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Discussion Starter · #1 ·
Hello everybody, from distant Croatia! :)

I am new to the EV game but eager to learn and to try and build something by myself. As you may or may not know, our country is going down the drain as fuel prices are rising (gasoline almost 9$ per gallon) so me and my buddy are looking to go green (and cheap!).

We have grasped the basics of electricity but still need some guidance, so if anybody's got the patience... :) it would be much appreciated.

WE would like to start with electric bikes since we already own solid cross-country mountain bikes, with aluminium frames and other parts of decent quality. Our problem lies in not having the option of ordering the parts from the manufactures that you mention here as customs/VAT would kill us. We'll have to improvise with locally available parts but I need some general specs.

The bikes should have an autonomy of about 40-50 miles (more better) and top speed of 30ish miles per hour.

1. How much power do we need in order to achieve this? (DC motor I suppose, what wattage?)
2. What voltage should we aim for and how many Ampere/hours shoud our system be able to store? (we got car batteries denominated in Ah Amperres/Hour)
3. Any other tips, advice, controller unit etc.?

Cheers all and thanx in advance for any piece of advice!

367 Posts
Search for posts by "Crodriver" - he has converted the most amazing BMW. He will know exactly what is available to you - a fellow Croatian.


120 Posts
Well since nobody seems to be biting on this post, and I'm an avid cyclist, I'll give this a shot.

I wasn't sure if you wanted to use mountain bike tires or road bike tires, so we'll go with something in between. let's call them cyclocross with knobby tires, which is hopefully what you're aiming for. Mountain bike tires have a rolling resistance coefficient of about .025, while a road bike tire's rolling resistance coefficient can be as low as .005 on nice flat pavement.

Let's assume these somewhat educated guesses for your bicycle's characteristics:

Base bike weight: 25 lbs
Passenger weight: 180 lbs
Motor weight: 10 lbs
Battery weight 80 lbs: 8 12V motorcycle batteries 13 amp hours each 4s2p
Rolling Drag coefficient: .008
Frontal Area: 380 inches
Coefficient of Air Drag: .8
Rolling Resistance Coefficient: .008
Motor efficiency: .9
Electrical efficiency: .9

I messed around a bit until I found the 4 series 2 parallel battery configuration. It will give you about a 49 mile range at cruising speeds of 25 mph. You will have no problem reaching your goal of 30 mph top speeds at 48 volts. Finding a motor to match should be pretty straight forward.
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