# a good electric bike

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Joined: 04/25/2008
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Points: 9

basically, im looking for an electric moped/bike that can go an average of 25(or more)mph, can last at least 25-30 per charge and has to cost less than \$800 for total, including shipping. i live in san jose, california and i am having trouble finding one. please help! i researched the xb-508, good bike but i would rather have it local incase of warranty issues. i have been looking for liberty but have not found the price for it. need a good bike!!!

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Joined: 12/06/2006
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Points: 1309
Re: a good electric bike

John,

I have not seen this mythical bike you speak of. I am sorry to say I doubt there is a bike in that price range with the speed and range you are asking for.

The speed of 25 MPH average is tough to start with, 25 MPH top speed is doable but it would be much harder to average 25 MPH. When you add the range of 25 to 30 miles now you are talking about lots of battery power. Here is an example - My bike which has a top speed of 23 MPH uses 9.8 watt hours per mile(WHPM) at 20 MPH on average, for easy figuring lets use 10 WHPM. 10 time 20 miles is 200 watt hours. This means to go 20 miles at about 20 MPH (NO stop and go) I use about 200 watt hours of battery. To figure amp hours divide the watt hours by the battery voltage, in my case 36 volts, so 200 / 36 = 5.555 AH. A lead acid battery can only be discharge to 50% of its rating if you want it to last very long. I use 3 12-volt 12-Amp Hour batteries to get 36-volts @ 12-AH on my bike so I can discharge them to 6 Amp hours. If we take 6 AH * 36-volts we get 216 watt hours. As you can see at the end of 20 miles I am at the end of my usable charge. One other factor is the faster you go the more watt hours you need to maintain speed.

If I wanted to make my bike match your requirements it would look something like this. To average 25 MPH would require about 15 WHPM @ 30 miles which is about 450 watt hours. I would need to increase my voltage to 48-volts to reach 25 MPH so we will use 48-volts for the battery voltage. 450 WH / 48-volts = 9.375 AH this would mean to keep with the 50% discharge I would need 18.75 AH of battery. This tells me I would need a 48-volt 20 AH lead acid battery pack, which is the closest standard size batteries I could get for this application. A battery pack this size would weigh about 75 to 80 pounds. At this time my bike with lead acid batteries weigh 76 pounds, this would almost double the weight of the bike, not a good thing. I would not want to pedal a bike that heavy if the batteries, motor, or controller died.

I hope this helps you understand what you are up against with your requirements. The reason I used Lead acid batteries for the example is because of you low cost estimate. You could make this happen if you were using Lithium ion batteries due to their light weight but the cost of the battery pack alone would blow your budget.

A more realistic view,
Grandpa Chas S.

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Joined: 04/25/2008
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Points: 9
Re: a good electric bike

what do you think about the xb-508? its the type i want but alot of people think its quality is not good. what is your opinion? (ok mabe the 30mph was going to far, i thought about it and i can live with 20-24mph.) if the xb-508 is not a good buy, what else do you recommend that comes close to the xb-508 in terms of speed, look, price, and distant coverage?

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