09
Sep 2010
by don

Cargo bike transmissions

I’ve focused rather heavily on cargo bike brakes in recent blog posts (like here), so I thought it would be a good idea to round things out with thoughts on other weak links in my cargo bike hardware.  After a year of biking in Copenhagen, and another year here in Seattle, the components that have required extra maintenance or occasionally interrupted my ride are these:

  • Brakes
  • Gears
  • Chain
  • Tires

The guy who built my Hammer Truck/BionX cargo bike knew that a flat tire would be challenging – especially if I had to change the rear tire under the cargo bags and with the added complexity of the hub motor.  To forestall that scenario, he installed extra heavy-duty tires filled with puncture-healing gel.  He wanted my tires to be “bullet-proof.”  Although I had several flat tires in Copenhagen, I’ve had no similar difficulty with my cargo bike (knock on wood!)  I haven’t even needed to top off inflation of the tires during the past year.

The drive chain was another source of problems in Copenhagen.  Occasionally, it would stretch enough to start falling off my crank when I went over big bumps.  I took it to a bike shop where a mechanic would re-tension the chain, and everything would be fine for a few more months.  On my cargo bike, with a longer chain and heavier loads, I feared chain problems would be more frequent.  Fortunately, that hasn’t been the case – no chain problems during the past year.

But alas, my gears have not been trouble-free.

The phantom gear and the wedged chain

Last week, my kids returned to school, and my 4th-grader and I resumed our daily journey up the hill to his school.  I have this deal with him: if he rides his bike twice during the week, I’ll give him a free ride on my bike on the third day.  The other two days he walks.

A couple of days ago my son was riding his bike, and I was riding the cargo bike without motor assistance so that our speed and effort would match.  To tackle the steepest part of the hill, I shifted into my lowest gear.  It took me a moment to remember: I don’t have the lowest gear.  This is part of the compromise I made when incorporating the BionX motor.  The width of the motor precludes a full 8-gear cluster.  My rear wheel has only 7 gears, but my shifter still shows eight.

My bike builder solved this mismatch by compressing the range of the shifter.  This allowed me to select only gears 2 through 8.  I hit a stop before I got to gear 1.  That worked fine for awhile, but the tolerances were pretty tight.  As time passed, there were other gears I couldn’t select.  I took the bike to a different shop, and they brought back the missing gears by expanding the range of the shifter.  Now there is no stop at gear 1; I just have to remember that there is no gear there.

When I temporarily forgot that important fact, the chain fell into the gap between my biggest gear and the hub motor.  Unfortunately, that gap is just wide enough so the chain can wedge itself so snugly that it can’t be extracted without tools.  It took me at least ten minutes to retrieve a couple of screwdrivers from my house and perform the necessary operation.  I arrived at my son’s school late and with very dirty hands (cooking oil works great to loosen tough chain grease from your skin, by the way).

This was just the latest episode in my love/hate relationship with bicycle gears.  I love the beauty and efficiency of this transmission system, but it still requires too much care and maintenance.  Not too mention the fact that I often seem to be in the wrong gear at the wrong time.  Even after two years of concentrated cycling, I don’t feel that I’ve mastered the art of smoothly shifting to precisely the right gear for the situation.  If biking is going to achieve broader acceptance, more fool-proof transmissions will be required.

My bike in Copenhagen was superior in this regard.  It had a 3-speed hub with internal gearing.  Shifting was smooth and easy, and there were no fiddly adjustments or maintenance required.  Three speeds were fine in the table-top flatness of Denmark.  One gear would probaby have sufficed if it weren’t for some pretty stiff headwinds.

Hubs for hill-dwellers

Rohloff Speedhub

Hubs with more gears and wider ranges have been available for at least a decade.  One example is the Rohloff Speedhub with 14 gears and an impressive 526% ratio between its highest and lowest gears.  It provides low maintenance, smooth shifting, shifting while stopped, and very reliable operation.  When you see the cut-away of the mechanism inside the hub, you’ll probably agree this is a miracle of engineering.  Unfortunately, it requires a miraculous number of dollars to buy: over $1000 on Amazon last time I checked.

NuVinci mechanism

On the day I wedged my chain, I coincidentally stumbled on an announcement for a new version of the NuVinci hub.  Unlike other hubs, NuVinci uses a clever system of balls rotating in oil to provide a continuously-variable transmission (with a 360% range) rather than discrete gear ratios.  The main disadvantages have been weight and price, but the new version (NuVinci N360)  has reduced both (less than 5.5 pounds and $350). 

Shimano Alfine 11

When I asked a cargo bike dealer about the NuVinci hub, he gave it a thumbs’ up, especially now that the weight has decreased.  But he was also getting quite excited about Shimano’s new 11-speed hub with a 409% range (Alfine 11).  If it debuts at $419, as has been speculated elsewhere, this will also be a hub to consider.

Stuck with my gears

As you can probably tell, I would ditch my derailleur and gear cluster for one of these hubs immediately, except for one major problem: my BionX motor is mounted exactly where these hubs need to be!  To me, this is the most serious disadvantage of a rear hub motor: you’re locked into the traditional bike transmission.  If this is an issue for you, perhaps it’s enough to give bikes with a front hub motor (like the elMundo or Electric Ute) a second look.

In my opinion, a hub transmission on the Electric Ute would be a pretty interesting combination because of the Ute’s torque-activated assistance.  To change your level of effort, you simply change gears, and the motor adds assistance depending on the level of torque you’re exerting on the pedals.  On the elMundo, you need to choose both the gear and the amount of electricity to use.  To my mind, that is one degree of freedom too many.  When I start to climb an incline, do I lower the gear or increase the motor effort, or some combination of both?  Perhaps some riders will find joy in mastering that art, but I have too many other things to think about.

Updated recommendations

It has been a few weeks since I published my last post comparing the elMundo, Electric Ute, and Transport+.   I’m hoping that my somewhat breathless description of the Transport+ doesn’t leave the impression that I think it’s the “best” bike.  That determination depends on what you want to haul, the geography over which you want to haul it, and who you are, physically and mentally.

For example, I’ve had a tendency to discount the Electric Ute because of its smaller motor and unimpressive performance on a steep hill.  These are important considerations for me, personally.  But if you have a longer, flatter commute, you might appreciate the Ute’s battery, which delivers 13 amp-hours compared to 10 for my (and Trek’s) BionX battery.  With its less thirsty motor, the Ute might have a 40-50% greater assisted range.  And at least one dealer I know of is selling the Ute at a discount that competes with the elMundo’s low price.  When you consider the possibility of upgrading to a hub transmission (I would love to see that as an option from Kona!), the Ute is a bike that is difficult to say no to.

If you’re planning to carry heavy loads, you should still consider the elMundo, unless you’ve got hills that would make the extra 30-40 pounds of its steel frame an issue.  I like the heavy-duty frame and the option of front and rear disc brakes.

With Trek’s Transport+, we’ve entered the awkward period between the announcement and the actual release of the bike.  Since we can’t easily get our hands on one for the next couple of months, speculation is ramping up.  One concern that has been hotly debated in cargo biking forums is the Trek’s weight distribution.  Like my bike, the Transport+ carries its motor and battery in the rear.  But the Transport+ battery is mounted waaay back (to incorporate the tail light) and quite high.  The side racks extend farther behind the rear wheel than any other cargo bike I’ve seen.  If you’re carrying a big load, will there be enough weight on the front wheel to steer precisely?  Will you be able to control the momentum of heavy cargo back there during a quick turn?  Of course, Trek claims this is not an issue, but time will tell.

It saddens me that I can’t include my Hammer Truck in this list of pre-built electric cargo bikes.  I’ve written a couple of emails to Rans, asking if they have any plans to include a motor as an option on the Hammer Truck.  I haven’t gotten a response, or even acknowledgement that they’ve received my emails.  That’s too bad, because the crankforward design of the Hammer Truck is, in my opinion, a significant advance in cargo bike design.  The lack of pressure on my hands, shoulders, and crotch make it more comfortable to ride than most bikes.  I wish it were more competitive in this arena.

Dreaming of a maintenance-free bike

Shaft drive bike

It’s hard to imagine that any bike will ever be maintenance-free, but with heavy-duty tires, a hub transmission, and good brakes, it’s possible to reduce maintenance and breakdowns.  The chain is the only item left in my list of trouble areas.  There are several companies that offer bikes with a shaft drive instead of a chain (and internal hubs, of course).  Nothing like that for a cargo bike yet, but perhaps that will be the next step in the evolution.

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  • http://www.flickr.com/photos/markstos Mark Stosberg

    Thanks for the insights.

    Here’s a review of the NuVinci hub by a family using it on a Yuba Mundo to carry two kids on:

    http://longwalktogreen.blogspot.com/2009/11/nuvinci-longterm-follow-up.html

    • http://mycargobike.net Don

      Thanks for the link, Mark. That review and the glowing comments that followed only increased my desire for a NuVinci hub (which unfortunately remains impossible for me in the near future). But it’s nice to hear from other families who want their “mission-critical” cargo bikes to be as reliable and maintenance-free as possible.