Yet, yet another gem.

[Archie]

There seems to be far far too many variables. Wind most of the time isn't constant anyway, it varies in strength and direction. surely even the incline / decline of the surface being cycled on would effect this. what about road material and smoothness. what about camber? surely even the barometric pressure would effect this as well? tyre pressures?

Yeah, but surely these variables contribute to your base speed in zero wind, so your still comparing like with like?

 

[ColinJ]

I've been having a think about my question about why riding at 33 mph on a still day wouldn't be equivalent to riding at 3 mph into a 30 mph headwind. Finally, it dawned on me...

At 33 mph, the rolling resistance, losses in the chain and gears, and the wheel bearings would be higher than at 3 mph.

Probably more important though is the fact that the tops of your wheels are effectively going at twice your speed into the air (a tyre in contact with the road is stationary at the point of contact otherwise it would be skidding, the hub is going at the same speed as the rest of the bike, hence the top of the wheel is going at double speed). Riding in still air at 33 mph, the top of each wheel is slicing through the air at 66 mph. Riding at 3 mph into a 30 mph wind, the tops of the wheels are effectively cutting through the air at 36 mph. That's a huge difference and would help to explain why aerodynamic wheels are an advantage.

Okay Jimbo - I believe you!

 

[jimboalee]

Jimbo, I personally love the fact that you have taken the trouble to load all this up for us, but your initial statement may only be true for Audax riders. What about a broad shouldered fat bloke wearing baggy clothes on a XC bike? It may be a fashion show to some, but to be honest I ride for serious fun, if such a statement can be made. Therefore, if it's windy I know I'll be knackered.

Keep it up though, seriously, because whether they like it or not, even a commuter/leisure cyclist should understand how much more effort they'll have to put in to get to the office/pub in a force 8. Without figures and tables, knowledge is nothing.

PowerCalc gives four examples of cyclists.

Any cyclist can get a reasonable figure for m^2 Xsection area by getting a friend to take a photo of them from the 'head on' viewpoint. Place a transparent gridded polysheet over the photo and count the squares. If you know how wide your helmet is, scale depending on the width of your helmet.
Then Cd by doing a 'roll down a hill' test or as MachinHead calls it "Freewheeling in equilibrium".

Baggy clothes and bulky bodies will be included in the calcs when the Xsection area and Cd numbers are representative.

 

[ursus_major]

Power requirement is a function of (Vw+V)^2xV, that is, wind speed plus road speed squared, times road speed. So for the example of 33mph with no wind, compared to 3mph with a 30mph wind, the power requirement for the former is more than 10 times the latter, all other things being equal.
Which explains why I can ride home when it's windy, but have never seriously challenged for the Tour de France...

 

[jimboalee]

Which is exactly what it has in common with every other jimboalee pronouncement. Usually by four pages later he's "clarified" what he meant to say and it turns out to be something completely different.

I mean, yes, call it a "gem" if you like, but so is mollusc mucus

I had a think about this.

A pearl, being made of hardened Mollusc mucus is of organic structure. A gemstone however, is a crysalised mineral structure.

Folks in the jewellery business do classify pearls as gemstones, but it's a bit of 'Poetic licence' in order to not confuse the customer.

Early in human history, pearls were found inside molluscs gathered for food. They were collected and used to make body decoration. They were considered the most valuable commodity to mount onto gold until high quality Diamonds, Rubies, Sapphires or Emeralds were found.

Recently, a gemstone called Tanzanite has gained popularity for mounting into engagement rings instead of Diamond. Very good Tanzanite changes colour from blue to Violet when turned in the light. It is only found in Tanzania.

It would have been a worse insult Coruskate if you had refered to my postings as "Cubic Zirconia".

 

[brodie]

Power requirement is a function of (Vw+V)^2xV, that is, wind speed plus road speed squared, times road speed. So for the example of 33mph with no wind, compared to 3mph with a 30mph wind, the power requirement for the former is more than 10 times the latter, all other things being equal.
Which explains why I can ride home when it's windy, but have never seriously challenged for the Tour de France...

I though the answer would be something like this, but what is the cause of the difference in power needed, in non-technical language?

 

[jimboalee]

Power requirement is a function of (Vw+V)^2xV, that is, wind speed plus road speed squared, times road speed. So for the example of 33mph with no wind, compared to 3mph with a 30mph wind, the power requirement for the former is more than 10 times the latter, all other things being equal.
Which explains why I can ride home when it's windy, but have never seriously challenged for the Tour de France...

PowerCalc ( on the CTC website ) asks the user for a value of Cd and frontal area. MachineHead does too. The very top-left of his PowerCalc screen in 'Bike classification'.

A cyclist in the tuck is more aerodynamic than a young man inside a tea chest on wheels.

If they both have the same XSection area and mass, and try to maintain the same speed against a headwind in a side-by-side trial, which one will need to produce more power?

Power is a function of CdA.

Any additional power requirement for headwind is the aerodynamic element only. Coeff of rolling resistance and geartrain friction is not carried on the breeze.

 

[jimboalee]

The aerodynamic element (FL) is :-

0.5 x Air density ( kg/m^2) x Cd x Area (m^2) x ( velocity ( m/s ) ^2) in Newtons.

To calculate Power use the wheel diameter and wheel rotational speed.

Power at the cranks will be greater by a factor of drivetrain efficiency ( another variable PowerCalc asks for ).

 

[jimboalee]

The aerodynamic element (FL) is :-

0.5 x Air density ( kg/m^2) x Cd x Area (m^2) x ( velocity ( m/s ) ^2) in Newtons.

To calculate Power use the wheel diameter and wheel rotational speed.

Power at the cranks will be greater by a factor of drivetrain efficiency ( another variable PowerCalc asks for ).

Has anyone got the foggiest why Aerodynamic force is FL ?

 

[skwerl]

I had a think about this.

A pearl, being made of hardened Mollusc mucus is of organic structure. A gemstone however, is a crysalised mineral structure.

Hmmm. Depends where you stand on the whole organic/inorganic debate. Pearls are Ca carbonate whcih historically is inorganic, as are diamonds. if you go for the everything-with-carbon-in-it approach then a diamond's organic too.

 

[jimboalee]

Hmmm. Depends where you stand on the whole organic/inorganic debate. Pearls are Ca carbonate whcih historically is inorganic, as are diamonds. if you go for the everything-with-carbon-in-it approach then a diamond's organic too.

It is a compound of biological origin.

Diamond is a Carbon allotrope constructed of a latice structure of C atoms. No Oxygen and not a compound with anything so inorganic.

 

[skwerl]

It is a compound of biological origin.

Diamond is a Carbon allotrope constructed of a latice structure of C atoms. No Oxygen and not a compound with anything so inorganic.

well. if you sit on that side of the fence you're right. The biological origin thing is historical, which is why the allotropes, carbonates etc were left out. That doesn't result in a universally-accepted classification.

Also, something doesn't have to be a compound to be organic. It does to be an organic compound. The non-compound organic is of course Carbon

I'm struggling to see where oxygen comes into it.

 

[jimboalee]

well. if you sit on that side of the fence you're right. The biological origin thing is historical, which is why the allotropes, carbonates etc were left out. That doesn't result in a universally-accepted classification.

Also, something doesn't have to be a compound to be organic. It does to be an organic compound. The non-compound organic is of course Carbon

I'm struggling to see where oxygen comes into it.

Chalk this one up for yourself.

You're a Diamond Geezer.

 

[Watt-O]

What was the question again?

 

[skwerl]

What was the question again?

something about mollusc mucus adding 20% effort to the average commute