Mid Drive Kits Dump the Derailleur
Dropout, vertical or horizontal?
The part of the rear axle that connects to the bicycle frame is called the “dropout”. A common style is a vertical drop (or sometimes a slight slope), so called because if you lift the frame and loosen the axle nut…the wheel will “fall off” from the frame.
Since most common bikes use derailleurs, vertical tripping is a good design. If the axle nuts start to loosen during the ride, the weight of the bike and rider will help hold them together. As a result, riders often feel something is wrong before the wheel is actually fully out, leading to a crash.
The drop-out style shown in the image below is a horizontal “track” style. In the Olympics, as well as in college-style cycling, they use “fixed-gear” bikes. Since it was a single speed and had no derailleurs, the frame designer needed a way to mount the chain on the sprocket and then properly tension the chain. Links can be added or removed to the chain to adjust the length, but the chain length must be loose enough to assemble to the sprocket, which must then allow the wheel to travel to the rear of the frame far enough to properly tension the chain.
Track-type releases are a simple, lightweight and robust way to do this without the added weight and complexity of a chain tensioner. These are more common on some new cruiser bikes.
The picture below is the “chain tensioner”. In this example it is used to convert a bike with a multi-speed transmission to a single speed. A stock derailleur can be used as a “poor man’s” tensioner, but many enthusiasts prefer to keep the chain as short as possible and keep the resulting tensioner as light and simple as possible. A chain tensioner is often the best option when converting a derailleur bike to an IGH.
Why would anyone use an IGH instead of a derailleur? Derailleurs are lighter, which is the main reason they are mass produced for bikes. Also, if you add an electric motor to the drivetrain, you can damage something, and the 7-speed cassette can be replaced very cheaply.
The first reason some cyclists switch to the IGH is because they often ride in mud and snow, and the derailleur can get so dirty that it stops working during the ride.
The second most frequently cited reason is for riders who log a lot of off-road miles each year. They have to clean the transmission frequently. Additionally, they often need to completely replace their derailleurs at the beginning of each riding season, as the grit that builds up during the ride acts as an abrasive, causing wear. If you do, then you can save money by getting an IGH, which usually lasts for many years with proper maintenance, and…”post-ride” cleanup is reduced to just two sprockets and a chain…
As for using the IGH on an electric intermediate drive, there are several notable omissions from the list below. To keep this article compact, I will only list the IGHs I recommend. SRAMs in particular are hard to come by in North America, and few riders have written about them, so there isn’t enough data available (SRAM…email me!). If you want SRAM products, you “probably” can buy them from Europe via ebay, since they are made in Schweinfurt, Germany.
Why no 11, 7 or 5 speed?
This article will mainly focus on the strengths of the various IGHs as we try to find the right option for a mid-drive e-bike.
If you’re just pedaling (without a motor) in a different grade area, go for the 11-speed. With the addition of the electric motor, you get an 8-speed. There are two reasons. First, the more power you have, the fewer gears you need, and frequent shifting can become tedious. One Rohloff owner said he ended up shifting two gears at a time because the Rohloff gears were all close together, essentially turning the 14-speed into a 7-speed.
The second reason is that the 8-speed listed below has a very strong 1:1 ratio fifth gear. With the 8-speed IGH, I recommend you get used to starting in 5th gear on your daily riding. Unless, of course, you stop on an uphill road. Then you should start in a lower gear, but… take it easy on the throttle. Don’t get a hot rod unless you’re using a 3-speed in second gear. It’s relevant because…for many riders, the only reason they want to go mid-speed in the first place is because they need help on the hills.
For 5-speed hubs (and some 7-speeds?), the middle gear is a 1:1 lockup of drive to hub, like the mighty 3-speed listed below, so… 3rd gear in 5- Speed is usually very powerful. The reason I don’t recommend them (trust me, I’d like to have a 5-speed and a 7-speed in this list), riders abusing them in rough service profiles don’t have enough data. Here’s a german video, it’s me The clearest video I could find, it shows the 7-speed components (the 5-speed is very similar). The dog shown here is very strong, but the axial clutch and some gears are not strong enough for the motor (depending on the model).
Once hub designers started using modern style pawls, the 7-speed IGH became the lowest number of gears most customers bought (so 5-speeds were rare) as a 7-speed chainset with a common external. Most 5-speeds in 3rd are as powerful as any available gear, but if you want the strength of a modern-style axle dog and other speed gears, an 8-speed hub is the way to go…even if you don’t need all 8 kind of speed.
I wish someone produced a wide-ratio 5-speed with a very powerful axle dog, but it doesn’t exist yet. Here’s a short video on a Shimano Alfine-11 showing a shaftshift shift (which is pretty much the same as my recommended Alfine 8-speed). This is a 2 minute video of the sliding pawl and axial spline clutch operating at SRAM 7 speed.
Classic Fichtel & Sachs 7-speed (often abbreviated as Sachs or F&S, purchased by SRAM) is designed with stronger dogs (two dogs per gear), but creates a weaker gearset, offering 2- and 6-speeds ( The 1 and 5 speeds don’t look too healthy either, it’s just… 2/6 break first at high power, like in this clip).
In the classic style 3-, 5- and 7-speeds, the intermediate gears are locked 1:1 (modern 7-speeds sometimes use a different design). A gear set has been added that provides two speeds, depending on whether it’s driven or driven. The strength of the intermediate gear depends on the strength of the clutch style it uses. 5-speeds usually have one clutch and two gear sets, and 7-speeds have one clutch and 3 gear sets.
For the 7-speed, they took the classic 5-speed design, but instead of adding a physically larger gearset on one end, they added a smaller gearset on the other. Also, since the Sachs had blocks on both sides of the axle, more material had to be removed from the smaller gear set to create a slot at the gear ID for the block to grab. Also, most 5-speed 1:1 ratio axial clutches are designed to look sturdy enough for human legs, but…not a motor.
The 3-speed sun gear listed below is cut from a single piece of steel and axle. Classic 5 and 7 speeds have rotating sun gears that are locked and unlocked by a dog. In 3-speed, select 2nd and 3rd gears at the planet case or planet pin (do not go close to the shaft with lifting or sliding pawls, as more leverage may be exerted and cause breakage), it is determined by The four-arm axial clutch (no pawls) is finished, so it is very strong. I state these design features so that the reader can understand why I claim that a 3-speed is much more powerful than a 5- or 7-speed in all gears.
If you want to switch to the IGH but don’t know how many gears to buy, ask yourself this question…how many gears are you happy with your derailleur equipped bike right now?
Do you have seven gears on your BBSHD, but… do you really only use two or three gears? If you have a lightly assisted BBS01 on a 7-speed bike in very hilly terrain (and you use all those gears a lot), you’re definitely not going to be happy with a 3-speed, so… an 8-speed IGH might be You are most satisfied.
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