Hi Peter!
If I may paraphrase, it sounds as if you're now at a drivetrain crossroads due to wear and attrition and view this as a good opportunity to explore some drive alternatives for your Sherpa frame.
If I've summarized fairly (apologies if I didn't!), then you have some alternatives:
1) Our very own rualexander did one of the nicest Rohloff conversions I've
ever seen, and he managed it eventually without use of a chain tensioner. A truly professional job, it looks as if it came straight from the designer's drawing board that way. You can see some photos of it and a bit of description here:
http://www.thorncycles.co.uk/forums/index.php?topic=3235.02) You may wish to see if another kind of IGH (Internally-Geared Hub) will fill your needs for less money. Shimano offer the Nexus and Alfine hub gears in several varieties including 8- and 11-speeds and a variety of included brakes, but unlike the Rohloff, their steps are not even and there's some sizable gaps/jumps in progression as you go through the range. This can be split with a hybrid system (i.e. chain tensioner, front mech and two chainrings), but the results are not as good as one would hope, due to the gaps in the range and resulting duplicates. I've charted some, and the results for a Nexus/Alfine hybrid are generally messy.
3) Summarizing my own view of the NuVinci, the stepless shifting holds great intellectual appeal, but in practice friends who have them have found many of the changes are either too fine to feel or they miss the reference points provided by steps. In other words, they found its greatest strength to be a weakness for them. For me, I would find it convenient but lacking in overall range. That is my own opinion, but in truth, it seems the user's happiness depends on their particular use. Many commuters seem especially happy with them.
4) Your consideration of a hybrid gearing system (there's several possibilities, but here we're considering mostly an IGH rear hub with a front mech and a couple chainrings) is spot-on to my thinking
before owning a Rohloff-hubbed Nomad. Andre tried patiently and at times valiantly to educate me, but I coudn't wrap my mind fully around the concept of Rohloff as-is, coming to that world from 35 years' worth of derailleurs, primarily in half-step shifting configurations.
In truth (
by the numbers), you can make the world's best half-step shifting arrangement with a Rohloff. A really nice setup would be a 17T cog on the rear and 36/38T chainrings up front. Imagine -- a 28-speed half-step with essentially no chainline issues, and beautiful split around 7% between gears. Incredible.
The trouble is (again, as Andre pointed out to me from the beginning), hybridizing a Rohloff is not the best use of a Rohloff's strengths:
• You're back to a chain tensioner (really a rear derailleur that only tensions the chain and doesn't "shift" anything) and...
• Small 10T or 11T pulleys that cause the chain to wrap back on itself sharply, introducing greater wear and cleaning hassle compared to the single-speedlike chainline of the Rohloff.
• It is hard to find a proper half-step front derailleur these days; moreso if the 'ring difference is only a couple teeth. As a result, you'd have to grind and reprofile a road derailleur that merely "came close" to your needs.
• Then, you've got the issues of two chainrings, neither of which is on the perfect 54mm Rohloff-recommended chainline, and that introduces more wear and friction.
• And, while I never found it particularly troublesome even in desert dust so long as I used mudguards and generous mudflaps, those pulleys are vulnerable to picking up dirt, debris, and being fouled in the woods by sticks and such.
None of those concerns obtain with a stock Rohloff-only installation that uses some means
other than a spring-loaded tensioner to keep the chain properly tensioned.
Before getting my Rohloff, I was really concerned about the gearing. Would the steps be too wide? Would I terribly miss the logarithmic gearing of my der mechs (wider steps between gears in the low range, narrow steps at the upper end)? What about overall range?
Since half-steps are hard to configure with modern wide-range front derailleurs and 9-speed gearing, my first adaptation was to the crossover 9-speed gearing on Sherpa. It
wasn't my familiar 5-, 6-, or 7-speed half-step. I went through three cassettes before I got it right for myself, ending up with a 12-36 at the rear and 22/32/44 up front. With chainline considerations and one duplicate gear in the mix, I effectively had only 13-speeds out of 27 theoretically available, and it required a lot of double-shifting to get any next available gear in the progression. By the time I actually found my desired gear, my momentum had dropped off to where it wasn't quite right.
By contrast, the switch to the Rohloff gave me 14 distinct and usable speeds, no chainline concerns (and no looking back inside my right thigh to see which cassette cog the chain was on), no duplicates, and the same range.
I started with a 40x17, and found I never used the upper two gears and wished I had two that were lower to match the final setup on Sherpa. It was the lowest "Rohloff-legal" combo at the time.
A switch to Rohloff's newly approved 36x17 has transformed the Nomad positively for my use. I no longer have the two unused upper gears, I picked up two below, and all the combos in the middle fell spot-on the familiar for me -- even the direct-drive Gear 11 cruising gear and the next-most used combo just above and below it. The 1-7 low range has gears from 15-33 gear-inches, and it truly serves as a Low Range for me. It is quieter when coasting and noisier when pedaling and suits me fine. Gears 8-14 are my Most Used Upper Range, silent or nearly so in pedaling and louder when freewheeling. The upper range goes from 37-80 gear-inches. I spend most of my time in 55" (direct-drive Gear 11), or 62 (Gear 12) as I do on all my half-step derailleur bikes; they're just my favorite gears when combined with my fast, light 110-120RPM cadence. My Headwind Gear is my old favorite on the other bikes at 42 gear-inches (gear 9, still in the Upper Range).
Life is Good for
me now with the Rohloff 'cos the 36x17 is closer to my old, favored half-step arrangements in terms of having quick access to my old-most-favored combos. I find the twist-shifter can cover as many as 7 cogs in one of my twists (I can approach it from inline or from the end like a doorknob on my T-bar setup), and when I need/want big steps at the low end, they're just a multi-shift Big Twist away. Finer steps might be nice at the upper end, but to be honest they're just fine given my range tops out at 80". At my preferred 110-120RPM cadence, that 80" high is good for speeds of 26.4-28.8mph/42.2-46.1kph; plenty fast for me on level ground. I usually cruise flat, windless roads at 17-21mph/27-37kph in my 55" gear at the same 110-120RPM. Anything faster (usually downhill), I coast.
I don't really know anything about your riding style, Paul, but your choice of any gearing and setup will depend in part on whether you're a masher or a spinner. Mashers (low-cadence cyclists) can usually better tolerate wider steps between gears and don't much mind varying their cadence as required. Hummingbirds like myself need finer gear steps to keep in our preferred rev ranges.
To summarize the above...
1) IGH drivetrains require much less regular maintenance than do derailleurs.
2) Some IGH drivetrains are less suited to touring than others, due to overall range and steps between gears.
3) Some IGH divetrains are less suited to hybrid gearing setups than others (see 2 above).
4) Generally, the added complication of hybrid gearing detracts from the low-maintenance advantages of the IGH. In exchange, you can sometimes (Rohloff) get a wholebuncha gears in a superb pattern with easy access.
5) If you can find the high/low gears you need and the steps are where you expect them, you'll likely be happy with a switch to an IGH drivetrain; less so if you can't.
6) Your use, pedaling style, and terrain will also determine your Happiness Quotient™ with an IGH conversion.
I hope something in the above will help. For my two cents' worth, if I were in your position (and I once was), I might consider a rualexander-like conversion of the Sherpa and see how it went. If I found myself missing some gears or the steps were still too wide, then it could be easily hybridized with a rear tensioner, a modified front mech and shifter, and a second chainring. If the whole thing proved unsatisfactory, then there's the option of selling-on the Rohloff stuff and converting to derailleurs again or transferring all the components to a Rohloff-specific Thorn frame with eccentric BB and calling it good, selling-on the Sherpa frame.
Hope something in this helps.
Best,
Dan.
[Edit for typos and for some reason I wrote Peter as Paul.
]
