Why have a gear sensor? The purpose of a gear sensor is to protect your drive train from excessive power from a mid-drive motor while shifting a bike with a rear derailleur. A normal cyclist is around 150 watts of human power and most drive trains are designed to handle a little more than that much power.
But now add 450 to 750+ watts from a mid-drive motor to that which is equal to another 3-6 cyclists and you are way beyond what the drive train was intended be able to handle when the chain is across multiple cogs with only a few teeth on one of the gears. This is where a gear sensor comes in.
It detects that you are shifting and cuts power to the motor for about an .8 of a second. This is long enough for the shift to complete before the power comes back on.
How does a gear sensor work? To install the gear sensor you actually pass the shift cable through the gear sensor. When the gear sensor detects cable movement, it sends a signal to the motor to stop for 800ms. All Bafang mid-drive motors from Electrify Bike Co have a gear sensor cable coming from the motor controller so they are gear-sensor ready. If your motor does not have this cable you can hook the gear sensor up to a brake sensor cable instead. Although this does work brake sensors shut the motor off for a minimum of about 2 seconds instead of .8 seconds. This can be a bit of a nuisance to have the motor off for that long of a time.
I have a hub motor. Do I need a gear (shift) sensor? If you have a hub motor you do not need a shift sensor since the hub motor does not use the drive train.
I have a rear derailleur with a Bafang mid-drive motor. Do I need a gear (shift) sensor? Since you have to pedal through the shift on a rear derailleur drive train the motor will be on the whole time your are shifting. If you happen to be in a mid to high level of motor assistant you could be putting upwards of 450 watts through the drive train. With a BBS02 or BBSHD this could be more than 1000 watts. This is where the shift sensor is critical. If you have a mid-drive that is under 400 watts or you only shift in levels of assistance that are under 400 watts then you might get by without one.
I have an internal gear hub (IGH). Do I need a gear (shift) sensor with my mid-drive motor? If you have an internal gear hub like a 3-speed or 5-speed Shimano, you probably do not need a gear sensor since you are supposed to stop pedaling when you shift an IGH anyway. When you stop pedaling the motor will stop and you can shift. Start pedaling again and the motor will come back on. Some motors have a slight delay after you stop pedaling before the motor shuts off so you should wait until it stops before shifting. Electrify Bike Co. reprograms all of our mid-drive motors to cut off instantaneously when you stop pedaling so this is rarely an issue. Some still prefer the instantaneous cutoff of a shift sensor but there is lag before the motor comes back on so it is a trade-off.
I have a TSDZ2 mid-drive motor. Do I need a gear sensor? If you have a torque-sensing motor like the TSDZ2 then you do not need a gear sensor. Because the motor responds to the amount of torque you are applying to the pedals, you can simply ease off a bit when you pedal through the shift and the power will ease off as well. If you need to be able to shift when pedaling hard with a torque-sensing motor then you may still want one. Since the TSDZ2 does not have direct support for a gear sensor, it must be hooked up to a brake sensor. The problem with this is that instead of 800ms the brake sensor cuts power for 1500 - 2000ms which can feel like an excessive amount of time to lose power. But it does work!
Picking the right chainring for your BBSHD, BBS02, or TSDZ2 is important but can be tricky. There are a lot of factors to consider in getting the one that will be the best all around. Let's take a look at some of the more important ones.
That is a total of 27 combinations or speeds. With the mid-drive motor you typically have just one chainring which means your 27 speed is now a 9 speed. This is not as bad as it sounds in fact in some respects it is desirable. Riders find that they need fewer gears with electric assist and it is nice having fewer gears to shift through.
If your bike originally had 3 gears up front and they were 52 tooth, 42 tooth, and 38 tooth, you might want to pick the middle or gear or 42 tooth chainring as the best all around. If you still want a wide range of gears, especially low gears then you can trade out your rear cassette for a wider range cassette and have the full range you need. You can read more about that here.
As it turns out most newer mountain bikes and now many city and road bikes have only a single chainring up front and a wide range cassette in the back. This is known as a 1x drive-train. So adding a mid-drive doesn't require any of the trade offs mentioned above. In fact if you have an older bike you can look at going to a mid-drive to be a 1x drive-train upgrade as well.
If you really want more than one chainring it is possible. It is actually common with the TSDZ2 motor in fact we sell dual chainrings for that motor. It is less common with Bafang but is still possible. The problem is many front derailleurs won't go out far enough to reach the outer chainring. Since the TSDZ2 doesn't stick out quite as far as the Bafang motors more front derailleurs will work with the TSDZ2. If you just want to have it on one or the other based on city or mountain riding then you can move it by hand before you start out. The TSDZ2 comes with a 110 BCD spider. You simply mount a different chainring on either side of the spider. After-market spiders are available for the BBS02 and BBSHD as well and dual chainrings can be used with them as well. However, this is rarely done because of the cross-chain problems that arise from not using a single offset chainring.
Why are some mid-drive motor chainrings offset? Each mid-drive motor comes with a chainring, usually steel and between 42 to 46 teeth. This is usually a good size for all around riding and also 42 teeth is the typically the smallest you can go and have the chainring offset to return your chainline as close as possible to your original chainring(s). This simply means that the motor pushes your chainring mount point to the outside and by dishing or offsetting the chainring they can move it back inboard closer to where your original chainrings were. Chainrings smaller than 42T can't be dished because they would hit the motor housing so they are further outboard and the chainline will be off. This is not a problem on many bikes but you want to try to keep the chain as straight as possible. 42T is simply too big for many mountain bikers so they get a smaller chainring for overall lower gearing and the chainline is still fine through much of the range but is more cross chained in the lowest (large) gears on the rear wheel. Recently Lekkie introduced a 40T chainring for both the BBSHD and BBS02 with great offsets achieved by replacing the gear reduction cover on the motor. These are very nice but are more expensive and harder to install.
What size chainring is ideal? The ideal chainring size can be illusive because you are making tradeoffs. The Bafang motors want to run fast and perform at their best with smaller chainrings while the TSDZ2 motors tend to top out at a cadence of 90 to 100 so a somewhat larger chainring for riders that like a fast cadence can be better. If you just want overall lower gearing for mountain biking a 30-38T chainring is ideal. However, if you have chainline issues then you may want to go with a 42T and make sure you have ultra-low gears in the back in the 40-46T range. If you are a speed demon and want to feel like you are contributing and getting a good workout at higher speeds you may want a 48-52T chainring. I say "want to feel like you are contributing" because even if you are pedaling very hard the wind resistance is so significant that the motor will be doing the lions share of the work but you will still get a good workout.
Should I upgrade my chainring? This question may be answered for you if you choose a different size chainring than the one that comes with your motor. If you want higher or lower overall gearing you need an upgrade. Even if you decide you actually want the size that came with your motor, you may still want to get an upgrade. The upgrade chainrings made by Lekkie and others are typically CNC 7075 T6 hardened aluminum and are lighter, better looking. They also have a significant advantage by using a narrow/wide tooth profile. This means that every other tooth is wider or narrower to fill the entire space in the outer and inner chain links. This has the advantage of holding the chain onto the chainring so that it doesn't come off. If your bike had a front derailleur then you probably never had this happen because the front derailleur holds the chain on. Without the front derailleur you may find your chain frequently or infrequently coming off of the chainring. This is no fun. Some bikes never have that problem. We sometimes advise that want the size of chainring that comes with the motor to just run with the stock chainring to start out and then if they have their chain coming off they can upgrade to a narrow/wide tooth profile chainring to help solve the problem. Chainguides can also be used and if your rear derailleur has a clutch that will also help to keep the chain from popping off.
What about IGH hubs? All of the above applies to your chainring consideration except if your chain is properly tightened it won't ever pop off. You may still want a chainring upgrade to get higher or lower overall gearing or to trim weight and have a better looking bike.
The 3 most important factors in choosing a battery:
1. Trusted brand. 18650 Lithium Ion cells are by far the most popular cells found in ebike batteries. This is because the energy density is very high and they are being manufactured in huge quantities. They are being used everywhere including electric cars like Teslas. There are many cheap lithium ion 18650 cells that don't last and can be very dangerous especially in the quantities found in ebike battery packs. It is not uncommon for an ebike battery to have over 50 18650 cells. All it takes is one bad cell to destroy a pack and create a fire hazard. This is why the manufacturer of the cells is extremely important.
2. Power & Capacity. How many volts? How many Amps? How many amp hours? Without getting into how cells are made into battery packs if you know the answer to the first 3 questions you can calculate watts and watt hours which are the 2 most useful numbers. We use 52 volt packs everywhere we can and only sell motors that can support them. 52 volts is like 48 volts after morning coffee. It packs a little more punch and gets a little more speed out of your motor. However, if you are not using the speed or power the extra volts transfer directly into increased range. How does that work? It is simple math. Volts x amps = watts. Watts equal power. Volts x amp hours = watt hours. Watt hours = capacity or range. Think of watt hours as how much gas you have in the tank and think of watts as how much power it can put out. If you have a 2000 watt battery supplying a 750 watt motor but you are only asking it for 250 watts on your ride you have plenty of reserve power and your battery and motor will run cool. If that battery happens to have 750 watt hours of capacity it will be able to power the bike for 3 hours at 250 watts. 3 hours x 250 watts = 750 watt hours. If you were going 20 miles an hour that would mean your range was 60 miles. See! Simple math.
3. How big? We always ask our customers 3 questions. What is your average ride in miles? What is your longest ride? How many miles per week do you ride? This gives us a pretty good feel for the best battery options. If your longest ride is fairly frequent the you should pick a battery with that much range. If however, the long rides are infrequent you many want to think twice about adding that weight to your bike for all of your shorter rides as well. Sometimes it makes sense to get a smaller battery that will handle 90% or more of your rides and then get a second one to throw in your pack when you take longer rides or just want to know you have a spare tank. Our most popular battery is the 52v 14ah Panasonic Super Shark. We call this our 50 mile battery. It is 728 watt hours and mounts on the down tube on water bottle mounts. It fits in most bike frames but if it won't it can sometimes be put on the bottom of the down tube or on the rear rack. A step up for those that need even more range is the 52v 17.5ah Panasonic Jumbo Shark. We call this our 70 mile battery. It is 910 watt hours and mounts just like the Super Shark. For those that want to keep it light and most of their rides are under 15 miles, we have our 52v Samsung Mini-cube battery that fits in a saddle bag under the seat.
A few things to think about: Better chargers usually come in a metal case and are fan cooled. They come in different amperages which determines how fast your battery charges. Charging too fast at too high of an amperage can shorten the life of your battery.
This is why Tesla recommends that their cars not be charged at their super chargers very often. They are intended for fast charges on road trips with routine daily charges taking place at a slower charger at home or in a parking lot.
Electrify bike chargers come in 2 amp or fast charge 4 amp sizes. 4 amp chargers charge twice as fast as 2 amp. A 52v 700 watt hour battery will charge in 3.5 hours with a 4 amp charger if it is fully drained. The same battery will charge in 7 hours with a 2 amp charger. All of the batteries sold by Electrify Bike including the mini-cubes can take a 4 amp charge without any negative impact on battery life.
Increasing the number of charge cycles: A smart charger can increase the number of charge cycles of your battery dramatically. If you charge your battery to 100% every time, it will take about 400 charge cycles before the battery capacity is reduced to 85%. This is 2 charges a week for 4 years. Not bad! You may want a new battery in four years anyway. However, if you have a long commute and charge everyday you will exhaust your 400 charges in just over a year. Did you know that if you only charge your battery to 90% you can get close to 1000 charges? Or if you charge it to only 80% you will get closer to 2000 charges? This is true of all lithium ion batteries including your cell phone. The problem is everyone is competing on talk time so they always max the charge to 100% instead of optimizing for battery life.
A smart charger is has a selectable amount of charge. For example, Electrify Bike's smart charger have a rotary switch that is selectable for 80%, 90% and 100% charges. We recommend charging to 90% unless you are planning a long ride. For long rides top it off to 100%. The occasional 100% won't have a big impact on battery life.
The bottom bracket is where the bearings for the cranks that your pedals attach to are located. To install a mid-drive motor you remove the cranks and bottom bracket spindle and bearings. The mid-drive motor then slides into the bottom bracket shell and replaces all of that except for the pedals. Before 2013 most bottom brackets were the BSA/JIT English threaded standard. This is still the most popular type and is the type that mid-drive motors are designed for. Most bikes that originally sold for less than $1500 or are older than 2013 have English threaded bottom brackets and the motors will slide right in. If you have a square tapered spindle for your cranks then you have the required threaded bottom bracket.
Around 2012 many higher-end bikes started being fitted with various press-fit bottom brackets many of which can be adapted to English threaded so you can still do a mid-drive motor conversion on them. However, there are some exceptions. For an in depth article on adapting various bottom brackets and the exceptions see this thorough article by Matt Hughes
Electrify Bike Company carries threaded one piece adapters for 68 & 73mm BB30, 68 &73mm PF30. We also carry a 2 piece BB30 and PF30 for wider bottom brackets that use those standards. We also stock a 2 piece PF41/BB92 that works with a variety of bottom bracket widths that use that standard.
Some newer bikes and almost all fat tire bikes use a bottom bracket that is wider than the 68/73mm standard. In this case only the BBSHD comes in wider widths to accommodate this EBC stocks the BBSHD in 68/73mm, 100mm, and 120mm. Other widths can be accommodated with these 3 types by using bottom bracket spacers when required. TSDZ2 and BBS02 motors have after market extensions available for them to allow them to fit wider bottom brackets but these can be very difficult to install.
If you have an older style Schwinn or cruiser bike with a one piece crank and American style bottom brackets we have something for you as well. Give us a call.
We recommend using sleeve Loctite like Loctite 641 when installing the adapter into your press-fit bottom bracket. This is like thread lock but is specifically for sleeve inserts like these adapters.
The 2-piece adapters can be tapped in with a soft mallet. Tap all the way around and ensure that it goes in straight. A bottom bracket press can also be used. For the one piece adapter we recommend using a bottom bracket press. Ensure that it does not get crooked or it can bind up and be very difficult to straighten up or remove. If you do not have access to a bottom bracket press you can make one with hardware available at a hardware store. An example can be found on YouTube here.