Changing sprockets on a belt driven R&M

[VarioHSDelite]

I searched the forums here, and I see that Gates has a tool for determining how many sprocket teeth for a given cadence at speed, but I haven't seen anything about replacing sprockets on a belt-driven R&M.

Turns out, the Nuvinci is a bit maxed out at 28mph. I think I'd like one more tooth on the front cog.

Does anyone have any experience or input for this endeavor? Where to buy the cogs, how to replace, etc. Also, any input on how the motor will react to this change? Seems it would be impartial to the tooth count, but maybe someone else has a deeper understanding.

Thanks.

 

[Mapachin]

Interesting question. Any advice from forum members?

 

[Chris Nolte]

In theory you can go up one tooth in the front and down one in the rear and keep the same belt. This is a good starting place to research, but unfortunately we can’t endorse any modification like this as it could have adverse effects to how the motor works and it could impact your warranty with R&M.

 

[VarioHSDelite]

Interesting question. Any advice from forum members?

As the OP, I have a 1500 mile update on this topic.

I spoke with my local bike shop and we were able to find replacement cogs with different tooth counts, so it is possible. But this would not be a preferred modification.

Having ridden ~1500 miles now, I have come to know that the Bosch motor needs more RPM (which is effectively more cadence from the rider) for maximum power; if you were to bring the cadence down, it is my opinion that the motor would struggle at higher speeds. R&M appear to have been advised on this topic, and set the tooth count (and subsequent cadence at speed) to be commensurate with the motor's best performing RPM. The motor appears to be low on torque but makes up for it with horsepower (where horsepower is a function of torque at RPM). Battery life maybe?

This is unfortunate as it leaves the rider pedalling their legs off at 28mph. However this is all of little importance, as the bike begins to taper power at 25.6mph, and provides very little assist past 27mph anyway, so it's near impossible to sit at the 28mph limiter on flat ground. 22-24mph is about all its going to do (unless you are willing to try a lot harder than I am)

And more than likely, takeoff would be adversely affected as well, not providing sufficient power until maybe 3-4 MPH, leaving the rider to do the initial dig from a stop largely unassisted. Between the lossy transmission and the lossy front gear system, this bike is a bane to ride unassisted, so coming from a stop with a higher "first gear" combined with less output from the motor would be most unpleasant.

tl/dr: the engineer worked with what he had and came back with the best possible outcome; leave good enough alone

 

[Chris Nolte]

Glad to hear your feedback on this and I totally agree. One thing to note is that the Enviolo hub is most efficient in the center of its gear range and the loss happens most at its extremes. I would recommend when your at the extreme highest gear to back it off ever so slightly and that will be the optimal high gear to achieve a higher speed although it can be difficult as you mentioned. The new Bosch motor makes it easier the way the power curve bumps up past 20mph on the HS, but that doesn’t help the current Gen 2 system so much.

 

[Mapachin]

Thanks for the very useful information. I recently started commuting in my R&M Charger for a 19-mile commute one way in flat areas around DC. I find the enviolo hub difficult to reach speed beyond 23mph, and I have happily settled to cruise at 20-23mph with efficiency, beyond that the cadence is too fast and difficult to maintain, as VarioHSDelite says. Thanks Chris for the additional advice. I just bought my R&M and I find this forum extremely useful and practical. Thanks all for sharing.

 

[Molly45]

I've also got a Charger with the enviolo hub (limited to 15mph, I'm in the UK).
But I didn't choose it for speed, I bought it because I wanted a smooth, quiet, clean and virtually maintenance free drivetrain. (and it delivers that perfectly). If anyone wants to ride fast, this is not the right machine, it's simply not what it's designed for.
Having said all that, I may well fit a dongle at some point, just to give assistance up to about 20mph, but I know the limitations of the gearing will mean that's going to be the maximum speed, any higher and the cadence would be beyond me.

 

[VarioHSDelite]

when your at the extreme highest gear to back it off ever so slightly and that will be the optimal high gear to achieve a higher speed although it can be difficult as you mentioned

hahahahah naaaah Chris you just gotta put in the work!

I first noticed this sweet spot you mention, and rode exactly like that for the first few months.. turn it all the way to "orange man on a flat road" and then back it off a touch. But then! I have found, if you twist it completely to flat road, and then just try harder, it will actually make just as much steam as before. But it does require more from the rider. If you are just beginning or not in good shape, the aforementioned "back it off a hair sweet spot" is a good place to be. But the pro move is to go to full flat and power through

The new Bosch motor makes it easier the way the power curve bumps up past 20mph on the HS, but that doesn’t help the current Gen 2 system so much.

Did you really have to point that out?? I could have gone all day without knowing that..