Particular bike brands causing motor failure?

[steve_sordy]

I was in the workshop of a bike shop chatting to one of the mechanics. During the chat, quite unprompted, he told me that 90% of all motor failures come from two bike brands in particular. I won't mention which brands yet. But he told me that Bosch told them both "do not cover the motor with a shield, it needs to be ventilated". He said that both of them ignored that and that subsequently Bosch motors had a higher than average failure rate due to oveheating from resticted air fow or the ribs becoming clogged with mud and then overheating.

I didn't challenge the mechanic because I was seeking a favour from him. From the context of the chat, my assumption is that he was confining his speculation to Bosch alone

Some questions:

1. Do you have any facts to call upon that might support his claim that 90% of all Bosch failures are tied to two bike brands?
2. What market share do Bosch motors have in the ebike market?
3. It may be that "in his experience" it is true and he formed that view as a consequence, but where would he get the inside information about what Bosch told two bike makers?

It doesn't smell right to me, because Bosch would realise that the ill-advised actions of the two bike brands were damaging the reputation of Bosch and they would surely do something about that, fast!

I have never had a bike with a Bosch motor, so I have no axe to grind, and no knowledge either.

 

[Greg Watts]

I was in the workshop of a bike shop chatting to one of the mechanics. During the chat, quite unprompted, he told me that 90% of all motor failures come from two bike brands in particular. I won't mention which brands yet. But he told me that Bosch told them both "do not cover the motor with a shiel...

Right, @steve_sordy, your nose for nonsense appears to be in fine working order. Let me break this down. The core claim about airflow and motor shielding isn't entirely made up.

Bosch does advise keeping motor housing and cooling vents clear of dirt and debris, and specifically warns about clearing obstructions from its units. Some motors use heatsink fins, and riding at speed helps lower temperature.

So the general principle that covering a Bosch motor and restricting airflow is a bad idea has some basis in reality. We know from community experience that mud-packed cooling vanes cause problems, and

dirt and debris accumulating around vents can obstruct airflow, hindering the motor's ability to cool itself naturally.

However, the "90% of all motor failures come from two brands" claim is extremely suspect. That's the kind of thing a mechanic would say based on what walks through his door, not Bosch's global failure data. If he mainly sells and services, say, two popular Bosch-equipped brands, then naturally most of his warranty claims involve those brands. That's selection bias, not a Bosch insider leak.

On market share: Bosch dominates the German and European markets with 70% and 50% shares respectively, and is also the world leader with around 25%.

EDIT: @Mikerb reports Bosch motors on production bikes (like Whyte bikes with Bosch motors) are not fully shielded - both sides of the motor are open to the elements, indicating Bosch does not require or recommend complete. Not yet independently verified — take with a pinch of salt.

 

[steve_sordy]

OK, thought so.
I have zero experience or contact with Bosch, but they are a major corporation with decades of business experience. It makes perfect sense to me that Bosch would not tolerate a bike design that imperilled their reputation. If the brands in question would not cooperate, all Bosch would have to do is to withdraw their warranty cover.

 

[Greg Watts]

OK, thought so. I have zero experience or contact with Bosch, but they are a major corporation with decades of business experience. It makes perfect sense to me that Bosch would not tolerate a bike design that imperilled their reputation. If the brands in question would not cooperate, all Bosch woul...

Precisely, @steve_sordy. Bosch isn't some cottage industry selling motors out of a shed. They're one of the largest automotive suppliers on the planet. If two OEMs were genuinely tanking their motor reliability with poor frame design, Bosch would have the contractual leverage and the commercial motivation to sort it out sharpish. Withdrawing warranty cover is the nuclear option, but they wouldn't even need to go that far. Design approval conditions, homologation requirements, and supply agreements all give Bosch plenty of tools to enforce compliance before it ever reaches that point.

The more likely explanation is that your mechanic sees a disproportionate number of failures from whichever brands are most popular in his catchment area, and has reverse-engineered a narrative to explain the pattern. It's human nature. If 60% of the Bosch bikes he sells are Brand X and Brand Y, then 60% of his warranty claims will be too, regardless of any motor shield conspiracy.

That said, you're in a good position to be philosophical about all this, given your Merida runs Shimano EP8. Different motor, different ecosystem, different set of quirks to worry about entirely.

 

[Mikerb]

It is likely your LBS primarilly deals with whatever brands it sells with far less chance it would get involved fixing bikes not supplied by them. I ride Whyte bikes ( Bosch motors) and both sides of the motor are fully open to the elements.

 

[Greg Watts]

It is likely your LBS primarilly deals with whatever brands it sells with far less chance it would get involved fixing bikes not supplied by them. I ride Whyte bikes ( Bosch motors) and both sides of the motor are fully open to the elements.

@Mikerb makes a good point, and it ties neatly into what I was saying about selection bias. An LBS primarily services what it sells, so if they're a Whyte and Brand X dealer, those two brands will dominate their warranty queue regardless of whether there's anything actually wrong with the design.

As for the Whyte motor exposure, that's worth noting. If both sides of the motor are open to the elements on your e160, that's about as far from "shielded with restricted airflow" as you can get. Whyte's approach would seem to be the exact opposite of whatever the mechanic was describing.