect on KE is linear. The formula can also be expressed as (half of mass) x (velocity squared) = KE. As noted, in the real world there are numerous variables including the resistance from deep snow on the road surface, extra weight and wind resistance of clothing in cold weather, viscosity of lubricants in wheel and BB bearings at different temperatures, and compliance of tires on a cold vs. warm surface, even air density. I'm sure there are more.

+10 on having fun and enjoying the ride, but the geeky stuff is kind of fun too, at least to some of us. In the winter I used perceived exertion (qualitative) to gauge my efforts much more than average speed or other quantitative factors.

chisler

This is indeed the energy required at a given velocity ,in a nice world without friction forces, nor any fluid drag. It gets much worse for us engines trying to power through wind. The power required to overcome the air drag of a particle moving at a given velocity is a cubed function of the velocity, not a squared function of velocity as with no air drag. So to answer the OPS question, if he were to ride a 5 miles course and wanted to burn the most energy, he should proceed to finish that course as quickly as possible. (ohh now we neglect the caloric loss due cold temps, good enough)

Rowan

The air resistance thing is being overstated at the speed the OP is talking about, unless there is a strong headwind (and that was not mentioned).

How are we talking about air resistance at higher speed when the OP has already asked why his average speed is LOWER?

Darkness does not increase air resistance (although denser, damper air might slightly), and the snow has a much greater effect in reducing his speed from 20 to 12mph.

Really guys.

StephenH

If all other factors were equal, then riding the same distance faster will be better exercise. If you're working equally hard either way, the slower route will be better exercise as it has you riding at that intensity for longer.

North Coast Joe

Sure do, Ten Wheels, though night riding would be more fun and much faster with a much better headlight than the 3 LED model I'm currently using. Just can't see far enough in advance to go any faster. Much the same as the snow/ice doesn't limit my speed as much as the fear of becoming a pile of fractured bones by the side of the road.

North Coast Joe

Thanks again for further clarifying! Velocity squared (or cubed) is far less scary than squaring or cubing my massive weight!

chefisaac

Screw the math. Think about it like this: you are out there riding when the majority of people hung up their helmets for winter.

wphamilton

Just because no one has said it explicitly: Yes. Except that you work harder on the ice and snow, and bundled up.

FWIW, math is life.

Rowan

Not quite. Math does not explain emotion.

wphamilton

I'll grant you also need chemistry to explain emotion.

cyccommute 

You need chemistry to explain everything.

StephenH

That intrigues me. I'll have to start working on a mathmatical theory of emotion. See, we'll define the "Li" function as "Like" so that Y=Li(X) means person Y likes person X, and go from there. There's an entire field of PhD theses untapped.

Rowan

Indeed!

wphamilton

I recall a Scientific American article from the 70's - I think it was 1976 - that modeled the fight or flight response based on what they called "catastrophe theory." Very basic article, but since then I've always speculated that sudden onset emotions could be modeled on a similar basis.

Road Fan

Yes, this is what I was going to raise. The power required to overcome wind resistance increases with the cube, or third power, of speed. To go twice as fast with no wind and no hill takes 2X2X2=8 times the power. This is a simplified view of the power required to move a bike, but being a cubic function it's a dominant factor, at least at high-enough speed.

Bill Kapaun

I think that's a little too simplified.
There's more to moving a bike from point A to point B than just wind drag.
Even with a tail wind that equals your speed exactly, you still have some "work" to do, to maintain speed. FRICTION being one of them.