Re Chainset

[dezza]

Please at the risk of going totally public with my ignorance..

I have a nos Suntour XC Pro chainset and wonder will it be compatible with a Rohloff..if I use the middle ring.

I please welcome any advice.

Thank you,
Steve

[rualexander]

Yes should be ok, but if you are fussy about chainline you might need to change your bottom bracket to a different axle length.
Rohloff chainline is 54mm, unless you use a 13 tooth sprocket when it is 58mm.

[Andre Jute]

Please at the risk of going totally public with my ignorance..

This is the right place for it. People have nice manners here. Anyway, it's the sort of question everyone faces sooner or later.

I have a nos Suntour XC Pro chainset and wonder will it be compatible with a Rohloff..if I use the middle ring.

Yes, you can use it, but, as you've already been told, you may have to change the bottom bracket to make the chain line 54mm for the common Rohloff sprockets; the 13t Rohloff sprocket has a different chainline. It is important to get a Rohloff chain line to within 1mm of straight. The chain line is measured from the exact longitudinal centre of the frame to the centre of the chainring.

To measure the chain line with the bottom bracket on the bike, fit and torque up the chain set, then measure from the side of the seat tube to the middle of the chainring. Now measure the thickness of the seat tube and add half of its thickness to the measurement you already have (from the side of the tube to the centre of the chainring).

You can move the chain line 3mm to either side of the middle ring by using the outer or inner attachment points for your chainring.

Once you have the measurement of the chain line with the crankset you want to use and the bottom bracket in the bike, return here and we'll do the math for you and tell you how long the axle in your new BB should be. You will also need the width of the present bottom bracket, or a spec sheet telling us what the chain line of the crank is with an x-length bottom bracket, as originally advised by the manufacturer.

For everyone else: doesn't that Suntour XC crank remind you of the Sugino XD2? If it is the same crank, this could be easy, as we already know the BB axle length wanted, having gone through this exercise at length for my Cospea cranks, which have the same dimensions as the XD2.

[John Saxby]

we already know the BB axle length wanted, having gone through this exercise at length for my Cospea cranks, which have the same dimensions as the XD2

Andre, more on the XD2s:  I bought these cranks from Spa Cycles, to be fitted to my Raven with a Surly stainless 38T 110BCD chainring. 

What BB axle length do you reckon for the XD2/Cospea cranks?

I estimated 118 mm, as follows:

    > Spa Cycles' cranks were advertised as fitting a compact double chainset, to be mated to an axle 107 mm in length, giving a chain line of 43 mm on the outer ring. Spa recommended buying the "double" cranks if fitting them onto a single chainring.

     > I estimated that an axle length of 118 mm would give a chainline of 54 mm.  (i.e., an increase of 11 mm for both axle length & chainline.)

     > dotbike.com was selling a single chainring with these cranks, and gave 118 mm as the proper axle length. (I was reassured by their recommendation.)

So, I've used 118 mm as the guideline for the mechanic now building my Raven.
 

[Danneaux]

Hi Steve!

The thread Andre refers to for his Cospea crank chainlne is here: http://www.thorncycles.co.uk/forums/index.php?topic=3898.msg17120#msg17120

The information there may prove helpful to you going forward.

If you get stuck or just want a sounding board, give the Forum a shout.

Best,

Dan.

[Andre Jute]

Andre, more on the XD2s:  I bought these cranks from Spa Cycles, to be fitted to my Raven with a Surly stainless 38T 110BCD chainring.  

What BB axle length do you reckon for the XD2/Cospea cranks?

[snip]

So, I've used 118 mm as the guideline for the mechanic now building my Raven.

You done good, Master Saxby. (Surprise, surprise. Not everyone who speaks English good is also good with arithmetic.) 118mm will bring you within half a mm of 54mm and that's plenty good enough. If memory serves, Dan and I calculated that 119mm would be spot on, but where would you get a 119mm BB of the right quality? Stronglight, which rebrands Kinex BB as their own, for which I vouch enthusiastically, having owned Kinex on top Euro-elite bikes, supplies (or maybe just strongly recommends, can't remember now) the 118mm with their Rohloff-specific versions of the XD2, which comes with a bash guard or guards. I also messed around, but only briefly, with fitting the chainring on various sides of the spider, and with using spacers (a set of suitable spacers intended for this specific purpose comes with the Rohloff, though I don't know whether SJS passes them on), but in the end decided that the straight fitting was closest to perfect. The point is that the 118mm BB gives you options around the right place, which 122 doesn't (too long) and for which 115mm would require a grotesque stack of spacers. So the one that works in almost all installations is 118mm.

[John Saxby]

Thanks, Andre.  Much obliged and slightly relieved.

On the spacers to assist with the chainline:  the Rohloff supplied by Starbike, my online supplier in Deutschland, did include spacers in the kit which came with the hub itself.  Phil Wood offers a square-taper BB with a 119 mm axle.  I think we'll stay with the 118 mm axle length, using a Shimano UN55. 

[Danneaux]

Phil Wood offers a square-taper BB with a 119 mm axle.  I think we'll stay with the 118 mm axle length, using a Shimano UN55.

The Shimano should do you fine, John. For reference sake, the Phil's chainline is adjustable from side to side because it is retained by two rings, each of which can be screwed in independently, allowing one to get the chainlne spot-on without need for spacers. This isn't always obvious unless one has owned previous Phil internal BBs. A special Phil tool is required, available for separate purchase. Most quality bike shops have at least one; installation is even easier and faster with two.

Best,

Dan.

[Andre Jute]

Yes, I too used the Shimano 55, a step up from the ubiquitous 26, mainly because the size wasn't available instantly in the 26.

On Dan's fave Phil BB, this side of the water the plutocrat's BB is the titanium Royce.

I'm not even considering it. I don't like titanium much, though I have titanium flying watch that does double duty as a cycling watch.

[dezza]

Hi, Thanks for all the sound and informed advice. I'm no techno..so once I get my head round it all should be clear. I just bought the Thorn Raven Sport recently advertised on the forum and wanted to change the chainset as though it hasn't arrived yet looks as though it has some scratches..its a Thorn ...Just happened to have the nos suntour in the loft and with what looks like a suntour greaseguard system b/b again unused. Thought it might look better ..I also have some Avid arch rival brakes and thought I'd put them on to replace the current v's.
Again thank you I'm grateful for your advice.
Regards
Steve

[John Saxby]

Yes, I too used the Shimano 55

Thanks, Andre, and also Dan for your advice on these BBs.  When I visited SJS Cycles last March, I learned about the Royce item and the cost thereof, and had of course checked the Phil and SKF variants here as well. (I do like the adjustability which the Phil offers -- thanks for pointing that out, Dan.)

Tall Tree Cycles, my LBS, do a lot of MTB/Cyclocross bikes, and recommended the cro-moly UN 55 if I wanted something bombproof but not as expensive as the three items above.  I try to avoid false economies as much as poss, but equally, my riding in the next 10 - 20 years is not likely to make any extravagant demands on my Raven-in-the-making. So, the one-step-up-from-humble 55 should do the necessary - although I might also look again at VO's spiffy polished 118 mm BB.

And good luck, Steve, with your rehab of the RST -- look forward to the fotos.

J.