Author Topic: Looking for a lighter Rohloff bike than my Mercury  (Read 4655 times)

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #30 on: November 27, 2021, 08:08:16 PM »
I did give a little consideration to the Ti frame but didn't feel I could justify the extra 500 to save about 3/4kg. John at Spa Cycles reminded me more than once that if i wanted a lightweight bike then I shouldn't be weighing it down with a Rohloff hub. Hence my objective of a "less heavy" bike.

A custom axleplate would be the ideal solution and not one I've thought about. Something like this https://get-it-made.co.uk/guides/cnc-machining-guide/ would do the job but would likely need a 3D drawing. Also, while I've got some full-sized mudguards on the way for winter use I've stumbled on, and ordered, these https://www.amazon.co.uk/gp/product/B004R4I6XI for use in the summer. Worth trying at that price!

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #31 on: November 28, 2021, 12:03:34 PM »
I did give a little consideration to the Ti frame but didn't feel I could justify the extra 500 to save about 3/4kg.
I'd be surprised if it was anything like as much as that, a review in Cycle magazine suggested the difference between Spa's steel and ti tourer was around 300g.  The advantages of ti are IMO other than the weight, when I replaced my Raven with a custom ti frame, it was actually heavier! OK it suited me better in all other regards but it kicked into the long grass any ideas I'd had about bike weight.
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A custom axleplate would be the ideal solution and not one I've thought about.
I hadn't really got as far as design, though it would probably have modified the most appropriate standard one. 
Looking again at your dropouts - having a plate made that utilised both those holes, with a cut out between them for an OEM plate bolt, might be the easiest and neatest solution. plus it would spread the force.

EDIT - While browsing for something else, I've noticed a couple of extended designs of Speedbone/Monkeybone type fittings, I have no idea what these are for or how they're used, but they might be worth investigating.
« Last Edit: November 28, 2021, 12:21:32 PM by PH »

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #32 on: November 28, 2021, 07:43:41 PM »
I was told that the weight of a 54cm Elan frame is 2.24kg which I assume is without the headset as my 52cm Elan frame weighed in at 2.46kg with the headset fitted. There's a table at https://spacycles.co.uk/m1b0s223p4501/SPA-CYCLES-Elan-Ti-%28Ultegra-11-Speed-Hydraulic%29 which puts the weight of the 54cm Ti frame as 1.65kg, so it might be 0.59kg lighter than the steel frame. However, the only way to be sure of the weight difference is to go to Harrogate with some scales and get new frames out of boxes to ensure measurements are comparing like for like.

You got me thinking about a custom axleplate and I found this site https://www.machining-4u.co.uk/ together with Rohloff CAD drawings at the bottom of this web page https://www.rohloff.de/en/service/handbook/oem. .stp file are 3D CAD files which I'm able to view using software called ABviewer but none of the axleplates provided seem to represent part 8227. Nonetheless, I might find I can send one of those files plus a sketch of my requirements and get a quote. Editing a Rohloff file to create 8227 with longer fingers and a cut-out on the side should be straightforward for someone with the right software and skills after which it's a matter of telling a machine to carve a lump of metal. However, I'll first wait for SJS to send me a few bits (I've ordered both Rohloff Support Bolt for Axle Plate OEM2 - 8560 and Rohloff OEM2 Adapter for M5 Fender / Luggage Rack Bolt - 8552 to see what fits best) and how much further modification is needed. Rohloff support suggested that the PM bone with corresponding axleplate would work but would shift the brake caliper out so I'd also need a 180mm brake rotor. Hence I'm starting with the parts I've already got.

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #33 on: November 29, 2021, 11:55:09 AM »
Looks like you've got a few options to work through, there's plenty who have been there before and fond the solution to suit them, I'll follow with interest. 
I still think you're over estimating the weight difference between steel and ti, but as you say the only way to know is with a set of scales.
Are you going for the Rohloff tensioner?  it's a bit of a lump, but the usual Rohloff quality, I prefer it to the Shimano Alfine equivalent that sometimes allows the chain to skip of rough ground.

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #34 on: November 29, 2021, 01:12:20 PM »
My Birdy Rohloff has the Rohloff chain tensioner which I feel is a source of extra drag, perhaps not helped by the Birdy's imperfect chainline. Therefore I'm starting off with a cheap chain tensioner https://www.ebay.co.uk/itm/363524913744 but am looking out for a Surly Singleator at a nice price. I've also got an open Chainglider to provide some protection for me and the chain but should have the added benefit of reducing the risk of a loose chain jumping off the chainring. I'm waiting to see how loose the chain is with the frame and the 42 + 17 gearing combination I want. There could be justification in changing to a 41 or 43T chainring or fit a half link if the result is a chain which doesn't jump off without a tensioner and with the extra guidance from the Chainglider. Plenty of options to try.  ;D

mickeg

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #35 on: November 30, 2021, 02:13:23 PM »
Titanium is light, but the weight of a bike is the sum of the parts.  My light touring bike is titanium, but the rest of the bike is built for touring.  Touring weight rims, 36 spokes in rear and 32 spokes up front.  Steel axle in rear with quarter inch ball bearings.  Steel fork.  Sprung Brooks saddle.  So, although the frame weighs less than the rear wheel with tire mounted, the bike is probably only 5 or 10 percent lighter by being titanium than it would be with steel.  But I was not building it to be light, I was building it to be robust, easy to repair, easy to replace components, reliable, etc. 

Any tensioner will add drag as a tighter chain increases chain friction and also jockey pulley friction, but the percentage of the total drag that is added by the tensioner is quite small.  Drive train drag and tire friction will slow you down much more than an extra kg of weight because weight is not that critical unless you are a racer.  If I was trying to build a really light bike that had a Rohloff, I would try to eliminate or minimize tensioner drag as much as possible. 

Is there any estimate for chain glider drag?  That might slow you down more than an extra kg, but I have seen no data so I am only guessing that it adds several watts of friction. 

You will need some way to adjust the chain tension, changing chainring sizes and half links is not the solution.

martinf

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #36 on: November 30, 2021, 05:54:11 PM »
Any tensioner will add drag as a tighter chain increases chain friction and also jockey pulley friction, but the percentage of the total drag that is added by the tensioner is quite small.

A Surly Singleator set pushing up, with just enough tension to prevent the chain from unshipping, adds, IMO, very little friction. I reckon less than a conventional tensioner or derailleur with 2 pulleys. I have this setup on a bike with vertical dropouts and a hub gear.

I still have to clean the single pulley, the presence of a tensioner also prevents me from fitting a Chainglider, so I have to clean the chain, chainring and sprocket regularly.

Is there any estimate for chain glider drag?  That might slow you down more than an extra kg, but I have seen no data so I am only guessing that it adds several watts of friction.
 

A Chainglider must add some drag. Also a bit of weight, somewhere around 300 g from memory.

I was very sceptical when I first tried one, so I did 4 rides with and 4 rides without Chainglider over a 25 km circuit.

Contrary to my expectations I didn't notice any difference in my average times to complete the circuit, but I did notice a rubbing noise. I was testing a sub-optimal setup with 1/8" chain and relatively thick chainring and sprocket. The rubbing noise reduced sufficiently for me to no longer notice it after a few hundred kms.

So I concluded that the Chainglider drag was negligible. And I now have Chaingliders on all the family bikes except for aforementioned bike with vertical dropouts and the Brompton folding bikes.

Maybe I was lucky, some people have reported excessive drag, particularly with the thick Thorn chainrings.

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #37 on: November 30, 2021, 08:58:27 PM »
My securely wrapped SJS order arrived today. The attached photos show that, as expected, the OEM2 axleplate only half engages with the support bolt (part 8552) although there's potential to cut a notch in the axleplate so a bolt through the mudguard mounting hole also provides some torque restraint.

However, my bigger, and unexpected headache, is that I expected the screw-on sprocket adaptor to screw onto the threads revealed after I had unscrewed (with great difficulty) the Gates sprocket. I was evidently wrong as part 8542S has a smaller diameter than those threads. Did I, in my joy of managing to unscrew the Gates sprocket, overlook the need to also unscrew that screw-on adaptor shuch needs a very big spanner to hold those very narrow flats? Has anyone previously beaten this path and can offer advice?

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #38 on: November 30, 2021, 09:56:55 PM »
What a shame that OEM plate is so close!  How does it line up with the cut out between the bolts?  If that were a good fit a plate between them and a bolt for the OEM plate would spread the load.
I don't recognise that sprocket part on your hub, isn't your Mercury splined sprocket?  Could you compare?
That copper finish looks good in the close ups, I haven't seen it other than in photos, I imagine it'll sparkle n the sunshine.

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #39 on: November 30, 2021, 10:10:11 PM »
So, although the frame weighs less than the rear wheel with tire mounted
Do you know what the frame weighs? 
I went into a fair bit of detail when I designed my own, ti is 45% lighter and 38% more elastic, lots of ways to build the required stiffness back in, but they all eat away at the weight difference.  Spa is a good example to look at as they make several models in both materials that are identical sizes and geometry.
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Any tensioner will add drag as a tighter chain increases chain friction and also jockey pulley friction, but the percentage of the total drag that is added by the tensioner is quite small.  Drive train drag and tire friction will slow you down much more than an extra kg of weight because weight is not that critical unless you are a racer.  If I was trying to build a really light bike that had a Rohloff, I would try to eliminate or minimize tensioner drag as much as possible.
Plenty of drivetrain efficiency testing had been done, at 150w a single speed without tensioner is around 98% and the most efficient gear on a derailleur is around 96%, so 2% difference, or about 4w. Assuming everything is clean, lubricated and in prime condition.
As with weight, if you start not counting the small increases/inefficiencies, they soon add up. 
« Last Edit: November 30, 2021, 10:11:55 PM by PH »

mickeg

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #40 on: November 30, 2021, 10:17:29 PM »
So, the Gates sprocket had an adapter that appears to have a big hex shape that is threaded onto the Rohloff? 

My first thought was that a big vice should clamp onto the adapter just fine, but after thinking about it, the vice jaws could prevent you from putting a wrench (spanner) on the Rohloff tool. 

I have a few other ideas, but those ideas could damage the Rohloff shell, so I am keeping my thoughts to myself.  They are ideas I would try on my own but not recommend that others try.



JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #41 on: November 30, 2021, 10:35:40 PM »
What a shame that OEM plate is so close!  How does it line up with the cut out between the bolts?  If that were a good fit a plate between them and a bolt for the OEM plate would spread the load.
Thanks for this suggestion that I will investigate.

I've measured the flats on that screw-on adaptor as 46mm so this spanner https://www.ebay.co.uk/itm/233976816130 should fit and has a long handle. However, I presume that I need Rohloff tool 8508 again to hold the hub and, if this is also need for routine removal of the carrier, then I might as well get my own. Which is the tool for removing the spined carrier? Do I also need one of these https://www.sjscycles.co.uk/hub-spares/rohloff-lock-ring-8538 ?

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #42 on: November 30, 2021, 11:17:39 PM »
Which is the tool for removing the spined carrier?
It's the same tool as for removing a threaded sprocket, you remove the carrier with the sprocket attached, the two parts are effectively the same as a threaded sprocket.
The part you link to is a lockring to be used on a different sort of carrier that doesn't have a circlip, most commonly found on belt drives, but can be used on chain sprockets as well, I've never actually seen one. One of these
https://www.sjscycles.co.uk/hub-spares/rohloff-splined-carrier-sl-slim-lock/

mickeg

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #43 on: December 01, 2021, 12:09:16 AM »
...
I've measured the flats on that screw-on adaptor as 46mm so this spanner https://www.ebay.co.uk/itm/233976816130 should fit and has a long handle. However, I presume that I need Rohloff tool 8508 again to hold the hub and, if this is also need for routine removal of the carrier, then I might as well get my own. Which is the tool for removing the spined carrier? Do I also need one of these https://www.sjscycles.co.uk/hub-spares/rohloff-lock-ring-8538 ?

With the corners cut off the way they are on the adapter,  12 point wrench might not get it done right and might make things worse.  It looks like aluminum in the photo, the wrench might finish rounding off the corners.

I would look for either an adjustable wrench like I use or a six point wrench.  The adjustable might work best, as the 6 point wrench might have enough bevel that it might not grip it well.

It is my understanding that the splined carriers that are recommended for chain drive use a circlip spring, but the splined carrier used for belt drive uses a threaded on piece to hold the sprocket on the carrier.  I am guessing that lock nut you linked to is a spare for the belt sprocket carrier.

It is my understanding that the Rohloff tool for the threaded sprockets is the same as the one with the splined sprockets, you keep the sprocket on the carrier to use a chain wrench on it the same as you would with a threaded one.

ANd now I get a warning that Ph has already said much of what I just said.




PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #44 on: December 01, 2021, 01:43:04 AM »
It is my understanding that the splined carriers that are recommended for chain drive use a circlip spring, but the splined carrier used for belt drive uses a threaded on piece to hold the sprocket on the carrier.  I am guessing that lock nut you linked to is a spare for the belt sprocket carrier.

From the Rohloff website
"Lock-Ring versions come with a lock-ring to secure Carbon Drive sprockets to them (can also be used with chain sprockets of 15 tooth and above)."
https://www.rohloff.de/en/products/speedhub/speedhub-accessories

Some people just prefer the idea of a lockring and a tool rather than learning the technique of fitting and removing a circlip.