Crankset recommendations for Rohloff?

[pakcyclist]

I've had 2 Rohloff-equipped bike for some years now.  I noticed my road bike was rather noisy when pedaling (basically a grinding sound), while my MTB was virtually silent, despite using the same chain (KMC stainless steel).  I recently noticed the chainline on the road bike isn't very straight.  I'm using a SRAMS300 1.1 GXP external BB crankset.  (Not sure if its considered a SS or 1X.)  The MTB has a 2 ring crankset, and the chainline is perfectly straight.  Am I safe in assuming I'd be better with a 2 ring crank?  Any recommendations?

[mickeg]

I use a square taper double crankset, use a bash guard or chainguard in the outer position and the chainring in the inner position.

If you use a square taper crankset, since the bottom brackets come in a wide variety of sizes you should do the measurements and do the math to get what you need.

I chose to use a spindle that is about 10mm shorter than the ideal chainline, I wanted my Q factor (width between pedals) to be about the same on my Rohloff bike as on my derailleur bikes.  Thus my chainline is about 5mm off.  I notice a slight increase in wear on the sides of some of my sprocket teeth because of that error, but it is not a significant issue to me.

I can't comment on other crankset systems, I always try to buy square taper as a personal preference, all of the bikes that I have built up have square taper.

[Andre Jute]

Have you considered moving the chainring to a different mounting position on the spider, either the attachment for a different chainring or merely the other side of a mounting surface? That can get you closer to a good chainline, and from there you can use spacers on either the chainring bolts or bottom bracket fixings to perfect it.

Back in the day, when Rohloff was young, chainring spacers came in the box with the gearbox but I don't know if OEM like Thorn got them or passed them on or even whether the practice of including these spacers is still maintained.

Rohloff expects a chainline to within 1mm of perfect, and I had no problem reaching it with spacers to fine-tune the nearest size of bottom bracket available, though determining what was required was a fraught experience even with considerable invaluable help from Dan. See http://thorncyclesforum.co.uk/index.php?topic=3898.msg19617#msg19617 for additional considerations about axle symmetry and clearances for balloon tyres I don't touch on in this post.

The best way to measure the chainline with enough precision to satisfy such a tight tolerance is to take two measurements, one from the far side of the seat tube to the outside of the chainring, one from the nearest side of the seat tube to the inside of the chainring, add the two measurements together, divide the sum by two, and thus arrive at a pretty precise measurement from the centre of the seat post (standing in for the centreline of the bike) to the centre of the chainring thickness (which is the chainline). The correct chainline for the particular model of Rohloff sprocket tooth-count (one chainline for 13 teeth, another chainline for all other tooth counts) and fastener (threaded or splined) you can get from the latest handbook or the Rohloff website or ask here: someone is bound to have the same setup.

***
On the other hand, there are reports of cyclists who ride with chainlines 5mm out of line and observing no harm except a suspicion of slight to imperceptible accelerated chain wear and perhaps some sprocket wear as George (mickeg) reports -- though in evaluating these reports one has to take into account that on a very long-lived quality gearbox like the Rohloff harm from misalignment may not evidence itself until a very high mileage has been covered. I'd take a little faster chain or sprocket wear any day over possible wear to Rohloff shafts, but we don't know how the extra angular load is distributed. George clearly thinks it is a small price to pay for a narrow tread.

My opinion is that precision is a harmless obsession, and if it keeps cyclists out of the bar, that's all to the good.

[PH]

As above, step one is to measure your chainline to see just how far out it is. If it's less than 5mm I might look for other causes of the noise before messing with it. As you have two, is it possible to swap test the chainsets?
What sort of BB is it?  if it's an EBB that slides in the frame, there's usually a couple of mm you can offset that without problem.  Chainset spacers are available in sizes up to 5mm and only a couple of quid, I'm assuming they're compatible with all chainrings, but haven't checked, you may need longer bolts.
I don't know how far out would be significant, the traditional difference between a road double and a MTB triple is around 6mm and a MTB triple with the ring in the outside position is close to a Rohloff, so any road chainset is likely to be well off.  I run my chainlines within 1mm, I can imagine some circumstances where that might not be possible, but it generally is.  It's one of those jobs that can be a bit of a faff to get right, but you only need to do it once.

[JohnR]

My post http://thorncyclesforum.co.uk/index.php?topic=14235.0 regarding a 6mm chainline offset on the Birdy Rohloff is relevant. I would add that the Birdy Rohloff's chain is noisy compared to the silence of my Thorn Mercury (although the Hebie Chainglider must help the latter) although the Birdy is quieter after 400 miles than when new. The bike was fitted with a 9 speed chain which has better lateral flexibility than a singlespeed chain but will also wear out faster. The Birdy also has the Rohloff chain tensioner which I suspect contributes to the noise whereas the Mercury has an eccentric bottom bracket for adjusting the chain tension (not an option on the Birdy as the chain has to fold up when the back wheel is folded and the chain tensioner helps with this).

[pakcyclist]

I measured best I could, it appears the chainline is off by about 10mm.  Is it possible to move the chainring to the outside?  (It's a single-ring crank.)  Don't know much about the tech side of these things, but I don't think that would be safe;  the slots for the the ring mounts are on the inside, and the outside doesn't appear to be perfectly flat.  As for the BB, isn't the type that can be used determined by the frame's design (i.e., external vs square taper)?  (Again, I know little about the tech stuff.)

[JohnR]

I would suggest that you take a photo of each side of the cranks and post them here so someone can identify what you have. This is a typical square taper crankset https://www.sjscycles.co.uk/cranks/150-thorn-10464-pcd-triple-crankset-mk2-black/ (it says triple but was fitted on my Mercury with one chainring on the outside) and here's a crankset with integrated crankshaft https://www.sjscycles.co.uk/cranks/165-thorn-130-pcd-ex-bearing-single-crankset-with-integral-bottom-bracket/ .

I would add that if you are shopping for new cranks then this provides an opportunity to change the crank length. Bikes are often fitted with longer cranks than optimum for the rider's size.

[mickeg]

Don't forget that your sprocket is also part of the equation, threaded and slim splined are similar to each other, the regular splined will be several mm different from those.  I do not recall the numbers off hand, someone else that has that memorized might comment.

If you have threaded now, you will later have splined.  And if you have splined now, changing to the other splined carrier will change it a few mm.

[PH]

someone else that has that memorized might comment.

Threaded sprocket is 54mm or 57 with a 13T
Standard splined carrier is 57
Narrow is 55

So yes, changing to a std carrier from a threaded sprocket will increase the chainline by 3mm assuming they're not using a 13T sprocket (Why would anyone?) Seems an expensive way to gain 3mm unless the sprocket is in need of changing, or they have a use for the removed one, maybe on the other bike.

[pakcyclist]

Here's photos of the cranks, as well as the chainline, if that helps.  (BTW, I'm in the USA, if that helps with recommendations.)

[PH]

EDIT - Sorry I misinterpreted the last blurred photo, not sure what it's trying to show with the chain off?

[mickeg]

Looks like a titanium frame, from whom I do not know.

I have close to zero knowledge on external bottom bracket type cranksets, all the bikes I built up have square taper and my only external bottom bracket bike is my road bike with a Campy compact power torque crank.  Just putting that out there so you do not ask me any questions I am clueless about.

But, I am guessing that this being a titanium road bike, that the frame and crankset was designed for 130mm dropouts in back and you have a 135mm hub.  That only impacts chainline by 2.5mm, so that is not the cause, that could be a small contributing factor to chainline.  When you put the rear wheel in, does the hub drop right into the dropouts, or do you have to pull the stays outward a bit to squeeze the hub into the frame?  I am running a 135mm hub in my steel framed rando bike with a 130mm frame, I have to pull the stays outwards for the hub to drop in.

It is hard for me to clearly see what is going on in the photo, but I am guessing that your crankset needs to be replaced to give you a better chainline.  Likely with a double, as that would allow you to put the chainring in the outer position, and if that is insufficient you could also use chainring spacers to move it outwards a bit more.  WHen I bought my Rohloff hub in 2013, it came with five chainring spacers, the purpose of the included spacers was so that I could use a single chainring on a double crank, the spacers were to allow the longer crankset bolts for a double to be used with a single chainring.  Did you buy the hub and if it came with such spacers, do you still have them?  If not, chainring spacers are something that bike shops keep on the shelf.

But before you buy a crankset, I think you should (1) use a caliper to measure your chainline relative to your downtube or seat tube, or (2) take the chain off the bike, and then put a straight edge on the chainring so you can get a better measurement of how far off the chainline is. 

One more thing that I think is extremely unlikely, but with a titanium frame I raise the possibility that the bottom bracket shell is not aligned perfectly straight.  Most titanium frames are built by small builders and a lot of hand work is involved.  If they got the bottom bracket shell aligned slightly off in the welding process, that could slip passed quality control testing.

What sprocket do you have and do you have a carrier or threaded sprocket?

[JohnR]

It's clearly a single-piece crankset so you'll need to change it for one with provision for an outer chainring. The next task is to remove the left side crank so you can check the spindle diameter. There's a useful table of this type of crank at https://wheelsmfg.com/crankset-tech . If you are lucky it's one of the self-extracting cranks which can be removed with an allen key.

[pakcyclist]

EDIT - Sorry I misinterpreted the last blurred photo, not sure what it's trying to show with the chain off?

That shot was taken length-wise.  The chain is ON both the chainring and cog.  I'm using a 16-T cog, with a 48-T ring.  (Hey, my house is up the side of a mountain, I need low gears!)

[mickeg]

I asked which sprocket you have.  Threaded or splined, to clarify I should have also asked if splined, is it the slim or regular?

And I suggested a cailper to meaure chainline against the seat tube or downtube.  Or, a straight edge on the chainring with chain off.