Thorn Cycles Forum
Community => Rohloff Internal Hub Gears => Topic started by: JohnR on May 26, 2021, 08:59:41 pm
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For the record, I recently decided that there would be occasions when I wanted a more transportable bike than my Mercury but the bike would need to have a Rohloff hub gear. After due deliberation I invested in a Birdy Rohloff which, I have to note, goes over rough road surfaces more smoothly than my Mercury as the suspension more than compensates for the small wheels.
I happened to check the chainline. Rohloff's specs say that the sprocket chainline is 57mm (13T sprocket on splined carrier) which my measurements confirmed, but I found that the chainring chainline is only 51mm (ie 6mm offset). The Birdy's chain, however, is 9-speed which I assume is to provide the flexibility to fold up when the bike's back wheel is folded. Aware that comments in this forum suggest that any offset should be minimal I first asked the dealer who commented that R&M have been selling the Birdy Rohloff for 15 years and must know what they are doing. It's possible that R&M didn't want to fit a wider chainring chainline as it would interfere with the folding.
I then asked Rohloff support if the 6mm offset was OK and the reply was that it wouldn't hurt the hub but would result in slightly increased wear of the chain and sprocket. People have used Birdy bikes for light touring but are unlikely to load it as much as a full touring bike (the advertised "gross vehicle weight" is 120kg). Perhaps, therefore, a less-than-perfect chainline on a Thorn bike isn't bad news for the Rohloff hub (as some comments here have suggested) but would reduce the life of chain and sprocket.
I doubt if my Birdy is going to clock up the same miles as my Mercury so a bit of extra drivetrain wear doesn't worry me. However, I do want to get some miles on the bike and get the Rohloff hub run in. At the moment the noise in 7th gear makes me realise that the Rohloff on my Mercury (now over 4,000 miles) is running very sweetly with only a bit of extra noise in 7th.
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I have not measured my Rohloff chainline with great precision, but I am assuming it is about 5mm off. That assumption is based on buying a bottom bracket with a spindle about 10mm shorter than my calculations indicated that I should have used on that bike.
I wanted my Rohloff bike to have about the same Q factor (width between pedals) as my derailleur bikes, that was why I bought the shorter spindle.
I am using a double crank, bashguard or chainguard in outer position, chainring in the inner position. My calculations suggested that my chainline would be ideal if I had the chainring in the outer position.
I assumed since virtually no derailleur bikes have a perfect chainline, or if they do it is very transient in time, I was not going to worry about a 5mm chainline error.
I built up my Nomad Mk II from parts, did not buy it assembled from SJS, bought my Rohloff from a different dealer. Stock Rohloffs usually come with a 16T sprocket, but SJS fits 17T sprockets, mine is a 16T. Following the advice at this link, I put a notch in one tooth on the sprocket and on the chainring, when I put the chain on the bike I always put a link with outer plates on that notched tooth.
https://www.sheldonbrown.com/chain-life.html
Thus, every other tooth gets more wear because every other link has more elongation with a worn chain. Also, the links with inner plates will rub on the sides of every other sprocket teeth.
Last year after 7 years I finally flipped my sprocket for the first time. Photos attached.
First photo, note the notched tooth, which also has a bit of yellow paint marking that tooth, that does not have much wear on the side of the tooth, only outer plate links were used on that tooth, adjacent teeth show more wear on the sides of the teeth, those teeth had wear from inner plate links. This photo is taken from the outside of the sprocket or if the sprocket was still on the hub the camera would have been on the right side of the bike. The chain turned the sprocket clockwise. That short article that I provided the link above discussed why every other link would be elongated on the bike chain as it wore, the links with the inner plates also have more wear on the teeth because of that, the teeth that had outer plates have less wear.
Second photo, the other side of the sprocket, in this case the camera would be taking the photo from the hub side of the sprocket if the sprocket was still installed on the hub. There is a lot less side wear on the teeth that had inner plates on this side of the teeth, that difference in wear is from the chainline error.
I do not keep records of how many miles (or km) I put on each bike in a year, in a typical year I ride about five different bikes, today I did an exercise ride of about 30 km on my derailleur fitted titanium bike. So, I can't tell you how much wear there is on that sprocket in distance. But I can say that I built up that bike in the spring of 2013. I have ridden it a lot on local trails, a month long tour in Iceland and a five week tour in Canadian Maritimes. And some winters I fitted it with studded tires to use on ice and snow.
Did I answer your questions? No, but I am confirming that you get more wear on one side of a sprocket this way. Is that an issue of concern? I think not. I have no plans to get a longer bottom bracket spindle or add spacers to my bottom bracket, or shift the chainring to the outer position on the spider.
Based on your posting, it sounds like you use a 13T sprocket, that being an odd number, the wear on the sides of the sprocket teeth would be spread over all teeth, not every other one like on mine.
I think you should just ride the bike and accept that you might get a bit more wear on the chain and sprocket teeth. But chain elongation is likely not worse and I doubt that the sprocket teeth would have a shorter life span. So, I do not think you should worry about it. You might however want to make sure you do not let your chain get too loose, as the chainline error would constantly be trying to pull the chain off to one side.
I have no clue what your chainstay length is, I expect it is shorter than on my Nomad Mk II, thus, the angle that your chain is to the side is likely greater than on my bike. But I still think it is not worth worrying about.
Third photo, my Nomad in Iceland, just because I like that photo.
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I agree with George that 6 mm is probably not a big deal.
If you want the chainline spot on, you might be able to use spacers under the chainring, on most cranks there is ample room between chainring and crank. Another possibility with some of the old-style square taper bottom brackets is to use a spacer under the fixed cup (you won't be able to use 6 mm here, but 2 mm on the bottom bracket and 4 mm under the chainring might work). You would have to check whether these modifications affect the folding or not.
Transmission life will be shorter than on a full size bike because :
- a 13T sprocket wears quicker than a larger one,
- the chain is closer to the ground and will pick up more road muck.
I recently converted one of my Bromptons to Rohloff. I chose a 15T sprocket and fitted a fairly big chainring because I have previous experience of fast sprocket wear with 13T sprockets on Bromptons and Moultons. I used a 122.5 mm Stronglight JP400 BB unit with Stronglight 110 mm BCD cranks. A couple of very thin freewheel spacers under the fixed cup give a fairly good chainline, with aluminium spacers (from a set of chainring bolts) under the chainring (in the outer position) the chainline was a bit too far out. So I am running it with just the bottom bracket spacers for the moment.
I may try and get the chainline spot-on next time I do maintenance on that bike, using thin stainless-steel washers under the chainring instead of the aluminium spacers.
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Thanks for the comments and suggestions. I'm not planning to try to fix the Birdy's chainline. I was curious whether Rohloff thought that the offset is OK or would, in the long term, cause some damage to the hub. I am, however, planning to change the 13T sprocket to 14T as this will get the gearing to be almost identical to that on my Mercury. Sprockets and 9 speed chains are relatively cheap compared to a Rohloff hub.
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Perhaps, therefore, a less-than-perfect chainline on a Thorn bike isn't bad news for the Rohloff hub (as some comments here have suggested) but would reduce the life of chain and sprocket.
I don't think I've seen many such comments on here. It's one of those things where it is better to have perfect, and as in most circumstances you only have to do it once, makes sense to me to do so. But to put it into perspective, it's less than one degree off and when derailleur efficiency is tested the differences between straight and one over is less than 0.5% though it jumps from there. Where it would make a difference, IMO, is if there was a tight chain. You can feel (And hear) a slightly off chain line on a fixed gear bike. That's never going to be the case with a bike using a tensioner. The 9 speed chain is an odd choice, I can understand why they'd use derailleur chain. but I can't see an advantage of 9 over 8, there's no big disadvantage, just 8's are a little more robust. Maybe it wasn't a choice, just what they have for other bikes.
Nice choice of bike BTW, I was tempted by one, with the same purpose, but ended up going for an Airnimal Joey.
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The 9 speed chain is an odd choice, I can understand why they'd use derailleur chain. but I can't see an advantage of 9 over 8, there's no big disadvantage, just 8's are a little more robust. Maybe it wasn't a choice, just what they have for other bikes.
A Brompton still folds well even with a laterally rigid 1/8" chain. I have this on my "light" Brompton, which I used for commuting until I retired. The sprocket, chain and chainring last a wee bit longer than the narrow 8-speed sprocket, chain and chainring I used at first. 14T sprocket also lasts significantly longer than 13T, and has the added advantage of far less skipping if the transmission picks up mud, dead leaves or snow.
With a Rohloff hub on this type of bike it might be worth going for one of the expensive long-lasting 3/32" hub gear/single speed specific chains from KMC or Wipperman rather than using an 8 or 9 speed derailleur chain.
Nice choice of bike BTW, I was tempted by one, with the same purpose, but ended up going for an Airnimal Joey.
I also looked at Airnimal, but having used Bromptons for about 40,000 kms I decided to modify my "touring" Brompton and keep the sturdy steel frame I know rather than go for a lighter but (IMO) more fragile aluminium alloy frame as used in Airnimal or Birdy. The Brompton doesn't ride as well as either of these two bikes, but it is very quick to fold and AFAIK more compact than either.
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A Brompton still folds well even with a laterally rigid 1/8" chain.
I think we may be talking at cross purposes - I was thinking the advantage of a derailleur chain being they're designed to work with an imperfect chain line.
Nice choice of bike BTW, I was tempted by one, with the same purpose, but ended up going for an Airnimal Joey.
I also looked at Airnimal, but having used Bromptons for about 40,000 kms I decided to modify my "touring" Brompton and keep the sturdy steel frame I know rather than go for a lighter but (IMO) more fragile aluminium alloy frame as used in Airnimal or Birdy.
I've also recently become a Bromptoneer, it wasn't part of any plan, just the only way to make a short work contract across several sites practical. I'm still in wonder at the fold, without being as slick at it as I've seen some! I know they have many fans and I know people tour (And Audax!!) on them, but I can't imagine mine being used unless such a small fold is an absolute requirement. But, I reject the idea that an aluminium frame is in any way inherently more fragile, such things are the result of design rather than material.
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I think we may be talking at cross purposes - I was thinking the advantage of a derailleur chain being they're designed to work with an imperfect chain line.
A derailleur chain will certainly work better than a 1/8" chain when the chain line is way off (large chainring on largest sprocket on a derailleur bike). For 6 mm I reckon it won't matter much, although the small wheels on a folder will increase the effect compared to a large wheel bike. Although I generally try and get chainline as good as possible, in the past I have sometimes run 1/8" chain up to about 10 mm off the proper chainline on my old 650B utility bike without noticing any issues.
But, I reject the idea that an aluminium frame is in any way inherently more fragile, such things are the result of design rather than material.
Perhaps I should have put "my prejudice" instead of "IMO". I have seen a fair number of failed aluminium alloy frames over the years, but far fewer steel ones. And in the case of steel, generally after several decades of use.
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I'm resurrecting this old thread so I can note that I was getting some chain noise on a Rohloff bike I had built. Measurement revealed that the chainline at the chainring was 52mm whereas the sprocket on the hub was 55mm (slim sprocket carrier). I then remembered that I had bought some bottom bracket spacers in case I found a need for them so added them (total 2.5mm) on the drive side which shifted the bottom bracket and cranks to the right by 2.5mm. The chain (KMC Z1 narrow (3/32")) is now silent and a hint of rubbing on the Hebie Chainglider has disappeared.
I wonder if Rohloff's web page covering chainline https://www.rohloff.de/en/service/handbook/speedhub/assembly/crankset has been updated since I started this thread. It includes the statement:
Use of a SPEEDHUB on a frame with the average chainstay length of 450mm results in:
1° chainline offset / approximately 8mm
0.5° chainline offset / approximately 4mm
This is technically is harmless and unproblematic for the function.
Generally the goal is to create a chainline with as little offset as possible.
To extend the lifespan of all sprockets, it is also generally advised to use as many teeth as possible to achieve the desired transmission ratio.
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I distinctly remember a reliable German bike manufacturer telling me as a fact that a Rohloff chainline shouldn't be more than 1mm off. Since this person was chummy with Herr Rohloff, and had a longer commercial relationship with him than any other bike manufacturer, I took it for the gospel and didn't bother checking.
About what damage an angled chainline can do to a hub gearbox, that depends on the design and materials of the axle and its surrounding components plus, less obviously, the expected service life of the gearbox. An automobile gearbox has an acceptable amount of "lash" (sideways movement measured in thousandths of an inch) at the input and the output, depending on whether the shafts run in plain bearing (gearboxes for luxury cars where silence is important), roller or needle bearings, for 'boxes more likely to be subject to violent treatment in, for instance, racing. As a matter of personal outlook, I suspect that the same is true of bicycle hub gearboxes, but isn't a subject at the forefront of cyclists' minds because your average bicycle hub gearbox is not subject to huge forces combined with violent treatment as in a racing car. But the Rohloff is still raising life expectancy to extraordinary levels, year by year, so that the question may arise again, even if only for permanent circumnavigators. Certainly, it was clearly in Rohloff's mind when that 1mm chainline offset max was promulgated, and has with experience become a "no problemo" shrug-off. Anybody else remember that a few years ago Rohloff offered inducements for people with really high mileage Speed 14s? After they dismantled and inspected them, they pronounced that there was no worrying wear -- but what struck me is that they declined to take the opportunity to guesstimate the upper limit of their HGB's life. I'm therefore not surprised that Rohloff now says that a skew chainline isn't a big deal. However, I don't think the effort to give my bike a straight chainline to within 0.5mm* was wasted then or is wasted in the light of hindsight.
* Considering that a bike isn't a single-plane object, 0.5mm is an acceptable measuring error, which needs to be added to any manual measurement. In fact, I believe my chainline has zero offset.
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It would be interesting to hear from cyclists who've dismantled the Sturmei-Archer hub gearboxes that have such a reputation for longevity: What have they observed about the bearings the axle runs in, or wear on the axle itself at bearing surfaces?
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Seems to me that some small chain offset can be ameliorated by using the more flexible derailleur chains rather than the stiffer fixie chains, a subject already touched on above. (And note also the remarks about not running a tight chain on a Rohloff HGB.)
I like the derailleur KMC X8 (rather than the specced KMC Zx) because it is a high value/performance chain, which I buy a stock of every few years at a sale and give away most to other cyclists rather than use, because I believe that the extra flex will let me run further on the sprocket and the chainring than a stiff single-gear chain. I have spares of both sprocket and chain ring, of course, but mine is a near-zero maintenance bike and these small things help me align replacements with the Rohloff oil change schedule.
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It would be interesting to hear from cyclists who've dismantled the Sturmei-Archer hub gearboxes that have such a reputation for longevity: What have they observed about the bearings the axle runs in, or wear on the axle itself at bearing surfaces?
I've had up to about 8 mm offset on bikes with Sturmey-Archer hubs in the past. Not noticed any particularly uneven wear. The 3 main wheel bearings are cup and cone type, which can cope with a fair amount of misalignment.
I don't do that now, because of the Chaingliders I use on all but one of the family's hub geared full-size bikes. The Chainglider prefers à straight chain.
Currently at about 102,000 kms of use with my S5/2 hubs, the most-used hub on my old utility bike is at about 54,000 kms.
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I've had up to about 8 mm offset on bikes with Sturmey-Archer hubs in the past. Not noticed any particularly uneven wear. The 3 main wheel bearings are cup and cone type, which can cope with a fair amount of misalignment.
8mm sounds hugely out of line, though I think Rohloff are right to put it in context of only being 1°. The best visual to see if it's acceptable would be the way the chain sits on the first/last tooth, if a side plate is in contact I'd consider it too much, a couple of hundred miles like that and you'd see the wear on one face of the teeth. I don't know how far out of alignment it would need to be before that caused undue strain on the bearings, I'd guess a long way off, otherwise derailleur hub bearings wouldn't last as well as they do.
I also recall the advice from Rohloff being less tolerant and assume the current recommendations come from experience. Even so, I can't help feeling that perfect is still better than acceptable and it's the sort of job that needs doing once, then as long as worn parts are replaced like for like, it never needs doing again.
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8mm sounds hugely out of line, though I think Rohloff are right to put it in context of only being 1°.
I used to do this in order to reverse dished sprockets (to get extra use out of them) and sometimes to use up some less than ideal spare bottom-bracket parts I had.
Penny-pinching, as even now Sturmey-Archer sprockets only cost about 5 euros.
Though I suppose using Chaingliders could also be termed penny-pinching, as they seem to prolong the life of transmission components as well as reducing maintenance.
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It would be interesting to hear from cyclists who've dismantled the Sturmei-Archer hub gearboxes that have such a reputation for longevity: What have they observed about the bearings the axle runs in, or wear on the axle itself at bearing surfaces?
I've had up to about 8 mm offset on bikes with Sturmey-Archer hubs in the past. Not noticed any particularly uneven wear. The 3 main wheel bearings are cup and cone type, which can cope with a fair amount of misalignment.
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Currently at about 102,000 kms of use with my S5/2 hubs, the most-used hub on my old utility bike is at about 54,000 kms.
Thanks, Martin. That sort of mileage is pretty indicative, given that Shimano rate their well-regarded Nexus Premium HGB at 50,000km MTBF, and that I managed to wreck two of their boxes within a total of only about 5000km.
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That sort of mileage is pretty indicative, given that Shimano rate their well-regarded Nexus Premium HGB at 50,000km MTBF, and that I managed to wreck two of their boxes within a total of only about 5000km.
I've got nowhere near 50,000 km on the family Nexus 8 Premium hubs.
The latter are currently at about 16,000 kms, but this is spread out over 6 different hubs. The one with the most distance is at about 5,800 kms.
The 3 hubs used by my wife on her bikes are treated gently by a light rider, the two fitted to the visitor bikes are occasionally misused due to ignorance (not easing off when changing gear) and the Nexus Premium on my "new" utility bike is used harder with a fairly heavy rider, loads of up to 40 kg on the bike and far more than that when towing my trailer.
So far, no problems except for very occasional missed gear changes when I forget to check the cable adjustment. This is critical on the Shimano 7, 8 and 11 speed hubs.
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Interesting subject.
May I ask how folks are gauging the chain line measurement?
A straight metal ruler?
Best
Matt
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I have a length of angle aluminium I use for all sorts of straight line tasks including verifying chain line. But I'll set it by measuring the centre of the chainring from the seat tube, I know what it is at the hub, depending in the carrier I'm using, I just need to match that. It's a good idea to check frame alignment first and that the chainring is completely flat, or you can be chasing your tail.
Easiest cheat with an EBB bike if it's a couple of mm out is to simply run the insert slightly offset in the shell. There are people who say they can notice this at the pedals, I'm not one of them.
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May I ask how folks are gauging the chain line measurement?
I don't bother measuring chainline, I just try and align the chainring and sprocket as accurately as I can.
To do this I generally use a 1-metre builders straight edge in rectangular section aluminium.
Placed on the outside of the chainring before putting the chain on. Then I allow for any difference in the thickness of the chainring compared to the sprocket.
Eyeball method without the straight edge is slightly less accurate.
To align sprocket and chainline, several methods:
- changing the order of spacers at the sprocket end (not with Rohloff hubs)
- dished sprocket (not with Rohloff hubs)
- spacers or washers on the rear hub axle (not with Rohloff hubs)
- spacers between chainring and crank
- sliding the bottom bracket eccentric sideways (small adustments on Thorn frames)
- spacers between right hand bottom bracket cup and frame
- different bottom bracket unit if necessary
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...Shimano rate their well-regarded Nexus Premium HGB at 50,000km MTBF, and that I managed to wreck two of their boxes within a total of only about 5000km.
I've got nowhere near 50,000 km on the family Nexus 8 Premium hubs.
I'm still an admirer of Shimano and even of the Nexus hubs, despite that experience. There are millions of Nexus hubs running around The Netherlands on commuting and utility service in advanced stages of total neglect. Not many people know this, but you're supposed to soak the gubbins of the Nexus in an oil bath every so often, using a kit that costs almost as much as a complete new Nexus HGB strung into a reasonable quality wheel on Ebay. I can't remember anyone except you who even knew about the requirement and the service kit... Shimano makes good gear and sells it at a reasonable price with a range of qualities and prices offered to suit almost every pocket; I've never seen the point of going beyond Deore except bragging rights.
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May I ask how folks are gauging the chain line measurement?
The boy at the back there will instantly cease asking difficult questions!
The first thing is not to tie yourself up in knots trying to calculate everything. There's an example on this board where several people tried to help me in my aspiration of achieving a perfect chainline, with a permanent record of all the blind alleys.
In fact, it is real simple. From Thorn you know the diameter of your seat post. Take half of that and write it down. Don't try to measure from some notional centre of the seat post. The maker of your chainring tells you how thick it is. Write down half that thickness. From Rohloff you know the centre-line of your sprocket, which is the chainline you're trying to achieve. Now with a builder's steel rule, the kind that measures right to the edge of the metal, measure from the drive side edge of the seat post to the outside edge of the chainring. This measurement plus half the seat tube width minus half the chainring thickness is your starting point. the difference between this measure and the sprocket distance from the centre of the frame aka Rohloff's perfect chainline is the amount you want to move your chainring.
If the existing chainline is within 1mm, congratulations, the job is done. Unless you're a time-served mechanic, you're not likely to do better and the possibility of doing worse must be considered.
Under Rohloff's latest advice, even a few millimetres off will do the gearbox no harm, but may wear your sprocket and chainring and chain a bit faster than a perfect chainline.
If you have to adjust it, or want to, to make your components last a bit longer, read Martin's post for ways and means. All that I do differently is the order in which I approach the job, merely for convenience and the least amount of spannering (American: wrenching) for fear of upsetting some other relationship that I may not even know about.
First off, if you have one of the common so-called "compact" cranksets, there is no law that says you need to bolt your single chainring onto a particular set of threaded holes; you can move the chainring in or out a quite big chunk if you need a quite big chunk of realignment. Second adjustment, still fairly big: Rohloff supplies or at least supplied when I bought my Rohloff bike, with every bike a set of chainring spacers. I don't know if Thorn supplied these "free" spacers with the bikes or whether they took the view that they didn't want amateurs messing with a properly set-up bike, but you can buy them. Now you should be two or three millimeters away from a straight chainline, and can call it a day unless you're obsessive about perfection.
If you want to continue, you will need to remove at least the cranks and possibly the bottom bracket. First off, in theory, though I've never seen such a thing, you can buy an asymmetrical bottom bracket with unequal arm lengths to arrange the correct chainline without disturbing the tread-width, what the smart cyclists now call the Q Factor. You may also arrange your bottom bracket asymmetrically in the BB shell on the bike, in the case of your bike inside the eccentric bottom bracket carrier, to arrange a little more or less length of axle showing on the drive side; this would ba a small amount and would unbalance your tread width, which old roadies claim to be sensitive to. (I believe them, not because I'm that sensitive about where I put my number twelves, but because I'm extremely sensitive to putting my hands and arms in positions critical to 1mm in all directions to avoid buying my physio's teenage children a BMW convertible each.) Third, you can use spacers on the axle for fine-tuning. These are just washers of warning thicknesses, technically called shims. I used, from memory, a 1.6mm (what I had v. what was required for perfection) to make my final adjustment, plus a 2mm on the other side to obtain clearance from the frame for said size twelves, necessary because I cycle in street clothes including sturdy street shoes, and don't want to damage the irreplaceable heritage paintwork on my bike. I happened to have a can of spray paint that matched my bike colour (non-RAL "forest green", a custom colour mixed in The Netherlands, so I used that on the spacers to make them invisible, but plain matt black will also do the job.
That brought my chainline to less than 1mm from perfectly straight -- or even zero offset, actually perfectly straight, because 1mm is probably within the margin of measuring error. You'd need sophisticated fixtures bolted to the bike frame to make manual measurements down to say half a millimetre on a bike, and I'm not that obsessive. After that, you're into lasers and diminishing returns.
It's the sort of job you do only once unless you churn components all the time. The process last happened when I converted the bike to a bottom bracket shell-mounted central electric motor, probably a decade ago, so E&OE.
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May I ask how folks are gauging the chain line measurement?
A straight metal ruler?
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When I built up my Nomad, Mk II, used a calculator to calculate what the chainline would be based on the crankset manufacturer for their recommendation for bottom bracket spindle length (square taper crank) and based on Rohloff data for hub sprocket position.
I changed the bottom bracket spindle length from recommended to change (reduce) Q factor, and included that in the calculations.
And once built up, I think I put a short straight edge on the sprocket that was not long enough to reach the chainring, but a short straight edge increased my ability to sight the chainline better than simply looking at a sprocket.
Since I knew I would have some offset from the ideal chainline, I was only trying to estimate how much that offset is, and sighting it pretty much confirmed what my calculator said.
In the first two photos in the second post in this thread, I am showing the difference in wear on the sides of the sprocket teeth from my chainline offset which I think is about 5mm. It is clear that the side of the sprocket tooth has additional wear from the chainline offset.
And if the crankset manufacturer used a common spindle length based on availability for their suggestion instead of the perfect chain line spindle length, there could be some additional error in my calculations.
With this much discussion on this topic, perhaps next time I have the chain off, I should use a longer straight edge? Since I am using a double crank, I made some assumptions in my calculations for spindle length, I am using the inner position on the crankset for the chain.
In this post, I used the word offset for how far my chainline is different from ideal, but previously I used the word error. Reason for my wording change is the word error could also mean I made a calculation error or some other unintended mistake. Thus, I chose to reduce the ambiguity here.
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There's a useful table at https://www.firstcomponents.com/wp-content/uploads/2018/10/DX30-assembly.pdf which shows how dimension C1 (the drive side) varies in length with different bottom bracket lengths. They aren't quite symmetrical. This information is useful if wanting a different chainline.
As a starting place, the middle ring of a triple crankset is about 47.5mm chainline https://www.sheldonbrown.com/chainline.html and the outer ring is around 7mm further out. In my own case, my right foot is comfortable further out than the left foot so I bought the longest bottom bracket I could find (131.5mm) and put the chainring for the Rohloff on the inside of the spider. However, this resulted in the ring being about 3mm too far in until I used some spacers on the bottom bracket (placed between the frame and the drive side bearing cup) to move the BB across. One can't use spacers to move the chainline inwards.