IZIP Express - The EVO Hub

This fantastic new E-bike out of the stables of Currie Technologies has many new and exciting things that make it stand out in a crowd. The EVO rear hub kind of hides from view, but is undoubtedly the heart of its power system. My last post discussed the motor and drive layout and its operation, and this one will go even deeper into what makes it all work. Plus I will attempt to tell you how it feels when you ride. Attempt is the key word as you really need to try it for yourself to see what it’s all about.

Most electric-assist bikes allow the motor to drive the wheel directly. Whether it is a hub motor, drive chain or friction wheel, when the motor runs, the wheel turns proportionally. Not so with the IZIP Express. This is where the EVO-Drive hub comes in. Touted as a patented dual planetary drive system, it blends the power of the motor with the power of your legs. This sounds so simple (does it?), but how it feels and works will take some explaining.

I really want to get an inside look at the workings of this hub. You might be familiar with a planetary gear set. The most common use you might recognize is in an automatic transmission for a car or truck. I can totally envision what it looks like inside the EVO hub, but I think the better way to think of it is like a set of spider gears you would find in the differential of a car or truck, or maybe a adult tricycle. I am trying to focus my X-ray vision right now with no luck.
Regardless of the actual mechanical workings inside, here is what it does. A differential (spider gears) was designed so the two drive wheels on a car could rotate at different speeds during a turning maneuver. (I am hoping you already understand this principle). (If you don’t, follow along anyway until I get to the part about how this all works on this E-bike). If you have ever been stuck in the mud with a car, then you know that while one wheel doesn’t turn, the other one spins wildly. That spinning wheel turns much faster than normal because of the action of the spider gears.

Now the EVO hub uses its gear action in a completely different way. Instead of distributing drive power to two output units, it blends the power of two inputs into one drive unit. The two drive inputs are the motor (though the belt drive) and your leg power (through the standard chain and freewheel). It does give kind of a disconnected (maybe not the correct word) feeling that you don’t experience on a normal bike, but it is all good.

As you start to pedal the motor kicks in immediately. This is thanks to a super fast computer and ECU (electronic control unit). The motor may or may not be turning its side of the hub as fast as you are turning the freewheel side with your pedaling. This is where the blending part takes place. As you pedal faster, the motor speed also rises. If you pedal slower, the motor speed decreases. The two inputs blend to match the different speeds into forward action. This allows you to cruise or accelerate as you see fit. And we are talking accelerate.

The motor’s control system has five levels of assist and an off setting. At each different setting, you are experiencing a different gear ratio because of the EVO drive hub. This is even harder to explain, but don’t give up on me now. So the hub acts like a variable ratio geared hub in some ways. Once again, a nice long ride can tell you so much more than my words here. If you have ridden a dual-drive system then it might make more sense. These combine a 3-speed internal geared hub with a 8 or 9 speed rear cassette for 24 or 27 gears without a multi-geared front chain ring. Only the IZIP Express’s EVO hub gives the feel of a infinitely variable system.

To explain this better, let’s use a six speed bike drivetrain as a comparison. With the motor system in the off mode, first gear feels like first gear. The motor holds the belt side part of the drive from turning and the pedal side does all the driving. In this mode the gear train feels normal. In the lowest of the power levels, first gear feels (at the pedals) like second gear. And so on up to the highest power assist level where first gear feels like top (6^th) gear. Now this is only when you first start pedaling, because right away as the motor does its thing, everything changes.

You can feel what I mean by toggling the motor assist levels while you ride in any particular gear. You can feel the perceived gear ratio change at the pedals when you do this. It is an unusual effect, but becomes more normal the longer you ride the Express. The EVO hub is using its properties to match the inputs and the gear ratio change is part of that action. 

You can (and I often do) leave the bike in a middle gear (middle front chain ring gear and middle rear cassette gear), and ride at any speed you like. Because of the variable action the hub gives and the assist from the motor you really don’t need to do any shifting. The bike takes off well from a stop and moves out quite nicely at higher speeds. Of course the IZIP Express has a high-quality 27 speed drivetrain and shifting through the gears can really help you utilize its full potential.

The Express comes factory equipped with SPD clipless pedals because it works best with a smooth pedal cadence in the 60-90 RPM range. The smooth power input from you allows the motor’s power to respond to your needs more consistently. A changing RPM (during each rotation) at the pedals results in some surging effects from the motor. This is most evident in the lower gears during heavy climbs. This is due to the fast response of the motor’s sensing system (pedal cadence sensor). Plus it also comes from the continuously variable gear ratio effect the EVO hub offers.

I know this because not being a clipless pedal type, I installed a regular set of pedals before I took possession of this Express. The surging will not slow you down and doesn’t cause any ill effects on your ride. Like I said, it is the most noticeable in the lower gears on heavy climbs (while I am charging up steep grades faster than any bike or E-bike I have ridden before). 

The final thing you might notice is a mild kick (back) on the pedals when you are rolling and you begin pedaling again. It is part of the disconnected feel I mentioned before. It is from the instant the motor starts back up again and the hub is finding the right blend to the two power inputs. This is not a draw back, just one of the ways the bike responds as you ride.

The truth is that the IZIP Express is an awesome, fast, massive hill climbing machine, and just plain exciting. I constantly find myself smiling from ear-to-ear and burning up the road at a fantastic pace. I keep getting worried that this bike will spoil me for all others. Time will tell on that matter, but for now I am having the time of my life with this E-bike. I will report more on the bike, its handling and other interesting things about riding it.
Get your EVO on and ride, Turbo Bob.

“It is no exaggeration to affirm that a journey by bicycle is like none other; it is a thing apart; it has a tempo and a style of its own.”---James E. Starrs, The Noiseless Tenor.

The author of this post...Bob is a long-time cyclist living in San Diego, California. With favorable weather conditions, he and his wife Barbara, ride often. They each have an E-bike, along with a small fleet of vintage Schwinns. 

Activities include: Art, Photography, Model aviation, Model railroading.

Visit Bob's blog on E-bikes, Folding bikes. Bike rides, and Vintage Schwinns

For more information about the author of this article visit: Turbo Bob’s Bicycle Blog