Rohloff splined sprocket internal diameter?

Volvofan

100 mW
Joined
Feb 12, 2019
Messages
39
Location
MA
Fellow ebike enthusiasts-

As this is the ONLY bicycle forum for which I am registered, I thought I would start here with my inquiry.

I’m considering adding a TDCM IGH rear hub motor to my M2S All-Go Carbon. Would also like to use a belt drive. Have to go with VEER split belt vs Gates because I don’t want to split my all-CF frame. The TDCM IGH has a 5 speed Sturmey Archer IGH built into it, for those who may be unfamiliar. Veer only makes rear sprockets for the 3-speed S-A, the Enviolo, and the Rohloff.

Looking at the Rohloff rear sprocket from VEER, it’s a solid unit, so, I could theoretically hog out the hole in order to make it fit a 5-speed S-A. After nearly two hours of combing the internet, though, I came up empty in finding the minimum internal diameter of a typical Rohloff rear sprocket. Not concerned with its splines... just if you were to slide the sprocket over a perfectly round cylinder, what would be the max diameter the cylinder could be before the sprocket wouldn’t fit? This small - yet elusive - critical dimension will tell me whether I would have enough “meat” on the body of the sprocket to work with for my custom application.

Might someone have one, and a pair of calipers, handy? If so, could ya do me a solid and take a quick measurement? Trying to get a feel for whether this is a feasible idea.

Thanks in advance!

-Jon
 
Perhaps I don't understand which dimension you need, because the sprocket information appears to be right here:
https://www.rohloff.de/en/experience/technology-in-detail/specifications
Sprocket thread: M34x6 P1, tolerance 6H
for all versions I can see.

So the M number is the metric size (diameter) of the threading, the x number is the metric width of the threaded portion, the P number is the thread pitch and the tolerance is (I think) how different the thread cut might be from the ideal and still work.

Your best bet is, of course, to contact VEER directly and ask to be certain the part could be used the way you want.
 
Sorry about that! It is obvious to me what I’m looking for because I’ve been staring at it for hours, but I had a feeling my description would fall short. I did not post photos because I was being lazy but I know a pic is worth a thousand words, so... see below.

Rohloff’s site was the first one I went to. Lots of specs on that page, but not the one I’m looking for.

I doubt Veer would be helpful in advising me on how to hack up one of their products and employ it in a manner not intended by the manufacturer, lest they incur liability should something go awry (though I am not the litigious type).

Basically, I just need to know how much “meat is on the bone” of Veer’s Rohloff sprocket, specifically, but ANY Rohloff sprocket will be able to provide me the answer. If it’s 46.5mm or smaller, I should be all set. I can remove material via saw/file/dremel/whatever to make the Rohloff sprocket fit a 5 speed SA (which has a nominal internal diameter of 50mm, with an internal diameter to the tips of the three splines of 46.5mm). If the Rohloff sprocket’s ID is any larger, I’d need to ADD material to get it to fit, vs. removing it. In other words, my proposed low-tech Macgyver solution would go bye-bye.

-Jon

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Then you already have the needed info, in the data from rohloff, as long as you also know the minimum amount of metal required to leave between the ID and the belt teeth. :)

The "M34" dimension is the necessary data.
 
Sort of... but not precisely.

The hub has a splined sprocket “carrier” that threads onto the hub itself; that carrier is not zero mm thick.

Just eyeballing it, I “THINK” I’d be just fine, but would rather have someone with a set of calipers help me remove all doubt :)

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Hi mate,

If you can wait until the weekend I have calipers and a rohloff that I need to service, so win win. I'll read the thread more thoroughly and PM you Saturday (australian time) if I have any questions
 
Thanks so much! I am definitely not pulling the trigger on any purchases in the next week or two, so I’m in no rush and would be grateful for the assistance!

Stay safe and healthy,

-Jon
 
Grautuefel said:
Right, you want the OD (marked in blue) of the lumpy round doohicky. Got it

Yes, please! That’s the technical terminology I was lacking, too ;)

Thanks again!

-Jon
 
Volvofan said:
The hub has a splined sprocket “carrier” that threads onto the hub itself; that carrier is not zero mm thick.

Ah, I did not see that the carrier was separate from the sprocket itself on the Rohloff site or any of the cutaway drawings out there. It appeared to be a single unit that threaded on as one piece. :oops:

It's probably irrelevant since he's offered to caliper it for you, but a guesstimate can be made, using an image editor (like paint in windows) that shows you what pixel number your cursor is on at any given moment:

The red bracket line in your pic above would be 34mm. The diameter this line marks is about 830 pixels wide, and the space between it and the outside of the ring where the blue line marks is about 35 pixels.

So if 34mm = 830pixels, or 0.041mm/pixel.

0.041mm/pixel x 35 pixels = 1.44mm.

There's two of those thicknesses, so that's about 3mm more for the OD, to add to the 34mm ID.

So the OD is approximately 37mm, plus or minus a mm or so, for a possible range of 36mm to 38mm.

Assuming I can do math right now, which is not always guaranteed. ;)
 
amberwolf said:
Volvofan said:
The hub has a splined sprocket “carrier” that threads onto the hub itself; that carrier is not zero mm thick.

Ah, I did not see that the carrier was separate from the sprocket itself on the Rohloff site or any of the cutaway drawings out there. It appeared to be a single unit that threaded on as one piece. :oops:

It's probably irrelevant since he's offered to caliper it for you, but a guesstimate can be made, using an image editor (like paint in windows) that shows you what pixel number your cursor is on at any given moment:

The red bracket line in your pic above would be 34mm. The diameter this line marks is about 830 pixels wide, and the space between it and the outside of the ring where the blue line marks is about 35 pixels.

So if 34mm = 830pixels, or 0.041mm/pixel.

0.041mm/pixel x 35 pixels = 1.44mm.

There's two of those thicknesses, so that's about 3mm more for the OD, to add to the 34mm ID.

So the OD is approximately 37mm, plus or minus a mm or so, for a possible range of 36mm to 38mm.

Assuming I can do math right now, which is not always guaranteed. ;)

Indeed! I love the “count pixels in MS Paint” solution for rough estimates, though I trust the “caliper in one hand and part in the other” method even more. Even if your/our estimate is off by 100% (ie part is 6mm thick instead of three) I’m still looking at 46mm, which is more than sufficient.

Thanks for the help, all!

-Jon
 
OD is exactly 40mm.

Wall thickness min is 2mm max is 3mm

All lovely and metric. Is German after all
 
Grautuefel said:
OD is exactly 40mm.

Wall thickness min is 2mm max is 3mm

All lovely and metric. Is German after all

Beautiful! I ordered the Veer kit and the hub already. Frame clearance is gonna be tight, and belts leave little room for error in that regard. I’ll have 99 problems getting this to work properly, but it’s good to know that having a rear sprocket I can adapt ain’t one :)

Thank you once again!

-Jon
 
I hate you. I'd given up on belt drive and you've got me looking at this split belt system. If I can get away from noisy dirty chains it would be wonderful.
 
Grautuefel said:
I hate you. I'd given up on belt drive and you've got me looking at this split belt system. If I can get away from noisy dirty chains it would be wonderful.

Happy to be of service :)
 
FYI… took me a year to get around to doing it, but it worked :)

I ended up being more “lucky” than “good” with regards to the major obstacles one should expect to face in a belt drive and IGH conversion.

First, front beltline. In the front on the crankset, I wanted the LARGEST possible beltring because I use this bike as a commuter and have little use for super-low "climb a steep, rocky trail" gearing. My frame was, I suspected, less than conducive to this given the mid-drive motor and how the forks spread out rapidly towards the rear wheel. The 4x104 to 5x130 adapter bought me some clearance, and a couple mm of spacer washers (and some grinding on the back side of the beltring) gave me a mm or so of frame clearance as she sits. Once I’m pedaling and the frame starts to flex, I’ll probably scrape off a bit of paint, but I can live with that.

Next, rear beltline. I used a Dremel to hog out the center of the Rohloff-intended sprocket, then simply welded it to the 18T chain sprocket that the S-A 5-speed IGH came with… I ground off 2 out of every 3 teeth, and the remaining six happened to nestle in and perfectly center upon the wheel side of the Veer sprocket. Like I said… better lucky than good. It just so happens this brought beltline into alignment within a mm… time to buy a lottery ticket.

Third, IGH shifting. The Rohloff sprocket welded to the IGH’s flat sprocket now sits right in the way of the IGH’s cable entry and shifting mechanism. No problem. Bend the metal part with pliers and a vise, then heat and bend the plastic shifter cable holder with a heat gun. They barely miss the inner bore of the sprocket, and barely miss the frame. No way it should’ve worked out so well… but it did.

Finally, belt tension. I have vertical dropouts and fully expected to have to retrofit some sort of tensioning roller or horizontal dropouts to get tension right. The belt seemed juuuuust a little too tight to fit properly as-is when I mocked it up. They did say it was gonna stretch a little when you started running it, though, so maybe my luck will continue? Sure enough, I assembled the belt one tooth “looser” than the final intended length by putting the rivets in place but not crimping them down. I was able to drive around the block enough (5-10 minutes of light load) that the belt relaxed a bit and I was able to tighten it up to the “finished” length! No tensioner or modified dropouts required!

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More photos of modding the Sturmey-Archer 5-speed IGH to take the Rohloff Veer belt drive sprocket:

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Also, one footnote… that Veer rear sprocket was harder than woodpecker lips! I tried drilling through it around the circumference of the circle I wanted to cut out and it absolutely scoffed at me. Like… I could barely get the surface finish off and my perfectly new carbide-tipped milling bit was howling at me. Dremel tiny cutoff wheels and grinding stones were the only way.
 
That looks awesome, very clean. In fact looks far more professional than you bodged description would suggest.

One question, what happens when you need to take the rear wheel off?
 
Let us know how it works as you stack up some miles.

My observation so far (from dealing with them in the shop) is that belt drives wear out faster and cost more to maintain than chains. That isn't very surprising, since we've had over a century and a half to vet new cycling tech, and belts still haven't made the cut.
 
Chalo said:
Let us know how it works as you stack up some miles.

My observation so far (from dealing with them in the shop) is that belt drives wear out faster and cost more to maintain than chains. That isn't very surprising, since we've had over a century and a half to vet new cycling tech, and belts still haven't made the cut.

Wide V-Belts are used in nearly all Variable Speed scooters and motorcycles from 50cc up.
(example: every Chinese GY6 scooter ever produced)
I have always wondered why we do not see a similar system on ebikes.
I guess too much power is eaten up overpowering the springs in the front and rear pulleys.
 
Grautuefel said:
That looks awesome, very clean. In fact looks far more professional than you bodged description would suggest.

One question, what happens when you need to take the rear wheel off?

Thank you! Even a blind squirrel finds a nut once in a while ;)

Short answer to your question:
It’s a bitch.

Longer version:
First, remove axle nuts (which I actually cut external threads onto so I could still use my Rackstand, so… added challenge)

Next, drop wheel just a bit so I can access the shifting mechanism. The cable guide is only about 6” long so not much room to play with. I was actually able to reuse the 10-speed’s shifter cable and levers (two clicks per gear) so it saved me some money and work!

Third, work against the mechanism’s spring tension to slack the shifter cable and remove it. At that point, the wheel is free. The belt remains trapped in the frame for eternity, now that it's riveted together.

-Jon
 
LewTwo said:
Wide V-Belts are used in nearly all Variable Speed scooters and motorcycles from 50cc up.
(example: every Chinese GY6 scooter ever produced)
I have always wondered why we do not see a similar system on ebikes.
I guess too much power is eaten up overpowering the springs in the front and rear pulleys.

Friction is a factor, but I don't think it's the main factor. Requiring an openable frame is a problem, but it's surmountable. I think it's the space required to fit in a belt wide enough to do the job well.

Your pedals can only be so far apart (if you do pedal), chainstays only so long, rear hub only so wide-- before you make unwanted changes to ridability. However much extra belt width you need over that of a chain reduces your maximum tire width by double that amount. It can be done, but something's gotta give. And of course you'll pay more for belts and sprockets.

Then after those compromises, you probably need enough belt tension that the bearings in the hub and bottom bracket should be beefed up.

At the bottom line, what you give up is more valuable than the benefit of not having to oil your chain.

It's not out of the question that one day we get a materials breakthrough (cheap long fiber carbon nanotubes maybe?) that makes bicycle drive belts work as well as chains. But so far there have been many independent attempts at it, and none of them have succeeded.
 
Volvofan said:
I’m considering adding a TDCM IGH rear hub motor to my M2S All-Go Carbon. Would also like to use a belt drive.

What is it you're hoping to accomplish by the use of belt drive? If it's novelty, understand that you will pay not only in up front costs, but in durability and cost of ownership, for that novelty.
 
Chalo, I’d say I wanted all-weather, low maintenance durability and no more chain grease on my pants. So far… mission accomplished :)

Also, to some of your previous points, I guess I got lucky in the sense that my bike’s frame and wheel setup was conducive to the conversion… I get that not all will be so fortunate. Regarding tension - the Veer requires less than the Gates; I don’t know if bearings would need beefing up as a result but the S-A 5-speed is pretty stout, as is the Bofeili from the looks of its guts.

-Jon
 
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