Perspectives on Personal Power

Helping you figure out how much electric assist boost you need

Humans are powerful! However when it comes to navigating the wild world of electric assist options, to choose the right e-assist for your needs, it is helpful to know how powerful a human can be and how much additional power you really need your e-assist kit to add to your bike.

This article below was written by designer Alan Scholz to help you understand the amount of power a human can produce and then compare it to the amount of power most electric assist kits can provide. Enjoy!

-Hanna Scholz (Bike Friday President)

How Many Horses Do You Really Need?!?

By Alan Scholz

In the lab, experiments have shown an average “in-shape” cyclist can produce about 3 watts/kg-1.4 watts/lb for more than an hour (e.g., around 200 watts for a 70 kg/154lb rider), with top amateurs producing 5 watts/kg (350 watts 154lb person) and elite athletes achieving 6 watts/kg for similar lengths of time.(6 watts per kg – think world hour record of 400 watt output for 60 minutes and distance of about 30 miles/48 kilo) Elite track sprint cyclists are able to attain an instantaneous max output of around 2,000 watts (& can sometimes break chains doing it!), Elite road cyclists may produce 1,400 to 1,700 watts as an instantaneous maximum in their burst/sprint to the finish line at the end of a five-hour-long road race. (now you know how they do those 40 mph/65kph sprints at the end of those Tour de France stages!!)

Now look at this in terms of horsepower. Mechanical horsepower of 550 foot-lbs per second is equivalent to ~745/750 watts. A healthy human can produce & sustain ~ 0.1 hp/75 watts indefinitely; trained athletes can manage up to about 1800 watts briefly & 0.3 hp/220 watts for a period of several hours. Regular folks bicycling are riding at between 25 watts & 150 watts, if they are not a skilled cyclist. If we have some cycling skill we are not only able to put out more wattage within our comfort zone (for an hour) but also going faster per each watt we put out by riding a more efficient bike, doing it more ergonomically (because it fits us correctly), we are trained, fit, efficient in the proper movements, and our bodies are trained to be better heat exchangers (dumping the excess heat is also easier outside the “lab”).

Example Situation: A Moderate Cycling Commute Distance 

Assume a cyclist riding on flat ground, no wind, & motivated. We can expect about 200 watts of power output in an upright position (mountain bike) that should result in an average speed of about 16 mph, a road bike in its better aero position = 20mph, both have street tires on pavement. Let’s assume a distance of 8 miles one way. That will take 30 minutes to get to work, and the same to get back, a road bike rider in better more efficient aerodynamic position takes 24min. The total energy used of 200 watts X 1 hour = 0.2 kilowatt hours. So the cost would be about 2 to 4 cents if it was electricity. (the road rider 200 watts x .8hr = .16 kilowatt hours.)

A very comfortable commute (or slow touring pace) of 75 watts will produce a speed of about 10 to 13 mph. It takes more time but no sweat. These slower speeds makes the commute about 48 minutes to 37 min.

For watts vs. speed reference: 100watts = 12/15mph, 125watts = 13/17mph, 150watts = 15/18mph. (Thank you to Grin Technologies for their great  power/load simulator!)

Typical speed in American cities has been shown to be about 30 mph. Portland Oregon averages 23mph. During rush hour & in contested areas it runs more like 15mph. Sometimes this includes a lot of expressway parking & engine running at stop. In 2016 it was reported that the average speed in the U.K.’s busiest cities had dropped below 10 mph! Clearly travel by bike in cities is very competitive time wise.

Bicycles are very efficient if designed for actual riding and not as motor bikes or for extra large loads. Total weights of riders & loads over 100kg/ 220lbs take considerably more energy if there are hills and repeated start ups and stops are needed. And we don’t all have the same capacity legs, skill, or motivation all the time.

What the paragraphs above show is that anyone with an addition of 100 to 200 watts of assistance can ride like the breeze with predictable trip outcomes and feel the thrill of a gifted athletic while doing so. If you can do an easy 100 watts and 12 mph, an additional 100 watts will put you in the Sweet Spot that I have found to be 17-18mph. Fast enough to make real fast predictable trips and still stay safe.

This fun 3 min video gives you another way to see the power a human can produce compared to the power it takes to run a house hold.

Summary Guide:

By Hanna Scholz

How many horse power/watts a human can produce:

1 Horse Power = 750 watts

  • A healthy person can produce around . 1 hp / 75 watts which gives them a cruising speed of 10 to 13 mph
  • A fit cyclist can produce over .25 hp / 200 watts and cruise at close to 20 mph or more
  • A top amateur athlete cyclist can product up to .5 hp / 350 watts for more than 1 hour and ride at 25-28 mph
  • A top elite athlete cyclist can produce about 400 watts for 60 minutes for a 30mph (World Hour Record) pace

How many watts / horse power to add to your bike to boost your human legs:

When an average human adds between 100 to 200 watts (1/10 – 1/4 hp) to their output with electric assist they become just as capable as a fit athlete cyclist!

If you can already comfortably cruise at 12mph on flat ground then if you add an e-assist boost of 100 watts then you can cruise at 17-18mph with the same effort. This is the ‘sweet spot’ speed that makes for predictable and safe trips.

If you have some hills or plan to carry some heavy loads then you may want to add 200 watts of electric assist to smooth out the tough parts of your trip.

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14 thoughts on “Perspectives on Personal Power

  1. Steve Scarich

    I am slowly coming around on e-bikes, after starting out opposed. I was opposed because I thought everybody should ‘earn’ every mile, by their hard work. I know, I know….out of date thinking. My only concern, which I have actually encountered in bike lanes, is e-bikes going much faster than me (and I am faster than your average rider) and passing me at a 10 mph speed differential and riding as if they were a pro cyclist.

      1. Jac Thomas Post author

        That information will be available soon, for now if you are interested we recommend you contact one of our Design Consultants about your specific situation!

    1. Jac Thomas Post author

      That information will be available soon, for now if you are interested we recommend you contact one of our Design Consultants about your specific situation!

  2. Alan Johnson

    I’m a very happy pakiT owner but to me, it fundamentally is a “compromise” bike. Why would I want to install an electric assist system on a compromise bike?

    1. Jac Thomas Post author

      I’m afraid I don’t understand your question…How is the pakiT a compromise bike? The pakiT is designed to be a utility travel bike that can be packed into a small, easy to transport package. We absolutely see value in adding electric assist to the pakiT, so have many of our customers. Hope that helps!

  3. Scott McMahon

    I bought a high powered electric bike for my 12 mile commute, because I felt I was spending too much time getting to work. Before getting the electric bike, on my BF Pocket Rocket I would average 15-18 mph (not including stops). With stop lights and other traffic obstacles, my commute took about 45-50 minutes. I live in California, and electric bikes that can provide a pedal assisted 28 mph top speed are legal. That’s the kind of bike I have and it cuts my commute time to about 30-35 minutes. Saving me about 30 minutes on my commute (2 ways) each day.
    I think less powerful e-bikes are a good idea for folks who don’t want to work up a sweat, and don’t typically ride their (unassisted) bikes at more than 10 – 12 mph. For them, I think the kind of e-bikes BF is proposing would cut commute times significantly, or extend the practical range for riding. And I think we all want to see bikes (and e-bikes) become the practical alternative for more of the trips we now make in cars.
    Personally, a low power assist bike wouldn’t be worth the weight and expense for my commute. I already manage 15 – 18 mph average. Boosting that to 20 wouldn’t significantly shorten my commute. I calculate it out at just a few minutes a day. (I don’t get to go at top speed for the whole trip, there are lots of stops and starts.)
    Riding at 27 mph on the pedal assisted bike is not a low effort project. This is due to the fact that the motor control system starts reducing power output at around 22 mph. Any pedal-assisted e-bike will behave this way. It will happen near the max speed the control system has been programmed for.
    This was actually something I worried about. My wife got a different e-bike that wasn’t pedal assisted. It used a twist grip accelerator control like a motorcycle. It was possible to pedal, but it never felt like your effort was actually contributing. The motor just backed off so you could work harder without going faster. Psychologically, this didn’t work for me at all. It was a drag to pedal that bike. With pedal assist, (the harder you pedal, the faster it goes,) psychology is in your favor. Even if it is only a few mph extra, it feels natural. Seeing the speed increase with effort is incentive enough to keep pushing.
    On my commute, I end up working just as hard as I do on the Pocket Rocket, but I accelerate much faster and have a higher top speed. I could probably go 20 mph without breaking a sweat, but I want the exercise, and a shorter commute.
    At top speed, (which I can hit in about 1/4 block,) I feel like I do going down a steep hill. Its not like I’ve never gone that fast before, but there is some disorientation in overlaying that speed onto my usual commute routine. I am learning to treat stop signs and traffic differently. I’m not yet used to moving at downhill speed in and around the neighborhood, but I’m getting there.
    I like to think of the electric bike as my way to extend my range for bike life. I use it for commuting and errands. Personally, I would never want to use it for club rides or day trips.
    My e-bike has a 500 W-h (0.5kwh) battery and I use about 70% of the charge to go 24 miles. It has an 80Nm, 500W motor.
    I hope this information about my experience is useful. Get out and bike!

  4. Lin B

    I’ll be adding a Shareroller 4.5lb friction drive to my pakiT. Easy on/off in 10 seconds just for those rides where I want it. I’d love to see BF develop something super light and removable. Even the front hub kits at 10lbs with batteries is too much weight on a small folding bike. Imo friction drives (aside from the noise) are the perfect drives for folding bikes!

  5. Deby

    I bought an Urban-X wheel through their Kickstarter campaign and love it. I bought one for my heavy, hybrid non-folding bike. I only use the wheel to boost going up steep hills or to catch up to my biking buddies who have very light frames and can ride 15-20mph (I’m more a 10 mph rider, especially on a heavy bike). I can also use it for pedal assist, but I don’t as I still want that biking workout. The Urban-X wheel is a quick set up that allows me the option of using a standard wheel or the ewheel. I love that versatility. I can even charge my iPhone with it either when riding or not. They are now making 20″ wheels, which I can put on my Bike Friday. I’m going to hold off buying an Urban-X wheel for my BF while I wait to see if the BF electric assist is as nice – and affordable. The one thing I do not like about the Urban-X wheel is that it is heavy, especially if you don’t have a lot of upper body strength. But it is totally worth it as there is a steep hill going up to my house and having that wheel gets me out riding more, which is a very good thing. I use my BF for traveling and hope your e-kit doesn’t get in the way of packing everything into a suitcase. The Urban-X wheel is an engineering marvel, but I’d rather support BF so hope you wow me with your new product!

  6. Marianna Freeman

    I am in the “senior phase “of life. I have a New World Tourist Bike I purchased several years ago and
    do mainly “Rail to Trail” rides. Have done the Katy Bike Trail, The GAP Trail, the Paul Bunyon and Heartland Trail and
    tried to do the Couer de Lane Trail this fall, but the smoke stopped me. I find that I am needing an extra boost for
    any kind of hills and also with pulling my suitcase it is getting a bit harder (my age – 81 in April). My main concern is
    that I fly almost everywhere to do the trails (went to Holland last year). Will the electric assist be allowed on the airplanes? Please keep me in the loop with information because I am very interested. Also the pricing. I would like to do the Erie Canal ride this coming fall. I live in Arizona down by Yuma and have very few hills, so my hill legs just aren’t there anymore.

    1. Jac Thomas Post author

      Marianna, those are great questions! We are very close to unveiling all of our electric assist options (including retrofits for all of our available models) with pricing information. And yes, we absolutely made sure that we would have an option for those of you who want to bring you bike on a flight. Tis is Bike Friday, after all 😉

  7. Doris Phinney

    I’m with Marianna Freeman in the “senior phase” of my life. My New World Tourist was purchased from BF in 2004 with a Touring Plus Capreo 27. I believe an electric assist would help in running errands, grocery shopping and of course touring. I’m not in a hurry to take this step as I am recovering from total knee joint replacement on my right knee and when the right knee is good I will then have the same surgery on my left knee. I am very interested in pursuing the electric assist and would appreciate your updating information as it rolls out.

    My BF is green gear green and I love it.



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