Gearing

It’s a fact that a typical ‘bent needs wider and lower gearing than a typical upright bike.  Just how much wider and lower is a subjective, sometimes technical, and oft’ debated topic that can make large chunks of time vanish.  I’ll try to keep this brief.  I use Gear Inches in the following discussion because it is commonly used in trike specifications and it provides a good way to make relative comparisons between drivetrains.  Consult a Gear Inch Calculator to see how Gear Inches translate into speed.

It’s easy to fall into the “more is better” point of view.  Before I’d even ridden a tadpole trike, when my friend Paul and I were planning to build what would become my first, we already had a sense of our “ideal gear range.”  Mine was 12 – 120 gear inches based on very little data.  Paul comes from more of a road racing background, his ideal was 20 to 130 gear inches and no more than a 10% spacing between adjacent gears.  By combining a Schlumpf Mountain Drive with a SRAM DualDrive we could satisfy all except maybe the spacing while playing around with some cool technology.  However it quickly became apparent that this range was much lower than I could practically use.  I dumped the Mountain Drive and ran happily with the DualDrive for several years.

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Insanity: DualDrive and Mountain Drive

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DualDrive

I purchased an ICE Q in 2008 with stock 26/36/48 in front and 9-34 Capreo cassette in the rear, no IGH, and ran that way after I decided my DualDrive hub was too noisy.  I missed the convenience of the IGH and hated having to put the front derailleur back on but the gear range was about right for me.  Even though I could handle any hills with the DualDrive setup, the lower range didn’t hurt.

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Stock ICE Q (and Sprint), Capreo casette

After about a year with the stock Q configuration I wore out the chain and cassette, and couldn’t bring myself to replace it with another expensive Capreo cassette.  I built up a new wheel with a standard Shimano XTR hub and ran with an 11-34 cassette, intending to compensate for the shift down in gearing with some bigger rings in front (not an easy task BTW).  In this configuration I found that I spent most of my time on the big ring in front, whereas with the stock Q I spent it on the middle ring, which I prefer.  When I began planning for a cross country tour I decided to keep the lower gearing because I knew I’d be pulling a 9-year-old and all our stuff on the self-supported ride.  Keeping the roughly 15 gear inch low range proved to be a good bet, there were some climbs where I could have used even fewer.  But we never had to walk—that would have been a minor disaster with our rig.  The worst climbs on that trip?  I remember them well.  Beginning with the most difficult (the first two are probably a tie):

  1. Calf Creek to Boulder, UT
  2. Lexington to Love, VA
  3. Gunnison to Maysville, CO
  4. Much of Highway 1 along the California coast

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ICE Q with standard (not Capreo) cassette

Recently I put the Capreo wheel back on the HDQ, figuring that when I give this trike to my wife she’d never wear the thing out like I do.  I’m running the original worn out cassette with a comparably worn out chain and have a new Capreo cassette waiting for the day it becomes my wife’s trike.  So I’m back to the stock Q (same as the Sprint) gearing and am again finding myself on the middle chainring more than the big one.  Two teeth make a big difference.

So here’s what I’d like to achieve with this build:  Roughly the same range as the stock ICE trikes but using an Alfine 11 IGH.  Unfortunately the Alfine 11 doesn’t have quite enough range to achieve this without the help of another source of gears; either another IGH or a front derailleur.  The Rohloff IGH with its 14 gears comes closer, but still not quite there.  And it’s heavier, more expensive, the electric shift capability doesn’t look as developed as the Shimano offering, and you wind up with a big ring up front. I’ll stick with Alfine if I can.

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Rohloff

I don’t want to add another shift cable and/or front derailleur, so the only option is to pair the Alfine with a Schlumpf.  And the combination looks really good!  Using a 20-tooth rear cog, a standard offering for the Alfine, I wind up with a low that isn’t quite as low as what I used for my cross country adventure, but lower than what I was running for years with my DualDrive setup.  I don’t anticipate needing to haul a 9-year-old and 200 lbs of gear again, so taking a little hit on the low end seems reasonable.  And the high end, while lower than my “ideal” 120 gear inches, still yields about 30 MPH when pedaling at 90 RPM.  I can’t maintain that speed on the flats and am happy to let gravity prevail and just stop pedaling when I’m bombing down a hill big enough to exceed these speeds.

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Speed Drive and Alfine 11, first try

Ahh, but there’s a catch.  If you run this configuration in my Gear Inch Calculator you’ll notice some red:  The Gear Ratio calculation is less than the minimum specified by Shimano for Alfine 11.  This calculation is the number of teeth in the front chainring divided by the number of teeth in the rear sprocket, and represents the amount of mechanical stress to which the Alfine is subjected.  It’s hard to say how important this limit is.  The Sheldon Brown web site downplays it as follows:

Some internal-gear hubs are not rated for the stresses from extremely steep climbs and a heavy load, a potential problem with do-it-yourself hybrid gearing. Usually, manufacturers rate hubs in terms of the acceptable chainwheel/sprocket ratio, but this rating really amounts only to “we will make it so hard to pedal that you will get off and walk.” Pushing a lower gear up the same hill actually stresses the hub less. A small rear wheel and smooth pedaling reduce stress on the hub.

I’m more inclined to heed the limitations.  There are limits to any design and it isn’t in Shimano’s interest to place arbitrary restrictions that make their hub less marketable.  I’m guessing there’s a Shimano engineer somewhere who stands by these limits.  If I change the rear cog to 18 teeth instead of 20, also a standard cog for the Alfine, the Gear Ratio of 1.78 at least rounds up to Shimano’s lower limit of 1.8.  The resulting gear range trades off some low end for additional high end that is probably unusable for me.  It does one positive thing though:  it gives the 1:1 gear of the Schlumpf, the gear with no planetary losses, a range that will probably suffice for the bulk of my commuting.  This means I can keep the Schlumpf in it’s most efficient gear until I’m either cruising fast or going downhill.  And it’s about the same low end as the DualDrive setup that I ran for several years so I know I can make it work.  I think a 32 tooth chainring in front and 18 tooth sprocket in the rear could work, with a fallback of switching to 20 teeth in the rear if I feel I’m lacking on the bottom end and am wiling to ignore Shimano’s load limit.  It’s close but I think the Alfine 11 is still in the running.

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Speed Drive and Alfine 11, final

A note about % change between adjacent gears.  In an ideal world I’d combine the above gear range with small (between 6% and 10%) spacing.  Narrow spacing allows you to make small gearing adjustments to maintain constant cadence.  Racers like this because it allows them to operate more of the time at optimal aerobic efficiency.  I’m not a racer and have never missed having narrow gear spacing.  Particularly on a recumbent, I need the range more than I need narrow spacing.  And for me, the benefits of an IGH far outweigh any benefits of narrow gear spacing.

One final thought.  During a recent visit to Utah Trikes I was surprised to learn that one of their most popular IGH’s is the Schlumpf High Speed Drive (HSD).  This is the front hub that gives a huge 150% jump in gearing vs. the 65% jump of the Speed Drive that I’ve been discussing (the Mountain Drive I used at the very beginning of my trike career had the same jump, but down instead of up).  Further, they regularly pair the HSD with one of the Alfine hubs.  This makes no sense to me.  If you do nothing to my final Alfine 11 gearing choice (above) but switch to the HSD, you wind up with at least 4 gears that are unusable at the top end when shifted into overdrive.  This is using a 32 tooth front chainring instead of the standard 27 that comes with the HSD; using a smaller chainring exceeds the Alfine 11 load limits.  So too does switching to an Alfine 8 hub which has a more restrictive lower limit than the 11.  Clearly Utah Trikes, like the Sheldon Brown site, doesn’t take much stock in these limits.  But even ignoring the load limits, much of the gear range with this combination is unusable.  The Speed Drive seems like a better choice to me when paired with the Alfine.

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High Speed Drive and Alfine 11

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4 thoughts on “Gearing

  1. mkzig

    These drive combinations with their strengths and limitations make a lot more sense now. Thanks! I had a great time re-reading the account of the ascent from Calf Creek to Boulder, especially observing the scenery in geologic time. Not only would a two-wheeler fall over, but the tires might rot and fall off in one or two revolutions…
    mz

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    1. Kurt Post author

      Glad it helps! I finally had to write all this down, it was making me crazy. If I ever get this thing put together we’ll have to test it out together on the Calf Creek ascent.

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  2. Pingback: Recumbent Belt Drive | A Seasonal Commute

  3. Pingback: Life After Alfine | A Seasonal Commute

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