Replace chain

[mickeg]

Ok, but sometimes when your replace only the chain, an unpleasant noise appears the first hundred kilometers

How many teeth on your rear sprocket?

16 teeths and 36 in front (Surly stainless steel) but the noise it seems to be coming from the back..

As chains wear and elongate, the chain links with the inner plates do not elongate but the chain links with outer plates do elongate.  More on that here:
https://www.sheldonbrown.com/chain-life.html

Most people on this forum use a sprocket with 17 teeth, an odd number, thus every sprocket revolution a tooth that had a link with inner plates on it, the next revolution will have a link with outer plates on it.  That is because Thorn fits bikes with a 17 tooth sprocket when new.

Rohloff hubs when sold new come with a 16 tooth sprocket, I am also running a 16 tooth sprocket.  (For touring, I use the same gearing as you, 36T chainring, 16T sprocket.)  Thus as long as you do not change your chain, the chain and sprockets wear to match each other.  As a chain elongates and half of the links have an increased space between rollers, some teeth wear more than others.

If you put a new chain on without changing or flipping a sprocket, the teeth that were worn in to match an old chain will take some time to wear into match the new chain.

Also, if you take a worn chain off, clean it and put it back on, if you put it on so that it no longer is on the same teeth, the teeth might not be on the same links and that could cause the chain to be off somewhat.

I cut a small notch into one sprocket tooth and one chainring tooth.  Every time I put a chain on the bike, I am careful to always put a link with outer plates on the tooth with a notch.  Sometimes it is hard to see the notch, it fills in with grime so I also painted a spot on the sprocket and chainring.  This won't solve the issue of noise when you put a new chain on worn teeth, but it may help a little bit.

I ride several different bikes, one has a Rohloff and the others have derailleurs with seven or eight speed cassettes.  Most of my miles are on the derailleur bikes.  Since I am wearing out eight speed chains on the derailleur bikes and I change those chains more often than you would need to change them on a single speed or IGH hub, I now am putting chains that I wore out on a derailleur bike onto my Rohloff bike to get some more wear before I discard them.  Thus, I no longer put new chains on my Rohloff sprocket or chainring.

I got home from a bike tour a week ago with my Rohloff bike.  I discarded the chain where I did my tour, did not bring the chain home.  It was already quite worn when I started that tour.  I will be putting a chain on the Rohloff bike that already meets the definition of worn out from a derailleur bike to get some additional wear on it before I discard it.

Photo attached, several years ago I took this photo before I flipped my sprocket.  The tooth on the left has a lot more wear than the tooth on the right.

[PH]

If you're going down the route of swapping chains to preserve other components, you have to frequently measure and not go by mileage.

Riders can do what they choose, but there are two practical options, wear it all out and replace together or replace chains before anything else is worn.  Doing something between those two has no advantage and will cost more in components than either.

There's Martin's middle way of swapping chains in and out at quite short intervals when his bikes ran with open chains, which substitutes maintenance time for components costs.

I'd forgotten that, it was very popular on derailleur set ups at one time, I even tried it once myself, but the effort to keep the wear in synch was two much for me.

[jul]

Thanks Mickeg, interesting ..

Effectively, for me 36x16, the most important gear is the  first, i can climb almost  any hill..

But, my next Surly chainring  have 35 teeths, i got a good price for it,  I don’ t know if i have to keep my sprocket in 16 teeths or maybe 17 ! but i'm afraid to ́lost my first short gear..

For information, 36x16  transmission,  above 33km/h you can no longer pedal, sometimes it’s frustrating

[martinf]

For information, 36x16  transmission,  aboie 33km/h you can no longer pedal, sometimes it’s frustrating

Depends on your pedaling cadence.

I generally pedal relatively fast at about 90 rpm (tours par minute). With a 36x16 combination that translates into 36 km/h, which is way above a sustainable speed for me on the level, unless I have an exceptionally strong tail wind.

If necessary I can increase pedal cadence for very short periods. With a 36x16 combination at 120 rpm in the highest gear that would be 48 km/h. In practice, that kind of speed is not really useful for me, except perhaps when I negotiate medium size roundabouts, where I feel safer if I am doing roughly the same speed as most of the motor vehicules. 

My current highest gearing on any of my bikes is 42x19 on my Rohloff equipped Raven Sport Tour. I use that bike mainly for day rides with little luggage. Top gear with 42x19 is slightly lower than with a 36x16, the maximum speed I managed recently when pedaling (downhill) was 53 km/h at 137 rpm, just to see if I could still do that at age 69. But normally I would just stop pedaling and coast down the hill.   

[mickeg]

Thanks Mickeg, interesting ..

Effectively, for me 36x16, the most important gear is the  first, i can climb almost  any hill..

But, my next Surly chainring  have 35 teeths, i got a good price for it,  I don’ t know if i have to keep my sprocket in 16 teeths or maybe 17 ! but i'm afraid to ́lost my first short gear..

For information, 36x16  transmission,  above 33km/h you can no longer pedal, sometimes it’s frustrating

My cadence has varied over time.  For the past few years, it usually is in the range of 66 when I am doing a multi-hour ride.  If I am working to get up a hill in a low gear, I try to raise it up to 72.  But if I have been in the saddle for most of the day already, it might dip down to 60.

I mentioned I use 36T/16T (ratio of 2.25) for touring.  But for riding around near home with an unladen bike, I put a 44T chainring one the bike, add four more chain links for a ratio of 2.75.  For riding near home, I never need a gear higher than 14 with that higher range of gears. 

But for touring, I value that low gear, so I can live with the loss of the higher gear that I would otherwise use on shallow downhills.

When I built up my Nomad, I calculated that if I wanted to use the stock 16T sprocket, pedal at a cadence of 72, and have a speed of 3.5 miles per hour, that I wanted a 36T sprocket.  I find that I can't get below 3 mph without oversteering to try to maintain stability, both directional and vertical.  And a cadence of 72 feels smoother than anything slower.  My point is I did some calculations to figure out that I wanted the 36T, I did not pick it at random.

And the 44T, that range of gears pretty much mirrors my range of gears that I think are ideal for riding near home on my other bikes.

[jul]

I never thought about all that when making my choice, 

[mickeg]

I never thought about all that when making my choice, 

I am an engineer (retired), so I of course I tried to use a scientific approach.  I tried to pedal up a steep hill near my home several times to see how slow I could go and still feel comfortable that I am stable and not oversteering and overcorrecting.  That was how I came to the 3.5 mph criteria and the cadence of 72.  If I tried a cadence closer to 60, I noticed the slow down and speed up pattern as I pedaled, thus I set my target for hill climbing at a cadence of 72 that felt smoother.

I have pedaled up hills on my Nomad Mk II in first gear with a cadence of 60, thus about 2.9 mph, but those were on good days without wind, minimal traffic on the road so I felt more comfortable being further from the edge, etc.