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Someone please explain Watts to me....(9 posts)

Someone please explain Watts to me....AnotherNewbie
Apr 5, 2001 1:51 PM
..I have no clue, but have seen the word used several times. I'm sure its some measure of output/power, but thats a guess.
Chew on this....gimmeaminute
Apr 5, 2001 1:57 PM
Main Entry: watt
Pronunciation: 'wät
Function: noun
Etymology: James Watt died 1819
Date: 1882
: the absolute meter-kilogram-second unit of power equal to the work done at the rate of one joule per second or to the power produced by a current of one ampere across a potential difference of one volt : 1/746 horsepower

Get it?
Apr 5, 2001 1:58 PM
It's just a measure of power, meaning the rate of work done.

One horsepower = about 746 watts. The best bike sprinters make about 2200 watts temporarily, I've read.

Me, my peak is around 1000 watts on a trainer, which translates into sprinting at 36 mph for me.

A typical bike racer can maintain 250-400 watts. The best pros can maintain just over 500 watts continuously. Those are some reference points, I suppose.

Apr 5, 2001 2:18 PM do you measure your output?
We go down to the gym and get lied to ...Humma Hah
Apr 5, 2001 2:23 PM
... by exercise equipment that purports to read your power output in watts, but may be off by a factor of 2.

Doug and I are fond of some computing tools found at One can estimate their power from speed and hill grade, or enter power and calculate speed. All this depends on a bunch of guesses about wind drag, tire drag, etc, but default values in the program take care of that pretty well for road riders.
On my trainerDog
Apr 5, 2001 2:26 PM
I have a trainer with a computer thingy attached. Interestingly, the displayed watts with the corresponding speed matches almost right on the money to my observed top speed on the road. FWIW

Power TapHap
Apr 6, 2001 5:52 AM
It is difficult at best to estimate actual wattage while road riding. Wind speed and direction vary in the real world and road grade is typically not a constant. Most of us rely on distance, time, and heart rate to gage output, but because of the uncontrollable variables of road riding this does not provide an accurate measure. For example, on a very windy day you might actually produce more watts during your ride but have a slower time and lower ave speed than normal. HR helps but there are outside facters that can effect HR like rest, hydration, etc.

There are some products on the market that can be installed on the bike to measure output. The most common of them, Power Tap, works from the rear hub. Some work from the BB. Many pros use them on training rides. Lance has mentioned in several interviews, including the recent "Bicycling" interview, that he relies heavily on a watt measureing devise to control his training efforts. He doesn't endorse a product and once said this was the only bike gear he had to buy out of his own pocket since turning pro. The Power Tap is expensive ($500 to $800) and requires the use of a rear hub that is heavier than most road hubs. Therefore most mortal roadies don't currently use them. In fact, the company making Power Tap got into financial trouble but it was announced recently that they had been bought out. I look for the product to re-appear soon.

There are several watt output measuring devises available for use on indoor trainers. These products are more affordable and more practical than the "on-the-bike" devises. If you have both, you can better compare training efforts on the road and indoors since watts would be the constant.

The goal would be to train yourself to continually deliver more watts to the road over longer periods of time as well as higher peak wattage over short efforts.

Simple, one joule per second ...Humma Hah
Apr 5, 2001 2:17 PM
... as if that helps.

Watts are the unit of power of the SI system of metric units, the official system of units. (Joules are units of energy, watts are energy per second). Watts are widely used in electrical work, but are also used generally in physics and exercise physiology.

An incandescent 100 watt light bulb turns about 95% of its power into heat. A human being just sitting around may generate 2-3 times that much energy as heat, just with base metabolism and modest activity.

Exercising may generate 100 watts or so for an easy pace, maybe 250 watts to propel a roadracer at a brisk clip.

Human athletes can typically produce about 1/3 to 1/2 horsepower (a horsepower is something like 745 watts). A few can exceed one horsepower -- I believe a top trackie did this recently for about an hour.
Watts Up?Breck
Apr 5, 2001 7:29 PM
Nott much with me on the bike.

I believe this to be a difficult concept to understand unless you have the science back ground for it or have been working with gasoline engines/ electric motors. My physics /electrical back ground is a little rusty by about 30 or more years but will give you my take on it.

A horsepower is defined as the work required to lift 33,000 pounds one foot (33,000 foot-pounds) in one minute, which is equivalent to lifting 550 pounds one foot in one second. One horsepower is equal to 746 watts. Horse power and watts are merely two different ways of measuring or expressing the rate of work, or the power. If a lamp consumed 746 watts you would be correct if you called it a 1-hp lamp. Similarly you would be correct in saying that a 1-hp motor is a 746-watt motor.

The terms are watt or horsepower, not "watt" or 'horsepower" per hour. Both watts and horsepower denote a rate of work being done at a particular moment, not a quantity of work being done during a given time.

That's about as much as have ever figured out myself. The other good posts will help also.