On Tuesday, January 23, 2018 at 10:18:40 PM UTC, Bob Newman wrote:
I ride a road bike usually twice a week, usually 30-40 miles each. I used to ride (not average) about 15-16 mph. Due to a few health problems + hitting my 70th birthday I'm down to 13-14 mph and I'm terrible on hills (Florida hills). I'm considering getting an electric assist for my road bike by replacing the rear wheel with the assist, the battery would go in my water bottle holder. I would like it to assist me to get back to my 15-16 speed or close to it.

Opinions please. Would this be a doable solution?

Thanks in advance... Bob

I'm in your position, Bob. About ten years ago we moved up the steepest hill in town which I immediately used as a reason for upgrading from Shimano hub gearboxes to 14-speed Rohloff, and Rolls-Royce class bike at the same time.

A bit later I had heart surgery twice and looked into electric bikes. The first thing that struck me about the "official" electric bikes, of which the Bosch/Panasonic motored types are the best, was that they took all control out of your hands. But that's not the worst. Far worse is the fact that they're counterproductive. By law these so-called pedelecs prorate the input from the motor to your pedaling cadence. That is, the harder you pedal, the more the controller tells the motor to add. That's simply stupid. What you want is for the motor to provide more power when you can pedal no more. (Like Pete, and I presume like almost everyone else here, I take it you don't want an electric bike but a bike on which you can get electric assistance for help on the steepest hills, or to keep up with a social riding group.)

So I dismissed the pedelec types and decided to do my own conversion, and include manual controls.

Basically, how big a motor you want depends on how much torque you want. Torque is the potential for additional acceleration at any point of output; it's also what breaks the bike free when it is overloaded with a case of wine in each pannier (I use pannier baskets) at the supermarket. I dismissed the rear wheel motors not only because I have expensive hub gearboxes, but because bicycle-sized clusters under a third of a horsepower (the common 250W motors that are the smallest you should consider) are likely to have their life cut shorter than normal.

The first motor I fitted was a 250W 8FUN which I bought as a complete kit of a wheel with the motor built in, controls, 8Ah bottle battery, wiring loom and cutout brakes. I bought this merely as an experiment to establish parameters, and I specified it as the motor having the highest torque. It is a very popular motor. (Technically, it's a Bafang 8FUN QSWXK, the K meaning it is specially prepared for finicky European tastes at Bafang's Swiss installation. See a description of its choice and installation at http://coolmainpress.com/BICYCLINGbuildingpedelec1.html .) The controls included a thumb throttle. The purpose of the thumb throttle is to over come the disadvantage of the pedelec software, of giving less assistance just when you need more. This is a very good motor but, as I suspected, it wasn't quite up to my 215 pounds, or my speed (downhill!) o n very rough lanes. It melted its drive wheels in about 3500km. This leads to another point: an electric motor installation on your bike isn't a capital expense. Both the battery and the motor are consumptibles, only theoretically rebuildable because the special tools for opening them cost more than just buying new. Another surprise: the actual motor is cheap; it is the controls and above all the battery that costs. It just wasn't worth my while to rebuild the motor, though the battery was still good; if I were keeping that setup, I would simply have bought another but this time bare SWXK from China for about sixty bucks.

BTW, you must buy the biggest battery in Amp Hours that you can afford, but you don't need to go higher in voltage than 36V; Pete is not altogether mistaken about that but is presumably influenced by the Endless Sphere crowd who are not bicyclists at all but electric motorbikes; 48V on the sort of electric assistance bike you say you want is an altogether American excess. A large amp-hour rating is not only for distance, which can be important if you're the sort of rider who takes, or would like to take, day rides rather than one-or-two-hour outings, but because the instant current capability (coulomb rate) of the battery is directly related to both acceleration and velocity (actually maintainable speed).

So, after I invested five hundred bucks or so and some time in the modest front-drive kit, what did I decide? For a start I decided that the Sino-Swiss kit is one hell of a bargain, and would do most people. There was no speed shortage but, as we saw, the torque (=instant current load) I demanded near the top of hills when I ran out of puff, eventually overheated the motor to the point of melting gears; this was also a factor of having just marginally too small a battery to do all the business I demanded. I imagine for someone not 215 pounds, not a pretty heavily outfitted bike, not demanding very high current loads under unfavorable circumstances, and not otherwise abusing the motor, the SWXK kit would satisfy and last probably several years, and is rebuildable if you standardize on that sort of motor.

So which motor and battery did I buy to last me for the longterm? I stuck to the same manufacturer and went only one step up on the motor, but decided to make it a central motor for weight distribution and because, with the Rohloff, there is no fear the motor will destroy the gearbox. The motor I bought is the Bafang 8FUN centre motor, very popular also with the Endless Sphere electric motorbikes and offroaders in bigger versions than I thought enough. However, in the battery I went several steps up, and bought a 13.5Ah battery, which many this side of the Atlantic have considered overkill. Not so at all. Neither my motor nor my battery have ever been as much lukewarm. I got a really good battery in the my first Sino-Swiss set and it was still good when the motor clocked out but I didn't even try to run my new motor on it: it would have been adequate, I've been told, "But the way you ride, sure, it would have choked you off a few times on every ride." So I splashed out on the big battery and, another 3.5k later, both motor and battery are in perfect condition, and I foresee years of further service.

I cannot stress enough how much I suspect that the fact that the first, front, motor was slightly underpowered and the battery just barely big enough, contributed to its shortened life. Others with the same kit think I'm am an abuse. (Screw them too. I was making an experiment and I learned plenty from it.)

Nor can I stress enough how much more fun it is to ride on an electrified bike that goes as fast as you want and as far as you want. It isn't that with the 8Ah battery I had to cut rides short but at some point over 20km I was always conscious that it would be smart to have a reserve. With the 13.5V battery -- and using it to keep up with the crowd at the top of hills or on long slopes, rather than riding the thing like an electric bike constantly under power -- I imagine a 40km ride would not need economizing. I know this because I once kept the throttle open for an experiment for 22km there and then back again, and there was still excellent oomph up my home hill.

However, while you could possibly make up your own kit in front or rear drives, in the central kit, if you want the most sophisticated controls, you must buy a readymade kit. The best controls are well worth having: they include not only a throttle, but programmable operating sets, including settings to tailor the output to your requirements (i.e. to avoid the stupidities of the peddlers), including a program for full output from standstill. You won't get anything like this on the Bosch/Panasonic pedelecs because it is illegal in Germany, where these bikes are designed.

You also need to look after the battery by recharging it religiously after every ride, no matter how short.

***
Ralph, you can forget those calculations of yours based on the assumption of draining a lipo battery. If you do that at all often, it'll be dead within a year, and it's the most expensive component on an electric bike. Also, how much of its current a battery can delivery at any moment depends on it's absolute size as well as the quality of each individual cell in the battery pack, and on how the cells are arranged in series and parallel.

Andre Jute
Meet you on the road when we're 90