Bafang to Rohloff belt drive question.

[Cybersnow]

I am shooting an email to Ravi. Originally I wanted the bike to come with a Sram 11 speed gear set but Ravi talked me out of it. I just took the bike out after 3 cups of coffee to see what it can do by pushing up the power. In g11=17mph, g12=18.x, g13=19.9 g14=21. Now this was at power level 3, not sure of cadence. I did put the power to 5 and picked up 22mph. Coming up a known 35 degree grade, I down shifted to g6 but could not get lower. At the top of the hill it would go into g5, so I probably should have shifted earlier. I do like the idea of going 60/20 the best though!!

 

[il Munduato]

Not sure why you say it wouldn't shift down?
I realize you're in learning curve mode so...
Best practice with the Rohloff is pedals at 12/6 o'clock, pause pedaling and shift. Once practiced you can do this in a second, even on a hill.
If on a hill there's a few tricks....
Either use PAS Up or Throttle to gain a little momentum before shifting.. or as I prefer when anticipated, shift gear down and PAS up at the same time. If you start to stall just feather in a little throttle. The Ultra does this quite nicely as the throttle is additive to PAS and you can feather in as little as needed.

 

[Cybersnow]

I was climbing up about a 35 degree hill and wanted to see how it would climb in g5, in retrospect I probably was putting pressure on the Rohloff. I havent had any issues with shifting and will use your sage advice next time I ride home. Yep, that darn hill is on the way to the house.

 

[Jeremy McCreary]

I was climbing up about a 35 degree hill and wanted to see how it would climb in g5, in retrospect I probably was putting pressure on the Rohloff. I havent had any issues with shifting and will use your sage advice next time I ride home. Yep, that darn hill is on the way to the house.

Yikes! Which current gear gets you up that darn hill at a comfortable cadence?

Have you considered a bike funicular? Just let your wife ride up first and use her and her bike as the counterweight.
;^}

 

[Jeremy McCreary]

If on a hill there's a few tricks....
Either use PAS Up or Throttle to gain a little momentum before shifting.. or as I prefer when anticipated, shift gear down and PAS up at the same time. If you start to stall just feather in a little throttle. The Ultra does this quite nicely as the throttle is additive to PAS and you can feather in as little as needed.

My throttle's like that, too. Best kind, and quite a useful riding tool with many non-obvious uses having nothing to do with getting out of pedaling.

Think of it as adding a complementary form of pedal assist that can't really be duplicated with any kind of pedal-based control. Sure, you can ride throttle-only, but plenty of utility for always-pedalers.

 

[Ravi Kempaiah]

OK, so problem is It does not look like there is a 57T front sprocket, it goes from 55 to 60.
So the closest to the 22+55 = 77 would be 19 +60 =79

at a pedaling cadence of 60, here are the result for 19 rear 60 front
For a cadence of 70

So speed wise you are good with 19/60, but the length of the belt will vary a bit.

To double check the implications, we can use gates belt calculator, but I would need the following from you

1. What is your chainstay: distance between rear axle and center of bottom bracket?
2. Can you check the Belt model reference on the belt so we can know how many teeth it has (count the teeth if you have to )
3. Do you see any horizontal adjustment system on the rear axle, if so how much distance is there to move the wheel forward and backward from the current position?
4. Last you need to check if a larger front sprocket could interfere with the rear arm (what distance between the existing 55 T sprocket and the arm before it touches it.

Thanks for sharing this excellent analysis!
Very helpful for riders. Typically, most motors are tuned to provide high torque and power at around ~75 RPM cadence. This is also beneficial for knees.

On my previous bike, I did use 55T and 20T for Rohloff and was able to maintain 23mph average speed at a cadence of about ~75.
I did speak with @Cybersnow and he is going to look at either changing the rear sprocket to 20T and increasing his cadence or changing both front and rear sprockets to maintain his typical cadence.

 

[il Munduato]

I was climbing up about a 35 degree hill and wanted to see how it would climb in g5, in retrospect I probably was putting pressure on the Rohloff. I havent had any issues with shifting and will use your sage advice next time I ride home. Yep, that darn hill is on the way to the house.

I have one of those to get home as well... that's how I know all the work arounds.

My throttle's like that, too. Best kind, and quite a useful riding tool with many non-obvious uses having nothing to do with getting out of pedaling.

Think of it as adding a complementary form of pedal assist that can't really be duplicated with any kind of pedal-based control. Sure, you can ride throttle-only, but plenty of utility for always-pedalers.

The anti throttle crowd are clueless.
It's a tool just like the motor and gears are. I often continue pedaling and still under load for the brief moments I do use it. Better to throttle for 2 seconds than stall. Especially useful off_road when it's easy to bite off more than anticipated.

 

[Jeremy McCreary]

The anti throttle crowd are clueless.
It's a tool just like the motor and gears are. I often continue pedaling and still under load for the brief moments I do use it. Better to throttle for 2 seconds than stall. Especially useful off_road when it's easy to bite off more than anticipated.

It's clear that some throttles are better implemented than others. Some are all-or-nothing, some work only with assist turned off or when you're NOT pedaling, and some deliver more power at higher assist. These poor implementations might have contributed to anti-throttle bias.

You want to be able to slam or feather in instant power, up to full power, in any non-zero assist level — regardless of what the pedals are doing. That's a useful tool!

 

[Cybersnow]

I totally agree. I use the throttle very sparingl. It is great to get started when stopped going uphill. But now I will use it to shift rohloff gears going uphill!

 

[scrambler]

Thanks for sharing this excellent analysis!
Very helpful for riders. Typically, most motors are tuned to provide high torque and power at around ~75 RPM cadence. This is also beneficial for knees.

On my previous bike, I did use 55T and 20T for Rohloff and was able to maintain 23mph average speed at a cadence of about ~75.
I did speak with @Cybersnow and he is going to look at either changing the rear sprocket to 20T and increasing his cadence or changing both front and rear sprockets to maintain his typical cadence.

Always happy to help

Can you share how much range there is on the chainstay on either side of the nominal 489mm?

 

[Cybersnow]

Ravi and I had a informative phone call. While Ravi was adamant about increasing cadence, at 78 years old I am not sure I will ever be able to maintain a cadence of 75 for hours at a time. I guess I have to accept that I am now an old fart and that my marathon days are over. I guess that leaves me with a few choices. The first being buying another bike or trying to convert the existing one so I can enjoy it. After not riding for about a year I know that picking up the cadence will help. Rather than spending the money on another bike I have decided to adjust a few things on this bike. I don’t have the skills or tools to modify the belt system and the two tiny bike shops in my little town have declined on working on a belt system, so the bike gets transported to Boise Idaho on Thursday. I will have them contact Zen Sales and explore if it is possible to adjust the 2.5 ratio closer to 3.0. If that is not possible then I wonder if it would make sense to replace the Rohloff with a standard 11 speed gear set.

 

[scrambler]

I am not following. There is a lor more work involved in replacing the rohloff by a derailleur than simply changing the sprockets and belt. Replacing the rohloff would mean not only replacing both sprockets as required for the belt upgrade, but also completely rebuilding a new wheel. So more work and more money.... any store that can do one can do the other. And if you can remove the rear wheel (which you want to be able to do eventually) you can change the sprockets, and put the new belt...

 

[Cybersnow]

I am not following. There is a lor more work involved in replacing the rohloff by a derailleur than simply changing the sprockets and belt. Replacing the rohloff would mean not only replacing both sprockets as required for the belt upgrade, but also completely rebuilding a new wheel. So more work and more money.... any store that can do one can do the other. And if you can remove the rear wheel (which you want to be able to do eventually) you can change the sprockets, and put the new belt...

Over the decades I have built and converted bikes to e-bikes so I am aware of what would be the cost and labor involved. That is why my first choice is to modify the 55/22 belt system. Ravi wants me to get the folks in his sales department involved to see what options are feasible given the play in moving the rear axel and the availability of parts. I am going to a bike shop that has worked on Rohloff systems in the past. Replacing the Rohloff with a chain system would be my last resort before giving up on the bike and just spending another $4-5k On another bike.

 

[Ravi Kempaiah]

Ravi and I had a informative phone call. While Ravi was adamant about increasing cadence, at 78 years old I am not sure I will ever be able to maintain a cadence of 75 for hours at a time. I guess I have to accept that I am now an old fart and that my marathon days are over. I guess that leaves me with a few choices. The first being buying another bike or trying to convert the existing one so I can enjoy it. After not riding for about a year I know that picking up the cadence will help. Rather than spending the money on another bike I have decided to adjust a few things on this bike. I don’t have the skills or tools to modify the belt system and the two tiny bike shops in my little town have declined on working on a belt system, so the bike gets transported to Boise Idaho on Thursday. I will have them contact Zen Sales and explore if it is possible to adjust the 2.5 ratio closer to 3.0. If that is not possible then I wonder if it would make sense to replace the Rohloff with a standard 11 speed gear set.

Hey John,
@scrambler posted some detailed gear ratio analysis. What would be the speed at 65 RPM if you used 55T front and 20T rear?

 

[scrambler]

Over the decades I have built and converted bikes to e-bikes so I am aware of what would be the cost and labor involved. That is why my first choice is to modify the 55/22 belt system. Ravi wants me to get the folks in his sales department involved to see what options are feasible given the play in moving the rear axel and the availability of parts. I am going to a bike shop that has worked on Rohloff systems in the past. Replacing the Rohloff with a chain system would be my last resort before giving up on the bike and just spending another $4-5k On another bike.

From the gates calculation, we know 20/60 with the 130T belt would fit. Ravi can get you the right parts, and the shop install it. An hour of labor at most...

 

[Jeremy McCreary]

Hey John,
@scrambler posted some detailed gear ratio analysis. What would be the speed at 65 RPM if you used 55T front and 20T rear?

At 65 RPM cadence with the stock external ratio of 55/22 = 2.50, gear #11 gives 13.3 mph, #12 gives 15.1 mph, #13 gives 17.2 mph, #14 gives 19.5 mph, and #1 gives 3.7 mph.

With 60/20 external gearing, all of those speeds would increase by 20%, but I'd worry about the effect on the 35% climb the OP faces on every ride from home.

Curious, what does it take to change the belt on this bike?

 

[scrambler]

Hey John,
@scrambler posted some detailed gear ratio analysis. What would be the speed at 65 RPM if you used 55T front and 20T rear?

You can download the excel sheet in post #4 to run any simulation
below the screen copy of 20/55 65

With the same 128 belt, this corresponds to a 494mm chainstay or 5mm more, so the bike needs to have at least 7/10 mm available to move the wheel back

 

[Cybersnow]

How much does changing from 2.5 to 2.75 help? I can’t change your great spreadsheet on my little iPad. If we have to change the belt and rear sprocket, wouldn’t it make sense to change all three at the same time?

 

[Cybersnow]

Thanks, I see you were way ahead of me. Contractors taking me away as we remodel the deck.

 

[scrambler]

How much does changing from 2.5 to 2.75 help? I can’t change your great spreadsheet on my little iPad. If we have to change the belt and rear sprocket, wouldn’t it make sense to change all three at the same time?

I agree, if a 60T sprocket fits, I think you should go for 20/60 with 130T belt.

@Ravi Kempaiah would only needs to confirm that a 60T gates sprocket would not interfere with the rear arm!