City Bikes

A city bike will normally have smoother tires and a heavier frame, your posture will be rather upright, they can have a cargo basket in the front and the back. Most people will use it for commuting, shopping or errands around the city, but you can do road trips too, as long as it is mostly on paved roads and the road is not extremely steep. It’s a wonderful replacement for a scooter and can even replace your car, if you live in a city and your winters are not too harsh. This kind of e-bike works best with a small (250W) front hub motor and a small to medium size battery (~300Wh). You should probably buy a ready-made one, there is not much advantage to DIY here and they are the cheapest kind of e-bikes sold.

Cargo Bikes

A cargo bike is much like a city bike, but will have an even heavier frame and more storage space. Many even have a trailer or dedicated storage units. If you live in a large European city to the north of say, Adriatic, you probably see them every day. People use them for work (transport and deliveries for small businesses) and shopping. Like city bikes, there are many ready-made options here, but there is more space for DIY, since the needs are more diverse: Do you need a stronger motor for your heavy load? Do you drive a lot each day and need to make the battery larger? Would you like to convert your city bike to a cargo bike? Do you already have a cargo bike, but just want to electrify it?

Depending on your needs you could with a hub motor or a mid-motor setup. A (bigger) hub motor should still be enough for the lighter cargo bikes, as long as there are no very steep hills to climb. If this is not the case, a mid-motor setup is a must. You will need a bigger battery: Take the weight of a fully laden bike with you on it in kilograms (e.g. 200 kg) and multiply by 3-5 to get an estimate of what you need in Watt-hours. A somewhat oversized battery on a cargo bike is less of an issue weight-wise than on other types of bikes.

Mountain Bikes

A mountain bike should be familiar to you already. The posture is intermediate and the tires are usually thicker with more profile for a better grip on gravel and mud. Almost all have front suspension and some have rear suspension too. Mountain bikes with front suspension are a good candidate to DIY-electrify, but beware the rear suspension: it is likely it will be hard to work around the linkages and there is less space for the motor/battery. It’s probably best to buy a ready made fully-suspended e-bike instead, but it can be expensive. It makes sense to pick a slightly larger frame size for an e-bike conversion, but if you like your existing bike, just go for it.

A mid-motor setup is a must with mountain bikes, the hub motors simply do not work well on very steep climbs. When I look at people electrifying mountain bikes, I see a clear tendency to oversize the motors and batteries. People will install 1kW or larger motors and huge 72V batteries, but this is not a bike anymore—we will discuss mopeds later. Instead, think about your physical fitness and size:

• A thin and fit person will hardly need the motor in any case, except for steep climbs. A 250W or 350W mid motor is more than enough for them, along with a small 350Wh battery. The reward for not over-sizing is a lighter bike and a much cheaper conversion.
• Most people (medium height/build, not totally sedentary) should choose a 350W or 500W motor with ~500Wh battery.
• Bigger people (tall and/or overweight, sedentary) will need a 500W or 750W motor. Choose the battery size by taking the combined weight of the fully laden bike (saddlebags and all) and the rider in kilograms (e.g. 150-170kg), and multiply by 4-5 to get the battery size in Wh. This should last you the whole day.

Gravel Bikes

A gravel bike is a bit of a cross between a mountain and a road bike, with no suspension, but a sturdier build. The posture is usually quite low. Most of my comments about mountain bikes apply, but these bikes are normally chosen by fitter people and you will likely want to keep the motor and battery size on the lower end of the ranges I mention there.

E-mopeds

An e-moped is an e-bike with a massively oversized motor and battery. Several kilowatts of motors and thousands of watt-hours of batteries are not uncommon—all bets are off here. To me, these are simply electric motorbikes and out of scope here. But they do have (mostly unused) pedals, obviously make for a fascinating hobby, and seem to have a lively community of people building them.

What If You Just Want To Build Something?

What if you have no clue about what to build, but still want a DIY e-bike? The answer is simple: Get a second-hand mountain bike and buy a decent mid-drive kit in line with my recommendations for a mountain bike. It will be a cool thing to build, quite useful for anything from commuting to bike trips to errands, but it should not break the bank. After you ride it for a while, you will know what you want/need, and if you need a different bike, you will be able to recoup most of the costs by selling what you made.

During that cool period people started writing about e-bikes and I got curious. I wanted to build one and check out all these cool new technologies on my own. It was a bit of a journey and I’ll simplify somewhat:

• My first e-bike was a used city bike with a front hub motor and rear hub gearbox.

  

  I got it from my neighbor as payment for helping them run some wires in their new guest house. It was missing a battery and the motor controller was one of the brand-locked ones where the manufacturer will not let you use it unless you had their battery too. So I ditched it and bought a cheap chinese motor controller and battery off e-bay.

  It was a minimal investment to start with and so I 3d-printed a custom battery mount with controller housing. It worked well, considering, and I started using it for daily exercise; it lasted a couple of seasons until the old hub motor started developing insulation faults. I guess it was just a bit underpowered for the controller I bought. I removed all the electrics from the bike and sold it to a friend who still uses it.

• Next I bought a used midsize mountain bike and converted it to rear hub motor system, building my first homebrew battery as well.

  

  It was similar to the city bike, but it had some more torque and could go up steep hills better. But the main advantage was not the motor, it was the mountain bike: I could finally be more relaxed on gravel and mud I sometimes encountered on my drives.

  But the bike had a fatal flaw, the combined weight was too much for the rear wheel spokes and I spent more time repairing these than driving. Turns out rear spokes are a limiting factor for an e-bike with a big guy like me driving it and it gets worse with a rear hub motor. It also still had limited torque on the really steep climbs.

• After rethinking everything, I decided to buy a larger used mountain bike and go with a mid-drive system. I was by now used to building homebrew batteries, so I only had to buy a Bafang BBS system and the rest was homebrew.

  

  This was the jackpot—mid drive (which lets you use gears better) and larger bike were the combination that let me drive anywhere. I bought some saddlebags and suddenly I was able to do the same kind of summer vacations I did with my motorbike, just with slightly shorter daily distances. The motorbike soon lost my interest, so I sold it after a few seasons :)

  The bike needed just a few more upgrades: 4-piston disc brakes and a stronger rear wheel to handle the extra weight, and larger tires to make it even easier to drive anywhere I liked. Now, everything just works!

I love e-bikes! I love how they make you a superman and give you the option to just go almost anywhere. I love how I can do vacations with them. When you drive and see an attraction at the side of the road, a motorbike requires extra work: first you need to stop safely, then get out of your hot protective gear, lock it up, the shoes are not really built for longer walks etc. With a bike, you just stop, hang the helmet on handlebars and throw a lock on the bike; 20 seconds and you can do whatever you like. (E-)bikes are pure freedom!

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