My Gravity Hybrid E-Bike

Another bike build for me as I continue to search for E-bike "perfection", or at least my idea of it. It started with the notion that I would build a multi-purpose bike using a 29'er disc frame and the Bafang mid-drive. I picked up the bare frame off of craigslist. It can handle some of the biggest 29" tires or with a relatively high bottom bracket I could use 26" if I wished. My dream was to have one bike I could use with relatively smooth skinny 700C tires for the road or pop on a set of 26" wheels with big 2.35" tires for unpaved stuff but nothing real gnarly. Unfortunately the Bafang mid-drive has a few flaws which I find unacceptable.

I already have my Jeep bike that pedals nicely with narrower tires or can accommodate big tires for a plusher ride. And I built up a more aggressive bike purely for the road using a Nashbar cyclocross frame. The latter is by far the more efficient bike as I consistently use 25% less battery energy compared to the Jeep for the same route at the same average speed. I still enjoy riding the Jeep more however, it's simply more comfortable.

With that in mind I left the big BA's on the Jeep, stripped the Nashbar and built a new "inbetweener" bike. I just finished it and took it out for the first time this afternoon. For the most part it met all my expectations; more comfortable than the Nashbar bike, more efficient than the Jeep. At a base weight of about 41 pounds it also is lighter than just about any commercial bike. Once the accessories are added; fenders, kickstand, rear rack and bag, mirror, barends, etc it does rise to 45 pounds. An assortment of tools, spare tube and pump run it up even more to 47.5 lbs but that's still not bad.



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This is my 9th build...and I'm already thinking about the next.

-R

Very nice.

Where did you buy all the parts from?

lester12483 said:

Very nice.

Where did you buy all the parts from?

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Oh my gosh...all over the place, and some were from previous builds or new stuff I bought and squirreled away.

The more recent parts just for this build:

Frame-Craigslist
Fork-Online bike store, Tree Fort I think
Headset-Ebay
Disc Brakes-Ebay
Rear wheel-BikeWagon
Tires/tubes/handlebars/barends/chain/WB cage-Nashbar
Rear Derailleur-Online bike store, forget which one
Bottom Bracket-Ebay
Kickstand-Amazon
RUSSELL sticker-VeloInk
GRAVITY stickers-BikeIsland

Slightly used stuff from other builds:

Crankset-a long time ago from Ebay
Battery-AliExpress
Motor-AliExpress
Spokes-Grin
Mavic Rim-Online bike store, forget which one
Controller-ElifeBike
Fenders-Amazon
Brake Levers/shifter-Ebay
Computer-Amazon
Throttle-Modified scooter trigger throttle
Rest of the parts were obtained either from online bike stores or Ebay.

It's rather expensive and time-consuming building a bike this way but it's also rewarding to see it come together from a pile of parts. My last two builds, Nashbar flatbar and Electra Townie Cruiser, were also frame up builds. Even my Jeep bike which started as a $150 purchase off of Ebay is vastly modified so that the only original parts remaining are the frame/fork/headset,front brake and rear derailleur.

-R

After just a handful of rides I have rebuilt this bike. There was nothing wrong with it however the Outrider motor I installed on my Jeep Comanche bike turned out to be a disappointment so I returned the YOUE front motor/wheel to that bike restoring it to the configuration I so much enjoyed last season. No worries though, I acquired an Easy Motion rear geared cassette motor from a forum member last year. The motor is manufactured in China by Dapu, a Japanese company. I laced it (2X) into a Mavic A119 rim. The motor spins at 7.9 RPM/V or almost exactly the same as the YOUE it replaces. It is a bit larger than the YOUE, 155mm vs 144mm, and is about 2 lbs heavier.



I also moved the Schwalbe Big Apple tires from the Jeep bike along with the Planet Bike Cascadia fenders. I bought these tires about two years ago and tried them briefly on the Jeep bike. They dampened road imperfections however I also found they slowed the bike and made it feel less responsive. I returned to using the previous lightweight Kenda tires but did want to give them another go. I installed the BA’s and the big fenders once more on the Jeep bike when I switched to the aforementioned 7.2 RPM/V (260RPM) Outrider front motor. Again I found them to really sap the power of the Outrider plus they caused the front end to shake quite severely at 20 mph when I sat up and removed my hands from the handlebars. They would have their last chance on this bike before finding their way to the trash heap!

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I also switched controllers from the 6-FET 14A KU63 clone to an older 9-FET 15A KU93 (one shunt clipped). The 6-FET with the YOUE and the 48V downtube battery provided satisfactory power but I also sensed some “buzzing” through the frame that I wanted to see if the KU93 would cure.



My first ride was disappointing. Top speed was less than nearly identically wound YOUE and overall the bike felt under-powered. And just like with the Jeep the Big Apples caused front end instability. I rode the bike again with the big front fender removed and there seemed to be some improvement but the front end still shook violently when un-weighted at higher speeds.

For my next test I swapped the KU93 for an old “Cellman” 4110 6-FET 23.6Ap controller. As you might imagine the performance increase from upping power 50% was dramatic.

Finally, I reinstalled the Vittoria Randonneur Hyper 700 x 38 tires. Wow what a difference. Pedaling is much easier and top speed actually increased. Power used from the battery decreased 12% over the same course at the same average speed. Furthermore the front end was rock-steady at over 30 mph with my hands lifted from the bars. I wanted the Big Apples to deliver the goods but I gave them every chance and they struck out!

-R