Installing larger chain ring on a gen 4 motor

[Stefan Mikes]

Are the Giant Syncdrive/Yamaha PX2 motors as sensitive to gear ratio changes as the Bosch Gen4?...I don't think they have the "shift sensing" you mention the Bosch Gen 4's have?

I think SyncDrive motors are far more tolerant. And no, there is no shift sensing in them. Not actually sure what is the Bolt Circle Diameter of your chainring but chainrings don't need to be e-bike specific (not sure for Bosch as I don't own a Bosch e-bike). Only BCD, number of teeth, type of bolts and tolerance between the rear of the chainring and the chain-stay really matter.

 

[almikel]

Not actually sure what is the Bolt Circle Diameter of your chainring but chainrings don't need to be e-bike specific (not sure for Bosch as I don't own a Bosch e-bike). Only BCD, number of teeth, type of bolts and tolerance between the rear of the chainring and the chain-stay really matter.

BCD is 104 with 4 bolts and the current chain ring is 42T with loads of room between the chain ring and chain stay.
The OEM crankset/chain ring on my Giant is FSA, and they have plenty of options for larger 1X/narrow/wide chainrings.

Riding today I was paying more attention to the rear gear I was in - on the flats once up to speed, I'm in the smallest few cogs.
Anything sloping down and I'm in the smallest cog.
Mostly through habit from riding my acoustic, I still avoid the steepest way home, and fly up my old acoustic route at a comfortable 80 rpm in the smaller half of my cassette.

When I replace the chain I'll put a bigger chain ring on - I'll need to check what the rear mech can cope with (and chain stay clearance), but likely a 46T, which would provide a 4/42=9.5% increase in gearing.

cheers,
Mike

 

[Ravi Kempaiah]

Hi Ravi,
Are the Giant Syncdrive/Yamaha PX2 motors as sensitive to gear ratio changes as the Bosch Gen4?...I don't think they have the "shift sensing" you mention the Bosch Gen 4's have?

Hi Mike,

Yamaha drives don't have the shift sensing mechanism but if you can back off pedal pressure for a second, the shift happens smoothly.
The motor unit is programmed for certain gear ratios and if you install one of those delimiting dongles or devices, then it will get messed up and may throw up some errors or incorrect speed reading.
But, otherwise, it should be fine.

 

[Alaskan]

Actually, earlier this afternoon, I sourced what we need from a cycle shop in the UK

FSA G3/4 Bosch EBike Bicycle Cycle Alloy 104 BCD 1X11 Chainring Black

FSA G3/4 Bosch E-Bike Bicycle Cycle Alloy 104 BCD 1X11 Chainring Black | eBay

Find many great new & used options and get the best deals for FSA G3/4 Bosch E-Bike Bicycle Cycle Alloy 104 BCD 1X11 Chainring Black at the best online prices at eBay! Free shipping for many products!

ebay.us

Holy Mackerel!!! The 46 tooth chainring arrived from England yesterday. It was waiting on our porch when we got home from our covid shots. THis was ordered on Sunday and it arrived in Bellingham Washington on Thursday. I swapped it out with the stock 44 tooth before dinner. Test ride probably won't happen for a few more days. The chainring delivered to the door was $69.83. Kudos to the .ebay seller, Velozone Cycles...

 

[Deacon Blues]

I just ordered the same ring The bike shop I bought the bike from said couldn't get one from Cannondale/Bosch.
Since mine is coming to Canada it will probably take considerably longer and shipping will be significantly more.

Did you do anything to your chain? You mention that your stock ring is 44T. Are you sure? Mine is a 42T.

 

[Alaskan]

I just ordered the same ring The bike shop I bought the bike from said couldn't get one from Cannondale/Bosch.
Since mine is coming to Canada it will probably take considerably longer and shipping will be significantly more.

Did you do anything to your chain? You mention that your stock ring is 44T. Are you sure? Mine is a 42T.

Mine was a 44 as per spec on the speed bike. Now I can do the same speed at a more comfortable cadence.

The chain is unchanged but it worked fine on the stand. We'll see how it goes on the road. I may have to add two links.

If this works, the next step is to see if a 11-46 cassette can be made to work to recapture lost climbing leversge. I will have to add four links for this.

 

[Deacon Blues]

@Alaskan, I've been told that if the size of the front ring is changed the motor's electronics have to be recalibrated. Do you plan on doing this, or are you going to see how the bike rides first?

 

[Alaskan]

@Alaskan, I've been told that if the size of the front ring is changed the motor's electronics have to be recalibrated. Do you plan on doing this, or are you going to see how the bike rides first?

I got an inside tip from an unquestionably reliable source that the official answer is that the manufacturer of the bike is responsible for establishing and setting the gear ratio parameters used within the Bosch system so we would need to go to a Cannondale dealer, they would have to get permission or even hook Cannondale in over the internet to adjust those ratios in the Bosch motor software. The unofficial answer is that most likely adding 2 teeth can be done without adjusting the system, which is exactly what I have found.

A few test rides have confirmed that adding two teeth dropped my cadence in the smallest 11 tooth cog, at 26mph from around 82 rpm to a much more comfortable 75 rpm. I was concerned that adding two teeth up front would adversely compromise the bikes ability to get up the 17% grade to our home but that has not seem to be the case thus far, so I may not try to put the 11-46 tooth cassette on the bike to make up for the lost low end. There just was not that big a difference to open that can of worms

 

[Deacon Blues]

I've found that my biggest concern, when going up a steep hill in turbo, is keeping the front wheel on the ground.

 

[Alaskan]

I was amazed at the prompt shipping from the ebay seller in the UK. Ordered last Sunday, arrive here in Bellingham on Thursday.

 

[Alaskan]

I've found that my biggest concern, when going up a steep hill in turbo, is keeping the front wheel on the ground.

I haven't had that experience yet but I probably outweigh you by enough lbs. to keep both wheels on the ground, that I I am not climbing the kind of inclines you are.

 

[Deacon Blues]

If I have to add a link or two to my chain I may just buy a new chain, since the bike already has 3000km on the odometer.
I'd also like to replace the smallest three cassette rings, since I use these three for most of my riding, but these days they're as rare as hens teeth.
I wonder why it seems there is plenty of Sram components in stock, but with Shimano many of its components are on back order.

 

[Alaskan]

If I have to add a link or two to my chain I may just buy a new chain, since the bike already has 3000km on the odometer.
I'd also like to replace the smallest three cassette rings, since I use these three for most of my riding, but these days they're as rare as hens teeth.
I wonder why it seems there is plenty of Sram components in stock, but with Shimano many of its components are on back order.

I have recently bought small cogs for shimano 11 & 12 speed cassettes both at our local trek shop (took a long time) and an ebay seller in taiwan, took three weeks.

 

[Alaskan]

SHIMANO XTR/XT/SLX CSM9100/M8100/M7100 12 Spd Sprocket Wheel 10T 12T Cog unit https://ebay.us/w1dr79

 

[Deacon Blues]

I think I'd rather replace my 11 & 13 with the same size, since I'm going up to a 46T front ring.

 

[Alaskan]

I think I'd rather replace my 11 & 13 with the same size, since I'm going up to a 46T front ring.

I would like to do that too. I have done some preliminary research and there is a question as to whether the derailleur will work properly with the 46 tooth cog. If it will s*it up to and back down from the 46 that would be ideal. Please let us know what you learn about how well it works. I looked into possibly changing out the derailleur to an XT long cage built to handle large cogs but was told the amount of cable pull in the GRX shifter is not the same as that required by the XT derailleur. What Shimano needs to do is make a cassette with an 11-46 tooth cassette for the GRX series.

Here is a review of an acoustic equipped with the grx and and 11-46 cassette. Apparently, Shimano is famous for being conservative on their compatibility charts. Word is that it take some adjustment on the B screw in the derailleur to work well. It looks like we should be able to get away with it. It will definitely need a longer chain too.

The Corvid MAP (More Adventure Please)

Just in case you misread the title, this isn't a map depicting the spreading pandemic that's currently upending the world. Instead, on a much needed lighter note, this is all about Corvid Cycles' new MAP (More Adventure Please), a titanium drop-bar bikepacking bike made for Betsy Welch, complete...

bikepacking.com

 

[Alaskan]

Here is a link to a pdf of the shimano GRX derailleur dealers manual that may be useful

https://si.shimano.com/pdfs/dm/DM-GARD001-01-ENG.pdf

 

[Deacon Blues]

I'm staying with the 11-42 cassette....it's the front ring that will be 46T.
I took off my GRX shifting kit when I switched to a flat bar setup. I'm now using Deore XT shifter and derailleur, which shifts about the same as the GRX shifter/derailleur. I'm not really happy with either shifter/derailleur-shifting is kinda clunky on both.
I am toying with the idea of going with an Archer electric shifter kit: https://archercomponents.com/

 

[Alaskan]

Just saying that the climbing ability of the top 42 tooth cog will be compromised somewhat by a larger front chainring...not a huge change but if you are riding really steep stuff much over there on Van Isle you might think about a bigger cog in back to recover the lost leverage. I am on the fence about it but already have the 11-46 cassette and a 136 link chain as a spare for my Riese & Muller Delite mountain so I might just fit it all on the Neo 2 and see if it works.

Frankly I would really like to get the drive train for the Neo 2 on my bike. It is a 2 by 11 with 32 & 48 tooth front chain rings with the front derailliur on the left and an 11-34 on the back with controls on the right. The gear range is tremendous 572% - huge climbing ability and very fast with engagement even down hill at attainable cadence. The problem is that FSA makes the only 2x crank set I can find that is compatible with Bosch motors and it is only made as OEM for Cannondale. My local REI bike tech is checking to see if he can get that for me from Cannondale. If he can then I need the cassette, front derailleur, new chain and a new left front brake lever/shifter combo.

 

[Alaskan]

@Deacon Blues I completed the installation of the 11-46 tooth cassette and new longer chain. I installed the Sunrace CSMX8 in the black color It is a bit less money in straight silver but looks way cooler and does not look dirty so quickly. I have been using this cassette for over two years on another bike that has a Shimano XT group set and found that it is at least as durable and offers crisper, more accurate shifting.

SunRace | CSMX8

SunRace develops and produces bicycle drivetrain and brake components. SunRace products are specified by the world’s leading bicycle manufacturers and are also used extensively in the aftermarket.

www.sunrace.com

I used Shimano 11speed chain (CNHG70111) 116L w/QuickLink Chain NIB https://ebay.us/I0vczb

It did take lowering the derailleur a bit to accommodate the 46 tooth cog, using the stroke adjustment bolt found on page 17 of the dealer installation pdf manual - copy attached below. I have not road tested it but it shift up and down well on the stand. I hope to get out and test it in real life tomorrow.

Here are two photos, one in the smallest cog and one in the largest. This took the gear range from 382% to 420%.

I used this bike gear speed calculator https://www.bikecalc.com/speed_at_cadence

I came up with the following results you can enter your own data and change speeds from mph to kmph.
This is the result with OEM drive train as per spec

This is the result with my mods. Everything is entered accurately except tire width which were in preset increments. Mine are 47mm but 50mm was the closest value I could select.

I accomplished what I wanted, a lower low gear for climbing and a higher high gear for cruising fast, not quite to the degree at the high end that I had hoped but better than OEM. If end up not being able to do the 2x11 setup that is on the Neo 2, I am sure I can live quite happily with this.