Gearing help for our Raven Tours

[gregmacc]

Hi all ... my wife and I have recently had a pair of Raven Tours shipped out to us here in Australia. We are extremely happy with the bikes and the excellent customer service provided by SJS. The only thing we are thinking of changing is the gearing. We went for the 17/40 sprocket/chain-wheel combo but after some initial rides around our hilly neighbourhood we believe we will be running out of low gears when fully packed and touring. So we are considering getting a couple of 39T chain wheels sent out. I'm just wondering if there are any issues I need to consider. I'm assuming I will need to adjust the EBB or maybe even remove a chain link. Is there anything else I should be aware of?
Cheers
Greg

[rualexander]

I believe that using 17t sprocket and 40t chainring gives you the lowest gearing that remains within Rohloff's recommended limits, therefore if you use a 39t chainring with the 17t sprocket you may invalidate your warranty, although you are unlikely to suffer any ill effects with such a small change in the syatem.

[JimK]

If you're going to the fuss of buying new chainrings, and invalidating your warranty on top of that, I would push further, to the 38 tooth chainring. Each step of the Rohloff is about 13%. Moving from 40 to 39 is 2.5%. I suspect it'd be hard to notice. Moving to the 38 would be 5%.

I have the 38 in the front... I do get tempted to put the 17 tooth sprocket in the back. I notion that I could over-torque the hub is a bit ridiculous!

[Danneaux]

Hi Greg,

Congratulations to you and your wife on the new Raven Tours!

I notice Andy Blance has issued an Autumn, 2011 update for his online publication, "Living With A Rohloff Hub".  It is available for download as a PDF here:

http://www.thorncycles.co.uk/thornpdf/ThornLivingWithARohloff.pdf

Page 24 has a nice chart showing various chainring/cog combinations for the Rohloff, and makes clear what constitute "unadvised" ratios, shows at which point (in gear-inches) the 7-8 shift occurs, and where the various ratios place direct-drive 11th gear.

I found it a nicely done piece of work and it answers in one place several questions that have occurred to me.

Hope this helps,

Dan.

[gregmacc]

Thanks people ... Yes rualexander, I'm aware or the warranty issues but we are both lightweight/average in the leg strength/weight  department. From what I can gather from the Thorn  documents we would need to be built like gorillas to overly stress the hubs.
On second thoughts, Jim's suggestion of the 38T chainring sounds like a more sensible choice.
Dan ... thanks for the link ... I've been looking at the previous PDF for a while now. The new charts are a worthwhile update. It's all pretty clear ...
Cheers
Greg

[gregmacc]

Will I need any special tools to swap to the  38T chainwheel? (other than the supplied EBB adjuster and a chain link remover).  My chain is Sram 3/32 Inch PC830 Chain 114 Links 7/8 Speed HG Compatible.  Cheers.
Greg

[Danneaux]

Greg,

I wouldn't think you'd need anything more than a 5mm allen wrench for the chainring bolts and perhaps a wide-bladed slotted screwdriver or peg spanner for the sleeve nuts.  Where the bikes are new, you should be able to get by with just the 5mm allen (there are those of us -- like me -- who prefer to get the slots on the sleeve nuts lined up at 90 degrees to the crank spider.  It just looks neater, and the peg spanner allows for full torque without spinning the sleeve nut).  Put a little anti-seize on the chainring bolts where they enter the sleeve nuts to ensure future ease in removal.

If you don't already have one, this might be a good opportunity to add a SRAM connecting link for tool-free chain removal in the future.

Best,

Dan.

[il padrone]

Hi Greg,

Congratulations to you and your wife on the new Raven Tours!

I notice Andy Blance has issued an Autumn, 2011 update for his online publication, "Living With A Rohloff Hub".  It is available for download as a PDF here:

http://www.thorncycles.co.uk/thornpdf/ThornLivingWithARohloff.pdf

Page 24 has a nice chart showing various chainring/cog combinations for the Rohloff, and makes clear what constitute "unadvised" ratios, shows at which point (in gear-inches) the 7-8 shift occurs, and where the various ratios place direct-drive 11th gear.

Despite this advice, the photos of his Raven eXXp in the saga of his 2005 tour of the wilds of southern Chile and Argentina show he was using gearing waaaay under any Rohloff recommendation. Check out page 8 - his gearing is something like 38-24 I reckon.

 

[Danneaux]

It surely looks that way.

Page 2, crossing the stream, as well.

However, looking closely at the SJS Cycles listings, they only carry Rohloff replacement sprockets in 13, 15, 16, 17, and 21t.  Rohloff's home site lists them in 13, 15, 16, and 17t.  I notice each cog has one hole drilled per tooth except the 13t, which is solid.  The resolution on the photo isn't good enough to make a perfect count, but it also looks like there is quite a bit more metal around the holes on his than shown in the pics on the Rohloff site.  Cycle Monkey have a 24t available, but that is for use with the Gates CarbonDrive belt system, and it seems to have a different pitch than the usual 1/2" used on chains and cogs.  Andy's chainring does look smaller than I would have expected.  

I daresay Andy likely doesn't have the same warranty concerns we might, and as test pilot, I suppose he might have pushed the limits to see how low one could go before breakage.  I suspect Rohloff build a pretty healthy safety margin into their hubs, and keep their recommendations somewhat conservative to prevent an erm, "unfortunate owner experience" (i.e. breakage and stranding).

I have managed to ride a 12" (11.8") low in the past, using a 15t freewheel cog as a chainring combined with a 34t freewheel cog and 700C wheels.  I had fun trying to go lower, but that was about the limit for maintaining balance at low speed with a reasonable cadence.  The real trouble came at startup, where such low gears meant the opposite crankarm came 'round too quickly to pick up easily with the offside shoe's cleat.  100RPM in a 12" low only gets you 3.5mph/6kph with a 700Cx32mm tire (see http://www.machars.net/bikecalc.htm), so in comparison, I'm not sure a 38-24 Rohloff would be any more usable (with 26" wheels, a 38-24 Rohloff would give an 11.5" low and a 60.4" high; see: http://sheldonbrown.com/gears/internal.html ).  Looked at that way, it seems less likely he's running that combo, but it's hard to tell; the chainring still looks awfully small and the sprocket appears pretty large.  A 36-21 might get pretty close, but it seems unlikely at 12.1 gear-inches.

Lots to ponder in those photos, and I can't enlarge them with quite enough clarity to get an actual count....  It'd be fun to know what Andy really is using, to serve as a reference point.  He and Fiona have surely climbed many steep grades in rugged terrain.

Best,

Dan.

[Danneaux]

As an aside, it is remarkable how much torque can be generated by a rider using low gears (at least with derailleur gearing, where I have my experience).  One has only to look at the marks and indentations left by a cassette on a freehub to see the effect, or to try and remove an old screw-on freewheel that has seen serious use with a strong rider on steep hills powering a heavily-laden touring bike.  I managed to twist a shop vise free of it's through-moorings on my workbench, and neatly sheared the peg off a puller one time trying to remove mine, in the days before I used spacers and lots of high-pressure molybdenum-disulfide grease on the mating hub/freewheel threads.  I remember hillclimbing tandem teams in the early 1980s breaking their freewheel pawls on steep climbs at the local tandem races.  Shimano makes stern warnings to avoid using their 12-36t cassettes on hubs that are not designed specifically for them.  Though intended for the 29er market (MTBs with fat 700C knobby trail tires; the larger cogs compensate for the larger-diameter wheels), I know folks who are using them successfully with 26" wheels.  One may well get away with it, but the safety margin will be slimmer, just as it was when I successfully played with 12" low derailleur gears (15t chainring/34t cog, 700C wheels).  Bottom line is, most manufacturer's recommendations tend to be conservative *in order* to reduce costly warranty claims (also known as user breakage experiences).  The closer one approaches design and fatigue limits, the more likely failure becomes at some point in the use curve; stress and fatigue can be cumulative.

Best,

Dan.

[JimK]

I have managed to ride a 12" (11.8") low in the past, using a 15t freewheel cog as a chainring combined with a 34t freewheel cog and 700C wheels.  I had fun trying to go lower, but that was about the limit for maintaining balance at low speed with a reasonable cadence.  The real trouble came at startup, where such low gears meant the opposite crankarm came 'round too quickly to pick up easily with the offside shoe's cleat.  

I find it difficult to start on a steep slope with my lowest gear, around 17". What I do with the Rohloff is first switch up to about gear 4. I can pick up a bit of momentum in 4 with a few strong strokes, then I can quickly switch back down to 1 to pick up the rpm and resume working my way up the hill.

I find this capability, to switch quickly across three or four gears at very low speed, to be one of the Rohloff outstanding virtues.

Looking at that photo on page 8 of Andy and Fiona's adventure, I just measured the radii on my computer screen of the chainring and sprocket - I get a ratio of about 3:2. Could be the 21 tooth sprocket with a 34 tooth chainring. Hmmm, that looks like fun!

[philb0412]

I was thinking about posting a similar question about whether going much lower than the Rohloff recommendation was wise for a solo tour with plenty of time fully loaded in the mountains. Some good responses here thanks, and the thought of Jim measuring the radii on his screen really made me smile!

[Andre Jute]

I assume Greg has long since fitted whatever he decided upon.

Some notes.

A useful all-round closure for the chain is the Hebie Chainglider, on which I have reported several time on this board. I don't know whether I would go on a tour to the rougher places on earth with it, but it would be good for commuting, and it turns your bike into a utility bike you just jump onto in whatever clothes you're wearing to pop out to the shops. The smallest chain ring the Chainglider caters for is 38T. It doesn't cater for 39t at all, and in fact only has two more front end sizes. At the back it caters for all the official Rohloff sprocket sizes of 15, 16, 17.

A Rohloff box comes with a 16T sprocket fitted as standard. 38x16T is the lowest ratio (2.375) that Rohloff officially supports.

Andy Blance has several times (from memory) recommended 36x16 as a reasonable step down from 38x16. Frankly, I thought he said bluntly that that was what he fitted to his own bikes.

I have 38x16, which with 60x622 Big Apples gives me 19.5 gear inches, which with my masher's cadence of about 40rpm is already not too far from the limit set by being able to keep your balance.

I live in hilly country, and my town is also hilly. I find 38x16 is adequate at the low end but on the downhills you run out of top gear if you're a speed freak, and if you have hills with a good grade, you're probably sacrificing 20 or 30kph of "free" speed by not being able to pedal up a storm on the downhill. Gear 14 on my bike is 102.6 gear inches, quite respectable, possibly a bit high for loaded touring.

For myself I consider the loss of downhill speed a worthwhile sacrifice. Even if I were younger and fitter, I wouldn't sacrifice the ability to get up any hill for a notional top speed I'll never achieve on the flat. In fact, the only road where I would, at least theoretically, go flat out in gear 11. 1:1, on the flat, is now too dangerous for me to ride on; when I used to ride there in the middle of the night I always rode in gear 12 or 13 or even 14 because 11 was too slow for a cadence achievable only in the cool of the night.

38x16, though theoretically perhaps not a perfect match, has thus in practice worked out extremely well for me, and the 17T sprocket I ordered with bike (after the German supplier refused to fit it for me on the ground that he couldn't be a party to a breach of Rohloff's warranty requirements!) has never been fitted.

The question remains whether Master Blance's 36x16 or my Chainglider friendly 38x17 would be better for someone with a higher cadence than mine, as most of the roadies are likely to have. Those choices would cut even deeper into the top end. Why should a laden tourer need a top gear over 90 gear inches?