Tutorial: Changing the Transmission of Your Ebike: Chainring, Cassette and Chain

The electric bike transmission wears out more quickly because it’s subject to the force of the pedals as well as the motor. Replacing it ensures a long, smooth-running ebike. It’s recommended to change your transmission approximately every 5,000 to 10,000 kilometers. Wear will depend on various factors such as your riding style, the weather you ride or expose your bike to, and whether you’re used to riding loaded or tackling steep climbs. You can simply change only certain parts.

1. When change the drivetrain
2. Tools for changing drivetrain parts
3. The parts you need
4. Changing the chainring
5. Installing the cassette
6. Installing the chain

The right time to change the wear parts on your bike

1) When change the drivetrain

Use a chain measuring tool. First, take its narrowest side, where it says “0 point 75.” Place it on the chain and check if it fits into the links. If the smallest gap of the tool fits into the links, you can change the chain and continue with the same chainring and cassette. Some time later, if you’re back at the 0.75 limit, you’ll need to replace the entire drivetrain: chain, cassette, and chainring. The same applies if the 1.0 side of the tool also fits.

On some cassettes, you can also change the smallest lower sprockets. These are the most stressed sprockets on an ebike. This way, you can delay wear until you actually replace the entire cassette from top to bottom.

2) Tools for changing drivetrain parts

What tools do you need if you want to replace your ebike drivetrain? There’s, of course, the chain wear measuring tool I mentioned earlier.

You’ll also likely need an Allen key, a cassette extractor, a crank extractor, and a chain tool with which you can then shorten the chain. A chain whip to loosen the cassette, and pliers to open and close the chain’s quick link are also recommended. And for some chainrings that aren’t secured with two Allen screws, you’ll need a chainring wrench to hold the grooved chainring nut securely in place. Next, you’ll need a lockring tool to loosen the chainring lockring, and a quarter-turn ratchet to secure this tool, or this special extractor available in our shop. You can also use a 24mm adjustable wrench to loosen the chainring lockring. Finally, I recommend purchasing some universal assembly grease.

3) The parts you need

As mentioned earlier, you’ll of course need a new, suitable chainring, as well as a new, suitable cassette and an ebike chain that matches your drivetrain and components.

All parts depend on the drivetrain installed on your ebike. For example, you may have a SRAM, Shimano Deore, or Shimano Linkglide drivetrain; the parts will also depend on your cassette’s gear ratio and number of teeth. Also, check your motor model.

To save you time, we’ve designed ready-to-use wear parts kits. All you have to do is choose your motor and drivetrain, and then all the parts—chain, cassette, and chainring—will be delivered directly to your home. If you want to order one of these kits, you’ll simply have to check three things:

1. The type and model of motor installed on your ebike. In our case, it’s a fourth-generation Bosch Performance Line CX motor.
2. Second, we need to know what type of chainring is mounted on the front. In our case, it’s a 36-tooth chainring. Simply count the number of teeth or read the information directly on the chainring. Our chainring has 4 holes, meaning it mounts on a mount, also called a spider. There’s also the possibility that the chainring is placed directly on the motor axle. This is called direct mounting.
3. Third, we need to take a look at the derailleur and cassette. On the derailleur, you’ll usually find an inscription indicating which group it belongs to. So Shimano or Sram is usually written in large letters on it or in a booklet that comes with your ebike. In this case, we have a Shimano 12-speed derailleur. We can also count the number of sprockets. In our case, it’s the SLX version, which is also noted on the derailleur. Now, let’s take a last look at the cassette, specifically the largest drive sprocket here. How many teeth does it have? You can look it up directly on it. Or you can count it yourself.

Once you have this information, you can go to our online store and order your drivetrain kit in just a few clicks.

For this bike, we’ll need a wear parts kit for the Bosch Gen4 or Gen5 motor, for the Shimano SLX groupset. With the large cassette of up to 51 teeth and a spider chainring of 36 teeth in total.

4) Let’s start by changing the chainring.

• First, we need to loosen the crank arm from our axle. To do this, we first remove the crank bolt located directly in the center of the crank arm and then pull the crank arm out.
• Next, we take our crank arm extractor. Turn it clockwise until the crank arm comes off the axle. Be careful that any washer under the crank bolt doesn’t get stuck inside and come out, otherwise, removing the crank arm would become impossible.
• Once we’ve removed the crank arm and set it aside, we can then work on the lockring. To do this, we’ll need the lockring loosening tool, here for a Bosch Gen 4 motor. This is a standard lockring size used on other motors such as Brose or Yamaha.
• The special feature here is that it has a left-hand thread, meaning we loosen the chainring in a clockwise direction. As you can see, the rear wheel will tend to come with it.
• Use the remaining chain and block the rear wheel with the brake lever. This will provide you with a counterweight to loosen the lockring from your motor axle.
• Then we can easily remove the lockring by hand; Detach it from the axle and also remove the chainring, in our case with the spider.
• We may also need to remove the chain guide if there is one.

There you go. The chainring is now removed.

If your chainring isn’t direct-mount, but instead mounts with a spider, as in our case, you’ll need to remove the spider by removing the four screws with a suitable tool.

• The chainring screws can be removed by using two Allen keys to counterbalance them, but you can also use a chainring wrench.
• Insert an Allen key on one side, and the chainring wrench on the other, which fits into the nut.
• When mounting the new chainring on the spider, make sure the correct side is facing out. This is usually the side with the manufacturer’s logo. And make sure the teeth of the chainring match the spider. This prevents it from twisting.
• Now secure everything securely with the screws you set aside. Once you’ve done this, or you’ve opted for a direct-mount chainring, we can now install the new chainring onto the motor shaft.
• Take this opportunity to wipe it down with a cloth and a little cleaning product to roughly remove any dirt, and treat everything with a little assembly paste. This will make it easier to loosen next time.
• Insert the chainring onto the shaft, then the locking ring.
• Make sure you don’t forget the rubber gasket, if one came with the ring. Bosch includes it. It’s also possible to purchase it separately if it ever gets damaged. Next, tighten the locking ring by hand. Then, using the appropriate tightening tool, tighten firmly to the specified number of Newtons.
• Now reassemble the chain guide, if there was one, and then the crank.
• Install it and secure it with the crank bolt you set aside. The recommended tightening torque is generally indicated directly on the crank bolt.

Installing the Cassette

• We need to start by removing the rear wheel. Here we have an electric bike with a thru-axle. So unscrew it and remove the rear wheel.
• Next, take your cassette remover and insert it into the cassette. The problem now is that we need to unscrew the cassette in the direction of the freewheel, which, of course, doesn’t work.
• That’s why we’re going to take the chain whip, place it on the sprocket block, and thus act as a counterweight. This will allow us to loosen the cassette’s security screw.
• Now, remove the old cassette from the freehub body.
• And also the freewheels, if that’s the case for you. Take this opportunity to clean the freehub body if there’s any dirt or grease on it.
• Then, reapply the assembly paste. Go over the entire freehub body thoroughly before installing the cassette.

Now you can install the new sprocket block.

If you have freewheels, be careful not to mix up their assembly order and also not to lose the washers.

Logically, you shouldn’t make any mistakes when installing them, as the gearing determines how the sprockets should be mounted on the freehub body. Now tighten the cassette with the lockring and the cassette remover. Here too, you’ll find the recommended torque engraved on the lockring.

Now we can reassemble the rear wheel, and the cassette replacement is complete.

Chain assembly

To determine the degree of chain wear, you need a chain wear indicator; see the second paragraph above, “When to Change the Drivetrain.”

• You should use the quick-link pliers, if you have one on your chain. Let’s look for them on your chain. Quick links are generally quite easy to identify. Once located, we can use the quick link pliers to easily open the link in the appropriate direction.
• Now we need to install the new chain on your ebike. To do this, we first need to adjust it to the correct length. All drivetrain kits include a chain with 126 links. This length is sufficient for most ebikes. If you have a longtail or cargo bike, you may need a longer chain. For e-mountain bikes, 126 links will be more than enough.
• To shorten our new chain, we’ll use the length of our old chain as a guide. Place the two chains side by side to determine where we need to shorten the chain using the chain tool.

• Important to note: only use this method if you haven’t changed your gear ratio, i.e., if you always ride with the same number of sprockets front and rear.
• Once you’ve found the right link, you can now secure it with the chain tool. By turning the adjusting screw, as I call it, push the pin outward and thus shorten the chain.
• In the next step, we simply thread the chain along the chain guide of your ebike.
• And we connect it with, in this case, the quick link. For this, we can also use the quick link pliers, as they can close the chain link in addition to opening it. Connect the two ends of the chain with the quick link and use the link pliers to connect everything with a quick snap.

And there you have it, the replacement of our drivetrain components is now complete.

You’ll find the parts you need thanks to our new drivetrain kits available online.