Well, we've been in our new store for over 2 months, but now that spring is just around the corner, we're having a Grand Opening Party on Saturday March 7, 10am-5pm! As part of the party, we'll be doing a benefit for The ReCYCLEry, a very cool local non-profit that teaches people how to work on their bikes and runs a bicycle sharing program around town. You can check out their work at http://recyclery.info/ . A portion of all sales and proceeds from a bike raffle will go to the ReCYCLEry.
So, why should you come? First off - FOOD! We'll have Free coffee and bagels in the morning to get you going. The coffee will be supplied by Johnny's, a Carrboro favorite. In the afternoon, we'll whip out the Xtracycle Blender for some Bike-Blended Smoothies! Pedal your way from frozen berries and ice to a smooth and delicious treat - it's amazingly easy. Come an' get 'em while their HOT (or COLD as the case may be).
We'll be raffling off a Full Suspension Mountain Bike. Complete with disc brakes, this will take the trails or the streets in style. Tickets are only $2 or 3 for $5 and all proceeds will go to the ReCYCLEry. You don't need to be present to win, but you DO need to buy a ticket! (anytime between now and Saturday the 7th at 5PM)
All our accessories will be on SALE - 7% goes back in your pocket and 7% does good in the community through the ReCYCLEry. All tubes will be ONLY $2 - we have 12" through 700c sizes, all shapes and configurations. Stock up for the summer at this awesome price!
We'll also have some new bikes to check out in the electric and cargo realms. Come see and ride our new offerings! We'll be getting electric bikes by EcoBike, tried and tested in the hills of San Francisco. http://www.ecobike-usa.com/index.asp . We'll also have a few step-through models of our Cycle 9 electric bikes available. If carrying stuff is on your mind this spring, come check out the new Radish from Xtracycle. This longtail bike is compatible with all Xtracycle accessories but not as pricey as the Big Dummy. http://store.xtracycle.com/_e/Xtracycle_Complete_Bikes/product/BK-RAD-01/_Xtracycle_Radish.htm . And brand new is the Madsen cargo bike. This longtail can carry up to 4 small kids on the rear bench seats, or load it up with anything you can throw at it. The small rear wheel (20") and extra wide kickstand make it easy to load and handle. Come in for a test ride! http://www.madsencycles.com/
See you Saturday!
Saturday MARCH 7th
10am - 5pm
601 W. Main Street, Carrboro
919-636-5909
Thursday, February 26, 2009
Wednesday, February 18, 2009
The slow ride: geeking out on energy
When I'm biking, I often have a chance to ponder things. One thing I like to ponder is the amount of energy used to transport humans and things around. My electric bike is a great way to explore that geeky subject.
Today I did an experiment. I was riding my Big Dummy with a typical load, for a gross vehicle weight of around 300 lbs. I only used the electric assist to "take the edge off" the hills. I didn't use it to increase my speed (except on hills), or to accelerate from stops. I was able to get my energy consumption for the round trip down to 6.3 watt hours per mile. In other words, my round trip consumed 90 watt-hours. Of course, I invested more of my own energy in the ride, because the ride was longer than usual, about 13 minutes extra. But I didn't feel substantially more worn out or tired, because of using the electric on the hills.
For perspective, if I kept energy use at this level, with my single 10-lb LiFePO4 battery (48V/10Ah = 480 watt hours), I could ride 76 miles! I typically use more like 16 watt hours/mile, which would reduce the range to 30 miles.
The only real difference in the ride is the speed. Normally I average around 18 mph for the ~15-18 mile ride (depending on route). Today I averaged 13 mph. Wow, that seems slow! On my road bike, I would have averaged more like 17 mph on this route. Why such a difference?
I did a little mapping of my route using bikely, an online bike route mapping tool. It can show an elevation profile of the ride. I was amazed to find out that during my round trip of 17 miles, I do a total of 1000 feet of climbing (gross, not net)! That's more than when I lived in a Canyon in the mountains of Utah. The difference is that here, it is not nearly as obvious, because that 1,000 feet comes as a series of small ups and downs (some of them quite steep). So by the end of the ride into the office, I've only gained a net of 50 feet, even though I pedaled up 550 feet of hills (and 450 more feet of climb for the ride home, with a net loss of 50 feet).
No wonder I was so slow on the cargo bike. I'm hauling at least 60-70 pounds extra compared to the road bike, with the Xtracycle, all my gear, the heavy gearhub, the battery, etc. Carrying 60-70 pounds up 1,000 feet is not a trivial energy investment. This was very instructive - I suggest that readers try it for their own routes, they might be surprised.
Now when people ask me whether I will "wean myself" from my electric assist, I will answer them: "let's see you pedal a loaded cargo bike up a 17-mile, 1,000 foot climb every day without electric assist." In reality, I would simply not do this ride every day (or more than 1-2 times per week) without electric. I would just be too wiped out to have the energy for everything else that needs energy in my life (like Cycle 9, and my full-time day job as a professor, or kids).
All of this generated some additional thoughts. When I show people the batteries for electric kits, they often ask me, "does it really make up for its own weight?" The answer is emphatically yes for shorter rides like this. On a normal day, I will do my 17 mile 1,000 foot climb with a 300+ pound bike at an average of 17 mph (riding faster than most folks could do on a road bike for this route). This definitely pays its own way. But, I wonder, how much climbing could I do, before I would I reach the "break even" point, where further climbing would just be me dragging the battery + motor up the hill. Here's a rough estimate:
The 48V/10Ah battery weighs 10 lbs, or 4.5 kg. It holds 480 watt hours, which is about 1.72 million Joules. We'll use Joules to figure out how much energy it takes to lift a 300 pound bike up a hill. Neglecting friction for the moment, the energy used in climbing is given by m g h, where m=mass of bike, g=gravitational acceleration, and h is height. So for my bike on this climb we have U (potential energy in metric units) = 136 kg * 9.8 m/s^2 * 304 m = 405 kJ of energy needed to lift the bike up those hills. If we figure the hub motor is only 80% efficient, then we used 506 kJ of energy, about 1/3 of the battery capacity. I'll address friction losses later.
Now we can estimate for just hauling the battery and motor up the hills: the motor is another 8 lbs, or 3.6 kg. With controller and wiring added in, we'll call it an even 20 lbs, or 9 kg. So, U = 9 kg * 9.9 m/s^2 * 304 m = 26,812 Joules, or accounting for 80% efficiency, 33.5 kJ. In other words, the energy used by the motor system to lift itself up the hills consumes only 2% of the energy it holds in the battery. We can approximate how far the system could lift itself before I would start having to lift it. Here, U = 1.72MJ * 0.8 (80% efficiency) = 1.37MJ = 9 kg * 9.8 m/s^2 * h. We want to solve for h, so: h = 1.37 MJ/(88.2 kg m/s^2) = 15 kM - yes, 15,568 meters. This system most definitely pays for itself - even if I'm climbing mount Everest. How high can it carry the whole bike and I, if I were too lazy to pedal? h = 1.37 MJ/(1332 kg m/s^2) = 1,208 M, or about 3,374 feet. Not bad - that's a pretty big mountain.
So there we have it - the electric system pays for itself in spades where climbing is involved.
But what about friction?
So far, I'm having trouble finding good numbers for friction on a bike. I know this: The frictional losses due to wind resistance go up with the square of the velocity (v^2). That's why when I increase my average speed from today's 13 mph to my regular 17 mph - only a 4 mph difference, or about 25% - my energy usage goes up so much. I am burning up much more energy on friction - but I am also contributing less total leg power, because I have less total time spent pedaling.
Here's a rough estimate: we know that all the potential energy gained in the 1,000 ft of climbing is burned up as friction on the way down the hills (I don't use the brakes much since the hills are short). Typically on the downhills I am traveling closer to 20mph average. So, we can get a very rough estimate of total friction, by starting with U = 405 MJ = downhill frictional losses for the downhill parts, and figuring out how much I loose on the uphills. If my speed on the uphills is 1/2 that on the downhills (average of 10 mph), then the total wind resistance losses are 1/4 of that on the downhills. Plus, I'm sure there are some additional losses for bearings in the bike and static interaction of tire to road, which we'll add in as a fudge factor of 100 kJ. So we have U = (405 kJ (downhill total) + 405 kJ * 0.25 (uphill wind) + 100 kJ (fudge)) / 0.8 (80% efficient) = 757 kJ = 210 watt hours. Yay - that is about what I actually end up using, except on days that I travel really fast, or have particularly heavy loads. So that means my estimate of frictional losses on the uphill parts, of about 205 kJ total, is in the ballpark. That's about 57 watt hours, or 8 wh/mile burnt on friction when at low speeds (total input combining motor + legs - efficiency losses of both).
That's way geeky. But, hey, it is nice to know where the energy goes, and more importantly, that my electric bike system really does carry its own weight (and then some). It all boils down to this:
1. If I want to save energy, I go slowly. It makes a very big difference.
2. At 10 mph, I'm burning around 6-8 wh/mile on friction (electric + pedaling), and at 20 mph it is around 25-30 wh/mile (electric + pedaling). At 30 mph, this rises to 60-70 wh/mile.
3. The electric system will carry itself, and me along with it, up some very big hills, as long as I don't burn up its energy on friction by going fast
4. It is fun to ride a loaded cargo bike on a 17-mile, 1,000 ft hilly commute, often passing roadies and watching in my rear view mirror as they pedal really hard to try to keep up (and knowing that I'm being super energy efficient in the process)!
Wednesday, February 4, 2009
Work and pleasure
Today I got to combine work and pleasure: I rode 38 miles round trip on my electrified Big Dummy (the Firefly) to Duke University. I gave a seminar on Bioinformatics, and then rode home. It was a cold day out (at least for these parts), with my ride home dipping well below freezing. I brought along a thermos with hot tea, and stopped several times to top off my tea cup (mounted in my handlebar beverage holder). On the way home, I even stopped at my favorite place to waste spend money, A Southern Season, to buy some more tea and sundries.
Why is such a trip even of note? For a couple reasons. First, today we spoke to one of our bicycle suppliers on the phone. He was asking us about electric assist, and saying that he didn’t really “grok” (understand) the whole electric bike thing.
Today’s trip is a perfect example of why an e-bike works. I have ridden many miles on road bikes; I could have ridden the ~40 miles on my (non-electric) road bike on a recreational ride in better weather - easily. HOWEVER, I wouldn’t have done that in a down coat, with insulated boots, with a thermos of tea, with a handlebar stereo, with a large U-lock, with a full change of dress clothes (to give the talk), with my computer, with a full array of bike lights for after dark, and other miscellany. If I had ridden my road bike with that assortment of gear, I would have arrived very tired out (and also about 1 hour later).
With the e-bike, I got two hours of exercise (I was pedaling moderately the whole time), but I did the trip in luxury (especially since the Big Dummy allows me to carry so much stuff). I never got cold, since I had plenty of spare warm gear, and big heavy duty boots, down parka, etc. I was drinking hot tea for the whole ride there and back. I had good tunes. In the narrow, fast moving parts of the road, I used the electric assist to keep my speed faster to not impede traffic. I hauled my load of stuff up some steep hills without problem. I arrived for the seminar feeling good from the ride, but not worn out. I left after the talk with plenty of energy, and had a (mostly) pleasant ride home, through some back neighborhoods up some very steep hills (to avoid the more traffic filled routes).
Simply put, I wouldn’t have done this trip without the electrified longtail bike. I would have ended up driving a car. Comparing the energy usage of that:
Car: 25 miles per gallon. That’s about 1,320 watt-hours (KwH) per mile. If I still had a Prius, that might have been as good as 45 mpg (doesn’t do as well in cold weather), or 733 watt hours per mile. In other words, each mile traveled in a Prius would have consumed the equivalent of 7-hours running a 100 watt lightbulb. For the whole trip, that would would amount to 27 kWh - the equivalent of leaving a 100 watt lightbulb on in my house for 278 hours or 11 days straight (that’s with the more efficient Prius!)
Bike: 18 watt hours per mile (about 1,833 miles per gallon). The whole ride consumed 684 watt hours of electricity. That’s equal to less than one mile in the Prius, and about 1/2 mile in the big car! I could charge my battery with the equivalent of 7 hours of 100-watt lightbulb usage, easily doable with the solar panel on my roof.
Why highlight the stark difference? Simple: I never used to think about how much energy I was using when I got into the car to drive. And I suspect most people don’t. Gas has been so cheap for so long, there is no motivation to think about it. But, when put in the above context, it is all the more clear how much energy it takes to move that hulk of steel around. It doesn’t matter whether the car is electric or hybrid or whatever. It is heavy, and it travels fast. Both of those factors mean that it is intrinsically inefficient, and consumes a lot of energy. For those folks concerned about CO2 emissions, the above numbers say a lot.
But here’s the sad part. I studied the maps carefully before going, to find a route where I wasn’t going to be fighting traffic. And the best route I could find was far less than ideal. There was a 5-mile stretch of former country road, that is now used by commuter traffic. It was busy. It was narrow. It had no shoulder. And it was the least of all evils connecting the towns of Chapel Hill and Durham. Sure, I know about things like “ride big” and “take the lane”. I did those things. But as I watched in my rearview mirror for approaching traffic, it was a constant concern; would the car slow for me? Would I have to get out of the way? Statistics show that for slower-paced roads, concerns about being hit from the rear are overblown. That doesn’t change the basic human instinct to want to know what is going on behind, and not liking having a zillion cars whiz by. It is the number one reason more people don’t bike.
It just seems absolutely crazy that two neighboring college towns, Chapel Hill and Durham, don’t have a reasonable bike route connecting them. I blame this firmly on the old boy network in North Carolina’s DOT. Maybe I shouldn’t say this on a public blog, but those guys need to get their heads out of their rear ends and realize that we are in the 21st century, not the 1950’s. Maybe in the 1950’s we needed more roads to be built; now we don’t. Now, we need more bike paths, sidewalks, railways, and other means for people to get around without burning ridiculous amounts of energy. And doing this would benefit the drivers too - it is never fun for a cyclist to be passed by a bunch of cars on a narrow busy road. But it is no fun for the drivers, either. Building out infrastructure to appropriately accommodate both would make everyone’s lives better.
Would I do the trip to Durham/Duke again? Yes. It was great. Much better than sitting in a car or bus. I got exercise, and an adventure, all wrapped within some important work-related business. I would probably plan my ride for a bit less busy time, if possible. But, regardless of whether I would do it, most people just won’t face such a ride, without the kind of experience I have commuting by bike. And some people think I’m crazy, anyway. To get more people on their bikes, and less people using up tremendous amounts of energy to move metal boxes around, we need to invest in bike facilities, now.
Why isn’t that part of the economic stimulus?
(note: there are token amounts in the stimulus for bike paths, but they pale in comparison to road funds).
Why is such a trip even of note? For a couple reasons. First, today we spoke to one of our bicycle suppliers on the phone. He was asking us about electric assist, and saying that he didn’t really “grok” (understand) the whole electric bike thing.
Today’s trip is a perfect example of why an e-bike works. I have ridden many miles on road bikes; I could have ridden the ~40 miles on my (non-electric) road bike on a recreational ride in better weather - easily. HOWEVER, I wouldn’t have done that in a down coat, with insulated boots, with a thermos of tea, with a handlebar stereo, with a large U-lock, with a full change of dress clothes (to give the talk), with my computer, with a full array of bike lights for after dark, and other miscellany. If I had ridden my road bike with that assortment of gear, I would have arrived very tired out (and also about 1 hour later).
With the e-bike, I got two hours of exercise (I was pedaling moderately the whole time), but I did the trip in luxury (especially since the Big Dummy allows me to carry so much stuff). I never got cold, since I had plenty of spare warm gear, and big heavy duty boots, down parka, etc. I was drinking hot tea for the whole ride there and back. I had good tunes. In the narrow, fast moving parts of the road, I used the electric assist to keep my speed faster to not impede traffic. I hauled my load of stuff up some steep hills without problem. I arrived for the seminar feeling good from the ride, but not worn out. I left after the talk with plenty of energy, and had a (mostly) pleasant ride home, through some back neighborhoods up some very steep hills (to avoid the more traffic filled routes).
Simply put, I wouldn’t have done this trip without the electrified longtail bike. I would have ended up driving a car. Comparing the energy usage of that:
Car: 25 miles per gallon. That’s about 1,320 watt-hours (KwH) per mile. If I still had a Prius, that might have been as good as 45 mpg (doesn’t do as well in cold weather), or 733 watt hours per mile. In other words, each mile traveled in a Prius would have consumed the equivalent of 7-hours running a 100 watt lightbulb. For the whole trip, that would would amount to 27 kWh - the equivalent of leaving a 100 watt lightbulb on in my house for 278 hours or 11 days straight (that’s with the more efficient Prius!)
Bike: 18 watt hours per mile (about 1,833 miles per gallon). The whole ride consumed 684 watt hours of electricity. That’s equal to less than one mile in the Prius, and about 1/2 mile in the big car! I could charge my battery with the equivalent of 7 hours of 100-watt lightbulb usage, easily doable with the solar panel on my roof.
Why highlight the stark difference? Simple: I never used to think about how much energy I was using when I got into the car to drive. And I suspect most people don’t. Gas has been so cheap for so long, there is no motivation to think about it. But, when put in the above context, it is all the more clear how much energy it takes to move that hulk of steel around. It doesn’t matter whether the car is electric or hybrid or whatever. It is heavy, and it travels fast. Both of those factors mean that it is intrinsically inefficient, and consumes a lot of energy. For those folks concerned about CO2 emissions, the above numbers say a lot.
But here’s the sad part. I studied the maps carefully before going, to find a route where I wasn’t going to be fighting traffic. And the best route I could find was far less than ideal. There was a 5-mile stretch of former country road, that is now used by commuter traffic. It was busy. It was narrow. It had no shoulder. And it was the least of all evils connecting the towns of Chapel Hill and Durham. Sure, I know about things like “ride big” and “take the lane”. I did those things. But as I watched in my rearview mirror for approaching traffic, it was a constant concern; would the car slow for me? Would I have to get out of the way? Statistics show that for slower-paced roads, concerns about being hit from the rear are overblown. That doesn’t change the basic human instinct to want to know what is going on behind, and not liking having a zillion cars whiz by. It is the number one reason more people don’t bike.
It just seems absolutely crazy that two neighboring college towns, Chapel Hill and Durham, don’t have a reasonable bike route connecting them. I blame this firmly on the old boy network in North Carolina’s DOT. Maybe I shouldn’t say this on a public blog, but those guys need to get their heads out of their rear ends and realize that we are in the 21st century, not the 1950’s. Maybe in the 1950’s we needed more roads to be built; now we don’t. Now, we need more bike paths, sidewalks, railways, and other means for people to get around without burning ridiculous amounts of energy. And doing this would benefit the drivers too - it is never fun for a cyclist to be passed by a bunch of cars on a narrow busy road. But it is no fun for the drivers, either. Building out infrastructure to appropriately accommodate both would make everyone’s lives better.
Would I do the trip to Durham/Duke again? Yes. It was great. Much better than sitting in a car or bus. I got exercise, and an adventure, all wrapped within some important work-related business. I would probably plan my ride for a bit less busy time, if possible. But, regardless of whether I would do it, most people just won’t face such a ride, without the kind of experience I have commuting by bike. And some people think I’m crazy, anyway. To get more people on their bikes, and less people using up tremendous amounts of energy to move metal boxes around, we need to invest in bike facilities, now.
Why isn’t that part of the economic stimulus?
(note: there are token amounts in the stimulus for bike paths, but they pale in comparison to road funds).
Subscribe to:
Posts (Atom)