Going to a larger front chain ring on a gen 4 motor

[Dallant]

“TODAY BIG BIG PROBLEMS I CANNOT make ANY changes to MY BIKE with the Bosch CX GEN4 Drive system at all without FOCUS and BOSCH input AND PERMISSION

They had called Bosch and been told no no no no.

I was then given a load of rubbish about why this would not work probably damaging the Motor, the 9 speed cassette and the Alfine 11 hub NOT that they would now fit one to my bike and no I could not change to an 11 speed SRAM 10 - 40 cassette either!!!

ALL POLITICAL and rubbish about needing trained and they as Bosch dealer could not undertake any of the modification to MY BIKE (with a 2021 CX GEN4 DU) which is NOT under warrantee as it was bought from a friend after they damaged their leg and the warrantee is NOT transferable NOT that I care about that.

But they then went onto the liabilities that they MIGHT incur if they did the work for me without permission from Bosch and Focus................................. they also said I was going to make the bike ILLEGAL by changing the front chain ring or the back cassette !!!”

You’re an engineer, so why do you care what Bosch or anyone else says since the Gen 4 is already out of warranty and you seem to know what you’re doing? Just go for it and find out if it works or not, and for how long.
It’s not political, it’s legal. Clearly Bosch doesn’t want to be liable and I don’t blame them.

 

[Dallant]

Boże...

So Spesh do that?

 

[Stefan Mikes]

So Spesh do that?

You can replace the chainring or whatever without asking Specialized. I have recently swapped the 48T ring for the 38T one on the Vado, and the stock cassette with a 11-36t on Vado SL and everything works just fine.

 

[Dallant]

You can replace the chainring or whatever without asking Specialized. I have recently swapped the 48T ring for the 38T one on the Vado, and the stock cassette with a 11-36t on Vado SL and everything works just fine.

But would Specialized officially aid you in doing so and warranty your changes? Of course anyone can modify their ebikes without permission.

 

[webcurl]

That's all a bit harsh!
It is not unreasonable to have some level of expectation that the whole process could be flexible and easier to implement (like Bafang or Android, not always reliable) but ending up being surprised with the hoops to travel through (Bosch or Apple, usually reliable).

 

[Stefan Mikes]

But would Specialized officially aid you in doing so and warranty your changes? Of course anyone can modify their ebikes without permission.

The point is if you used another size chainring on a Bosch e-bike, the restrictive system would respond with an error message. Never happens to Specialized e-bikes. It simply works. (Several users of our Vado/Como User Club have already replaced their chainrings to different sizes and no word of complaint). How in the world is the motor dependent on EXTERNAL drivetrain to check for gearing ratio?! Are your legs dependent on the drivetrain in a traditional bike?
I wouldn't ever buy a Bosch e-bike. I got used to good things that simply work.

 

[Dallant]

The point is if you used another size chainring on a Bosch e-bike, the restrictive system would respond with an error message. Never happens to Specialized e-bikes. It simply works. (Several users of our Vado/Como User Club have already replaced their chainrings to different sizes and no word of complaint). How in the world is the motor dependent on EXTERNAL drivetrain to check for gearing ratio?! Are your legs dependent on the drivetrain in a traditional bike?
I wouldn't ever buy a Bosch e-bike. I got used to good things that simply work.

So in other words, no, Specialized wouldn’t assist you as the OP is suggesting Bosch do. I’m curious what errors have you seen the Bosch system kick out in a similar case?

 

[Stefan Mikes]

So in other words, no, Specialized wouldn’t assist you as the OP is suggesting Bosch do.

So, in other words, Specialized wouldn't be a pita. If it just were Bosch to allow you changing the chainring size but no! You would need to negotiate things with:

• Trek, or
• Cannondale, or
• Focus, or,
• Riese & Muller, or,
• name either of fifty other brands you were mislucky to buy your Bosch e-bike from.

Why should the motor maker AND the e-bike manufacturer assist with something that takes a regular user 10 minutes to complete? Next, ask Bosch Bikes and Trek if you can replace your tyres for some other size. Because perhaps the Drive Unit will detect inconsistency in the wheel size and brick your system?

 

[Dallant]

So, in other words, Specialized wouldn't be a pita. If it just were Bosch to allow you changing the chainring size but no! You would need to negotiate things with:

• Trek, or
• Cannondale, or
• Focus, or,
• Riese & Muller, or,
• name either of fifty other brands you were mislucky to buy your Bosch e-bike from.

Why should the motor maker AND the e-bike manufacturer assist with something that takes a regular user 10 minutes to complete? Next, ask Bosch Bikes and Trek if you can replace your tyres for some other size. Because perhaps the Drive Unit will detect inconsistency in the wheel size and brick your system?

I’m not saying they should assist. I’m asking you yes or no if Spech would have any warranty issues with changes you do make.

 

[Stefan Mikes]

I’m not saying they should assist. I’m asking you yes or no if Spech would have any warranty issues with changes you do make.

I didn't ask, and they are not asking. Just bringing my e-bikes for service, and they are servicing them. For instance, I brought my modded Vado 5/6 for warranty upgrade of 2017 to 2020 electronics and no questions were asked. Or, bearings in the rear wheel were serviced. Or, firmware updated. Two different LBS. No questions, just warranty card presented.

The strictness of Bosch seems very German to me. Ordnung muss sein. I could not buy from such a company. Luckily, I don't have to.

 

[FlyingScot]

So in other words, no, Specialized wouldn’t assist you as the OP is suggesting Bosch do. I’m curious what errors have you seen the Bosch system kick out in a similar case?

MY Best responder said that the CX GEN4 DU cannot error on anything external, all errors are internal like sensors going faulty or electronics playing silly games.

SEEMS BANANAS as if you have the right Bosch display you can alter the wheel circumference YOURSELF

BUT I think that is ONLY to get the display to show the correct speed and I believe but have no real info or experience to back this up, - is that you can only change the values by a small fixed percentage.

I also think that this maybe to do with torque settings as I DO KNOW that the pre-programmed {max?} torque output is different for a derailleur back end and an internal hub gear from Shimano and Rholhoff

I cannot imagine Bosch getting away with this crazy nonsense in the USA

Also, it seems to be handicapping and handcuffing a really nice system, but I can understand in some ways that Bosch don't want 'US USERS' mucking about with their drive train set up

BUT I don't see why a trained dealer is not allowed to do that, and I totally don't understand why the bike manufacturer needs to be involved.

Also, since there now are a few superspeed add-ons for these Bosch motors, sooner or later someone will come out with the software to run the diagnostics and configure the DU.....

Soon to be online on YouTube

Maybe Bosch should consider USER training courses as a nice new revenue stream.

Since Torque is a moment on the back cassette that drives the bike along and is calculated in Nm and that is simply calculated by multiplying force applied and distance travelled.

Without getting out my calculator and wearing out my brain IF I changed from a 36T chain wheel to even a 40T chain wheel that means that for one revolution of the crank I will have moved the chain FOUR MORE links or an increase of about 11% changing to a 38T means that it is an increase of only 5.5% and assuming that the power from the motor remains constant {which it does not as it is torque sensing} is that a big deal for the DU. Doubly so since what I am trying to do is pedal slower at speeds way past the CX GEN4 cut off speeds

AND listening to the Bosh bike guy who was talking sense and who said IF I put a 42T chain ring on the DU would need reprogrammed this suggests that the DU is totally capable of driving a bike with a 42T chain ring, so I really cannot see why changing from a 36T to either a 38T or a 40T chain wheel is even an issue (OR VERBOTEN) for the bike shop to implement.

 

[TrevorB]

I just had TWO LONG chats with bike people, one sensible one with someone in a London bike shop and one totally crazy one with someone in what I thought was a top Glasgow bike shop

Let's look at the Glasgow one first

Last week I went in there to enquire about fitting a Shimano Alfine 11 to my Focus Jafira 6.7 NINE

NOT a problem, bring the bike in and let us have a look at it.

TODAY BIG BIG PROBLEMS I CANNOT make ANY changes to MY BIKE with the Bosch CX GEN4 Drive system at all without FOCUS and BOSCH input AND PERMISSION

They had called Bosch and been told no no no no.

I was then given a load of rubbish about why this would not work probably damaging the Motor, the 9 speed cassette and the Alfine 11 hub NOT that they would now fit one to my bike and no I could not change to an 11 speed SRAM 10 - 40 cassette either!!!

I wouldn't recommend using Alfine with CX motor. They are only rated for 50nm. Google reviews on 11spd alfine, people have had mixed results on reliabilty that is on unassisted bikes. 8spd Alfine and Nexus on other hand are very reliable even on 50nm ebikes. There is recommended min chainring to rear spocket gear ratio. 2:1 is lowest you should go.

If you want internal hub use Nuvinci or Rohloff.

 

[FlyingScot]

WOOOOO HOO was in a LBS today and guess what I spied with my little eye

A BOSCH CX GEN4 (SPEED) with a 48T chain ring

Now this is a full suspension derestricted road bike the Moustache Friday 27 FS Speed

Moustache Friday 27 FS Speed

The Moustache Friday 27 FS Speed is a true sporty, practical urban bike, that's full suspension! With the new 625Wh battery, optional 1125Wh and lightweight Bosch CX motor, there may not be a better bike to

www.fullycharged.com

The Moustache Friday 27 FS Speed classifies as a speed pedelec. This means the bike has to be type approved and registered with the DVLA before it can be road compliant. You will also need a CBT license to ride. Included is an electronic horn, a rear view mirror as well as a holder for the license plate and a light system.



The LBS guy said that few buyers of that bike go down the DVLA official route re making that bike totally legit and legal.

It has the CX GEN 4 Performance Speed Motor and is capable of reaching speeds of 30MPH, the Performance Speed is the fastest eBike motor available from Bosch.

So I imagine that apart from being derestricted with different software to change the motor cut off speed from 25 km/h to 45 km/h then this is exactly the same Motor/DU as the CX GEN 4 Performance Line. IF it is then that Motor/DU is totally capable of driving a 48T chain ring, so I would have though my desire to change from a 36T to a 38, possibly 40, or 42 should really have no issues whatsoever.

Since the CX Performance Line DU cannot know what gear you are in, then it has to get the speed info from the back wheel, and since I am not looking to increase the DU's cut off speed only be able to go faster when peddling looks like that is going to be possible with no real issues.

Bosch SAY
The Performance Cruise Drive Unit provides support with a torque of up to 65 Nm and a maximum speed of 25 km/h {NOW WITH A FREE SOFTWARE UPGRADE TO 85Nm} and offers a naturally sporty riding sensation. It enables riders to get the most out of outings, even in mountainous terrain.

The Performance Speed Drive Unit enables high speeds to be reached even faster, while long distances can be covered with ease. It supports S-Pedelecs up to 45 km/h and will speed riders on their way with a torque of 85 Nm from model year 2021 onwards { that is THE SAME torque output as the CX Performance Line DU with the software upgrade}.
From model year 2021 onwards, the powerful motor of the Performance Line Speed Drive Unit provides support with a maximum torque of 85 Nm and thus provides even more thrust.

 

[William - Bosch Team]

Bosch SAY
The Performance Cruise Drive Unit provides support with a torque of up to 65 Nm and a maximum speed of 25 km/h {NOW WITH A FREE SOFTWARE UPGRADE TO 85Nm} and offers a naturally sporty riding sensation. It enables riders to get the most out of outings, even in mountainous terrain.

My apologies, but this is inaccurate. The Performance Line Cruise DU does offer up to 65 Nm of torque, but is not included in the 85 Nm update as it is a Gen3 DU design. The 85 Nm software update only applies to some Gen4 DUs, depending on region.

Again, sorry for any confusion.


As a reminder, the OEM determines the gear ratio for any given model as they can factor in effective rolling circumference, chainstay vs. chain ring clearance (including flex allowance), etc. In other words, the engineers at the OEM can look at all aspects of the complete bike spec to maximize safety and reliability. You will likely see many different chain ring sizes on different models with the "same" DU. They all use different software packages, frame designs, etc., that factor in all of the different parts used on that model by the OEM. While the DU doesn't know the exact specifics of each gear ratio, it is aware of the high and the low. The DU "knows" the speed at which its output shaft is turning the chainring, and it knows the speed that the rear wheel is moving. Using this info, the algorithms can determine if the gear ratio between DU output and wheel speed exceeds the max programmed value. If the physical ratio exceeds the programmed max ratio by too much, it may trigger an error code and/or a tuning alert.

Owners of eBikes can of course make the decision that they are most comfortable with. All we can do is offer information and warnings about potential issues that may arise from modification.

I hope this helps!

 

[PedalUma]

This is why I try to stay away from the proprietary stuff. It is like asking Apple if you can use Your computer. When the new longer chain goes on it should look like this.

I use a piece of bent spoke with hooks on each end to hold the chain together so I can spot where to place the quick link. It will be about two links longer than the old chain when you hang them side by side over a door knob. Mark that spot with a dot. The bent spoke visual works better an a calculator.

Chain Length Calculator

This chain length calculator will prevent you from damaging your bike's sprocket by calculating the required chain length for your bicycle!

www.omnicalculator.com

Look up Right to Repair and show local legislative support for it in your area.

 

[jim cahill]

Bosch Active Line Plus my wife bike was so down on power so i got a speedbox 3.0 as long you pedal the bike went from 24km to 34km and
up to 40km know i am looking at her crank gear on this Bosch Active Line Plus motor.
l have a rad rover 500w motor 52v battery know she can keep up with me on the flat but when we go up a hills Bosch Active Line Plus down on power
for anyone that has a Bosch Active Line Plus look at the speedbox

 

[mjp_hyi]

The DU looks at wheel speed and motor output, among many other things. It is able to determine what the max speed should be based on the max gear ratio, etc.

If a larger chain ring is installed, it may trigger an error code as the max wheel speed won't "make sense" to the DU if the new gear ratio is much larger than stock gearing.

The OEM must approve the change, as well as remotely adjust the value in your DU. Your dealer will assist with this process, but is not able to complete it on their own. The OEM must be involved.

William, thanks for your explanation of all this process. I'll reserve my opinion on the necessity of it being this way, but as I have 2 Trek bikes which need this done, it seems I need a little more explanation of the process.

I took this post of yours to my LBS who is a Trek dealer, and of course they know nothing of this process, and have been told it just can't be done. In particular, they have issues with your statement above, "as well as remotely adjust the value in your DU". They tell me that although they believe the earlier part (that the OEM, Trek) must approve the change, they dent vehemently that Trek will play any part in remotely adjusting the values in the DU, because they believe there is no arrangement they have with Trek to perform Bosch firmware updates, and that the post must mean instead "Bosch will remotely adjust the values in the DU", because it is a Bosch program that does this.

So while they would rather I go away, and probably Bosch would also, I need to ask you to clarify the process for me, particulary with regard to what happens (and who does what) after Trek approves the ratio changes being changed in the DU to match what's on the modified bike.

I realize you may have to consult others in Bosch about this, so it would be good to hear that you've seen this post and have begun to work on it.
Thanks in advance.

 

[Alaskan]

I changed out the front chainring on my Cannondale Topstone Neo Carbon 3 from 44 tooth to 48 tooth to lower cadence at higher speed to a sustainable rpm. To recapture some lost climbing ability, I also changed out the cassette from 11-42 to 11-46 even though the spec on the Shimano GRX 810 derailleur said max 42 teeth. SImple B screw adjustment with no road link needed. I realized I was taking a chance that it might create an issue with Mr. Bosch or Mr. Cannondale. No problems or error codes at all. Way better top end ( I can crank along on flat ground at 25 mph with a cadence of 75 and she still good for climbing 17% grades sustainably - 2,600 miles thus far and running like a Swiss watch with no corporate interference.

So @Stefan Mikes I know you love to bash Bosch but my experience indicates that you are putting out bogus info in support of your biases.

 

[mjp_hyi]

I changed out the front chainring on my Cannondale Topstone Neo Carbon 3 from 44 tooth to 48 tooth to lower cadence at higher speed to a sustainable rpm. To recapture some lost climbing ability, I also changed out the cassette from 11-42 to 11-46 even though the spec on the Shimano GRX 810 derailleur said max 42 teeth. SImple B screw adjustment with no road link needed. I realized I was taking a chance that it might create an issue with Mr. Bosch or Mr. Cannondale. No problems or error codes at all. Way better top end ( I can crank along on flat ground at 25 mph with a cadence of 75 and she still good for climbing 17% grades sustainably - 2,600 miles thus far and running like a Swiss watch with no corporate interference.

So @Stefan Mikes I know you love to bash Bosch but my experience indicates that you are putting out bogus info in support of your biases.

Thanks Alaskan. It sounds like you took an informed gamble and won. For all the same reasons as you, I would like to go from a 40T chain ring and an 11-36 9 speed cassette to a 52T chain ring and an 11-42 cassette. I can't find an11-42 cassette in 9 speed, so I have to change to a 10 speed. And this is on a bike Europe with its 15.5mph assist cutoff, so there's no question about pedalling the bike to go too fast, it's all about reduced cadence at a comfortable speed with the motor already not assisting. You managed to gear up by just under 10% with no issues, so that's good to know. I may have to settle for a 44T or a 46T chain ring. We'll see.