This E-bike’s design is not subtle or sophisticated, it’s very simple. Take a large rear hub-motor, and feed it a huge amount of watts. It is a hot rod for the street, and it is all about power and style.
If you are interested in something similar, the first consideration is to find a bike frame that you like, and that also has someplace in the frame to mount a very large battery pack. Here, an endless-sphere.com forum member Mark from from Spokane, Washington (username: “Brake“) chose the Electra Straight 8 as a starting point.
Let’s get started!
After the frame question was settled, he had to decide what motor and voltage would provide him with the kind of performance he wanted.
Mark chose the Monster Cromotor, from Zelena Vozila (“Green Vehicles” in Croatian). The rear wheel has a 17-inch by 1.6 wide rim from the rear of a 1982 Honda XL 250R dirt bike. The rear tire is a Full Bore M-66 King Tour 100/80-17, originally spec’t for the front of a Harley Davidson (and rated for 150-MPH). Read our article on how to use moped rims and tires on a large rear hub. And…if you are interested in a rear hub that is a little bigger or a little smaller than this one, read our article on large hot rod hubmotors.
One of the things Mark liked about the original Straight 8 was the checkered flag pattern on the rim, along with the distinctive red spokes. He ordered custom-length spokes from John Rob Holmes, and after they arrived, Mark used a very tough powder coating (stronger than paint) to make them a fire-engine red. Mark also found a vinyl “wrap” with a black & White checkered pattern. The wrap was difficult to heat and form, but the results were well worth the effort.
Since the frame is made from aluminum, Mark decided to make the custom drop-outs from aluminum to make the welding options simpler. In order for aluminum torque-arms to work on a motor this powerful, they had to be very thick, and also have clamping bolts built-in. He bought a TIG-welder, and got to work.
As long as Mark knew he was going to have to weld-up new clamping drop-outs to the rear of the frame, he also decided to take this opportunity to make an entirely new frame section for the back half that was stronger and longer. The added length will help to tone down the tendency of the stock bike to wheelie, when using this much power.
Something very interesting that Mark was able to do with the larger diameter tubes in the newly fabricated section, is to run the motor phase wires through the hollow chain stay. This type of custom detail really knocked me out, and I really appreciate Marks extra effort.
This may seem like a lot of time and effort to extend the frame just four inches, but I think the results are well worth it.
Mark purchased a front hub that had the mounting flange on the left for a disc, and laced the front rim to it.
He chose the popular Avid BB7 cable-operated caliper, and the disc is a 203mm diameter Shimano Ice. The frame is definitely aluminum, but…the fork is cromo steel, so he machined a mount and properly welded it on. for the rear, he has been using regenerative braking (regen) as a magnetic brake.
Battery Pack Housing
One of the major reasons Mark chose this frame is the generous space in the center of it, to allow for a significant battery pack. He decided to make top and bottom housing supports from curved aluminum. For this, Mark dusted off an old body-panel forming trick from decades ago, used in the European custom sports-car prototyping tradition. He made and shaped wooden “styling bucks”.
“…I made wood forms. Annealed the 6061 T6 and beat it into shape. Had to anneal several times. This was tough…”
There was a time in England and Italy, when skilled craftsmen were very affordable to hire, and wealthy clients could order a unique “one off” custom body, made to bolt onto a specific frame. King Leopold III of Belgium once purchased a 1953 Ferrari 342, but had a custom cabriolet body made to his design by the Italian studio Pininfarina, so that…his Ferrari didn’t look like any other.
After all the effort required to do a good job using the wooden styling bucks, Mark decided to buy an English Wheel to try his hand at forming compound-curved aluminum fenders with that.
I love the shiny-black next to flat-black styling theme on the front fender. It reminds me of the beautiful black-on-black native-American Martinez pottery from New Mexico.
Building a Battery Pack
If you look closely, you can see the white fiberglass insulating cloth between the parallel groups to reduce chafing wear from vibration over time. On an 18650-format cell (18mm diameter, 65mm long), the entire bottom and sides are the negative electrode (anode), and only the small button tip is the positive electrode (cathode). Some of these cells look like their sides are bare metal, but they have a clear shrink-wrap on them.
“…This 3-kWH Tesla-cell pack is a huge improvement, my range is now somewhere between 50 and 100 miles…”
This is a 21S / 12P pack, using 252 of the 18650-format cells. If you use the recommended charging protocol of 4.1V per cell, a 21S arrangement provides 86.1V when the pack is fully charged. The Tesla-Panasonic NCR18650B cells are 3400-mAh each, so a 12P pack provides a whopping 40.8-Ah of range.
The Watt-Hours (Wh) of a battery pack are Volts X Amp-Hours, so 86.1 X 40.8 = 3512 Wh
A few acessories
The tail-light, and “Cycle Luminator” headlight are from Grin Technologies in Vancouver, Canada.
Mark also chose the 2-speed “Metropolis Patterson” bottom-bracket crank-set. Since the second gear is an overdrive, this compact unit equals a 60T chainring, to make pedaling along with a fast E-bike a little easier.
I would be reluctant to run this much power through a hardtail frame (even with such fat tires), and in order to take some of the jolts of the road out of the ride, Mark upgraded to a suspension seat-post. we like these too, so read our article on the various suspension seat-post options.
Back in March of 2013, an ES member “willow” posted a beautiful Electra Straight-8, and the hand-made leather battery enclosure really caught my attention. Mark saw this too, and decided that he wanted to use this same model as the basis for his own version.
“… The bike has been fantastic, I absolutely love it. There is no way I could imagine living without an ebike now….”
Here’s a 6-minute video. At 2:12, he does a 0-50 MPH run up in about 3 seconds! and no…its not for sale.
Written by Ron/spinningmagnets, August 2015