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Building a R15k 65km/h bike

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The goal

When I decided I wanted an electric bike, I had a few goals in mind.
-Top speed of 50km/h: easily exceeded, my top speed is 65km/h.
-Range of 30km: also exceeded, I comfortably do 50km. It seems really efficient, but I guess it's because I pedal, and mostly only do 30km/h so I can get some exercise. From 40km/h onwards I struggle to spin my legs fast enough.
-Weight: Light enough down 3 flights of stairs: I manage, barely. The bike weighs 38kg.
-Full suspension: It is.
-Battery in the triangle, I hate rear racks on a fully suspended bike.
-Must look cool: I think it does, but looks are relative.
-Must work as simply as my cellphone, ie. I want to plug one plug in to charge, and flip one switch to turn it on.
-Tough enough to go single track riding: I can, I don't do jumps even though it should be able to. Dirt roads are no problem though.
-Not too pricy... As the title says, I spent R15000, back in 2009. Some things would have become more expensive, others like batteries cheaper. I'll put updated prices in the thread as I go along.

So having reached my goals, and now with 7000km on the clock I think it's fair to say this is a tried and tested method, so I'll now tell you how to build one.

Here's what the finished product looked like before it was grey

After going grey:

And some video:

Step 1: Picking a bicycle

I wanted an ebike. I don't need one, but I want one. My old motorbike was doing a fantastic job of getting me around cheaply, but it had some problems. It was making me fat, and I couldn't pack it into the boot of my car when I went on holiday. Oh and of course it smelt of petrol and oil. So an ebike had to be born. There are thousands of options to building one but this post will be about my tried and tested method for a bike that's performed flawlessly for 7000km and counting.

So step number one means getting hold of a bicycle. If you want to go faster than 50km/h you need full suspension. And a helmet. Never forget the helmet. I did once on a regular bike and ended up jumping the queue in the ER ward. If you're going to be going motorbike speeds, get a motorbike helmet. People will think you look like a fool wearing one on a bicycle, but they stop that after you pull away from them at the lights...

Ok so what should you look for in a bike. First the good points. Expensive bicycles make poor ebikes. Carbon fibre is a lousy material for this conversion, don't even try. You also can't convert a road bike into a high powered ebike. Maybe they could handle a tiny motor, but why bother. Best case scenario is to find a mid range bike with a steel frame so you can weld on to it if needed, but since they're in extremely short supply, like most people you're going to end up with an aluminium frame.

Not all frames are created equal either. If you're like me, you won't want to put 8kg of batteries onto a rear seatpost rack. It'll either break your seatpost after some time, of you'll have to lean way forward whenever you pull off to avoid wheelie starts. If you have an expensive triple crown fork you could attach the batteries to the handle bar with some home made mounts, that works pretty well, but ideally you'll want the batteries inside the frame triangle. You're also not concerned about the weight of the frame, so you can look at old spec downhill bikes.

This is my trusty steed I picked for the job:

It's a kona kahuna full suspension with disk brakes. Initially I wanted a kona stinky which is the downhill bike with the same frame deisgn but better suspension. Unfortunately I couldn't find one at the time. I picked this bike because it has quite a decent sized triangle, and it was cheap. Just under R5k if I remember right. and using my mildly primitive cad software I'd worked out that I could get a 24 of my choice in batteries into the triangle without too much difficulty.

Because the batteries I use and recommend are 38mm wide, it means I can get three next to each other and 8 groups to get a total of 24.

Coming soon will be step 2. Picking the motor.

Step 2: Picking the motor

For the electrically challenged note that it's a motor, not an engine. Engines have 200+ moving parts, and need to be serviced and fed explosive fuel, motors have 1 moving part, don't need servicing and can run on sunlight if you really wanted them to.

So there are a lot of motors around in the ebike world. The one I used on my bike was a Crystalyte 5305. It weighs 12kg and has bucket loads of tordue. Motors have advanced since then, and Crystalyte don't make that motor anymore. In it's place there are a number of other motors. Of course you could also shop at other manufacturers, but if you want good value for money I'd stick to Crystalyte. Whatever you do though, don't buy a cheap geared hub motor from ebay, all that will happen is that you'll get a motor that strips it's gears the first time you actually apply any throttle. Direct drive hubs are far more reliable, and far quieter.

To get to 65km/h, which is of course plenty fast on a regular bicycle, I'm going to recommend the Crystalyte H4065. That 65 at the end there means this motor does 65km/h with a 72v battery in a 26 inch wheel. They also make a H4080, which does 80km/h, but you get more speed for less torque, and trust me, you don't need any more speed. I'd much rather have a lower top end and accelerate so hard my balls ache! The motors with more torque are also far kinder on the controller, so you're less likely to blow up controllers (we'll choose those later) in the long run. Incidently the 5305 I chose was also the motor with the most torque, and I am yet to blow anything up. At least nothing bicycle related!

So how does this motor perform. Well I haven't ridden one, but many people I know have. Here's a couple of videos for you.


As you can see things get pretty good once you up the voltage. The bike I'm recommending here runs 76.8v nominal, but will spend most of it's time in the 79v range. For those who haven't tried electric power, I can only describe the feeling as being shot out of a giant kettie. It's one long wave of power, and it's always there. Instantly. No gears to change or clutches to release. Sadly this also means that I don't let too many people ride my bike. It's got a 2 from 4 record, half the people to have tried it have been thrown off at some stage. Now I have a power limiting switch...

If you're in the mood for some hill climbing, here's a quick test on a very steep slope:

I use my bike on most of the mountain bike trails, delta park, emmerentia etc, and I've never come across a hill that steep. It's nice to know that if you did there'd be power to do it. It would likely even be easier as I'd approach with speed. All in all I think it's a pretty impressive motor, and you save about 3kg in weight over the bike I've got.

Hi Patrick

any updates on this?

Or are you too busy zooming around?  >:D

Yep, been far too busy. I'll get the next entry done soon. Still have the controller, batteries and management system to do, plus the little random bits and pieces.


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