Survey evaluation: Has your engine already been defective?

Time and again, we receive letters from readers who are struggling with defective motors and batteries or other drive faults. No wonder, as the extensive electronics package is a completely new, sensitive component on the E-MTB. In preparation for the issue
EMTB 04/20
we have therefore launched a survey - "Engine damage on the EMTB?" - which was intended to put the isolated letters from readers on a somewhat broader basis.

However, we had not expected such a great response: Around 1900 e-MTB fans took part in our survey. This alone confirms what we had already suspected - motor damage on e-MTBs is unfortunately not uncommon. Here is an overview of the results in detail.

Note: Despite the relatively high number of participants, the survey is not representative. The selection of participants was random, and only the number of participants with engine problems could be allocated to the respective manufacturers, not those without engine problems. It is therefore not possible to draw conclusions about the actual failure rate of the individual manufacturers. In view of these limitations of the survey, we ask that the following results be understood only as a rough trend.

Bosch and Brose as front runners - only 43 per cent without motor problems

Firstly, the obvious: Bosch and Brose are unfortunately clearly ahead in absolute numbers. 454 participants, i.e. 22 per cent, reported problems with Bosch, 449 participants (21 per cent) had already had problems with Brose. Both manufacturers are therefore almost on a par, while Shimano is clearly behind with 5 per cent (111 participants), as is the "other manufacturers" pool with 9 per cent. (For the correlation between absolute figures and percentages, see below1 )

The fact that only 43 per cent of participants stated that they had not had any problems to date is probably due to the question posed in our survey ("Motor damage on an e-MTB?"). It also suggests that those e-mountain bikers who have already had bad experiences with their drives are more willing to take the time to participate in the survey. In reality, the number of e-MTB riders who have so far been spared problems is certainly higher.

Bosch and Brose on a par: What do the figures mean?

So are the Bosch and Brose drives equally problematic? Unfortunately, we cannot answer this question conclusively due to the limits of the survey mentioned above. However, anyone who has been involved with e-MTBs for some time will assume that, in absolute terms, there are significantly more riders on Bosch motors than on Brose drives. This puts the supposedly high failure rate of Bosch drives into perspective.

To at least roughly categorise the market shares of the motors, it helps to take a look at our large 2020 reader survey with around 9,000 participants: Almost three times as many readers are travelling with a Bosch motor than with a Brose drive. Shimano was clearly behind Bosch but even ahead of Brose. Of course, the absolute figures from these two independent surveys cannot be directly correlated. However, the trend is that the failure rate is highest for Brose, while Shimano seems to cause hardly any problems.

Detailed comparison: Many problems with Drive S Mag and CX Gen2

In addition to the absolute figures, the correlation between the individual answers is also striking. A more detailed analysis shows that the participants who reported problems with Brose had significantly more problems with the current top model (Drive S Mag: 63.4%, older model: 36.6%) than the participants who reported problems with Bosch (CX Gen4: 37%, older model: 63%).

Against this background, it is also astonishing that only 21 per cent of participants at Bosch stated that they were already on the road with at least the second replacement motor, while the rate at Brose is 31.2 per cent - although the problems at Brose mainly occur with more recent models, which should have a significantly shorter service life compared to the older Bosch models.

The figures, supported by the participants' comments, thus confirm two much-discussed problems: Bosch's predecessor to the current top model caused problems relatively frequently. A weakened seal on the Performance CX Gen2 (up to model year 2019) allowed dirt and water to penetrate, resulting in grinding noises in the transmission. At Brose, the drive belt in the motor of the current top-of-the-range Drive S Mag model tore conspicuously often.

Brose and Specialized have already responded to the problem. You can find everything about the new software update for Brose drivetrains and the warranty extension at Specialized here here.

Warranty and service

When it comes to warranty and service, however, the two competitors do not seem to have much in common: Only around 40 per cent of survey participants at both Brose and Bosch stated that service and warranty processing were "quick and uncomplicated". The response option "slow and sluggish" was chosen by 22 per cent of participants with Brose problems and 27 per cent of participants with Bosch problems.

Where does Shimano stand?

And with Shimano? Only 111 participants in total stated that they had problems with Shimano; unfortunately, the amount of data in the detailed questions is even lower. For this reason, a valid detailed evaluation is hardly possible. As far as the Japanese company's service is concerned, we can say that the participants had no excessive reason to complain compared to the competition.

1 The deviation between the absolute number of responses and the percentage (e.g. Bosch: 454 x 100 % / 1908 = 23.8 % → de facto 454 x 100 % / 2102 = 22 %) is due to multiple responses. Participants were able to give multiple answers if they already had experience with different manufacturers. The total number of respondents is 1908, the total number of answers in this case is 2102.