Changing crank length and primary gear reduction on Rohloff/Gates equipped 2021 Homage GT with Class-1 CX Gen-4 motor.

BMWzenRider

Active Member
Tech Warning: This post has numbers and spreadsheets involved! ;)
I am going to be changing the primary gear reduction of my Gates belt drive, and need to know if my proposed changes will require any changes to the programming of the Bosch software/firmware?

I bought the standard Class-1 version of the 2021 Homage to get the Performance Line CX motor with the excellent adaptive eMTB mode which works spectacularly well with my bad knees.
Additionally, I went with the Rohloff gear hub option with Gates Carbon Drive belt for a wider gear range and less maintenance.

First, let me say, that overall I am still in love with this bike!
The suspension, the assist, the range, and the ease of getting on/off are all worlds ahead of any other model I have owned or tried.


But no bike designed to fit the widest range of owners is going to be perfect in every way.
And I would like to change mine to be a bit more perfect for ME!
For instance, I have swapped out the optional 70mm dropper post for a 100mm drop, and now I can get both feet flat on the ground at a stop without having to slide off of the saddle!!!


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Crank Length:
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I have a fairly short inseam for my height, and the aforementioned bad knees, so I have already installed shorter 160mm cranks to help keep my knees happy.
So far I am very much enjoying that change.
The shorter cranks allow me to maintain my spin much more comfortably from the smaller circle the pedals rotate around, and noticeably reduces the total flexure of my knees and hips, which also helps.
The shorter crank arms also allow me to pedal while leaned farther over into a turn/curve without striking the ground, which is also a good thing.
I also have an even shorter set of 155mm cranks which I intend to try as well to see how they feel.


My understanding is that there is a setting in the dealer software which can be toggled for different crank lengths.
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- Does anybody know if there are pre-sets for 160mm or 155mm cranks?
- How does this setting affect the assist level? (would I get more or less assist from the motor for a given crank torque with the shorter cranks programed in?)

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The Current Issue:
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To provide less strain on my knees, I try to maintain a pedal cadence of 80-90rpm.
What this means in practice with the stock primary belt drive gearing on the Rohloff equipped Homage is that I am spinning out of my Assistance Cut-Off Limit of 20mph in 10th gear.
This leaves the upper 4 gears of the Rohloff hub basically useless to me.

I am a recreational rider, and do not intent to be pedaling furiously downhill to maximize my top speed, and I will never again have the leg strength to push a bicycle past 20mph without power assist, even with a stiff tailwind.
This area is fairly hilly, not mountainous, but the Kettle Moraine Forest around here was formed by the glaciers pushing up mounds of dirt, and deep holes where buried chunks of ice melted. It results in frequent changes in slope, some quite steep.
Even with Turbo mode and 340% assist, I have rather often found myself wanting a shorter low gear, and am never shifting above 10th, because I am coasting to recover on the descents.

Which brought up the idea of changing the cogs on the belt drive to shift the overall gear range lower for my needs.

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Below is the spreadsheet that I cooked up to help with the decision making.
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The upper block shows the current stock Homage/Rohloff/Gates gearing and the resulting gear rations and development for each gear of the Rohloff hub.
Just below the stock bicycle setup numbers are the alternate gearing ratios I am looking at.
The upper left number in the resulting gearing cells is the overall gear ratio for the belt & hub gearing, and the lower right number is the development per pedal revolution in meters.
The column at the far right in the upper block shows the speed that each gearing combination would deliver in both 1st & 14th gear when pedaling at 80rpm.

For each alternate gearing I have shown the difference in the theoretical center-line distance between the pulleys according to the Gates online calculators, and the difference from the stock setup.
I have measured that the rear dropouts have approximately +5mm to -8mm of adjustment space available.

The lower blocks in the spreadsheet show various gearing combinations for other R&M Full-Suspension models, including all three of the primary drive options (Rohloff, Nuvinci, & chain), a few custom ratios using cogs R&M uses across the modesls, as well as my previous E-bike's drivetrain thrown in for me to be able to compare them against another bike that I am familiar with.

The color-coding of the developed gearing cells to the right side is as follows:
- Green = Granny gears (less than 1 wheel revolution for each turn at the cranks)
- Yellow = Direct-Drive (approx.) 1:1 wheel to crank revolution
- Blue = most frequently used gears in level or slightly rolling terrain
- Orange = 20mph motor assist cut-off when pedaling at 80-90rpm
- Red & Pink = No motor assist at normal pedal cadence.


1638508956648.png


One thing that becomes very obvious when looking at the chain drive versions is that R&M DOES change the gearing on those models between the HS and standard Class-1 bikes, and goes even lower for the "Mountain" versions by changing the size of the chainrings for each.
So, with all the other belt drive gear ratios that R&M is currently using across the various Full-Suspension models, why do they not offer different gear ratios for the HS vs. Class-1 versions???

My aim is to fix that oversight.
And it is clear that there are several options for doing so with parts that R&M is already using on other models.

1638515906927.png


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Hub Considerations:
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Another factor to take into account when using the Rohloff hub is that it is more efficient in the upper 7 gears,
AND, that the shift between 7th & 8th gear is a bit more clunky and takes longer than other transitions because the Rohloff is basically a 7-speed hub with a 2-speed transfer case.

The transfer case under-drives the seven gears for the low-range 1-thru-7 gears, which causes them to spin faster.
That is what causes the additional losses in the hub in the lower range gears.
To change between 7th-to-8th (or 8th-to-7th) the hub does two separate shift operations in sequence, going from low-to-high on the transfer gears, as well as 7th-to-1st in the main geartrain.

1638512491013.png

You can see the definitive change of the internal hub efficiency in this graph from the Rohloff website.

SO, ideally, I want to also pick a primary gear reduction which lets me stay in the upper range of the hub as much as possible.
Since I have already proven to myself that pretty much any final gearing above 2.80-2.90 is not usable for my physical condition,
Adding in the hub considerations puts me looking most intently at the 2.29 or 2.27 primary belt drive ratios most closely,

My preferred solution is to go with the 55/24 combination which will allow me to use the stock belt length, since I already bought a spare to get me home if disaster strikes.
And if I do decide that is too low, I can swap the 24T rear cog for a 22T while still using the same belts.
(and keeping the sprockets as large as possible reduces hysteresis losses from less belt bending)
Yes, I know that the 24T Gates sprocket for Rohloff was only made for the older threaded fitting and is technically discontinued, but I do have a source for one and the required threaded adapter ring.


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My question are:
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- Does the programing for the Bosch system need to be changed if the overall gear range of the drive belt/hub combination is changed?
- IF SO, can the dealer do that themselves in their accessible settings, or does it need to come down from higher up?
- IF it needs to come from higher up, is that from Bosch, or R&M?

- AND, if it needs to come from higher up, is it better for me to contact those people, or to leave it to the LBS?
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Thanks in advance for any/all who can help me get this sorted out.

Karl
 
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BMWzenRider

Active Member
After speaking with a VERY friendly and helpful tech at Bosch Consumer Technical Support I do have a few answers to my questions.
Sharing here for anyone who cares.

My understanding is that there is a setting in the dealer software which can be toggled for different crank lengths.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

- Does anybody know if there are pre-sets for 160mm or 155mm cranks?
- How does this setting affect the assist level? (would I get more or less assist from the motor for a given crank torque with the shorter cranks programed in?)

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

- According to the Bosch tech, the setting for crank length that the LBS can access is a simple toggle to indicate cranks being either less than 165mm long, or 165mm and up cranks.
So those who switch from the stock R&M 170mm cranks down to 165mm don't need to do anything, if you install 160mm, 155mm or shorter, then they suggest getting that setting toggled by your LBS.

- As far as what changing the setting actually does for the amount of assist the motor provides, he did not have an immediate answer for me.
However, he is going to consult with higher level tech people and call me back.
He promised to call back even if it was just to tell me that the information is proprietary and not able to be released to the end-user, which I found thoughtful and excellent customer service.


---------------------
My question are:
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

- Does the programing for the Bosch system need to be changed if the overall gear range of the drive belt/hub combination is changed?
- IF SO, can the dealer do that themselves in their accessible settings, or does it need to come down from higher up?
- IF it needs to come from higher up, is that from Bosch, or R&M?

- AND, if it needs to come from higher up, is it better for me to contact those people, or to leave it to the LBS?

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

- As far as changing the gear ratios of the belt/chain drive, the answer was that yes, the Bosch software does have the bike's gearing programed into the system, and should be adjusted if large changes in gearing are done to avoid errors.
- The LBS does not have access to that programing.
- The higher entity which controls that is the bicycle manufacturer, who works with the LBS to implement any changes if the manufacturer agrees to do so.
- The Bosch Tech suggested that it would probably be better for the owner to contact the manufacturer support system directly to provide relevant information and to facilitate better coordination between the manufacturer and the LBS.


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Meanwhile, the tracking on the threaded 24T rear cog and adapter ring seems to have hit some kind of snag.
This morning, after nearly 2 days of no updates, USPS tracking is no longer indicating an actual delivery date and has this message:

December 3, 2021
In Transit, Arriving Late
Your package will arrive later than expected, but is still on its way. It is currently in transit to the next facility.

December 1, 2021, 5:27 pm
Departed USPS Regional Origin Facility
NASHUA NH DISTRIBUTION CENTER

I am worried that the package may have gotten lost in the system.
 

BMWzenRider

Active Member
BTW - When I mention having bad knees, this is what I mean:
left leg 01 small.jpg
left leg 02 small.jpg
left leg 03.jpg

It was a nasty compound fracture of the left leg right at the knee with loss of muscles as well as extensive nerve damage.
There was also the femur fracture, as well as multiple tib/fib fractures farther below...

And this is one of my ankles, as well:
Ankle 02.jpg


I really NEED my bike to be geared lower overall to reduce pressure on my beat up legs!
 
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verysideways

New Member
I have a Delite Mountain Rohloff with the 50/20 set up and a 132T belt, and was thinking about doing something similar to you.
I use 1st reasonably regularly and rarely have cause to want anything lower, but i hit the 15.5mph assistance limit in 8th or 9th.

Even when i am on flat tarmac and cruising along without power, i rarely go above about 22mph which is comfortable in 11th or 12th.
I'm not sure i've ever used 13th and 14th apart from to test that they function correctly.

Just debating whether to go down on the crank (i think the next size is a 46 tooth) or up on the hub (i guess to a 21 or 22 tooth).
Any thoughts?
 

BMWzenRider

Active Member
I have a Delite Mountain Rohloff with the 50/20 set up and a 132T belt, and was thinking about doing something similar to you.
I use 1st reasonably regularly and rarely have cause to want anything lower, but i hit the 15.5mph assistance limit in 8th or 9th.

Even when i am on flat tarmac and cruising along without power, i rarely go above about 22mph which is comfortable in 11th or 12th.
I'm not sure i've ever used 13th and 14th apart from to test that they function correctly.

Just debating whether to go down on the crank (i think the next size is a 46 tooth) or up on the hub (i guess to a 21 or 22 tooth).
Any thoughts?

Just for fun {and because I LOVE playing with spreadsheets and gathering data!} I updated my spreadsheet to include some lower primary gear ratio options.
Here is the result:

1639112835753.png


You can now compare several more options for your Delight Mountain Rohloff!!!

Notes:
- The differences from stock center distance shown above is in comparison to the Homage 60/19 stock gearing, which is 0.5mm more than the theoretical center distance for the stock Delight Mountain Rohloff 50/20 gearing. The distances are similar to the Delite because the two models use the same rear swingarm assembly.
- Available adjustment range refers to actual measurements taken on the rear adjustable dropouts on my personal 2021 R&M Homage with stock gearing and belt.
- All measurements are in metric except for the speeds developed at 80rpm cadence in the second from last column which are in miles-per-hour.)

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Gates does offer a 48T front chainring in 4-bolt and 5-bolt versions as well.
With a 48/22 gearing combination you will get a primary reduction of 2.27 compared to the stock 2.50 gearing.
Nice thing about that setup is that you are going up the same number of teeth in the rear as you are going down at the front, which nets virtually the same center distance according to the Gates gearing calculator.
531.0mm (50/20) vs 531.6mm (48/22)

You can find the Gates center distance calculator tool near the bottom of this page:
https://www.gatessanitycheck.com/
There is a small check box under the button for the drivetrain sanity check calculator for the Center Distance Calculator.

You can use that to look at the differences in distances between the sprockets for a 46T front sprocket.
46/22 (2.09) gearing with a 132T belt = 537.5mm center distance
46/22 (2.09) gearing with a 130T belt = 526.4mm center distance

If you have or switch to a 4-bolt chainring spider, you can also go down to a 42T front sprocket and get the lowest primary gear reduction that the Rohloff hub allows of 1.90 you can also consider these combinations:
42/22 (1.91) gearing with a 130T belt = 537.9mm center distance
42/22 (1.91) gearing with a 128T belt = 526.9mm center distance

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As always, YMMV.
 
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BMWzenRider

Active Member
Rohloff threaded sprocket adapter ring arrived in the mail last night and the bike was put back together with the new 55/24 gearing installed.
As expected, a quick test ride showed that the Bosch control system along with the Rohloff E14 integrated shifting is not happy with the new gearing and cuts motor assist within a few feet of beginning to pedal.

The bike is now at my LBS awaiting word from the R&M Service Center whether they will support the change and download appropriate changes to the programming.

Film at 11...
🕐🕑🕒🕓🕔🕕🕖🕗🕘🕙🕚
 

BMWzenRider

Active Member
This all looks like the rocket science to me :)

I'm no rocket surgeon, but I did stay at a Holiday Inn Express last night!
😆

Ok, I do have to admit to being a mechanical engineer who has had a life-long love of cycling both pedal and engine powered.
So, I tend to enjoy playing around with the way my machines function, as well as trying to modify them to suit my wants.
And have been doing so for over 40 years.

In my college days I would buy up the derelict bicycles and Honda Spree scooters from university maintenance department when they removed them after being abandoned around campus.
I would then take the best frames and parts scavenged from other bikes/scooters to build up complete bikes to sell at a profit.
Students loved to buy the scooters from me, because I would offer them any combination of colors for the body panels from my stock to let them personalize the look. It made them much easier to locate among the sea of identical machines parked outside of the buildings. And, because I had built up a reputation as only selling scooters which ran well and were reliable. (And for a little extra $$$, I would be willing to "adjust" the governor on the engine so that they had a faster scooter than their friends!!!) ;)
AND, I always kept the best bits for my own bicycles & scooter...

I also have been working with industrial machinery using Gates toothed drive belts since back in the 1980's, so I have some experience with varying the gear ratios, calculating center distances, etc.
Way back in 1989/1990 I tried to adapt the older Gates HTD belt drive system to a recumbent bicycle I designed and built by hand, but the belt strength just wasn't there at the time to have a compact enough packaging of the belt drive and pulleys.
So I have been thrilled having the Carbon Drive on my new Homage!!!
 

JimAndArrow

Member
Region
USA
City
SoCal
Rohloff threaded sprocket adapter ring arrived in the mail last night and the bike was put back together with the new 55/24 gearing installed.
As expected, a quick test ride showed that the Bosch control system along with the Rohloff E14 integrated shifting is not happy with the new gearing and cuts motor assist within a few feet of beginning to pedal.

The bike is now at my LBS awaiting word from the R&M Service Center whether they will support the change and download appropriate changes to the programming.

Film at 11...
🕐🕑🕒🕓🕔🕕🕖🕗🕘🕙🕚
What makes you think R&M are the ones who need to support reprogramming as opposed to Bosch?

Best,
Jim
 

BMWzenRider

Active Member
What makes you think R&M are the ones who need to support reprogramming as opposed to Bosch?

Best,
Jim

Jim,
If you had read the second post of this thread you would have seen that I called Bosch first, and they confirmed that the manufacturer is the one responsible for maintaining that part of the programming.

Post #2

Cheers!
 

JimAndArrow

Member
Region
USA
City
SoCal
Jim,
If you had read the second post of this thread you would have seen that I called Bosch first, and they confirmed that the manufacturer is the one responsible for maintaining that part of the programming.

Post #2

Cheers!
Ah, whoops, missed that. That’s… strange, to me, but ok, hopefully they will provide the support then!
 

Jay Kay

Well-Known Member
Region
New Zealand
Latest News:
Heard today that R&M is authorizing the change to the primary gearing change.
Currently working with my LBS to schedule a time for R&M to connect to my bike remotely to download the changes needed.

I am STOKED!!!
🚴‍♂️
That is a pretty awesome outcome. Enjoy!
 

JimAndArrow

Member
Region
USA
City
SoCal
Heard today that R&M is authorizing the change to the primary gearing change.
Currently working with my LBS to schedule a time for R&M to connect to my bike remotely to download the changes needed.

I am STOKED!!!
🚴‍♂️

So did this happen yet? I feel like the gearing on the Rohloff Load is already low enough for me given that it starts with the 55, in 1st I’m going slow enough to be borderline balance constrained with the dog up front, and my cadence is lower than yours, but very curious to hear the results!
 

BMWzenRider

Active Member
So did this happen yet? I feel like the gearing on the Rohloff Load is already low enough for me given that it starts with the 55, in 1st I’m going slow enough to be borderline balance constrained with the dog up front, and my cadence is lower than yours, but very curious to hear the results!

Not yet.
With the holiday hours for both R&M and my shop, they could not coordinate a date till January 6th.
Given the fact that there is currently snow falling in Wisconsin with predicted high temps only reaching around 10-F this weekend, I can wait.

While they have the bike, they are also swapping the brake levers so that they match motorcycle standards with the front brake being actuated by the right hand.
Unfortunately, that requires a longer brake hose from the rear brake caliper because of the way it is routed through the frame.
I kept grabbing the wrong brake lever given the fact that I have been riding motorcycles since 1980, and have been swapping my cable-actuated bicycle brakes to match for most of those years as well.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
While they have the bike, they are also swapping the brake levers so that they match motorcycle standards with the front brake being actuated by the right hand.
Only don't let anyone else ride your e-bike afterwards!
A family member did such a swap on his bike. Then his son took that bike for a ride, and he did the over-the-bars at the first violent braking... (A broken shoulder).
 

JimAndArrow

Member
Region
USA
City
SoCal
Not yet.
With the holiday hours for both R&M and my shop, they could not coordinate a date till January 6th.
Given the fact that there is currently snow falling in Wisconsin with predicted high temps only reaching around 10-F this weekend, I can wait.

While they have the bike, they are also swapping the brake levers so that they match motorcycle standards with the front brake being actuated by the right hand.
Unfortunately, that requires a longer brake hose from the rear brake caliper because of the way it is routed through the frame.
I kept grabbing the wrong brake lever given the fact that I have been riding motorcycles since 1980, and have been swapping my cable-actuated bicycle brakes to match for most of those years as well.
I have the same issue! 40 years of motorcycling, this is not something I want to unlearn…
 

BMWzenRider

Active Member
Only don't let anyone else ride your e-bike afterwards!
A family member did such a swap on his bike. Then his son took that bike for a ride, and he did the over-the-bars at the first violent braking... (A broken shoulder).

My understanding was that EU bicycles come with the front brake being actuated by the right hand lever, which matches the motorcycle standard.
Am I mistaken?
 

JimAndArrow

Member
Region
USA
City
SoCal
My understanding was that EU bicycles come with the front brake being actuated by the right hand lever, which matches the motorcycle standard.
Am I mistaken?
On my Load 75 the right lever is the rear brake, not the front brake which is what that lever is on a motorcycle or scooter. Or were you wondering if R&M deliver them with right/front in the EU? If so, that would suggest maybe they have the right cable and/or hose lengths and we could just buy them pre-cut from R&M to swap… I actually did the same thing as you on my last bike build, had them swap levers, which is apparently not a common request though I find that surprising.