What rear sprocket do I need to help me get up hills and mountains easier?

[Joseph_]

Thanks again JohnR, really helpful all this.
Indeed that's why I was confused, thanks for the clarification.
I've no idea wether my rear sprocket's splined or threaded, but in attachment's I made a quick pic, maybe you can make it out?
But I'm reaching out to my local Koga dealer on Tuesday, he''ll know.
I guess 2nd hand is always an option though for this upgrade I'd prefer to buy new because I wouldn't know quality from problematic parts, and I'm pretty sure I'm going to love the lower gears so will be using them for a long time to come.

Thanks mickeg, I thought changing teeth in the front chainring (beltring?  ) would have more effect since it's bigger but it seems it's the other way around.
For this I'm also going to reach out to my Koga dealer as he'll have to perform the change anyway, so I guess he'll be able to tell me my options.
Part costs here are : rear cog 95€ front chainring 90€ belt 90€, but as you said very long life so well worth it (imo).
The only way to be certain about which combination is ideal for me is trying out the different combinations beforehand, which is pretty impossible or too expensive.
So I'm just going to use calculators and aim for two extra lower gears and two less upper gears, which a 24t rear sprocket would provide (I'm told).
As for possible combinations, the Gates Carbon Drive Bicycle Calculator https://www.gatescarbondrive.com/Apps/DriveCalculator/index.html is pretty good at that, but the chainstay length remains a gamble for me as I don't know how much slack my EBB has.

Cheers, Joseph.

[JohnR]

I can't figure out the fixing detail in your photo. I therefore attach a photo of a standard (chain) Rohloff splined sprocket with the lockring clearly visible. A Gates sprocket has different teeth but the mounting on the carrier is (I think) the same.

I also attach (if the forum software) will let me a simple spreadsheet where you can change the chainring and sprocket teeth and quickly see how the gear inches change. For example, changing the chainring from 50T to 39T (which seems to be one of the standard Gates sizes https://www.bike24.com/p2181007.html ) moves the gearing by two Rohloff gear steps (change the numbers in the yellow boxes).

[mickeg]

I think you have the splined sprocket carrier, but it has a threaded fitting on it to hold the sprocket on it instead of a spring circlip.
https://www.rohloff.de/en/service/handbook/speedhub/workshop/splined-carrier-lockring-conversion

[Joseph_]

Thanks again JohnR!
I can clearly see the locking ring, good to know.
And that spreadsheet is really handy too, easy to see know how many gears I'd win/lose, awesome.

Yes mickeg, I also think I've got splined (because Alee Denham who has the same bike as me also has a 50-22t config and I'm sure he went as low as he could go in the rear cog) I'll know for sure as soon as my Koga dealer gets back to me.
I don't reckon  there exists a splined-to-threaded 'adapter' or anything of the sorts? (just wild guessing here)

I got a lot of solid information here from you guys, really appreciate it.
Now all I have to do is think about all the possible combinations and make a decision, which will be very personal one so that one's on me 

Cheers, Joseph.

[JohnR]

Now all I have to do is think about all the possible combinations and make a decision, which will be very personal one so that one's on me 

One unfinished business is whether the desired gearing combination will work within the variation provided by the EBB. Using the calculator at https://www.gatescarbondrive.com/Apps/DriveCalculator/index.html shows that a 39 : 19 combination (which drops the gearing by two Rohloff gear steps) needs a 115 tooth belt and a chainstay length of 471.70 mm. I would expect that to be well within the adjustment range of the EBB.

I would also note that while belts are not inherently messy in the same way as chains, they do like to be kept clean. I used a bike with a CDX belt one winter and, thinking it was maintenance free, let it get dirty. The bike developed worrying creaking noises which disappeared when I gave the belt a good scrub.

[Joseph_]

Ccorrectomundo.
In the meantime I've got more info on the front sprocket; apparently there's only 1 smaller size, a 46T (CDX CENTERTRACK) https://www.gatescarbondrive.com/products/front-sprockets?productline=cdc%20centertrack
Which means my two best choices are :
- if threaded sprocket : 24T rear sprocket + new compatible belt.
- if splined sprocket : 22T rear sprocket + new front sprocket 46T (belt should fit I think because the new chainstay length would be 471 mm vs 469,5mm now).
So far no noise problems on my current belt (about 8000 km), but I've only ridden in about 15-25 degrees weather mostly.
I did read that in very dry/dusty environmonts it can get very noisy too, and that a Silicone Belt Lubricant can fix that.
Other than that, a plain old toothbrush and water 

[JohnR]

In the meantime I've got more info on the front sprocket; apparently there's only 1 smaller size, a 46T (CDX CENTERTRACK) https://www.gatescarbondrive.com/products/front-sprockets?productline=cdc%20centertrack

That table is for the CDC range. Your photo of the rear sprocket suggests it is CDX in which case the relevant product range is at https://www.gatescarbondrive.com/products/front-sprockets?product_line=CDX . One potential obstacle is that the 39T front sprocket is only available as 4 bolt 104mm BCD so I hope your 50T sprocket is not 5 bolt 130mm BCD. The 46T sprocket is available for both BCD options so your option to change both sprockets but keep the belt is feasible although the gearing ratio is nearer 1.5 Rohloff gear steps than the 2 steps of the 39:20 option.

[Joseph_]

Dear God, you saved my life here JohnR!
I was about to send the order email to my Koga dealer when I saw your reply come in, great timing!
These last few days I've been so busy researching all this that I simply failed to see this difference, which is of utmost importance, phew!
And I should've read your posts more carefully as you've suggested the 39:19 option two times already, so sorry my bad .
I indeed have a CDX front sprocket, a CDX:EXP to be more exact and part# CT1150MBA-5.8 to be very exact.
Apparently the surface area on the EXP is 25% larger but the 39T should be an option : https://www.cyclingabout.com/new-gates-cdxexp-expedition-carbon-belt-drivetrain/
So first thing tomorrow morning I'm calling my Koga dealer to know exactly which front and rear sprockets are possible, after which I can finally make a decision, hopefully 39:19!
Thanks again you lifesaver! 

[mickeg]

...
So first thing tomorrow morning I'm calling my Koga dealer to know exactly which front and rear sprockets are possible, after which I can finally make a decision, ...

Given the high costs, you might consider asking their best Rohloff expert when will he or she be in and available so you can go talk with them, and bring your bike along so that you can make sure it gets decided right.

[JohnR]

Apparently the surface area on the EXP is 25% larger but the 39T should be an option : https://www.cyclingabout.com/new-gates-cdxexp-expedition-carbon-belt-drivetrain/
So first thing tomorrow morning I'm calling my Koga dealer to know exactly which front and rear sprockets are possible, after which I can finally make a decision, hopefully 39:19!

39T CDX:EXP is listed by Gates https://www.gatescarbondrive.com/products/front-sprockets/39t-4-bolt-cdx-exp . The good news is that the 50T part is also 4 bolt 104 BCD https://www.gatescarbondrive.com/products/front-sprockets/50t-4-bolt-cdx-exp .

Given the high costs

Ideally one only gets a belt drive system after knowing the preferred gearing for the intended use. I haggled a discount on my belt drive bike because I knew I would need to change the gearing.

[Joseph_]

Evening, just a quick update.
Went to my Koga dealer today and he confirmed I do indeed have a splined rear sprocket.
As I understand it threaded is older technology :
"Previously, belt cogs screwed directly onto Rohloff hubs, but now there is a much more user-friendly ‘splined carrier’ (part #8540L) with three splined belt cogs available (19t, 20t, 22t). This carrier makes cog changes much easier. There was a known issue for the 1st-generation splined carriers, but this was fixed mid-2018 (and warranty parts sent out), so won’t be an issue going forward."
Tomorow morning I have to call our national Rohloff dealer and I'll be able to get prices, availability and delivery times (which could be long I'm told).
I guess there's only two viable options now :
46:22 > change both sprockets and keep the 120t belt
39:19 > only change the front sprocket and change the belt to 115t
Costs are about identical and the gear ratios are also very closely knit together : http://ritzelrechner.de/?GR=RLSH&KB=46&RZ=22&UF=2281&TF=60&SL=2.6&UN=KMH&DV=speed&GR2=RLSH&KB2=39&RZ2=19&UF2=2281
The 39:19 has as a bonus that it resets the belt longevity, but the 46:22 distributes the drive train force over 10 more teeth (68 vs 58) and someone told me this is a good thing?

Please advice, it's the final choice 

Cheers again, Joseph.

[JohnR]

The final decision may depend on parts availability and price. You will struggle to notice the difference in gearing. There are those who believe that an odd-numbered total of teeth spreads out the wear on chains but I doubt it is significant with a belt. You may want to investigate getting the parts from a USA distributor if not available in Europe - some advertise on UK ebay so they may also advertise on European ebay platforms and it's also worthwhile checking Amazon.

[mickeg]

These ratios that you have picked of about 46/22 or 39/19, that is 2.05 to 2.09.  That is pretty low.  I use 2.25 for my lower gears.  Your gears would be about one half of a gear lower than mine when I use my lower touring gearing.  You would in effect be gaining almost two entire lower gears and never having the use of your existing 13th and 14th gear that you now have.

I am assuming that your body weight is under 100 kg.  Rohloff has a requirement that the ratio be higher for riders over 100 kg.

Bigger chainring will mean you put less tension on the belt when you pedal.  I would expect that is a good thing, with chains it is but since belts are supposed to have some pre-tension then maybe it is less important to a belt user.

If you are really convinced that you need gearing this low, if I was you, I would change both chainring and sprocket to the larger ones (46 and 22), buy a new belt that is the same length as my old belt, my old belt would become my spare belt that I carry on tours.

And I would keep my older chainring and sprocket, there might be a reason to have them later.

If the cost of tools to change the parts did not cost much more than the cost to have someone do that at a shop, I would learn how to do it and buy the tools.  And I would figure out how to set belt tension, although you probably should only need to do that once.

Good luck.

The final decision may depend on parts availability and price. You will struggle to notice the difference in gearing. There are those who believe that an odd-numbered total of teeth spreads out the wear on chains but I doubt it is significant with a belt. You may want to investigate getting the parts from a USA distributor if not available in Europe - some advertise on UK ebay so they may also advertise on European ebay platforms and it's also worthwhile checking Amazon.

I am in USA, most of my Rohloff related purchases were not from a USA source but instead from a German retailer.  I bought my hub and 250ml oil bottles from Bike24.

The odd number of teeth would be a chain thing, as unless someone makes an effort to install a half link in a chain, when you have an even number of teeth, half your teeth will always have a link with outer plates and half always have inner plates.  The outer plate links elongate, the inner plate links don't.  Belts, all teeth are the same.

[JohnR]

These ratios that you have picked of about 46/22 or 39/19, that is 2.05 to 2.09.  That is pretty low.  I use 2.25 for my lower gears.  Your gears would be about one half of a gear lower than mine when I use my lower touring gearing.  You would in effect be gaining almost two entire lower gears and never having the use of your existing 13th and 14th gear that you now have.

I agree that the result will be low gearing but is consistent with the objective noted earlier.

Hi mickeg, my tyre size is 28" 50mm so 50-622? I agree on your gear logic, I almost never use the top 3 gears (12-13-14). Ideally I'd like to lose 2 top gears and win 2 low gears and I'm told a 24t will achieve that.

In a separate comment 30% slopes were mentioned.

Given the cost of the Gates components it's almost worthwhile fitting a normal chain-based drivetrain to use while determining the optimum gearing before spending money on the final belt solution.

[mickeg]

...
In a separate comment 30% slopes were mentioned.

Given the cost of the Gates components it's almost worthwhile fitting a normal chain-based drivetrain to use while determining the optimum gearing before spending money on the final belt solution.

When I get up close to 10 percent on a loaded bike, my heart rate monitor tells me a number that I know means I better get off and walk.  (I am 68 years young.)  So, I do not think of slopes that steep.

When I built up my Nomad Mk II, I knew that I wanted two ranges of gears:

For touring I wanted the lowest I could go in first gear at a reasonably smooth cadence (I picked 72 for that), but still at a speed that was not so slow that I fall over (I picked 3.5 mph for that).  It took some calculations to work that one out.  But I am an engineer so it was not THAT complicated.  There were a few hills where I let my cadence fall to low or mid 60s, but with good tarmac and lack of side winds, I could maintain balance at speeds a bit lower than 3.5 mph.

And for my higher range of gearing for all other things, I wanted it pretty close to my Thorn Sherpa derailleur touring bike.  My Sherpa has a lowest gear of 19.2 gear inches and highest of 106.8 gear inches with 40mm wide tires, for my Nomad Mk II gearing for around town I chose 19.8 to 104.0 gear inches which almost perfectly matches that.

But if you are new to touring and your new custom bike is your first one for touring, that might be the ideal way to figure out what you want, start with chain and figure it out.  If your crankset can be used for both chain and belt, your redundant costs should not be too high.