How to minimise wear on the e-bike drive unit

The problem: 12-speed drivetrains are not really designed for full load on E-MTBs

Tearing chains, breaking teeth. Our Large wear test was a complete disgrace. We loaded seven twelve-speed drivetrains from Sram and Shimano for comparison and maltreated them on the test bench with typical E-MTB peak outputs of up to 800 watts and 110 Newton metres. The inexpensive Sram groupsets in particular were not convincing, but even the better drivetrains almost invariably dropped out before the 400 kilometre mark. The descriptions of many EMTB readers confirm the sobering results of our lab test. One thing is clear: Even the best drives are not really designed for full load on an E-MTB.

Switch correctly

The moderate use of power plays a major role in practice, especially with e-MTBs due to their high performance. An absolute no-go: starting off in heavy gears and at the maximum assistance level. Especially at low cadence, the motor tears at a few teeth with brute torque. At full chain skew. Better: downshift before starting off or accelerating. In general, the motor and drive components benefit from lighter gears and higher pedalling frequencies - when riding smoothly, but especially when accelerating. This is because the higher the cadence, the lower the load on the chain for the same power. In addition, the chain then tends to run on sprockets with more teeth. This leads to a more even power distribution and less chain slippage, especially when travelling faster. If you tend to forget to shift gears on an E-MTB, you can also help yourself with lower support levels. This will automatically give you a better feel for the power in the drive, pedalling smoother, accelerating more moderately and shifting more.

But shifting gears can also be poison for the drivetrain. Broken chains or damaged cassette teeth are often caused by gear changes under load, as the load is distributed unfavourably in the drivetrain. Shifting over several sprockets is taboo. Sram prevents this with its single-click technology, which only allows individual clicks on the shifter. Shimano requires an attentive rider with a restrained thumb. Another rule: ride with foresight. If you can, only press lightly on the pedal when changing gear. For example, if you have forgotten to change to a lower gear before setting off. It is also a good idea to change gear before entering steep stretches or key uphill sections, as long as the terrain is still flat. The crisp passage itself is best tackled without changing gear. This also makes it easier to balance on the bike. Incidentally, with most cassettes, the second largest sprocket is the most stable; smaller sprockets are more susceptible to wear. Bikers should therefore fit the right gear ratio. If you ride a lot on flat terrain, you may need a larger chainring so that you are not always stuck in the smallest sprockets at the 25 km/h limit. If you ride a lot on steep climbs, you need a slightly smaller chainring.

Clean the chain and cassette regularly

After every significant ride on the e-bike, the chain should be cleaned of coarse protection and then re-greased. All you need to do is run the chain through a cloth. If it is very dirty, the bike should be given a complete wash. Use a brush and bucket or garden hose to prevent premature wear of the drive and bearings. Once the e-MTB is clean, you can hang it on the assembly stand or, if necessary, turn it upside down (watch out for fittings!) and use a second brush (only use for the drivetrain) to brush the coarse dirt out of the cassette and off the chainring first. An oil collection mat protects the environment.

For stubborn stains, do not use a wire brush, but rather a small amount of Degreaser on Cloth or brush. This makes it easier to dissolve the oil/dirt mixture. Use degreaser sparingly. Small sausages of dirt on the derailleur pulleys are best removed by pulling the chain with a soft plastic object such as a tyre lever. Clean the chain by pulling it through a brush and cloth from all sides. Special chain cleaning tools should be avoided altogether in favour of basic lubrication. For the finishing touches, pull the cloth through the gaps in the cassette. Allow to dry and relubricate quickly, especially when using degreaser.

Grease & lubricate

Once the bike and drivetrain are clean and dry, you can start re-greasing. Especially if you Degreaser or Chain cleaner should not wait too long, otherwise rust will quickly build up. The assembly stand is also useful for re-greasing the E-MTB so that the rear wheel can rotate freely. Then, while cranking slowly, apply a small amount of Chain oil to the inside of the chain. Unlike with bearing grease, the following applies here: Less is more.

If the chain is greased too much, it attracts too much dirt, which promotes premature wear. It is better to lubricate sparingly and rework it with a cloth and chain oil after every ride. More viscous oils tend to wash out less easily and are more suitable for winter or commuting, while thinner oils lubricate better and attract less dirt - the tip for summer. After lubricating, continue turning the crank for a short time so that the oil is well distributed in the drive. Then allow it to work in properly. This gives the oil enough time to creep deep between the chain links, where lubrication is particularly important. Wipe off any excess grease with a cloth before the next ride at the latest. Especially in winter, bolt heads appreciate a little penetrating oil from time to time to prevent flash rust, and the inside of the derailleur pulleys can do with a little bearing grease if used for a long time.

Choice of material

Steel is the main thing? What applies to the chainring in any case is more complicated for the cassette. In our wear test, the inexpensive Sram NX and GX groupsets were unusable particularly early despite their high steel content, which can be attributed to the poorer hardening of the material and the rivet construction of the cassettes. Significantly more durable: the steel sprockets of the Deore drivetrain, which were even outperformed by the Deore XT with two aluminium sprockets. The XX1 drivetrain from Sram, which is milled from steel down to the smallest sprocket, performed best. Low weight and high durability are therefore not mutually exclusive. If you're on a tight budget, however, the recommendation still clearly goes to Shimano's groupsets, not least because of the option of replacing individual sprockets when they wear out.

For professionals: chain waxing

Hardly attracts any dirt and lubricates excellently: Silca's wax was convincing in the laboratory. Disadvantage: Flash rust forms quickly in wet conditions, the drive often has to be reworked and completely degreased beforehand. A recommendation only for technically experienced frequent riders and good weather.

E-bike chain & cassette: check and replace in good time

Because the cassette is so much more expensive than the chain, you can also prevent high costs by regularly checking the chain wear. The idea: If you replace the chain in good time, the expensive cassette will not be affected. If the old chain is left on for too long, the sprockets wear out more quickly - then it creaks when pedalling or the chain slips completely. Therefore, regularly check the chain wear with a wear gauge or an accurate caliper gauge. When new, the distance between ten chain rollers is 119.5 millimetres; the chain should be replaced at 120.5 millimetres at the latest. Depending on the type of use, this can be the case after just a few hundred kilometres on an E-MTB.

You can check the wear of the chainring and sprocket by feeling the teeth after cleaning: If burrs have formed, the part must be replaced. The same applies to damage such as broken or torn teeth. Incidentally, worn sprockets on Shimano cassettes can be replaced individually - a good option if the cassette is otherwise in good condition. Derailleur pulleys should be replaced at the latest when the teeth start to become sharp. However, wear here only affects the function of the drivetrain, not the wear of other components.

Warranty for wearing parts? Does that even exist?

You will find answers to questions about warranty, service life and manufacturer complaints in our article here.