bobotech

I am just kind of curious. I'm at 337 pounds now and I have been able to climb a few hills that I couldn't imagine a year or two ago. One of them was a shorter 7 percent grade. I'm just curious how many watts it takes to push a 30 pound loaded cross bike up a 7 percent grade at around 340 pounds? I just kind of curious how many watts a big person can generate short term. This isn't for any legitimate stats, more like "oh wow, it takes about 200 watts at any second to move my big butt up a 7 percent grade at say 10mph."

Willbird

IMHO the flat ground numbers will be more accurate as to wattage. So if you have a Heart Rate Monitor you can find the HR that it requires to climb that grade. Then duplicate that HR on level ground and see what your speed is and roughly translate that to watts.

But I gave 2-3 routes worked out locally, I run them forwards and backwards so they do not become boring, but WIND makes them seem very different power requirement wise.

Big cyclists can make as much power as cyclists at 7% body fat :-).

The wattage required will depend on so many diverse factors, wind, road surface, cadence, speed of ascent, wind, saddle height...that it may be impossible to calculate.

The latest thing I am seeing is roads with a soft sticky surface from summer heat, the roads are far more consistant in colder weather :-).

Up North

Too many variables to compute accurately, power meter best option.

CliffordK

Here is a power calculator.
Bike Calculator


Cadence is independent from Watts.
Saddle Height? Perhaps with wind resistance? Not that important for watts.

Wind, road surface, etc may all be issues.

Anyway, putting 337 lbs + 30 lbs, 7% grade, 10 mph (assuming steady state), I get about 650 watts.

ColaJacket

Right, but at 4 mph, it's a more reasonable 232 watts.

GH

Willbird

Cadence may be "independent" from watts in a mechanical sense, but it directly impacts the riders efficiency, it takes the same number of watts to ascend the grade at 100 RPM cadence as 50 RPM, however the rider may be more efficient at one than the other, and the same is true of saddle height, again it comes back to efficiency.

Also crank length/leg speed again can supposedly have a decent impact on efficiency.

You are correct that it does not mean anything in sheer watts required, "what output servo motor would it take to ascend the 7% grade with a rider weighing XXX lbs not pedaling at all".

Bill

andr0id

Yeah, that would be damn hard for a large person.

I'm half that weight and run about 300-350 watts to go uphill that fast and I don't last that long.

On a longish 5% uphill, I like to plug away around 200w and that puts me at 7 or 8 mph if I remember right.

CliffordK

If you put on a rear wheel power meter, it shouldn't care whether you are pedalling at 30 RPM in high gears, or 120 RPM in low gears, although many cycle computers can detect power spikes from the pedal stroke. The energy is still the same if the speed is the same.

Some research seems to indicate that much of the energy consumption of your body (eg. O[SUB]2[/SUB] consumption) is more related to watts than cadence or standing vs sitting.

Although, there may be aspects of endurance and long sustained effort that is related to cadence and body position.

RollCNY

This is another calculator, if one prefers a different look:

Bicycle Speed (Velocity) And Power Calculator

Drew Eckhardt 

If you want to be pedantic, metabolic efficiency is higher at lower cadences.

Fatigue can vary a lot - _Training and Racing with a Power Meter_ tells the tale of a racer who got dropped every time he spent more than 5 minutes at his one-hour power but 70RPM.

Within reason it doesn't seem to make much of a difference for me 60-95 RPM although it feels very different and I prefer 90+ RPM on flat ground with about 10 less climbing.

Flat ride Thursday, hilly ride Saturday 2 days later. Heart rate is effectively the same - ~205W and 157 BMP on flat ground average cadence 91, ~195W and 155 BPM up-hill average 68 although the steep part is all closer to 60. I wasn't sweating enough for my heart rate strap to work before the hill so the working portion is listed separately. The drop-out was where I took off my wind jacket.

[TABLE="align: center"]
[TR]
[TD]Interval Name[/TD]
[TD]Duration[/TD]
[TD]Time Riding[/TD]
[TD]Distance (miles)[/TD]
[TD]Work (kJ)[/TD]
[TD]Average Power (watts)[/TD]
[TD]xPower (watts)[/TD]
[TD]Max Power (watts)[/TD]
[TD]Average Heart Rate (bpm)[/TD]
[TD]95% Heartrate (bpm)[/TD]
[TD]Average Cadence (rpm)[/TD]
[TD]Average Speed (mph)[/TD]
[TD]Elevation Gain (feet)[/TD]
[/TR]
[TR="bgcolor: #efefef"]
[TD="align: center"]flat 60min (207 watts)[/TD]
[TD="align: center"]1:00:00[/TD]
[TD="align: center"]59:43[/TD]
[TD="align: center"]19.8[/TD]
[TD="align: center"]745[/TD]
[TD="align: center"]207[/TD]
[TD="align: center"]207[/TD]
[TD="align: center"]509[/TD]
[TD="align: center"]157[/TD]
[TD="align: center"]161[/TD]
[TD="align: center"]91[/TD]
[TD="align: center"]19.9[/TD]
[TD="align: center"]99[/TD]
[/TR]
[TR]
[TD="align: center"]8.5% grade @ 198W[/TD]
[TD="align: center"]24:01[/TD]
[TD="align: center"]23:14[/TD]
[TD="align: center"]2.5[/TD]
[TD="align: center"]285[/TD]
[TD="align: center"]198[/TD]
[TD="align: center"]202[/TD]
[TD="align: center"]372[/TD]
[TD="align: center"]146[/TD]
[TD="align: center"]163[/TD]
[TD="align: center"]68[/TD]
[TD="align: center"]6.5[/TD]
[TD="align: center"]1133[/TD]
[/TR]
[TR="bgcolor: #efefef"]
[TD="align: center"]8.5% grade working HR[/TD]
[TD="align: center"]21:19[/TD]
[TD="align: center"]20:33[/TD]
[TD="align: center"]2.2[/TD]
[TD="align: center"]245[/TD]
[TD="align: center"]192[/TD]
[TD="align: center"]195[/TD]
[TD="align: center"]336[/TD]
[TD="align: center"]155[/TD]
[TD="align: center"]164[/TD]
[TD="align: center"]68[/TD]
[TD="align: center"]6.6[/TD]
[TD="align: center"]966[/TD]
[/TR]
[/TABLE]

flat:


climb:

Willbird

Drew I'm not trying for "Pedantic" but from screwing around with resistance rollers and Trainerroadf I know for me anyway there is a difference watts/HR depending on cadence, I can go longer duration at 100RPM than 75-80...but I get more watts at maximum HR at 75-80. It was about 20w difference, which is 10% of my measly 200w, but if I could train to put out 300, it still might be 20w and not as much of a % ?

On the crank length and leg speed issue they were seeing in the neighborhood of 3% benefit in VO2 efficiency from shortening cranks to lower the rider position, this revealed the VO2 advantage, there is an aero benefit from moving the rider closer to the crank centerline but the VO2 difference was something they were not exactly expecting.


Bicycle Crank Length
But anyway :-).

bobotech

Very interesting guys. This thread explains a lot about power numbers and so on to me.

Willbird

I would not be surprised if several billions of dollars have been spent on that subject over the years, a billion is "only" a thousand million...over all the years of cycling adjusted to modern $$, easily I bet :-).