Bosch bearings

[flecc]

Time will tell if the Mk2 Bosch is any better, but I don't like the look of that small front chain sprocket. Why have it?

Some technical reasons and consumer advantage apply with this.

Firstly the smaller higher speed sprocket means less gear reduction necessary within the unit, increasing efficiency. Second, there's very much less chance of a chain jumping off the chainwheel. Third, soiling of clothes and legs are much less likely. Fourth, it's much easier to fit a decent chainguard.

Against those four positives there's one negative, the gearing imposed between rider and high speed chainwheel to allow sensible cadences has a small cost in loss of rider efficiency. For many that won't matter with e-assistance, so overall I understand the Bosch decision to implement this.
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[Deleted member 4366]

Yamaha also have world class quality control systems. I have it from a good source that they've already been round their main Chinese suppliers, training them in their quality control and manufacturing techniques. I guess soon we'll see complete Yamaha electric bicycles, which should be something to look out for.

 

[tillson]

Some technical reasons and consumer advantage apply with this.

Firstly the smaller higher speed sprocket means less gear reduction necessary within the unit, increasing efficiency. Second, there's very much less chance of a chain jumping off the chainwheel. Third, soiling of clothes and legs are much less likely. Fourth, it's much easier to fit a decent chainguard.

Against those four positives there's one negative, the gearing imposed between rider and high speed chainwheel to allow sensible cadences has a small cost in loss of rider efficiency. For many that won't matter with e-assistance, so overall I understand the Bosch decision to implement this.
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As far as I know, points 2, 3 and 4 could apply to any bicycle and not exclusively to electrically assisted ones, so why don't we see tiny chain wheels implemented more widely? Bikes have evolved over many years, but what we think of as a conventional chain setup has remained. Perhaps this is because it doesn't need to change, it has developed to its optimum configuration.

The efficiency aspect makes me wonder too. We increase the drive speed to give greater efficiency, but then make the human input side correspondingly less efficient to accommodate it.

I'm still no clearer why Bosch have done this. It looks silly and don't think the concept will last.

 

[Artstu]

We're not a Bosch dealer

That's odd, why would you place a large order with Bosch.

They told me they had no plans for a UK agent, as they handle all other countries from Germany with no problems.

So I left the meeting having placed a large order for spares to ensure we can support UK customers and we'll deal with the warranties second hand, is the plan.

 

[KTM Bike Industries UK]

That's odd, why would you place a large order with Bosch.

To support our dealers. We do not supply the public direct.

 

[flecc]

As far as I know, points 2, 3 and 4 could apply to any bicycle and not exclusively to electrically assisted ones, so why don't we see tiny chain wheels implemented more widely? Bikes have evolved over many years, but what we think of as a conventional chain setup has remained. Perhaps this is because it doesn't need to change,

I strongly disagree on points 2, 3 and 4. Chain jumping off is a well known and very inconvenient phenomena with large chainwheels. It will be near to impossible for this to happen with the small chainwheel due to the much sharper link angles not allowing the necessary twist. The soiling of legs and clothes is very unlikely when the small chainwheel doesn't reach far enough out to do that. It reaches above the ball of the foot on the pedals to a point just above the footwear and below any trousers worn. A foot would have to be at a crazy angle to the leg for any contact. And the chaincase fitting advantages are very obvious, as posted I am speaking of chaincase, not just chain guard. The small height means much more stability due to the closeness of contact points and periphery, so very much less chance of internal rubbing. Chain guards and cases on large chainwheels often suffer rubbing between chain and case due to minor shifts following accidental contact.

We don't see this on normal bikes and probably never will, precisely because the efficiency loss is not offset in any way, so is unwelcome. On an e-bike having motor assistance of double the rider power that loss becomes unimportant for most riders. After all, the fact they are buying an e-bike indicates they are not sport cyclists concerned with nth degree efficiency.
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[RobF]

But it seems that the Panasonic is better in the most important respect. It's reliable and won't need replacing unless you're very unlucky. But this first Bosch is a lemon, and it's not much use being able to take the thing apart if you can't get the parts to fix it.

For all the bullshit and smoke and mirrors about warranties etc. The main issue here is a badly designed unit practically guaranteed to fail in a couple of years, and no spares available even though it is possible to repair it if they were available.

I lack your obvious electrical engineering qualifications, so cannot comment on the design of the motor.

What I do have is two Bosch units which have performed correctly so far.

These things are very hard to judge objectively, but given the large number of Bosch units in use, it's surprising there are not more reports of failure.

And as I've said, the motor is replaceable on an exchange basis.

No one - including me - wants to pull out £500, but when I bought the bikes I noted the 12 month warranty and realised I would be on my own after that.

 

[JohnCade]

I lack your obvious electrical engineering qualifications, so cannot comment on the design of the motor.

What I do have is two Bosch units which have performed correctly so far.

These things are very hard to judge objectively, but given the large number of Bosch units in use, it's surprising there are not more reports of failure.

And as I've said, the motor is replaceable on an exchange basis.

No one - including me - wants to pull out £500, but when I bought the bikes I noted the 12 month warranty and realised I would be on my own after that.

It's a mechanical failure not an electrical one. The fact that the Mark 11 version has a very much larger bearing than the one which failed here is rather indicative of the company implicitly accepting that they made the thing too small at first. Don't you think?

 

[RobF]

It's a mechanical failure not an electrical one. The fact that the Mark 11 version has a very much larger bearing than the one which failed here is rather indicative of the company implicitly accepting that they made the thing too small at first. Don't you think?

The load on the bearing is pathetically small in bearing terms - a wheel bearing on a car isn't much bigger.

One might think Bosch would have an idea on what loading a bearing can take, and have had such knowledge for years.

There is no need to use the customer as a test bed for bearing wear, even if there might be for other things.

Is there evidence of dozens or hundreds of these bearings failing?

I've not seen any, so Bosch may have a known tiny failure rate which does not call for a redesign.

So I don't think the 'very much larger' bearing in the new unit is an admission of anything.

 

[tillson]

I strongly disagree on points 2, 3 and 4. Chain jumping off is a well known and very inconvenient phenomena with large chainwheels. It will be near to impossible for this to happen with the small chainwheel due to the much sharper link angles not allowing the necessary twist. The soiling of legs and clothes is very unlikely when the small chainwheel doesn't reach far enough out to do that. It reaches above the ball of the foot on the pedals to a point just above the footwear and below any trousers worn. A foot would have to be at a crazy angle to the leg for any contact. And the chaincase fitting advantages are very obvious, as posted I am speaking of chaincase, not just chain guard. The small height means much more stability due to the closeness of contact points and periphery, so very much less chance of internal rubbing. Chain guards and cases on large chainwheels often suffer rubbing between chain and case due to minor shifts following accidental contact.

We don't see this on normal bikes and probably never will, precisely because the efficiency loss is not offset in any way, so is unwelcome. On an e-bike having motor assistance of double the rider power that loss becomes unimportant for most riders. After all, the fact they are buying an e-bike indicates they are not sport cyclists concerned with nth degree efficiency.
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Perhaps it's because I've never had the chain fall off or got an oil stain on my trousers which makes it difficult for me to comprehend the need for the small sprocket. I didn't realise that this was such a significant problem and how greatly I had underestimated it.

 

[flecc]

Perhaps it's because I've never had the chain fall off or got an oil stain on my trousers which makes it difficult for me to comprehend the need for the small sprocket. I didn't realise that this was such a significant problem and how greatly I had underestimated it.

The stain on clothing problem is sufficient for cycle clips to have been marketed over the life of the safety bicycle, but even they are not foolproof. I've got oil marks on trousers from large chainwheels even when using them.

As for the chain coming off the chainwheel, it's common enough for it to often appear in this forum, a few times recently. Have a look at this post from very active member Phill and the post below it from equally active Wissy, and you'll see how big and inconvenient a problem this can be. They would not have suffered this with the new type Bosch unit. Another sufferer here on this link, StitchUp with an EBCO hub motor bike.

So not just Bosch unit bikes, another recent one was persistent jumping off with a Wisper e-bike. It's also quite common on unpowered bikes, particularly derailleur equipped ones.

The things that cause a chain to jump off a chainwheel are minor issues that can easily develop, but when it occurs it's very inconvenient and messy. That the new design Bosch avoids it at hardly any cost on a powered bike is welcome, particularly as it introduces the other advantages as well.

The likelyhood of the chain coming off is far lower on hub gear bikes, so if that's what have, you are unlikely to regard this as a problem.
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[JohnCade]

The load on the bearing is pathetically small in bearing terms - a wheel bearing on a car isn't much bigger.

One might think Bosch would have an idea on what loading a bearing can take, and have had such knowledge for years.

There is no need to use the customer as a test bed for bearing wear, even if there might be for other things.

Is there evidence of dozens or hundreds of these bearings failing?

I've not seen any, so Bosch may have a known tiny failure rate which does not call for a redesign.

So I don't think the 'very much larger' bearing in the new unit is an admission of anything.

Bottom brackets can take a fair hammering, and that seems to have directly or indirectly caused the wear here.

They should know how to properly engineer their components, but companies cock things like this up all the time in new designs. Why do you think there are so many automotive recalls?

A couple of quotes from the OP.

however when having to exert a very high force to drag a loaded 26 kg bike up a hill with a flat battery the play was very evident.
It is clear to me that the bearing which has worn out simply isn't up to the job. The bike has covered around 4,200 miles and has climbed in the region of 250,000 feet.

This not up to the job bearing is going to be a serious problem for all Bosch users in the not too distant future.

No thank you for the picture. proof if it were needed that my thoughts about this failed bearing not being up to the job are clearly true, seeing as Bosch have seen it fit to fit one about twice the size in the new motor.

One from you.

I hope the conclusion is not: worn bottom bracket on a Bosch bike = new motor.

Bottom brackets wear out on all bikes, so it ought to be a reasonably easy part to replace.

Clearly not since for the last million pages lot's of people have been trying.

So why else would Bosch beef up this part if it wasn't under engineered to begin with? No company does that unless they need to.

There may well have been failures which were not plastered over forums like this because they were dealt with under warranty. He's done a fairly high milage in a short time too so the problem is likely to affect all of these motors sooner or later.

 

[SRS]

Very true, which leads me to quote something which I have said in the past, never buy a Mk1 anything.

Time will tell if the Mk2 Bosch is any better, but I do t like the look of that small front chain sprocket. Why have it?

I think that the latest Yamaha motor will be the one to have out of the latest generation motors available to us.

How do we get a Mk2 if nobody buys the Mk1's.

As far as the small front sprocket on the Mk2 I can only serve to increase chain wear. Why a small one? does anyone know.

 

[RobF]

How do we get a Mk2 if nobody buys the Mk1's.

As far as the small front sprocket on the Mk2 I can only serve to increase chain wear. Why a small one? does anyone know.

As posted by Flecc earlier, improved torque transmission - motorbikes use small front sprockets.

Also it's almost impossible for the chain to jump off which is an intermittent problem on all bikes.

The chain inevitably jumps to the inside and jams around the bottom bracket.

Jamming is increased by the forward motion of the pedals, albeit they swiftly grind to a halt.

I've seen instances where the chain has had to be snipped to free it.

It can certainly finish your ride unless someone happens by with a very beefy screwdriver or pry bar.

 

[SRS]

And as I've said, the motor is replaceable on an exchange basis

Presumably these exchanged units are reconditioned, whats the cost of these against a new one?

 

[RobF]

Presumably these exchanged units are reconditioned, whats the cost of these against a new one?

My understanding is they are new units, but Bosch won't sell you one unless you can supply a broken one in return because they don't want people trying to fit the motor as a kit to a 'non-Bosch' bike.

 

[flecc]

As far as the small front sprocket on the Mk2 I can only serve to increase chain wear. Why a small one? does anyone know.

See my post on this link
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[SRS]

As posted by Flecc earlier, improved torque transmission - motorbikes use small front sprockets.

Also it's almost impossible for the chain to jump off which is an intermittent problem on all bikes.

The chain inevitably jumps to the inside and jams around the bottom bracket.

Jamming is increased by the forward motion of the pedals, albeit they swiftly grind to a halt.

I've seen instances where the chain has had to be snipped to free it.

It can certainly finish your ride unless someone happens by with a very beefy screwdriver or pry bar.

Thanks, all sounds feasible but surely less teeth, more wear per tooth. Is this not the case.

Also, how do you change the gearing if you wish to. Are there a range of sprockets to choose from.

None of it sounds right to me, I've had two of the smallest rear sprockets snap in half so far this year.
Yes, the highest gear, both times they snapped on standing up to get a bit extra acceleration. Tells me that there a lot more load per tooth on a small one.

 

[Artstu]

This is a good article on the reasons for the smaller sprocket, 1000 readings a second seems rather excessive.

https://www.e-bikeshop.co.uk/blog/post/so-whats-different-on-the-new-2014-bosch-ebike-system/

 

[RobF]

Thanks, all sounds feasible but surely less teeth, more wear per tooth. Is this not the case.

Also, how do you change the gearing if you wish to. Are there a range of sprockets to choose from.

None of it sounds right to me, I've had two of the smallest rear sprockets snap in half so far this year.
Yes, the highest gear, both times they snapped on standing up to get a bit extra acceleration. Tells me that there a lot more load per tooth on a small one.

Not sure about the impact of a small front ring on chain/ring wear, but I agree it's unlikely to be possible to change the gearing from that end.

The small front ring does give a neat high chainline with a hub gear.

Even on the Rose with it's traditional big ring I've noticed the chain stays a lot cleaner than on a bike with a long cage derailleur.