This post is also available in: Deutsch
E-Bike motors produce a nominal 250 W of power, to which we add the power from our legs. So the energy passing through the parts of an E-Bike’s drive system, which includes the chain, cassette, derailleur, hubs and chain wheel, can be very high – significantly higher than a normal system. This means that drive systems are coming under increasing fatigue. We take a close look at one of our test bike’s drive train with a professional mechanic, to understand what basic checks to make for wear and when to replace certain elements or service them.
The chain is put under tremendous loads when shifting whilst E-Biking. Often double shifting and/or the extreme ends of the chain line plus the extra power increase wear on a chain. The key element to consider is the link to link distance on a chain. If it is too long, then the chain will slip and jump when pedalling under high loads or when shifting. We have observed that our chain life in the dry and dusty environment of Punta Ala, Italy, is about 2500 km. This really depends on where you’re riding, though.
To measure, how worn a chain is, we need a special chain tool that gives wear level indication. If the chain shows to be worn, then it should be replaced. There are now specific chains which have been developed for E-Bike usage which are slightly more resistant to the loads. Although the chain might be worn and putting a new one on is necessary, it doesn’t mean that the system will be ok. A cassette sometimes has to be replaced at the same time as a chain, as the two items tend to wear together – unless the chain is replaced before it has worn too far. If the chain does not sit centred on the cassette teeth properly, then it is time to replace the cassette, which we show in more detail below.
The cassette is a very sensitive item when it comes to smooth operation of a system. If it is worn or loose, then the gears will not function properly, as misalignment is introduced into the system. The chain and cassette tend to wear together – if you change the chain more frequently rather than waiting for it to be too stretched or near the end of its life, it is possible to extend the life of a cassette a lot.
It is fundamental that the cassette unit has as little play in it as possible, either from the freewheel or the actual sprockets on the freewheel hub. If it is loose, then when you pedal hard the cassette will move and shifting will become inaccurate and noisy. According to Davide, our mechanic with many years of experience, he has noticed, particularly with cassette play, lower end SRAM cassettes compared to Shimano don’t handle shifting inaccuracies as well. SRAM of course created their EX1 cassette to deal with the issues that result from E-Bike drive stresses to counter this. Shimano have yet to release an E-Bike drive train.
Free Wheel Check
Depending on the style of hubs used and freewheel installed checking this point is brand dependent. Lightweight aluminium freewheels need to be checked more often, as the sprockets on the cassette dig in to the body of the hub, causing play in the sprockets, which leads to shifting inaccuracies. In our test bike case the Shimano freewheel hub is made of steel and resists wear well. SRAM XD drivers don’t have this problem, but sometimes tend to creak, if dirt gets in. Taking the cassette off and cleaning all the interfaces will solve this. Our mechanic did suggest to check, how well the ratchet pawls engage, though, as they come under greater forces when engaging. Any wear at this point can cause play and mis-shifting. Essential to a solid cassette is to make sure it is torqued correctly according to the advice of the particular model of cassette by the manufacturer. You’ll often find this information on the lockring.
This part does all the work moving the chain around. In our case we have already had to replace the stock Shimano XT unit as it was worn and not working any more. Our XTR unit is fairly new, as is the cable, but it needs lubricating and checking. One feature often not checked is the tension spring that stops the chain jumping off on rough trails. Finally, check the gear cable as well and replace if necessary. Also make sure all the attachment bolts are tight that connect the derailleur to the frame.
When removing the cover on a Shimano system it is possible to change the force of the derailleur tension and lubricate the tension switch. We don’t touch anything else, as shifting is smooth with the newer derailleur, although the switch was sticky. It’s not possible to adjust the tension of SRAM clutches that are Type 2.1 or higher. Once lubricated it’s a good idea to check the gears shift properly and adjust the cable tension and limit screws if necessary. We will look at cable and derailleur setup in detail at a later date.
Chainring Bolts And Crank Bolts
If you have ever wondered, where the creaks are coming from within your drive train, sometimes the culprits are the chainring bolts. Using the correct tools, which vary by brand, tighten them to the correct torque settings. Our right crank arm had one loose bolt and was the source of a major creak – once tightened the system is now silent.
This is more of a warning. This bearing was removed from a two-year-old electric drive unit. This particular customer did some maintenance, but was not that accurate with the washing of the bike. Over time the bearings in the motor have become worn and degraded. The outcome is, the pedals jammed when riding. The bike shop did a full service on the motor, as it was out of guarantee, then replaced the bearings. This is one of the bearings that was removed. In general though, motors should be sent away for service to the manufacturer.
Chains, cassettes, derailleurs and hubs are still in their early days, when it comes to E-Bikes. There is only one system on the market so far, SRAM’s EX1, which is designed for E-Bike power. Some brands do have special hubs which are stronger, but there is still a long way to go. Basic checks like we have outlined will keep your system working smoothly and reduce the likely hood of sudden mid trail break-downs, meaning a long walk home with a heavy bike …
What kind of maintenance do you do yourself?
Text & Redaktion: Alex Boyce | eMTB-News.de
Bilder: Alex Boyce
This post is also available in: Deutsch