Perhaps the most overlooked asset of an Ebike is its’ most important feature next to a handlebar and seat. For when yer out of power, how else are you going to get back home? But more to the point – the function of a bike is to pedal. If you can’t pedal, and if the frame doesn’t have pedals – then legally it’s not a bike; that’s called a moped or a motorcycle.
What we want to do here today is provide clarity on how to configure the ebike so a person can still pedal while under power. Here’s the reasons why:
- Pedaling is healthy. Good for circulation, lowers heart risk, adds oxygen to the brain, lots of good stuff there.
- Pedaling extends the range of the Battery. Pedal soft or hard with the motor; let your body be the guide – it knows what it wants. Whatever is contributed will measurably offset forces of drag.
- Pedaling allows for a way to get back home in case of low or depleted Battery. We want that for sure.
- Some places in the world – like Europe, require pedaling before power can be applied to the motor; this is called a “Pedelic” system. At Kinaye, we sell the component that is required to create a Pedelic ebike configuration. It’s very inexpensive and easy to install.
- And, there are some places in North America where it is better to pedal in public view to avoid scrutiny by dubious legal dragnets, you know… them redneck towns.
- Finally, the best reason of all for pedaling is to demonstrate that – yes, it can be done comfortably, at 38 mph.
Let’s get our Kinaye on then and figure this out as we walk through the various options.
A Bit of History and Context
Next to fire, and perhaps beer, the Wheel is the most important invention of all time. The earliest examples of gears date from the 4th century BCE in China. Before that, friction rollers were used, however they tend to slip under load and are unable to maintain constant ratios. Think: belt-driven pulley. Gears on the other hand are toothed wheels that are able to positively transmit mechanical power and torque from one wheel to another.
The Chain Drive is a way of transferring that power from one place to another. The oldest known application of a chain drive appears in the Polybolos, a repeating crossbow described by the Greek engineer Philon of Byzantium (3rd century BC). Imagine - in one hundred years we go from Gears to Chain Drive, however it would take over a 1000 years before the first continuous and endless power-transmitting chain was depicted in writing.
Today the Roller Chain is the most efficient mechanism for transferring power from one ring to another. It was originally conceived by Leonardo da Vinci in the 16th century, although it would take nearly 300 years before industrial production made use of it. The most common forms of application are… go on, guess: Bicycles, motorcycles, cars, and conveyors. Bicycles made use of roller chains just 10 years after the production of roller chains (reference: 1890s Golden Age of Bicycles). In that time derailleurs, freewheels, and pneumatic tires were introduced to the mainstream. Can you imagine the game-changing liberation of personable mobility?
Theory of Gears
It begins with understanding Levers and Ratios. With Levers, the longer the lever is past the fulcrum, the greater the lifting force. A seesaw is a great example of this. Gears are like levers organized in a circle. But before we discuss that, consider that Gears work like pulleys:
- Imagine a barn with a single pulley above the door slung with a rope attached to say… a bale of hay. The pulley provides a 1:1 Ratio of lifting ability, same as if we pulled straight up on the rope (if we ignore gravity).
- Link a second pulley and we have compounded (doubled) the lifting ability.
- Each pulley we add further multiplies the lifting ability, like extending a lever; 3X, 4X, 5X, and so on.
Gears have teeth. Each tooth on the gear acts like adding another pulley; the more teeth we add – the greater the lifting ability. Now wrap a toothed rope, a “chain” around the gear. Relatively speaking, for the same chain-speed, more teeth cause the gear to rotate slower than a gear with less teeth. The difference between the two speeds is called “Gear Ratio”, also called “speed ratio” and “gear train”. Mathematically this is expressed as ωa/ωb = R, where ω = angular velocity, and the a and b part are the identities of the rotating elements; input:output. We can have a ratio of 1:1 where both are equal, our single pulley. We can also have 1:4, read aloud it sounds like “1 to 4”, meaning the input rotates 1X for every 4X rotation of the output.
Cranks, Chainrings, and Cogs
Forward motion begins with pedaling; they are attached to the Crank Arm: A long lever that is attached to the Crank Axle. This axle lives inside a “Bottom Bracket”; a special assembly of bearings and capture that, unlike almost every other part of a bicycle, does not loosen or hardly ever require maintenance through its’ lifetime. The Axle transfers mechanical power to the Chainring on the right side of the bike frame. There can be more than one chainring; normally though the count is 1 or 2 or 3 of varying sizes. If there is more than one chainring, then a front derailleur is involved to facilitate transfer of power from one ring to the next.
The Chainring is connected to the rear cog via the roller chain. The Rear Cog spins freely in a forward direction, ala coasting. Inside the cog are “pawls” which grasp an internally rotating gear fixed to the axle when the rider applies sufficient pressure on the chainring to cause engagement. The number of pawls varies between 2 and 3; more means better quality and load handling. It is the pawls that are the source of the clicking sound when coasting.
Cogs can be single-speed, meaning they have only one gear, or they can be multispeed, and if so – the common counts are 7, 8, 9, 11. For the majority of all ebike installations, 7-speed is typically the most that is able to fit within the wheel mounting space, called a “dropout”: More on that in a bit.
Chainring ratios vary from 20 to > 60 Teeth (notation: 20T to > 60T). Whilst Cog ratios vary from 11T to > 34T. In our opinion, Shimano makes the very best rear “freewheel” (FW) cogs. However, they stopped manufacturing 11T FW 7-speed multispeeds about 10 or 15 years ago. Chinese-manufactured DNP Epoch 7-speed 11T-32T Freewheel is about the only choice available, and guaranteed – it will only last about 2000 miles/one season before needing replacement. At Kinaye, we sell instead the Shimano MF-TZ21 7-speed 14T-28T Freewheel which is still manufactured. Repeating: Shimano makes the best quality FWs around bar none.
On the Cog - 11T vs everything else
11T grants the maximum leverage upon the rear wheel, though it comes at a price: Because the tooth count is low, the cog spins very fast and it is exposed to much more wear and tear than larger cogs. It is therefore more preferential to use slightly larger cogs to increase the component lifespan – at a cost: Larger cogs means less speed advantage relative to the chainring, therefore a balance must be struck.
We can increase the size/teeth of the chainring. However, some frames prohibit larger chainring sizes. The Vector Frame is an example; the stock chainring is 46T; the frame can handle 48T and smaller, however there is physically not enough room to go larger, like on many typical mountain bikes and recumbents. Example: Resident Engineer Kingfish uses a customized setup featuring the 53T Campagnolo road racing chainring paired with a MTB DNP Epoch 11T-32T FW, and this allows him to pedal up to 38 mph.
A Better System
Keep It Simple. Two paths to resolution are…
- We don’t need front derailleurs and multiple chainrings; we just need one chainring, the right chainring. A single-speed however doesn’t give us enough bandwidth, so we pair with a multispeed on the rear. This is a common solution for the Vector Frame because there is no place to mount a front derailleur.
- Two Chainrings at the very most: High Gear (high-T) and Low Gear (low-T). Pair with a single-speed on the rear. High gear for high-speed, low-gear when if ever we need it. This solution works on just about any normal mountain bike frame.
Single Speed require a tensioner; a very inexpensive part that provides positive tension on the chain drive to prevent the chain from slipping, especially on full-suspension frames. The simplicity of a single-speed cannot be overstated. People that use single-speed need only to pedal home and have no intension of pedaling at higher speeds, or maybe the flip-side (which makes it difficult to pedal home w/o power).
Multispeed cogs require a Rear Derailleur: Shimano is the best, followed by SRAM. Multispeed is a good choice for the all-around adventurer. Tips for ratios: For the “low gear”, always consider the possibility that the battery is depleted and there’s a mountain between you and home.
- Rear Cog Low Gear: 28T, 30T, 32T, 34T are good choices. It’s possible to find larger.
- Rear Cog High Gear: 11T, 12T, 13T, 14T, and even 16T are good choices.
Traditional Gear Ratio Tool
Now armed with gearing information, let’s consider the options in the demonstration below. There are 5 parts…
- Tire Size: Our old friend again makes a difference and determines wheel RPM and Cadence.
- Velocity: Ebike speed, powered or otherwise; the goal is to keep up with the bike when under power at a speed that is comfortable – and realistic. Together with Tire Diameter we calculate the Wheel RPM.
- Chainring: Forward Gear. Typical sizes range from 32T to 48T in MtB. Going beyond that requires custom fabrication. Word of caution: Road, Recumbent, and MtB chainrings are not interchangeable – thank you Campagnolo, Shimano, and the rest: The big issues are the Bolt Circles, 4 bolts verses 5 bolts, plus Crank Axle varietal; really opens a can o’ worms.
- Freewheel Cog: Single or multispeed, set to the desired value. Note that the smallest toothed cogs wear out faster. Together with Chainring we calculate the Gear Ratio (R).
- Cadence: Pedaling Rate given as RPM. Normal Cadence between 50 to 85 RPM is good for the heart, although a fast cadence up to 100 RPM can be maintained for quite some time if in good shape. Any higher than that – and we’re flogging.
Again, we believe the value of the Schlumpf Drive is apparent and are proud to offer it as an option.
Final Words
We feel the drivetrain is the most underutilized component of an ebike, yet the most important feature should the battery become depleted. Without pedals, it’s not an ebike. Without pedaling, why bother with a bike? Pedaling is useful, so let’s make the most of it and augment/extend our physical abilities to overcome and “level” hills, and to provide greater range.
On a personal note, it used to be that as a pedestrian, riding 5 to 10 miles in a day was about all that I wanted to do. Now, with the ebike, 20 to 30 miles is easily common, and can be achieved in less than an hour. Hills melt away. Frontiers open up. Park the car; go for a ride. Enjoy clean living. Aggressive riders can do even better; I once took a job in Seattle just so I could ride my 2WD ebike – 56 mile round trip through urban traffic and it was a frippen joy. Join us - It can be done.
Thanks for taking the time to read this compendium. Actually we have a lot more to say, though not just here. Tell us how we’re doing: Facebook/LinkedIn likes works well enough.
Thanks for listening. Stay tuned. Safe travels.
~KF