Author Topic: What's your Rohloff combo (chainring, cog)?  (Read 180318 times)

John Saxby

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #195 on: August 18, 2015, 03:01:16 am »
Snippets and bits from earlier posts on The Question of A 'Glider Mated to a 36T Ring:

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you can see why I am such a devotee of the 36x17 combo, and why I pine for a Chainglider suitably sized to fit a 36T 'ring

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I'm still interested to see if a modified 'glider can be used effectively with the smaller ring.

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I'll be watching eagerly, John. To Noble Experiments!

Well, we have some visual record of the early stages of my experiment. You can judge, gentle readers, whether or not it's "Noble"; the faint of heart, or purist 'glideristas, may want to avert their eyes.

Midweek last week, I made a 60-km ride of about 3 1/2 hours through some steep hill country about 150 kms northwest of Ottawa. I have ridden most of the route before, but I tweaked it a bit this time. I drove to the starting-point with my Raven on the bike rack at the rear of our station wagon, and my ride was pretty much all hills, with very few flat bits. Here's the link to the route, with the altitude profile: http://tinyurl.com/qdndq8k The route began with a steep climb, 14% for 2.5 kms, and ended with a rapid descent down the same hill.

I'll write about the ride, with some photos, in the "Rides of 2015" thread. The issue for this thread was testing my new 36 x 17 Rohloff ratios on some demanding hills, and to do so with a 'glider fitted to the 36T  'ring.

First things first: how did it work?  Pretty well.  The bike wasn't loaded, but I've planned past rides along this route to ensure that I only descended the really big steep suckers, like the 14% hill between Foymount at the top of the escarpment and the Bonnechere Valley. This time I was starting at the bottom...

So, the big 'un I did in 3rd gear.  It's really two hills with a short plateau in between, and the lower hill is the steeper of the two; since I was still fresh, I probably could have managed the upper half in 4th, but why bother?--especially as I didn't really know what was to come on the back half of the ride.  It turned out that there was an even steeper hill on the back half, a short-but-savage ungraded climb out of a valley with a pretty lake.  I had to use 2nd on that, so I guess it was steeper than, say, 15%.  I think I'd have been able to manage both hills on a loaded bike, in 1st gear or possibly second.

I couldn't pick up any difference between the Raven with 'glider on this ride, and the Raven sans 'glider in my earlier tests on easier hills with the smaller front 'ring.

So, how did I fit my 'glider onto the 36T ring?  When it was mounted on the 38T ring I have just replaced, I had noticed evidence of some friction on the portion of the front half of the 'glider which covers the rear section of the chainring. So, I cut that section away with a sharp blade, with the results you'll see in the photos attached below.

I used the two wraps of tape you see aft of the ring to reduce the length of the gap in coverage of the chain in the upper and lower arms of the 'glider which had resulted from my cutting off the plastic covering the rear portion of the 'ring.  Of course not all of the chainring is protected in this setup, but 99% of the chain run itself is protected; and importantly for me, the front part of the chain remains reasonably well-shielded from rain, spray and grit. We'll see how it works in practice.  If I have to clean the chain once or twice a season, I can tolerate that.

Adjusting a 38T 'glider to its new life embracing a 36T ring required only a little fiddling with the teeth and notches at the rear.  Surprisingly, I found the changed appearance quite OK.  I don't know if The Spirit of the 'Glider felt itself diminished and exposed and all, but I tend to be utilitarian about such matters.

In sum: so far it looks OK (to me), seems not have created any undue friction (maybe even did away with some), and offers better weather protection than no 'glider at all. Maybe I should ride to Nova Scotia to check it out?  More reports if & as the evidence creeps/trickles/pours in.
« Last Edit: August 18, 2015, 03:10:52 am by John Saxby »

Danneaux

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #196 on: August 18, 2015, 03:18:46 am »
Vive le bicycle vivisection, John!

Many thanks for creating and participating in this -- yes! -- most noble of experiments. I will look forward to future reports with greatest interest.

Meantime, as the owner of a 36x17 Rohloff and in "pass-hunting" mode, you simply must purchase one of these:
http://www.skymounti.com/html/gb.html
Also available from Amazon in two sizes:
http://www.amazon.com/Sky-Mounti-Inclinometer-26-0-Diameter/dp/B000PHO6K8
http://www.amazon.com/Sky-Mounti-Inclinometer-31-8-Diameter/dp/B004HUAYMI
...and from the good ol' Adventure Cycling Association: http://www.adventurecycling.org/brands/sky-mounti/sp/inclinometer/

I have owned mine for 8 years now, and found them so addictive, they have multiplied like Tribbles and now live on the handlebars of most of my bikes. I would have killed for one back in the days when I setup a local hill-climbing course totaling 10,000ft total elevation gain. Instead, I had to use an angle finder and convert the readings into slope percentages.

Thanks again for contributing so nobly to the Fund of Knowledge with bold courage, 'speermints (experiments), and pittsures (photographs).

All the best,

Dan.
« Last Edit: August 18, 2015, 05:49:14 am by Danneaux »

Danneaux

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #197 on: August 18, 2015, 03:20:35 am »
...as a followup, I wonder if the now detached rear arc of the front section might be reattached using Sugru or JB Weld, simply displaced rearward of its original position. The front arc looks remarkably good....

Best,

Dan.

Andre Jute

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #198 on: August 18, 2015, 11:27:34 am »
Fascinating report, John. I think you might be surprized at how little cleaning you have to do of the chainring and chain, as there is sure to be a wiping action when the chainring reenters the Chainglider. I also like Dan's idea of reattaching the rearmost part of the chainring cover in the correct place for a 36T chainring. The front part now looks tailor-made, dinnit?

Super experiment, John. Congratulations on its successful outcome.

il padrone

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #199 on: August 18, 2015, 11:56:38 am »
Danneaux, the marvels of this new technological stuff. Some cycle computers (Cateye Adventure, Specialized Speedzone Elite) come ready equipped with a gradient function built-in. Uses the altitude readings to give a gradient measure.

 ;)

Danneaux

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #200 on: August 18, 2015, 04:00:21 pm »
Quote
Some cycle computers (Cateye Adventure, Specialized Speedzone Elite) come ready equipped with a gradient function built-in.
<nods> Yes -- and marvelous! -- but Frugal Danneaux isn't going to trash a perfectly good cycle computer when a less expensive add-on will do!  ;)

All the best,

Dan. (...who used an original Cat-Eye CC-1000 from 1985 for 20+ years...)

John Saxby

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #201 on: August 18, 2015, 04:13:43 pm »
Thanks for the helpful thoughts & suggestions, all.  The Skymounti looks like a fascinating wee device -- no batteries, either!

A cycling buddy here has a Garmin with an altimeter and inclinometer, but on a recent ride in the Gatineau, it registered a 6% descent on one hill, and a 9% climb on our return. FWIW, my guesstimate would have been 5 - 6%.  Seems his Garmin does this frequently.

I still have the cut-off sections of the 'glider, so will keep open the option re-mounting them, depending on how things work out with the current setup.  We had a cool damp spring and early summer, but it's been dry since late June.  Might have to go in search of hills and rain -- Brittany? Scotland?

Danneaux

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #202 on: August 18, 2015, 04:25:09 pm »
All encouragement, John! Go, go!  ;D

<said without even a *hint* of self-interest! ;) >

All the best,

Dan.

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #203 on: August 18, 2015, 04:38:37 pm »
Back to the topic of chainring and cog sizes ...

Around home I use 44 and 16 on my Nomad Mk II.  But I am getting ready for a self supported mountain bike trip next month so I switched over to 36 chainring and 16cog.  This will be great for getting up steep hills on my trip, but I spin out every time I go down a hill around town here.  Maybe I should have waited a few more weeks before swapping out chainings and pulling out a few chain links.

Danneaux, the marvels of this new technological stuff. Some cycle computers (Cateye Adventure, Specialized Speedzone Elite) come ready equipped with a gradient function built-in. Uses the altitude readings to give a gradient measure.

 ;)

I have that capability in some of my GPS units.  I hope that the computer you cite is more accurate than the GPS units I have.  They are terrible at figuring out the slope.  Two of my GPS units have pressure sensors so they should be able to read changes in elevation better than the ones that use GPS information for elevation.

But for accurate gradient, I will take the inclinometer.  In the photo, the hill was at 20 percent slope, was not easy to hold my bike on that slope with one hand while I took the photo with the other.


Slammin Sammy

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #204 on: August 21, 2015, 09:44:54 pm »

 it registered a 6% descent on one hill, and a 9% climb on our return. FWIW, my guesstimate would have been 5 - 6%.  Seems his Garmin does this frequently.


Mine does too, which I've always put down to barometric variations, mostly diurnal, which bedevil any single point altimeter readings. Just last week, I happened to note on my Edge 800 the 88m high spot on a local track when passed at 10:30 became 95m a few hours later. As I'm pretty certain that level of tectonic activity has ceased in this part of the world, I'm chalking it up to the low pressure change that moved through at the time, coupled with lunar movement. (I think the published datum for that point is 85m, plus ~1m for the height of the instrument.)

Danneaux

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #205 on: August 21, 2015, 10:41:12 pm »
SkyMountis are bliss-on-wheels. Fascinators. I would be sorely torn to lose mine. They have added so much fun to my rides, read directly, instantly, and consistently and have the side effect of compelling me to search out hills and inclines.

All the best,

Dan.

Hoodatder

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #206 on: January 01, 2016, 10:41:47 pm »
Helllllo,

Why is the gear 11 the"critical/desired" gear to achieve?

I imagine it's to do with cadence - spinning?

Being ignorant of inches / gearing I have never ever really taken notice what gear I am cycling in - so long as I can get up most hills, I'm happy.

But, determination, ignorance and pure grit has had a lot to do with it, methinks.

I am going to replace my 40t chainwheel for a Surly 36t chainwheel and leave the 17t sprocket on the rear.

With the new set up, what will gear 11 be equivalent to on my existing set up?

I am not a speed merchant and will happily coast downhill and if gear 11 is THE gear to tootal along in, then I want to be in that club 8).

I have a few questions to ask but I feel your informed answers will not necessitate asking them - I hope

Thanks in advance - going to push some Z's now - nighty night.

Hoot


mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #207 on: January 02, 2016, 12:30:29 am »
Helllllo,

Why is the gear 11 the"critical/desired" gear to achieve?

I imagine it's to do with cadence - spinning?

Being ignorant of inches / gearing I have never ever really taken notice what gear I am cycling in - so long as I can get up most hills, I'm happy.

But, determination, ignorance and pure grit has had a lot to do with it, methinks.

I am going to replace my 40t chainwheel for a Surly 36t chainwheel and leave the 17t sprocket on the rear.

With the new set up, what will gear 11 be equivalent to on my existing set up?

I am not a speed merchant and will happily coast downhill and if gear 11 is THE gear to tootal along in, then I want to be in that club 8).

I have a few questions to ask but I feel your informed answers will not necessitate asking them - I hope

Thanks in advance - going to push some Z's now - nighty night.

Hoot

Gear 11 is direct drive, the rear wheel turns as if it was a single speed with no internal gearing.  It therefore is slightly more efficient from a mechanical perspective.  I say slightly because the inefficiencies caused by internal friction in all the other gears are so small they are not really noticeable.

That said, it is not that critical that you have gear 11 as your general riding gear, I often ride in gears from 9 to 12 on flat and level terrain, depending on windage.

If you have a 40/17 setup right now and go to a 36/17, that means that your new gear 11 will be very similar to your current gear 12. 

The concept of gear inches goes back to bicycles like the Penny Farthing where your crank was direct drive on the wheel.  Thus, if you have a bike with a gear of 50 inches, you would turn the crankset the same cadence as someone riding next to you on a Penny Farthing if they have a 50 inch diameter wheel.  (I have no idea what size wheels Penny Farthings used, I just used 50 inches as an example.)

Andre Jute

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #208 on: January 02, 2016, 01:36:35 am »
If you set up your gears so that in gear 11 on the flat you can reach your comfortable long ride cadence, that is the most efficient choice you can make. Gears 12, 13 and 14 are then overdrives for going faster down hills; when you run out of cadence on the downhill, as you say, you cruise at the high speeds courtesy of gravity. (Now that's my kind of cyclist!) Gears 8-10 would then be good for moving off, small inclines, heavy shopping and so on, and gears 1-7 would be a low range for loaded touring on heavy hills, stump pulling at the low end.

As George says, the inefficiencies in the other gears are too small to worry about, so you may as well calculate your gears any other way that seems advantageous to you, regardless of which gear then falls in as your main flatland gear.

Gear 11 is also the most silent gear in the Rohloff box. Even a little noise, if it persists, can cause stress. If you're a long distance tourer, or if you like conversing with the pedalpals while you ride, that is a (rather small) consideration.
« Last Edit: January 02, 2016, 11:44:37 pm by Andre Jute »

martinf

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #209 on: January 02, 2016, 08:00:38 am »
My current Rohloff setup is 38x16, the recommended minimum Rohloff ratio when I bought my Thorn Raven Tour.  In gear inches this is 17-89 with the tyres I have.

Rohloff now allow a much lower ratio.

Although my current gearing is low enough for nearly anything I have encountered, I would gear even lower for a touring bike if buying now, and ideally set the highest gear to about the same as the highest gear I regularly use (around 75" to 79").

I'd also take into account of whether or not I could fit a Chainglider, which I reckon saves chain maintenance, muck on the chain and the necessity of replacing it 3 times was an irritation on my last long tour with a derailleur bike.

38x17 definitely works, 38x19 or 44x21 might work with a different Chainglider and one of the 2016 model splined Rohloff sprockets.