I picked up a '93 Marin Bear Valley SE from a vintage store and spent time restoring it (surface rust, old components etc). I was pleased with how it turned out and enjoyed riding it, nice old steel frame. I then decided to convert it to electric with the Bafang BBSHD 1000W kit and have the motor already installed. Here is my slight dilemma; It's 1x7 speed (replaced front 3x chain-ring with BBSHD 1x chain-ring). I spent the extra money buying the BBSHD 1000W kit as I wanted the extra speed but don't want to be restricted with only 1x7. What to do?? My plan currently is to upgrade to 9 or 10 speed..but that involves a new rear wheel as my old freehub body only takes 7 speed..so new rear wheel, stretch out rear triangle, new rear derailleur, new shifter, new chain, maybe an upgrade to disk brakes? Or should I simply revert it back to normal and buy a new mtb already with 10+ speeds and convert that instead? I like the idea of having one bike only though. Please help! How difficult/expensive to upgrade drive train? Thanks
The cheapest update you can do is a bigger chainring. You have the BBSHD chainring (how many teeth? it exists up to 52 teeth), but there are alternatives:
- third-party compatible parts (google for "ChainRing for the BBSHD")
- adapters to regular BCD chainrings (I found some of them via googling "BBSHD to BCD adapter"), then you may find large or very large chainrings (I know they exist for recumbent and for small wheels track bicycle ... both are exotic bicycles, so do not expect to find them easily and of good quality).
However, a bicycle is made to go as fast as a bicycle. I guess you would like to go as fast as a moped. I have the feeling you are pushing the frame (and the fork!) at the edge of what was built for. The 1000W motor is already a quite a powerful one. You are adding weight, torque ... and speed, to a frame that was not designed for these additional loads.
Ride safe, respect the local laws (especially of physics, well, they will act anyhow with or without you paying attention) ... and compare the forks size/thickness of small mopeds with the fork of your nice steel frame ;) .
So you have a 7 speed bike, with presumably a cassette of 11 though 28 teeth, and a single chainring of 40/42/44 teeth.
Your rear wheel will be a 26" or 559 according to modern nomeclature, and your rear tyre is probably between 1.5 and 2 inches (37-52mm)
The motor will propel you faster, until either
- The assistance limiter kicks in,
- The maximum speed of the motor is reached,
- Aerodynamic and rolling resistance forces balance the power input by the motor plus the rider's efforts.
So the only way to get a higher top-end speed will be to move a factor stopping you. That may mean disabling a software-based limiter.
You can get more aero by using a thinner tyre, a more supple tyre with lower rolling resistance, a tyre with ideally a smooth tread, and increasing the air pressure in your tyres within-reason.
You can alter the ratio of input to output by increasing the size of the chainring, and decreasing the tooth-count on the cassette. 11 is the common smallest size, so if your bike has a 12 or 14 tooth smallest cog then consider something with a smaller smallest cog.
The cost here is that as top speed goes up, power and torque drop off. It is possible to go faster on a bike but take longer to get to that speed, so it is always a compromise.
You can go for a larger radius wheel too, but that also trades power/torque for top-end speed, and is likely such a swap would require a different frame.
You can additionally add more power by pedalling harder - a mid drive does not replace the rider's effort, and from a safety point it is important to keep your legs turning over all the time.
Every one of these changes could cost additional money.
Ultimately, if you crave speed without the required personal input of effort, then a bicycle might not be the right tool for you, and you should look onward to other powered transport options.
Specs for this kit are taken from https://bafangusadirect.com/products/bafang-1000w-bbshd-mid-drive-ebike-motor-kit