What chainring and rear cog for Rohloff? Need Help

[Brucey]

steel chainrings are usually thinner than aluminium ones where the bolts go through and counterboring them is not only not required, it is arguably counterproductive, in the 'big ring' position anyway, especially if the chainring is to be reversible. Provided the bolts are the correct length then un-counterbored reversible chainrings are preferable to counterbored ones in that the clamping load of the bolt is better distributed below the bolt head.

cheers

[tommydog]

steel chainrings are usually thinner than aluminium ones where the bolts go through and counterboring them is not only not required, it is arguably counterproductive, in the 'big ring' position anyway, especially if the chainring is to be reversible. Provided the bolts are the correct length then un-counterbored reversible chainrings are preferable to counterbored ones in that the clamping load of the bolt is better distributed below the bolt head.

Thanks for confirming this, I just thought that maybe it had some advantage other than ascetics, given that many manufactures seem to counterbore their chainrings.

bikepunx just sent me a drawing of one of their rings - commenting that "the teeth have a square profile like the newer Shimano 1x rings to help with chain retention" Below is the style of chainring that they do in 1/2" x 1/8"




I have ordered the KMC BSRR00316 1/2" x 1/8" sprocket to go with this. Although I don't have a drawing for the KMC sprocket, the below picture on their website indicates that the profile of the teeth are different to that of the chainwheel



In an optimum setup, should one always try and match the exact type of tooth profile for the chainwheel and rear sprocket, or from an engineering perspective does it not matter much as long as both are for 1/2" x 1/8" chain?

[Brucey]

it might not look it at first glance but those tooth profiles are functionally equivalent to one another. There are two obvious differences

1) the sprocket has pointed tooth tips and the chainring has truncated ones
2) the tooth flank shape on the sprocket looks different.

On the latter point, it only looks different. In fact the geometry of the tooth flanks is determined by the number of teeth on the sprocket. The lower half of the illustration below shows how the flank profile of neighbouring teeth is determined by a radius described from the roller centre in the neighbouring valley, as the chain disengages.



A mirror image of this figure shows the same thing for chain engagement.

The consequence of this is that the fewer teeth there are, the more 'pointy' the tooth flanks must be. Pointed tooth tips on sprockets help engagement (the bottom run is slack when pedalling and is where many derailments originate when the chain is slack) however pointed tooth tips are not a smart idea on chainrings, in good part because they tend to make holes in people.

Anyway the tooth flank shapes on both chainring and sprocket are 100% conventional, i.e. exactly as an engineering text would recommend them to be, IMHO.

cheers

[tommydog]

Thanks Brucey, they are helpful diagrams. Out of interest are you an engineer?

[Brucey]

by training I am a materials scientist. [Never bothered filling out the forms for CEng.]

cheers

[Johnmash1]

duplicate of OP removed

[geocycle]

You have stronger legs than me! I run 42 x 17 or 40 x 17. You are looking at a bigger chainring rather than smaller sprocket. Try a 46 which should give you a top gear of 106 gear inches and a 20 inch bottom gear if I’ve done the calculations correctly.

[531colin]

Gear 11 is direct drive, ie. losses are minimised.
Its not a bad idea to set it up so gear 11 is something useful.....maybe your "favourite" gear, or the gear you use when trying to maintain progress on a rising road, or into wind.

Does "JohnMASH" mean John the masher, by any chance?

[slowster]

I...have never used any of the gears 1-3, even on very steep hills.

You have a top gear of around 100 inches. Do you find yourself often spinning out in gear 14, and wishing for much higher gears? If not, the fact you don't use gears 1-3 does not matter.

Probably more important is what gear you use most when cruising on the flat. Ideally it should be gear 11, because that is the most efficient. Therefore if you tend to ride mostly in gear 10 for example, then you might do better to fit a smaller front ring, i.e. 36, 37 or 38, which should make gear 11 your most used gear, as shown in the comparison tool below, even at the penalty of losing your current highest gear.

http://www.gear-calculator.com/?GR=RLSH&KB=42&RZ=16&UF=2075&TF=90&SL=2.6&UN=KMH&DV=gearInches&GR2=RLSH&KB2=37&RZ2=16&UF2=2075

Edit - crossed posts with 531colin. Again.

[Mothy]

A different perspective:

I also have 42/16 on my Rohloff, on a 700c “hybrid” used for winter day-rides rather than touring. I’m about to lower my gearing so that I spend less time in 1-7, as I find the noise in the lower ratios irritating. (We also have a Rohloff tandem, where priorities are different). In our rolling Shropshire lanes I find that I often need lower than my 48” eighth, and don’t mind if I “waste” one or two lower gears to have a peaceful seven-speed setup with plenty of hilly gears for when needed.

Of course, everyone has their own priorities...

[Tigerbiten]

A Rohloff has 13.6% steps between gears.
So 42 x 1.136 = 48t chainring moves all your gears up by one gear.
And 42 x 1.136 x 1.136 = 54t chainring moves all your gears up by two gears.
These two are the easy options with the 16t sprocket.
But as others have mentioned, take into account where any change of gears moves the 7-8 shift.
There's no real point in shifting all your gear range upward if you end up using 7th gear on every slight uphill slope.

Luck ...........

[Cyril Haearn]

Do others find the noise in gears 1-7 irritating? Does it get quieter eventually? CJ wrote that the change between 7+8 was a bit clunky. If 11 is the best gear, is 4 the second best?

[geocycle]

Do others find the noise in gears 1-7 irritating? Does it get quieter eventually? CJ wrote that the change between 7+8 was a bit clunky. If 11 is the best gear, is 4 the second best?

I don’t notice it. It becomes less with use and I can only make out gear 7 now after 45k miles or so. The change between 7 and 8 can be clunky and I was thinking about this today. I’ve just put a new drive chain on and it is quite tight, I had to really back off to go from 8 to 7 whereas before with the old floppy chain it never occurred to me.

[rotavator]

Do others find the noise in gears 1-7 irritating? Does it get quieter eventually? CJ wrote that the change between 7+8 was a bit clunky. If 11 is the best gear, is 4 the second best?

The noise from gears 1-7 is a bit irritating to me when on smooth surfaces but I don't notice it on rougher surfaces like forestry roads etc. The noise from gear 7 is the worst and I assume it is the least efficient gear so I generally skip it when changing gear. Gear 4 is the quietest and presumably the most efficient of gears 1-7, so it is one I prefer to use when climbing hills. Gears 8-14 are all either fairly quiet or silent so there is no reason to favour one over another apart from choosing the best for effort/cadence/speed IMHO.

[NickJP]

On my Rohloff-equipped touring bike I use a 38t chainring and 17t cog, but that's for loaded touring in mountains. I've had it across the Alps and Pyrenees, and 1st gear gets quite a workout on some climbs. The most consistently steep climb I can recall was the Mostelegg pass in Switzerland, which averaged just over 13% gradient for about five and a half kilometres. As others have commented, the bottom seven gears are noisier, and on my hub I can also feel some vibration from the hub in those gears.