Wind and Hills

[neslon]

Is there a rough and ready way of equating windspeed with gradient? I was battling back in the wind today & wondered if there is a simple way of comparing a 10 mile ride into a 20mph head wind with a comparable-effort climb? (I realise there will be complicating factors such as riding speed, but there must a comparison of sorts - preferably one that puts me up Alpe de Huez while going through Blyth Valley!)

Neslon

 

[RedBike]

Try this spreadsheet
http://www.ctc.org.uk/resources/About_the_bike/PowerCalc.XLS

 

[neslon]

Now thats interesting! I will have to get DataBoy to switch his widget on next ride out - thanks

 

[Will1985]

Interesting - I wish I had taken my powertap for my Sunday ride home into the headwind - 77 miles. I figured I needed all the aero help I could get! I know when I got home that it felt much harder than a century.

That spreadsheet reckons that I averaged 280W for the entire ride which would equate to a similar time 100 mile time trial for me.

 

[jimboalee]

Yes, this PowerCalc spreadsheet is a 'rough & ready' aid.

Before you enter a number into the 'wind' column, you have to assess the 'Effective' windspeed based on YOUR riding direction and the WIND direction.
Firstly, work out your 'Angle of attack', and then multiply the WIND speed by the Cosine of the Angle of attack.
So if it IS a true headwind, the wind will be 1.00 x windspeed, and if its 45 degrees attack, the wind will be 0.71 of the reported wind speed.

You power requirement is the appropriate value on the 'cook book' RoadLoad curve for the resultant windspeed added to your roadspeed.


PowerCalc spreadsheet has some 'generic' values for Xsection A, Cd and mass; and it has 'generic' Roadload curves for these examples.

You are encouraged to enter your own Xsection A, Cd and mass, but this requires some further data collection I have described on another thread many months ago.

PowerCalc is a good starter for Brainiacs.

 

[jimboalee]

Here's something you might like to try with PowerCalc.

Create a row for your own self.
Use your correct Mass.
Use 0.4 m2 in this instance.
Use 0.95 Cd ( half way between race and touring )
Use 95 for trans eff.

Copy these down so you have several rows the same.
In the first row, enter a speed representative of the fastest you can sprint on the FLAT with NO WIND. ( I used 47 kmh which I know I can do, and computed to just less than 700 Watts ).
You will get a figure for Watts.
In the second row, enter 5 in Slope and then play with the speed until you get the same Power.
In the third row, enter 6 in Slope and play with the speed until you get the same Power.
Fourth row 7, Fifth row 8 and so on until you can't enter a positive speed to get the equivalent Power.
I looked at my table and saw 30% hill at 7.5 kmh. I don't have a gear for this speed.
I checked my gear chart and deduced I should manage a 25% at 9 kmh on my Dawes at 60 rpm.

Remembering back to San Francisco, I did grovel up a 25% at about that cadence on the hire bike.

Good, eh.

 

[jimboalee]

Now try a different scenario.

Assess your ability to input a speed you could keep for an hour round a track; knowing you must carry on riding slower for a further hour afterwards. Mine is 32 kmh.

Perform the same process as before to gauge your climbing capability in the longer term.

From this, I deduce I could only get up a 12% in my lowest gear for a non-stop duration of up to one hour.

 

[jimboalee]

Now try a different scenario.

Assess your ability to input a speed you could keep for an hour round a track; knowing you must carry on riding slower for a further hour afterwards. Mine is 32 kmh.

Perform the same process as before to gauge your climbing capability in the longer term.

From this, I deduce I could only get up a 12% in my lowest gear for a non-stop duration of up to one hour.

Has anyone done this yet?

I'm waiting for someone to pass a comment about it.

 

[Sittingduck]

According to the spreadsheet I do 374 Watts when crusing ona good flat road

 

[marinyork]

Interesting but is this thing right? I put in some info for the ride I did in howling gales the other night on the city bike and it comes up with values as high as 300W. On the home straight it goes as high as 1000W! If these values were right surely I wouldn't be the slowest rider in the known universe.

 

[jimboalee]

Interesting but is this thing right? I put in some info for the ride I did in howling gales the other night on the city bike and it comes up with values as high as 300W. On the home straight it goes as high as 1000W! If these values were right surely I wouldn't be the slowest rider in the known universe.

You must have the decimal point in the wrong place somewhere

 

[ASC1951]

1000w? Chapeau! I think pro cyclists can keep up 350w-ish for hours and the sprinters peak at about 850w.

Has madam perhaps inadvertantly added a zero to her kiloage?

 

[jimboalee]

1000w? Chapeau! I think pro cyclists can keep up 350w-ish for hours and the sprinters peak at about 850w.

Has madam perhaps inadvertantly added a zero to her kiloage?

350 Watts will get a 10st 7lb rider on a 15 lb roadrace bike along at 26ish mph.

10/10.

 

[jimboalee]

Interesting but is this thing right? I put in some info for the ride I did in howling gales the other night on the city bike and it comes up with values as high as 300W. On the home straight it goes as high as 1000W! If these values were right surely I wouldn't be the slowest rider in the known universe.

I wouldn't read too much into this PowerCalc thingy.

( what I was waiting for was someone to point out :- )

According to the math, it is possible to ride up a 45 degree slope ( 50% ) at 240 Watts, ( if your bike has a 10" gear that is. )

Incidentally, a 10" gear is a 16 tooth track sprocket welded to an old cottered crank, and the original 42 tooth chainring welded onto a singlespeed freewheel.

I've seen that attemted, and the young chap kept tipping over backward.

 

[Will1985]

Has anyone done this yet?

I'm waiting for someone to pass a comment about it.

If someone is happy to let me use a track, I'll take my road bike and powertap along to test it for you.