Author Topic: What rear sprocket do I need to help me get up hills and mountains easier?  (Read 5541 times)

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Offline 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 2293mm 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  :D

Cheers, Joseph

Offline John Nettles

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Joseph, welcome to the ACA Forums! Your post has a lot to unpack.
I have several bikes (too many my wife says).  Our house has 5 bikes with a traditional derailleur system, two bikes with a Rohloff, and one bike with a Pinion P1.18 gearbox.  One Rohloff and the Pinion have a belt, the only way to go I have discovered. All gear systems have their pros and cons.
NOTE:  These are my opinions, take them for what you want. I will try to address them in the order of your post.

Congrats on the bike.  I seriously considered getting one but wanted a Pinion which Koga does not offer unfortunately. Otherwise I would have gotten that wonderful bike.  On my Rohloffs, I run the absolute lowest ratio I can get. Yes, a 50/19 combo would indeed give a very high gear, at least for me. 

I am strongly in the "lower is better" group.  I started touring in 1977 as a young teen.  Only then when I was a very strong rider could I deal with anything with a lowest gear higher than 30 inches (sorry, I have yet to wrap my brain around anything other than inches) when touring but quickly learned lower is better.  I am now a couple of years from turning 60 and don't have the strength I used to.  However, the main reason I strongly prefer lower gears is I rarely spin out in my top (hardest) gear.  I use a 42/22 (1.91 ratio) on my Rohloffs.  This provides a low of 14.4" (using a 700x32 wheel), and high of only 75.6" for the high.  However, with a cadence of around 85-90rpms early in the tour and going to around 100rpms after 6+ weeks of touring, my top speed at 100rpms in my highest gear is around 23mph.  That is plenty fast with a loaded touring bike on flat ground!  I have only done this a literal handful of times so it is rare indeed. 

Also, I usually just gently pedal on major downhills just to keep the legs warm on downhills so I don't need a high high gear for that.  Since I am rarely (couple of times a week maybe when on tour) in gear 14 I figure why waste the gear range on unused gears.  The lower overall range of gears also allows closer spacing between the gears you mostly ride so that is better too.  I personally use the lower gears 1-11 much more than 12-14 which supports my belief in lower is better.  I actually wished Rohloff/Pinion would have a smaller range of gears so the gears would be even closer together.

BTW, your cadence will probably naturally speed up the more you ride on a daily basis and probably peak out between 90 & 105rpms if you are on a multi-month tour.

I would go lower than 1.9 ratio if I could but in reality, anytime I get below 2.5mph uphill, I have a hard time maintaining balance so therefore my low of 14.4 inches @ 60rpms just about does it.  While you say you mostly do flats, the 30% of hills/mountains is definitely something to consider.  Plus, if you go touring with gear a lower gear can't help assuming you prefer riding to walking. 

As far as the belt life goes, a $100 belt lasting 15k+ miles is not that unreasonable.  Plus there is the non-quantifiable aspects like the ease of maintenance or lack thereof compared to chains. The same goes for setting up your bike how YOU want it to be.  If it costs an extra $300 initially to resize the gear system, but it gives you comfort and enjoyment over 10+ years, is that really a big deal?

I have learned that to extend the life of the belt, keep it looser than what Gates recommends.  On my bikes with a Rohloff/Belt setup, the distance between the outer edges of the belt (top edge of "top" belt and bottom edge of "bottom" belt) measured halfway between the crank and the hub is just under 6" when just sitting there.  The measurement when I use my hand to squeeze the belt together is about 4.25".  It definitely is much looser than what the Gates App recommended but I noticed the belt lasts substantially longer (15k miles and no wear vs. 10k miles and the belt was done when tensioned "properly") plus it seems to be easier to pedal which I know is subjective but it really does seem easier.  Plus I don't have the pedals rotating when I roll the bikes forward which drove me nuts. My tension is not factory approved but I have not noticed any downsides and have heard a lot of world tourists also use "loose" tension.  Just don't make it so loose the belt slips on the rear cog.  If that happens, you will need to tighten it a bit.  I basically had the eccentric set for the loosest the belt could be.

I can't tell you what size belt, chainrings, or cogs to buy for your specific bike.  I didn't get it right the first time I resized and had to sell my new unused belt on eBay at a small loss.  I would maybe call/write Koga and ask them what can you do to get the lowest ratio.  Surprised they offered the dedicated touring bike with such a high ratio.  And honestly, I would go a little below Rohloff's required ratio if you need to if that is what is required to make it all work.  However, if you had to go up a little from the 1.9 allowed ration, that would not be a deal breaker either. 

Hope you have many enjoyable miles ahead of you!  Tailwinds, John

Offline ray b

And there you have it - folks usually have to pay for that kind of customized information.

I also run Rohloff's with a much lower ratio - especially if I am running 80 pounds of water, food, gear, and bicycle. (For me, the incline does not have to be much to require much lower gearing.)

I agree - your next stop for information might be the experts at Koga. I'm sure they've played with this issue in the shop, if not on the road. If you haven't put any miles on the bike, they might even trade out your gearing and belt as an even exchange.
“A good man always knows his limitations.”

Offline Joseph_

Wow John, your post (and Ray's) has been of the utmost help, many thanks!

I'm 47 and only discovered bike touring two years ago but have been hooked ever since.
I did notice that I mostly love hilly/mountainous scenery, but I did not love climbing those hills, at least not from the moment they got too steep and I had to get off my bike.
So every tour I try to take less weight, though I think having the right gears is far more important hence my question.
I totally follow your gear-logic and it's the exact reason I'm switching now, with the only difference I'm going for higher inches (somewhere between 16,7-18,2 depending on which largest rear sprocket I can place, plus 1,9 is also the Smallest Permissible Sprocket Ratio by Rohloff to prevent overstraining the hub).
I definitely also agree on the cost-comfort reasoning, the only problem is I don't know which gear configuration would best suit my needs so I'm going to have to test it out anyways.
I'll probably start with the largest rear sprocket my current front chainring/belt combination allow, and then work from there.
Thanks also for the belt tension tip, that's also something I learned from Alee Denham, so I may give that a try though it would be my first time and I have no idea where/how to do it (hello YouTube  ;D)
I will contact my local Koga dealer to ask for the specifics and see what they say, because it's hard figuring this stuff out on my own.
Actually this Worldtraveller is my second one. The first one was the standard version with a chain not a belt, but it was one size too big due to the bike shortages. But I fell in love with that bike and when the old one was sold bought the custom Signature version with Rohloff and Gates belt, and I must say it's an amazing bike.
But when I ordered my Signature I actually went to the Koga Testcenter in Ede, Holland (I'm from Belgium) and asked if I could change the gears to a lower ratio since I already noticed on my first bike that some hills I was just lacking.
But they said that almost no one does that and almost no one comes back later to change it.
I should've pressed on and went for it anyway but now it's too late I'm afraid.
I guess most bikes they sell is for driving around the Netherlands and that's 100% flat :-)
Anyway, many thanks again, really appreciate it.

Tailwinds, love it!

Cheers, Joseph

Offline ray b

Right - only 2 gears needed in the Netherlands. (With the wind and against the wind.)

As an old guy, without the power I used to have when I raced, I'll admit to running more than recommended ratios on my Rohloff. This summer past, I ran 32/13 (chain) (ratio 2.4) on a fully loaded back country tour without problem. 

That said, I have a great respect for the kind of damage one can cause with that kind of power advantage to gears, frames, and wheels; I did my share of walking. (Or, to paraphrase Matthew Lee, "You'll know when to get off and walk."

On the other hand, it was nice to have that super-low ratio toward the end of a long day with camp still waiting over the pass.

Try to have fun with this. With an eccentric bottom bracket, you can probably have 3 or 4 usable combinations of chainrings and sprockets to use for different geography and logistics.

Take care.
“A good man always knows his limitations.”

Offline John Nettles

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So every tour I try to take less weight... Not a bad thing to keep trying to do.  Just remember that the "best" amount of weight is a VERY personal decision that only you can decide.  As a touring buddy of mine says "If it makes you smile, then bring it." meaning if you are willing to carry the extra weight without complaint, then bring it.  If you start to complain about the weight, decide if it makes you smile or frown. If frown, leave it at home or ship it home if on tour.

... plus 1,9 is also the Smallest Permissible Sprocket Ratio by Rohloff to prevent overstraining the hub.  You must remember that Rohloff is covering their butt on this and going from a very strong rider (lots of torque) carrying a lot of gear.  If you are not a super strong rider, then you should be fine if you go just a little below the allowed amount.  However, since you want to go higher than the minimum then no concern.

.... I may give that a try though it would be my first time and I have no idea where/how to do itOnce you see how to loosen the eccentric, just go to the loosest setting.  Just be sure to look at (measure) how far the chainring is from the down tube to ensure you have the proper chainline when you put on the new chainring. 

I will contact my local Koga dealer to ask for the specifics and see what they say, because it's hard figuring this stuff out on my ownHoepfully, they will be able to give you the answer easily. 

Offline Joseph_

Thanks again.

And great to hear you guys are still going strong and enjoying the ride, I hope I'll be able to do the same as I get older  :)
Love your sayings and it's exactly my mindset now.
For instance on my first tour two years ago I took along a folding chair.
It was great when I used it but not often enough to warrant the extra weight and volume so I send it back.
And there was more stuff like that, like a fishing rod ;D
One thing I do always bring now since I'm a very light sleeper is a construction heaphone against any noise.
It's very voluminous and bulky but boy do I sleep well at night!  ;D
Thanks on the sprocket ratio tip, I did figure there was some leeway so will keep that in mind should I want to go (a bit) below 1,9.
I've already looked a bit into adjusting the EBB, doesn't look too difficult, I just have to make sure to put everything back correctly into place afterwards (like you said measure everything, and I'll take some photos beforehand).
But I will confirm with my local Koga dealer anyway before ordering since they'll probably have done this before.
Thanks again for all your kind help, really helped me out here.   

Tailwinds! Joseph.

Offline 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.

Offline John Nettles

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It is basically a toss up with a very slight preference to the 42/22 just because it is a very slightly lower gear even though they are both basically the same gearing.  As you say the longer belt will last longer since each tooth gets less where but as I said, these belts "improperly" tensioned can get 15k miles (24K km) so if the longer belt lasts say 10% longer it would take 150k miles before you earned a "free" belt so the cost really does not matter. One unspoken advantage of a smaller chainring is that it doesn't hit obstacles as much if you do off road touring and have to get the bike over logs and such thus limiting the damage to the belt potentially.

However, using the Gates Gear Calculator you referenced earlier, I noticed a 3rd option is the 39/20 with a 113t belt.  Gives the lowest gear of all (slightly) but it is also most expensive option so would rule that out unless you were starting from brand new everything. This would have been my preferred if it was optioned when new. 

I vote the 42/22 since the gearing is basically the same as a 39/19 and you might as well get extra life out of the belt.

Tailwinds, John

Offline Joseph_

Thanks on the update, really appreciate it John.
In the meantime I've received plenty of good information to make an informed decision.
I want to profusely thank everyone here who took their time to help me out, you're heroes  ;D
If anyone comes near Brussels in the future, drop me a line and beers are on me!
Cheers, Joseph.