The expected range for electric bikes depends on several factors, so it is difficult to compare different bikes. Added to this, the tendency for some sellers to exaggerate makes it even harder for the average consumer to make sense of it all. This post will attempt to demystify the factors that determine range and allow a potential customer to cut through the BS. First, lets go over the main factors that determine range for an e-bike. The weight of the rider, combined with the weight of the bike is a major contributor. Next in importance is the occurrence and slope of any hills. It takes allot more power to go up hills which will drain the battery two to three times faster. Speed is also a major factor, it takes more power to go faster. Other factors include wind, type of tires and inflation, and riding style. By riding style, I mean how quick you are starting off and how much you pedal. Acceleration takes about three times as much current than maintaining the same speed. So without specifying most of these factors, range specs by themselves are almost meaningless.
There are three general ways to specify range: absolute maximum under ideal conditions, expected under average conditions, and typical what most riders will get. In the first case, the spec will assume a light rider (>150 lbs), no wind or tail wind, level ground or slight down hill, pedaling the entire time, lowest power setting, speed 15 mph or less. The average setting will assume a medium rider 150-175 lbs, no wind, level ground, pedaling only sometimes, medium or high power setting, mixed speed. The typical setting assumes a medium rider, slight or no wind, level ground, maybe a short, slight hill, high power the entire time, full speed the entire time, pedaling only to start off. So the exaggerating seller will use the ideal conditions for their spec, though while technically possible, will not be typical. The more honest seller will use the average or typical spec. At Hightekbikes, we use the typical spec and assume the rider will go full speed the entire time with little pedaling.
This brings us to how range can be calculated given known values. One general rule of thumb is that you can expect to get 1.5 miles per AH (ampere hours) with a 36V battery. This assumes average conditions, so varying speed and pedaling some. So for example, with a common 36V 10AH battery, you would get 10 * 1.5 = 15 mile range. Going up some hills might decrease that to 1 mile per AH and by the same token, pedaling a lot on level ground and going 15 mph could increase the range to 2 miles per AH. What it gets down to is how much current will the motor require to move you. Maybe it take 10-12 amps at full speed (20 mph), 20 amps going up hill and accelerating, and only 7-8 amps at 15 mph. First lets clarify ampere hours; AH designates current, measured in amps (A), over time (hours). Amps * Hours = AH. So a 10 AH battery can output 1 amp for 10 hours, or 10 amps for one hour. For example, say it takes 10 amps to go 20 mph and you go full speed until the battery dies. How far have you gone? Going back to the formula, you divide 10A into 10AH and get one hour. So you went 20 mph for one hour. Multiplying one hour times 20 miles per hour gives you 20 miles. That’s a bit optimistic, a more common setup would require 15 amps to go 20 mph. So running the numbers again we get: 10AH/15A = .67 hr, next 20mph * .67 hr = 13.43 miles. Lets do one more to illustrate how a slower speed affects the range. We know slower speed take less current, so at 15 mph, it might only take 7 amps: 10AH/7A = 1.43 hr, 15mph * 1.43hr = 21.45 miles.
The above calculations are based on a 36V battery, the most common with ebikes. However, what happens if it is a different voltage? Given the same AH value, a lower voltage will give less range, and a higher voltage will give more range. To compare batteries of different voltages, we must use watt hours (AH * V) as our measurement. WHr takes voltage into account and allows us to compare apples to apples. For example, a 36V 10AH pack is 360 Whrs while a 48V 10AH pack is 480 Whrs. Clearly, the 48V pack has an additional 120 WHrs of capacity available. Production e-bikes generally stick to the legal 20 mph limit, so that extra capacity will go towards range. In contrast, motor kits are designed to reach 20 mph at 36v and when run at 48V, go faster. So the extra capacity could go towards the higher speed and result in the same range as the equivalent 36V system. It even might get less range at full speed due to the rate of increased power required to go over 20 mph (due to wind resistance). However, if the rider maintains the 20 mph speed, he can put the extra capacity to use as extra range. Some e-bikes are still using 24V, notably smaller foldup bikes. So you get less WHrs or capacity. Using the same example of 10AH, the 24V system gives you 240WHrs or 120 less than the 36V system. Like using the simpler AH rating above, you can use WHrs to determine range. Instead of miles per AH, it’s miles per WHr. Based on the typical 15 mile range for a 36V 10AH pack, you are using 26.8 WHrs per mile (360/13.43=26.8). So with a 24V system (240WHr) you would get 9 mile range, 36V system (360WHR) you would get 13 miles, and with a 48V system you would get 18 mile range. Note these calculations were for one situation and were for comparative purposes.
Some final points to consider are the efficiency of different motors under different conditions. For example a gear motor is more efficient at going up hills due to the internal gear ratio. A direct drive motor is better at high speed cruising. Also some battery manufacturers spec the AH rating at a lower current than you would typically use in operation. So the end result is you will not get the full rated amount of ampere hours out of the pack. Different tires and wheel size can also affect efficiency. Even so, the general guidelines above, give you a close approximation of what range you can realistically expect.
To summarize, don’t necessarily believe all the claims on range made by some sellers. Since potential customers use that for comparative purposes, there is a huge incentive to inflate this value. What you want to do is get the voltage and AH of the battery, make a judgment on the efficiency of the bike and components, factor in riding style and terrain, then plug the values into the formulas. As a general rule of thumb, you can expect 10-20 mile range from a 36V 10AH pack, with 15 miles being typical. Contact us at firstname.lastname@example.org for more information.