Joseph_

Hi I'm new here. I'm the proud owner of a Koga Worldtraveller Signature 2.0 with Rohloff and Gates belt. I have a 50t front chainring and a 19t rear cog with a 120t beltdrive plus Schwalbe Almotion 28" 50mm tires with 2300mm wheel circumference.

On my last trip I noticed that I lacked low gears when climbing and now after a lot of research I am still wondering which rear sprocket I should fit to improve this? Many say the lower the better, but I also have to take into account that I don't have to replace my belt too because that would make it twice as expensive. So basically I'd like to put the lowest rear sprocket possible while keeping my current belt, and using the tools Ritzelrechner and the Gates Carbon Drive Bicycle Calculator I get the following possibilities (FYI my chainstay length is 460mm, my crank is 170mm) :

• A 22t sprocket is best compatible with a 459mm chainstay so can I keep my current belt with that? (at 60 cadence = 18,2>95,8 Gear Inches - 1,45>7,65m development - 3,25>17,1 mph / 5,23>27,5 km/h Speed)
• A 23t sprocket is most compatible with a chainstay of 456mm so a little too short. (at 60 cadence = 17,4>91,6 Gear Inches - 1,39>7,31m development - 3,11>16,4 mph / 5,01>26,3 km/h Speed)
• A 24t sprocket is most compatible with a chainstay of 465mm so a little too long. (at 60 cadence = 16,7 Gear Inches / 1,33-7,01m development / 2,98>15,7 mph / 4,8>-25,2 km/h Speed)

Now someone told me that if you have an eccentric bottom bracket (EBB) like my bike has, those few mm in 23+24t can be adjusted for somehow? And is a 24t sprocket a good choice or is this much too low? FYI, I am 47 years old but have a very good fitness and mostly ride on flat terrain (+- 60%), but often I do slopes and/or mountains (+- 30%) and occasionally I go off road (+- 10%).

If you guys want to give me a gamble with this information (because I know it's still a gamble), I would be eternally grateful

Cheers, Joseph

Iride01 

Everyone will be different depending on their current physical condition and how use to climbing on a bike they are.

However I'm not familiar enough with your rohloff and gates belt drive to tell you what you might need parts wise. However for climbing long grades of more than 6% or very short grades of more than 10% slope, you'll probably want something that translates to 24 to 25 gear inches or about a .94 ratio if your bike is 700C wheels.

The stronger you are in the legs and more physically fit to handle long periods of exhertion, the more likely you'll be able to handle a higher amount of gear inches or higher ratio for those climbs.

If you are very new to riding such, then you might need way less at the moment, though if you are healthy, active and just ride often your body will catch up quick without needing to get lower ratio gearing.

Joseph_

Hi and thanks for the info.
I do think your gear inches are on the very high side, as most people say lower is better and recommend something in the lines of 18-17-16 inches (in the lowest gear).
So are you sure about those 24 to 25 gear inches?I have 50mm 28" wheels so 50-622.

djb

Joseph, I'm a long time touring guy so have my views on a preference for low gears, but depends on how much load and terrain. To me there is really no downside to getting your gearing down to 17 or 18 great inches. I have this on my expedition bike and having a really low first gear that even if it doesn't get used that often, is always, always appreciated when you need it.

BUT you are going to have to contact Koga and Rolhof about the maximum recommended low you can change to. Rolhof has specific limits, and while I've read of people who go past them, you really need to get the proper info from them, not internet strangers.
It should be fairly easy to get this, and Koga and Rolhof will have this asked a lot, so should be very clear, especially about the BB adjustment range.
You'll also want to read up on belt tension and this affect on belt life.
I don't have experience with both rolhof and belts, but I've read a lot about them, so reliable info is available.
Good luck.
Again, I've toured a lot on my bike with 17-104 gear inches and having this range is extremely useful. I've spent months touring loaded up in some very hilly and mountainy Latin American countries, and this low range is great. It seems to me that if you lower your gearing with a rolhof, you may have a high of about 90 g.i. --there's a regular in the touring section here who has a rolhof bike and changes the gearing for expedition trips, but he has a chain.

Pop over to touring, you'll probably get more informed answers than here, but I can't emphasise the importance of contacting both manufacturers.
Cheers

Dan Burkhart 

With your current gearing, you are at about 21 gear inches at the low end. A 22 tooth sprocket is as low as you can safely go without straying into the high torque warning range, and that would get you down to about 18 gear inches. That's about the equivalent of having one more gear to downshift to from your current gearing. That still leaves you at about 95 at the top end. I think that is the range I would shoot for if it were my bike.

GamblerGORD53

The OP now has the same range as me. He's 20 years younger and his bike likely 30 lbs lighter. LOL
I would just get a 20T and be done with it. Your bike is not the billy goat type anyway. May as well wear out what you have first.
Other wise going 1T smaller on the front and 2T bigger would be the way to go. You did spend $6,000+ if that bike is new.
I still say going less than 3.8 mph, you are better off pushing. I used my 111/ 115 GI LOTS. Every time on the downside of climbs. Also on the back side of dips. Momentum is a WONDERFUL thing. Tail winds too.
Mine has a chain, also Rohloff14 with 700c x 36 mm tires.

Joseph_

Many thanks for the information, appreciate it.

Hi djb, I also tour fully loaded I estimate 25kg full gear setup, maybe even 30kg with food and water included.
I did stumble unto a new problem, my max rear cog may "only" be a 22t, so I might have to replace the front chainring and belt to get a lower gear ratio.
Belt tension is indeed something to consider, I'm trying to keep it the same tension as it is now, well within Gates' limits.
Indeed, the loss of high gears is a non-issue to me, almost never use them.
I'm contacting my local Koga dealer tomorrow, he should have some answers for me .

Hi Dan thanks, that's also what a friend with good bike knowlegde told me.
But as you've said yourself I'd only win 1 lower gear which I think may be not enough so best to go 2 gears down I think so 24t (if possible).
I''ll have to change the front chainring and the belt anyway in that case, but that also means more options to choose from and no belt problems.

Hi Gambler, may I ask why you recommend the 1T smaller / 2T bigger combination? Thanks

Cheers, Joseph.

Iride01 

I don't know for you. Have no idea of your fitness and strength. But for me, that was the lowest gearing I had on my bike when I rode up Mt. Evans in Colorado last year. Pretty much a constant 4.5 % grade for 14 miles with a very brief max grade of 9% and 3200 feet of elevation gain to a height above sea level of just over 14,000 feet.

And I didn't stay in the lowest gear either for much of the ride. I don't consider myself that strong a rider and my watts/Kg is less than many other serious riders that are out for fitness rides.

So yes I'm sure.... for me. You need to figure out what you can do. For the 10% of the time you are off roads or if you are in gravel, if you are going to be climbing, you might need lower gearing. But for those few times, you should probably have a different bike. I wouldn't want to have gears I almost never need for my more typical cycling. After that ride up Mt. Evans, I changed the rings and cassette back to my normal gearing with a low of ≈32 gear inches.

Also, if you are touring with loaded up paniers hauling a lot of weight, then that will change what low gearing you might need too.

djb

This is the range of my bikes, sometimes I've had the weight you mention, I'm super happy with this range, low of 16.7 actually with 2 inch tires.
If you can, get as low as possible.

Joseph_

Hi Iride, I'm guessing you have legs of steel .
But of course it's like you said; this works well for you and that's all that matters.

Hi djb, a 24t rear sprocket would also give me 16,6 inches so I'm hoping that it's possible but I'll have to wait till Tuesday when my local Koga dealer opens.
A 24t would mean 'only' 87,4 top gear inches though I'm sure that'll be fine, mostly i'm just cruising at 15 kph on the flat, suffering at 5kph going uphill, and when downhilling I just pedal fast a bit in the beginning to get some momentum but then just let gravity do most of the work

djb

dont take this the wrong way, but roadies have no idea of the gearing that is suited to touring with a given amount of weight. The only reason I bring this up is because so many bike store employees havent toured, and make recommendations of what bikes and what gearing will "work" for touring.

I do get it, on an unloaded bike, and a roadbike to boot, its just incomprehensible to imagine pedalling a bike + load weight that can be easily 70, 80 or even more pounds. Its pretty average for a touring bike to be 30lbs, then add on whatever load--and for some far off trips carrying extra spares, extra water, extra food, extra clothes and whatnot because one is far off, its pretty easy to have 40lbs of stuff.
Sure, bike packing philosophy and much much lighter equipment can really reduce total weight, but on some trips, you just end up with a lot of weight on the bike.

I figure the "roadie" view of things has always been the same, and will always be--I had roadies laughing at my gearing 30 years ago in the Pyrenees.
And I get loving riding fast and light, I love it too, and thats what I meant by "don't be offended", its just that touring is a different kettle of fish.
And man, are we slow-ass kettles of fish with all the crap we (some of us anyway) take with us.

but its all good, everything on two wheels is a laugh, I love it all.

Iride01 

Wow, all pompous sounding there aren't we? <grin>

To be clear, I stated I had no idea what the requirements would be if the OP was carrying a lot of weight on their bike.

And to be more clear, even though I suspected this was a touring bike, the OP made no mention that they were going to use the bike for touring loaded up with weight.

So don't take me wrong, but I didn't assume the things you assumed. Though perhaps you just happen to be correct about the OPs intentions.

No harm, no foul though. Enjoy.

djb

No prob, I thought he had said how much he was carrying-- I see now it was just before, but probably while you were writing your stuff, so you wouldn't have seen it.

GamblerGORD53

Way to go djb. You converted another can't-a-hill-a-phobic. LOL. He'll be scared to tour in Florida.

Joseph_

Sorry my bad, I should've mentioned this in my initial post as yes, I'm a heavily laden tourer doing gradients almost every day (next stop : Norway ).
My touring bike weighs 38 pounds, then add all luggage for being 100% self-sufficient (all camping+sleeping gear, food, water, clothing, etc), easily another 50 pounds on top of that, probably (much) more.
I do sometimes envy people with lighter loads and/or bikes, but you simply may not compare as the goals are so different, but the love for cycling is the same of course.
Again my apologies.

Joseph_

Hi, just a quick update.
Went to my Koga dealer today and he confirmed I have a splined rear sprocket, which means a 22T rear cog is the lowest option which may not be sufficient.
So 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.
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.

djb

I just remembered, there's a guy in the touring forum where I usually hang out who has a co-motion with belt, and there probably are others.
so perhaps asking in touring will get more informed answers, although this is really a technical question that the companies may answer much better.

In any case, if interested, pop over to the touring section, it's generally a friendly place.
Norway-cool

GamblerGORD53

Geeze just try a 20 or 21T. NO gears will get you up any and every hill. It's just stupid trying.
You will NOT be happy with a top speed of 24 mph.

Joseph_

Thanks on the updates, appreciate it.
In the meantime I've received enough information to make an informed decision.
I want to profusely thank everyone here who took their time to help me out here, you're heroes .