How electric bikes perform in terms of speed, range, and elevation gain depends on many factors. The most important
factors are listed here with the (generally speaking) most important at the top:
As you can see, battery size ranks at the top. With a
pair of big car batteries mounted on a trailer, you can go for
hours. To double your range, double the size of your battery
pack. System efficiency ranks at the bottom because most systems
are 85% to 95% efficient. The speed you go makes a big
difference in how far you go.
- battery capacity (measured in volt-amp-hours)
- terrain (number and incline of hills)
- e-bike speed (range at 10 mph is 8 times as far as at 20 mph)
- wind conditions (going 10 mph against a 10 mph headwind feels like 20 mph to the bike)
- pulling a trailer (which is like pulling another bicycle)
- correct tire inflation (under-inflated tires slow you down)
- weight of rider and baggage
- motor/controller/drive system efficiency
e-bikes come with two 12-volt 12amp-hour batteries which will
take an average rider 8, to maybe 10, miles over moderate terrain
at 15 mph with no pedalling. The volt-amp-hour rating of such a
pack is 288 volt-amp-hours (2 * 12 * 12 or 24V * 12Ah). To
estimate the range of other battery packs, simply compare their
volt-amp-hours to 288. For example, a 36V 10Ah pack contains 360
volt-amp-hours of "juice" or 25% more than a 24V 12Ah pack
(1.25 * 288 = 360). Remember, however, that sealed lead-acid
batteries should not be fully discharged to ensure longest life.
All else being equal, range is a function of either
1) battery capacity (amp-hours X volts) or 2) speed and ease of
recharging (high-power chargers provide lots of miles in less
than one hour). There is a direct relationship between battery
capacity (amp-hrs) and both weight and physical size (total
volume). Commonly used sealed lead-acid batteries weigh twice as
much a NiMh batteries of the same rating and 3X a Lithium Polymer
Elevation Gain: For hill-climbing, expect
about 3 feet of elevation gain for every volt-amp-hour. For
example, a stock battery pack (24-volt, 12 amp-hour) will take you up about 800 feet without pedaling (3
feet X (24 X 12) = 864 feet). Another way to compare performance
is the ability to gain elevation. Here are some anecdotal
- ZAP DX system with
13-lb SLA battery can gain about 450 feet of elevation.
- Currie U.S. ProDrive
system with 20-lb SLA battery can gain about 800 feet of elevation.
- Betterbike Model 20
with two 20-lb SLA batteries can gain about 1600 feet of
- EV Global 36-volt bike with 20-lb SLA battery can gain about 800 feet of elevation.
Speed: All else being equal, speed is a
function of motor (watt rating) and controller. Most electric
bike motors are capable of higher performance characteristics
than the controller allows. Motors with roughly 500 watts
continuous rating are required to push a 160-lb. user down the
road at 18 mph when dressed normally (no spandex) on an upright
[Beware: Some e-bike advertising touts their
high-power motors (e.g. 600 watts), but only deliver 400 watts
through the controller.]
As for power, consider that Lance
Armstrong's average speed over a 2-hour ride is 20.5 mph.
That's just over the legal speed of e-bikes. Lance expended about
1/2 horsepower, or 373 watts, continuously. Most e-bike motors
operate continuously in the range of 300 - 600 watts. Most
e-bikes, therefore, will make a "Lance Armstrong" of
difference in getting you down the road and up the hill!
Regenerative braking doesn't yield much "juice"
back into the battery. Even the hi-tech regen on electric
automobiles gains less than 10% of the original charge.
Therefore, given a choice of either regen or freewheeling, you
will generaly get more range with freewheeling - unless you have
a hilly route.
Due to the nature of batteries, you can double the
battery life expectancy by discharging only 50% of capacity
instead of 75%; you get 6 times the battery life at 30%
capacity usage per cycle. Think of battery lifetime as having
$1000 in the bank and withdrawing a dollar with each 30% disharge
cycle -- and withdrawing $10 every time you deeply (85%)
discharge the battery.
Rules of Thumb:
a SLA battery pack that goes at least twice the range you
usually expect to ride to avoid deep discharges (past 50% discharge); Lithium
batteries can be deeply discharged (75%) without accumulating battery damage.
- Range is proportional to battery size; twice the battery size = twice the range.
- For every two miles you ride, plan on about one hour of charging and about one cent of electricity.
- When speed increases, range decreases even faster; 1/3 faster = 1/2 the range.
- A 400-watt motor takes an average rider up all but the steepest hills (but weak controllers can limit performance).
- Two 12-volt, 12 amp-hour batteries will take an average rider 8-10 miles at 15 mph or up a hill that's 800 feet tall.
"Bargain Buys" Most electric bikes
priced less than $500 at big box retailers and on-line are aimed
at the kid/teen/toy market. They generally lack the performance
and durability that people want and expect. Also, parts and
service can be problematic with both big box retailers and
on-line vendors. We urge you to invest in an e-bike that will
serve you (and others) for many years. If you choose to buy a
"Bargain" anyway, read our quality
control and final adjustment guidelines. Remember, if it's
poorly constructed and you can't get repair parts, it's likely to
become land-fill material.
Diagnose and fix e-bikes.
First off, distinguish between the bicycle and the
electric drive system. If you're having problems with a bike
part, your local bike shop can help. Or you can find lots of
useful fix-it information at:
If you start with our diagnostics page and
successfully isolate your problem, you'll know whether you can
fix it yourself or want a service company to fix it. To fix it
yourself, get parts from a parts retailer.
Do-It-Yourselfers may want to consider a set of plans
for the Slipstream
Electric Bike. Others will want to delve into motors,
controllers, batteries and gearing at our D-I-Y
introduction. Then check out the online
users group, especially the archives which are searchable for
your keyword interests. Also helpful is the book Electric
Bicycles: A Guide to Design and Use, William C. Morchin,
Henry Oman, ISBN: 0-471-67419-2, Paperback, 190 pages, November
2005, Wiley-IEEE Press, $39.95,
Resources for riding
(trailers, how-to, etc.)
Buying a bike.
Fixing a bike.
Learning to ride a bike.
trailers, tandems, technologies, and access
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