We’ve written articles before on mild-assist electric bikes before, but…this…is NOT one of those articles. And before anyone posts a comment to make sure to say that this is an electric motorcycle with pedals…we know!
The story of the Grayborg frame starts in 2001 with an engineer named Zvonimir (ES member HAL9000V2.0), who lives near Zagreb, in Croatia. This beautiful country is on the coast of the Adriatic Sea, between Italy and Greece. Next to Zvominirs home is a steep hill that is over 1,000 meters high. For fun and exercise, he used to pedal his mountain bike to the top, and then ride down very fast to the bottom.
Doing this takes about 4 hours, and he enjoyed doing it several times a week, but after his son was born he didn’t have enough spare time to do this as often as he wanted. As an engineer, he decided (of course) that he must learn everything about electric bikes, and then design the ultimate hill-climber to speed up the times when he does this.
Zvonimir has been experienced with bicycles and motorcycles since he was a young man, and he knew what he liked when it comes to the geometry on a full-suspension frame. He quickly put together some components on a mountain bike as a test mule for experiments (the Grayborg Warp G). This E-bike also had a series/parallel switch that allowed it run at 36V around town (for maximum range) and then switch to 72V for hill-climbing. However, it was immediately clear that even the strongest existing down-hill (DH) bicycle frames were not going to be strong enough for what he wanted.
Zvonimir began bending and welding Cromoly steel tubing to make a custom frame of his own design, taking into consideration the best ideas from the most respected DH frames, and also his many years as an experienced rider. The result was the Greyborg Warp production frame. As a side-note, he changed a letter in the name of the frame, so it was now the Greyborg Warp (with an “e” instead of an “a”). He showed it to his friends on the Croatian electric vehicle forum, e-vozila.com (e-vehicles.com in Croatian, if you visit there, use Google chrome so the website will be translated into English).
They encouraged him to build more frames and sell them, so he got busy making the first run of 30 Greyborg Warp frames in 2009. A friend named Vladimir (ES member Accountant) bought one of these frames, and was so impressed with it, he asked Zvonimir if he would like to form a company with him to sell them world-wide, and to also to develop new products. This was the beginning of the company Zelena Vozila (“Green Vehicles” in Croatian). At this time, the frames were designed around the Crystalyte 5305 motor using a 72V / 40A controller.
From that point on, growth has been steady. The first prototype frames had used 12V sealed-lead-acid (SLA) batteries, Crystalyte 5-series motors and high-amp Kelly controllers. The triangulated rear swingarm was set-up to accept a shock absorber between 145mm-185mm in length. Feedback from the first round of builders was vital in deciding on useful improvements to the frames, so that other optional motors, controllers, and batteries will be easier to fit in the next “V2” version.
In 2012, ES member “zombiess” (from Ventura, California) bought a Greyborg frame. He was so happy with the performance, he travelled to Croatia to find out more information, and he came home as the North American dealer for Greyborg frames.
To date, there have been over 200 Greyborg Warp frames sold, but for the next part of this story, we must move on to the next big stage in their growth, which resulted from the most powerful hub-motor in production today. They developed it to satisfy their customers requests….the Cromotor . The powerful Cromotor has been a big success, with over 500 units sold worldwide.
The Cromotor was made for the Greybog Warp frame. And while Greyborgs have been built up using a variety of motors, the Cromotor has also been installed in a variety of frames. The Greyborg Warp swingarm was improved to allow the Cromotor to fit better, and the V2 swingarm pivot was also redesigned to incorporate a concentric Bottom-Bracket, a sophisticated feature which eliminates chain-growth issues.
The most recent V3 version of the Grayborg Warp frame has several upgrades that are a response to Zelena Vozila’s communication with their passionate customers. A completely new swingarm was designed that has three specific features. First, the swingarm is slightly longer to reduce the bikes tendency to wheelie when using max power, such as the several 125V set-ups. Second, it allows a much longer shock absorber to be used, so a unit between 240mm-260mm is now recommended. Third, the swingarm was beefed up to allow the removal of the triangulation, and this helps a variety of custom builder options, such as using a Gates belt, instead of a chain.
Zvonmimir is now 44 years old, and for the last 3 years he has been working full-time as the head of mechanical engineering at Rimac Automobili (link http://www.rimac-automobili.com/). Rimac Automobili is the developer of the “Concept One” Electric car, which is a vehicle that we will all be hearing a lot about very soon (link http://www.rimac-automobili.com/concept_one/exterior-design-4).”
2009, the first production Greyborg batch.
The first version (V1) of the production Greyborg Warp frame was immediately popular. Then, in response to many customer requests, Zelena Vozila worked with a major Chinese electric hubmotor manufacturer to develop the Cromotor. Previously, the most common motor used was the Crystalyte 5304/5305/5306’s. The new Cromotor is not only more powerful, it is also lighter.
The white ABS canopy is made from automobile-grade materials that are UV resistant, and are heated and then vacuum-formed into their final shape. The frames are powder-coated (much tougher than paint). The canopy inner width is 110mm, and the swingarm accepts up to a 19-inch motorcycle tire. The wheelbase is 54-inches.
By focusing on using a rear hubmotor, the entire frame is available to hold a large controller and the maximum amount of battery (which is a restricting limit for most common frames). However, I have found one Greyborg owner who has decided to build up a light-weight mid-drive using an Astro motor, ES member “comradegerry”:
Written by Ron/Spinningmagnets, January 2014