Building my first bike.

[dne202]

I've been lurking and researching about ebikes for about a week. I'm looking to build or buy an ebike. I don't own a bike. Here are my specs.

Purpose: Daily Commute so I can ditch my car commute for environmental reasons
Distance: 12 Miles each way, can charge at work but would love something that can make the round trip.
Desired trip time: 30-35 mins
Desired Cruising Speed: 25-28 MPH
How hard I want to pedal: Same amount of energy as would get a normal bike going 8 mph
Weight: 180 lbs 5'10"
Location: Los Angeles
Terrain: Beach Bike Path, sometimes sandy, mostly flat, biggest incline is about 130 feet in a half mile.
Budget: As close to 1,000 bucks as possible, but willing to go 2,000
Motor Type: Hub Brushless Motor with a torque sensor

I tried an Aventon pace 500 yesterday with a cadence sensor on a hub motor and it just felt strange and unsafe. I'm willing to fork the extra cash for a torque sensor and make the ride more natural. I chose hub motor not only for the price but also since I'll be by the beach I figured the sand and salt air might get all stuck up into a mid-drive and require more maintenance. Ideally, I can contribute the amount of energy needed for a leisurely bike ride so I get some exercise but don't get to work sweaty.

Any advice is welcome... the guy at the bike shop said building a bike was a bad idea and dangerous because standard bikes were not meant to handle that kind of torque. But... he had a vested interest in me buying a pre-built bike so I'm gonna take that with a grain of salt.

 

[flat tire]

You are on the right track with direct drive hub motor and torque sensing bottom bracket. Not only are they low maintenance they are the smoothest and quietest option. You will need to add torque arms to your hub motor for peace of mind.

I don't have a recommendation for the bb cuz I ride throttle only. If you go throttle only you can reallocate a lot of your budget to the battery. You will need a big battery unless you ride in an exotic position covered in lycra.

1000W 9C direct drive hub motor kit, with sine wave controller cuz they are practically silent (awesome). If you remove your bike chain you will make almost no noise at all with a sine controller.

For a battery get something around 1000Wh or 1kWh. You might fall a little short of doing both ways or you could make it with energy to spare depending on how you ride. Your speeds are vaguely achievable depending on tires, body position, etc.

 

[E-HP]

9C hub with a 48V 14Ah battery gives you 29 miles of range @ 25mph, with 100W of human input. Does your budget include the cost of the bike?

https://www.ebikes.ca/tools/simulator.html?axis=mph&motor=M2706&batt=B4814_EZ&autothrot=true&throt=75.2

PS. If you go the torque sensing route, your choices of controllers and displays will be fairly limited, so you may want to start there.

 

[markz]

Building your own ebike is simple and straight forward.
Grab a bike you love to ride.
Buy a hub motor whether it be geared or direct drive or mid drive. There are pro's and con's to each.
Select a suitable controller.
Get a proper battery, not some ebay/aliexpress/alibaba mystery battery. Buy from a reputable source!

You will need to spend the $2kusd.
Here is what you do. You go ahead and buy the Leaf 1500W kit, rear hub, its a direct drive.
You buy your battery from EM3EV.
If you want geared motor, you buy the MAC and everything else from EM3EV.
If you want a mid drive, you go ahead and buy the BBSHD or the Cyclone. But your terrain aint hilly so dont bother.
Remember, buy a spare throttle.
Remember to buy or make torque arms.

E-Ride

the guy at the bike shop said building a bike was a bad idea and dangerous because standard bikes were not meant to handle that kind of torque. But... he had a vested interest in me buying a pre-built bike so I'm gonna take that with a grain of salt.

 

[dne202]

Thanks, everyone! So helpful! @E-HP, I am going the torque sensing route. But a quick question, if I use torque sensing and I get up to 25 mph, will I encounter resistance enough to contribute to the forward momentum of the bike? When I was on the aventon with cadence sensor, once I got up to 25 mph I wasn't even capable of encountering resistance on the pedals. It led me to be wildly spinning the pedals and made it hard to balance.

 

[RunForTheHills]

You need to make sure the bike has the right gearing for the speed you want to go. If the gearing is too low, you will spin out at higher speeds. You can use the late great Sheldon Brown's gear calculator to determine what chainring and gear cluster you need.

https://www.sheldonbrown.com/gear-calc.html

Under "Gear Units" choose what cadence you normally pedal at. If you aren't sure, choose 80. 60 would be if you like to use high gears and mash, 90 if you like to spin the pedals at an easier effort.

 

[RLutz]

There are a couple of different ways that the torque sensor can detect your input. The article in this link does a great job of explaining it all: https://www.ebikes.ca/product-info/advanced-pas-kits.html
If you can find an e-bike using the Bosch motor and controller for a good price used, go for it. The Bosch system is very intuitive. If not, I happen to prefer the Sempu unit for DIY bikes.

To get to your question,

will I encounter resistance enough to contribute to the forward momentum of the bike?

There must be torque or the controller will not send juice to the motor. The more effort you put in, the more power sent to the motor. If you are spinning with no resistance the controller will cut power to the motor. So to cruise at an average speed of 25-30MPH you will need a big chainring for when you are up to speed to provide a cadence where you still have resistance.

The good news is you can plug the Cassette brand and size into a calculator and enter the number of teeth needed on the chainring to achieve your goal here: https://mike-sherman.github.io/shift/
Make sure to enter the Cassette, Wheel size, Chainrings and your preferred cadence range in the tabs at the top. Most people who cruise at 8MPH using <100 watts are pedaling at around 70-80 RPM. Dedicated roadies often like to find a gear that puts them at 100-110 RPM.

I hope this helps. Looks like RunfortheHills beat me to the answer with a more concise response.