Have I become Superman?

[neptune]

I am 66 years old , and for much of my life I rarely cycled . I do a ten mile stint on my pedal cycle every day to try to keep fit . I am not a very strong rider , and I can probably only output about 80 watts . Today , on the outbound leg , I faced a headwind of 28 MPH . I was reduced to using the smallest "granny gear " chainwheel , something I seldom if ever do normally . I estimate my road speed at about 5 or 6 MPH . Now we know that above about 12 MPH , most of our energy is spent on aerodynamic drag . So , my "airspeed" would have been over 30 MPH . which I kept up for four miles before stopping to rest . So the real question is this . Is biking at 5 MPH into a 28MPH headwind really equivalent to biking at over 30 MPH in still air ? Even in still air I could not reach 30 MPH , let alone keep it up for 4 miles . Any theories ?

 

[Deleted member 4366]

Best keep quiet about it otherwise our Speed Police will be after you.

 

[10mph]

You have no worry about speed police. You were, if my understanding is correct, using a pedal cycle, and not an illegal e-bike. Also you were only travelling at 5 to 6 mph and I can't see how that speed could be illegal.

The important things you need to know about air resistance are:

1. The force needed to overcome it is proportional to the square of the effective wind speed (ie your speed + the headwind speed)
2. For calm conditions (no head wind), the power needed to overcome air resistance is proportional to the cube of your speed

The second point arises because power = force x your cycling speed.

So let's calculate what speed you can do in calm conditions based on the numbers you give:
If I assume you are travelling at 5.5 mph into a headwind of 28 mph. The air speed is 33.5 mph, so the force is

AirResistCoef x 33.5 x 33.5
​

and the Power at 5.5mph is

AirResistCoef x 33.5 x 33.5 X 5.5
=AirResistCoef x 6172
​

Now lets calculate the speed, V, which you can ride in calm air with this power:

AirResistCoef x V x V xV=AirResistCoef x 6172
So V x V X V= 6172
V = 18.4 mph
​

So you are not a superman, just an 18.4 mph rider in calm conditions

In the above calculation I have ignored the other main resistance, tyre resistance, since this will be small in comparison with the air resistance at the speeds considered here.

You can play with different conditions using the speed/power calculators available on the web. The one at Bike Calculator is particularly convenient since you can put in parameters for two different conditions and compare the speed reached.

 

[flash]

Yes

Next time you go out make sure you put your underpants over your trousers.

You are definitely Superman.

Bet it was good going back though

 

[flecc]

In addition to the major difference factor that 10mph has so perfectly detailed, there are three very small differences between the two riding cases you describe. One is the tyre rolling resistance that 10mph has mentioned, another is the bike's total mechanical friction/drag, both these increasing with road speed, and a third is wind ground drag. Wind strength increases with height as it moves further from the ground due to the drag effect of the ground, for example the top of a wind turbines blades suffer higher wind speed than the bottom, creating an unbalanced force for designers to consider.

To understand the effect of ground drag in your two cases, imagine you are being looked at from a near geo-stationary orbit so you are at a standstill in the two cases. In the case of riding at 30 mph in still air, from that viewpoint both the wind and the road are passing you at 30 mph, so there is no ground drag slowing the air. In the case where you are riding into a 30 mph headwind at 5 mph, the road is now passing stationary you at only 5 mph, so the road surface is exerting a 25 mph difference drag on the wind at ground level, slowing it down. The effect is small, but nevertheless real, so it's easier to ride slowly into a fast wind than ride fast into still air.

An e-bike interest rule of thumb on wind drag is that 1 square metre stopping the wind completely from 40 kph (25mph) is equal to 400 watts. Our area riding into the wind is mostly under 1 square metre (hopefully!), and we don't stop all the wind since much slips around us, especially with lycra or other tight fitting wear, so we can need a lot less than 400 watts at 25 mph.
.

 

[steveindenmark]

Keep away from telephone boxes.

Steve

 

[neptune]

@10mph . Thanks for those calculations , and thanks everyone for comments . Yes I was riding a hybrid type pedal cycle with35mm wide tyres . The bit about the speed police was intended as a joke . I am sure . Having looked at the bike calculator , to do 18.5 MPH in still air on my bike would take about 200 watts . I am surprised that I maintained that for 4 miles , and it is twice what I thought I was capable of . To me biking is meant to be a pleasure , so I guess on I normal day , I develop ,say , 100 watts . That gets me where I want to go , as fast as I want to go . No wonder I stopped for a rest .

 

[flecc]

@10mph . Thanks for those calculations , and thanks everyone for comments . Yes I was riding a hybrid type pedal cycle with35mm wide tyres . The bit about the speed police was intended as a joke . I am sure . Having looked at the bike calculator , to do 18.5 MPH in still air on my bike would take about 200 watts . I am surprised that I maintained that for 4 miles , and it is twice what I thought I was capable of . To me biking is meant to be a pleasure , so I guess on I normal day , I develop ,say , 100 watts . That gets me where I want to go , as fast as I want to go . No wonder I stopped for a rest .

NASA research figures for "healthy males" when cycling:

300 watts for about 10 minutes continuous.
200 watts for about 1 hour continuous.
100 watts for about 5 hours continuous.

 

[timidtom]

NASA? Equations? Is my bike more numerate than I?
I was going to go for a ride but I'll just lie down here, in this quiet, dark corrner and learn to count. Let's see: i,2,3, lots, many ...
Tom

 

[neptune]

OK , I suppose that it depends what NASAmeans by a healthy male . I think it only fair to say that as we get older our capabilities decline . But based on those figures , at 66 years old I am not in bad shape for my age . By the way flecc , how come we can trust NASA`s opinion on cycling , but not on cold fusion ? Sorry , I just could not resist that ! Actually , according to those figures , the human body behaves a bit like a lead acid battery . The faster that the energy is consumed , the less energy [watt hours] is available . Sounds like a good excuse for being a bit lazy sometimes .

 

[flecc]

OK , I suppose that it depends what NASAmeans by a healthy male . I think it only fair to say that as we get older our capabilities decline . But based on those figures , at 66 years old I am not in bad shape for my age . By the way flecc , how come we can trust NASA`s opinion on cycling , but not on cold fusion ? Sorry , I just could not resist that !

Since their research was related to their astronaut program, I've always treated the expression "healthy male" as 25 to 45 years old with no obvious disabilities. You are obviously in good shape on your result.

As for cycling versus cold fusion, the cycling figures were not opinion, they were results of research using actual people and bikes. The viable cold fusion is opinion since there are no ascertainable facts, just waffle and hype of the sort that emanates from all research bodies anxious to show a reason why they should get more funding. Remember the "star wars" nonsense of the Reagan era? That worked for a while to con idiot politicians out of cash, so one can hardly blame them for continuing to try with silly science projects.