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Can they be dangerous? I know a fixie will easily eat toe or finger. How do shaft drive bikes fair in this area?

How are you measuring this? According to my experience with dyno testing and the engineering books written on the subject, the difference between chain drive and shaft drive systems for transferring power is much larger than 5%. More like 15%.

Az

They look intersting and if I was rich I would buy one just to have one, but for actual commuting you can get an all around higher quality bike for the same price ranges (less at year end sales even) and in a better fit for almost anyone. Not to mention the difficulty in getting parts for immediate repairs.

I can see how they would be a good choice for rental and fleets though. Fewer parts to break and easy to keep a few spare shafts on hand. I would bet the downtime is less overall as well since it looks like less adjustments would be required.

Can't address efficiency issue without clarifying my basis for comparison.
The rest of my bicycle rental fleet consists of good quality chain driven hybrids and mountain bikes that normaly retail for CDN$350 to CDN$450.
Even when new and assembled by a professional bicycle mechanic there is no way you can compare the efficiecy of the chain drive to the theoretical efficiency mesured in a controlled "lab" test.
I inspect and maintain my bikes on a regular basis but normal wear takes its toll very quickly particularly on the chain drive system and it is a constant stuggle to keep the chain drive system running at peak efficiency.
On the other hand, I must say that the shaft-drive internal hub system maintains a consistant level of efficiecy over an extended period of time with vey little maintenance.
Bottom line, mine is a real life comparison!

When comparing chain/shaft drive efficiency, I should not have used a specific number (5%). I don't have any way of measuring the difference acurately. It's a gut feel when test riding my bikes. Could be 3% could be 8%. In any case, it's minor.

The shaft and hub are enclosed. The only exposed moving parts are the wheels.

Thanks alot for sharing your real life, practical experience w/t chainless bikes. Have been considering purchasing the Crosstown 8 to replace my chaindrive/derailleur commuters(1 road, 1 mtb). The debates pro and con re chainless/shaftdrive have been by some really informed people. I've read several here on BF with interest. Can't recall reading anything w/t day in/out perspective you've shared, however. Alot of arguments have taken issue about the loss of power-transfer and the fact that the bikes feature 100+ year old technology. Like Felix Wong's blog on airless tires(felixwong.com) your observances seem fair, balanced and are based on experience not data. You need to realize a profit from your bikes in as much as one who commutes by bike needs a dependable, low maintenance ride. Now if a commuter w/shaftdrive, airless tires, internally geared hub, mechanical disc-brakes and tri-spokes is available somewhere, sign me up.

Much like buying a manual transmission, I can't stand a 10% decrease in efficiency due to being lazy. I'll take my chain.

Looks cool though, but losses are no fun.

One of the manufacturers was going to send me one to review for my blog, but I was not able to commit the time when it was briefly available. I hope to do a test on one in the future though.

Can someone please explain why a shaft drive would have a decrease in efficiency? Where is that few % escaping to?

My guess would be that there would be more friction than a chain/cog. But we will definitely see more chainless bikes in the future. For recreation and commuting, they hold a lot of appeal. A shaft drive folder with 20" wheels could be the ultimate everything bike for a lot of people.

Without going into the physics, here's how it works. The energy you create by turning the crank is transfered to the shaft through a pair of bevel gears, friction on the gears consumes some of that energy. The crank loses some energy to torsion. Next, your energy has to change directions again to drive the hub, another pair of bevel gears, another loss of energy.

the key is indeed that there are two bevel drives, each time you change the direction of energy 90 degrees you lose some of that energy to heat. the alignment of the gears are critical for good efficiency, it is very important that the connection be rigid. any torsion or twisting of the drive shaft will be given back during a dead portion of the power cycle with very minor loss. The main problem is a 90 year gap in development for the bicycle. I have seen no relevent information relating to the efficiency of a bicycle shaft-drive versus chain drive.. I have seen many comparisons though for motorcycles and much older data relating to cam drives.

tire changes would be another problem, QR skewers would not work.

The main plus for a fully developed shaft drive is that it's efficiency would top a worn dirty chain no problem as well as keep a commuters pants clean... a chaincase would all but eliminate chain wear and address the greasy pantleg issue.

I would welcome the addition of a modern shaft drive to my collection.

anyone interested in "efficiency" should go direct drive, get a unicycle or penny farthing.

bicyclists have been a conservative lot, it's also unfair to compare anything to a machine that has been developed and refined over the last century to become what we know today.

Nothing new under the sun (Belgian FN bike ca.1908) :

The carbide lamp is a nice touch.

Great post. I’d love to see an efficiency comparison of a traditional chain drive bike and a direct drive bike after a couple months of commuting use. The winters here in Portland are pretty brutal on the drive train, lots of muck picked up, water seeping in, etc.

I’ve started commuting recently with my trusty-old 1991 Diamond Back Ascent. After a couple weeks of it I’ve decided to make a go of year-round commuting here in Portland, OR. After looking at the amount of maintenance required in keeping the typical bike drive train maintained in our climate, I’m thinking that the real-world efficiency drop between the two types of drive probably isn’t as steep as the controlled condition 15% being cited from “testing.” Direct drive is looking attractive. In the real world, most people have a life that doesn’t revolve around their bicycle. They aren’t going to devote much time to keeping a bike running at 100% of potential efficiency.

I’d like to see a direct comparison of the two systems after a couple of months of typical maintenance neglect under our winter commuting conditions. If the real world efficiency loss is only 5%-10%, I’d be happy to trade that off for the reduced maintenance costs (both time and money). My big concern is hill-climbing capabilities. Hills during a commute are unavoidable out here.

I also wonder how the efficency varies with rider output. As in, one might expect linear losses until things start flexing a bit, then perhaps some exponential losses. On either system, I should say. So, wild guesses here, perhaps chainless may have large losses at high outputs (say 10%) but much less at casual speeds (say 3%), while a "good" chain drive maybe 1% always (ignoring chainline losses). Wild numbers, just another tangent to beat a horse with.

As a rental bike, this does seem like a winner. Odds are, the customer (renter) isn't likely to be doing any work on the bike; complexity of repairs may be over-riden by their infrequency (from the perspective of the shop). I'm not going to say that all renters are going to be laid back while riding--but again, I'll guess that most are going to be. So, a bike on which they won't get dirty, and won't have to deal with (egads!) two shifters, they would probably be quite happy.

For a commuter or a casual rider, again, sounds like a nice beast. Once I stop buying $5 bikes, maybe I'll check one out.

That is one concern -- no easy way to change gearing. IIRC, it's "normal" or "sport", with the lowest gearing being like 36 gear inches for "normal" and 30 gear inches for "sport" (all gears reduced the same percentage). No way to easily change out cassettes or chainrings to fiddle with overal gearing.

You can certainly change chainrings. And we're talking 7 and 8 speed hubs. I'm pretty sure people made it up those same hills with a single speed, or a 3 speed hub.

So forgive my complete ignorance here - I'm trying to understand this better. With my 8 speed hub, if I want to change the gear ratios over time, I can simply get a different rear cog and put it on. Is there something analogous on a shaft drive bike? (Here's a visual since I can't visualize for crap.)

Oops. Nope. I blame all this on my conversation with Kemmer about the dual drive on folding bikes. I can't brain today, I have the dumb. I'll be quiet now.

Oh, you have mail.

That's too bad. Being able to fiddle with the gear ratios is one of the cool things about internal drivetrains.

Just whack a 12 bolt posi with 4:10 gears under that bike...

A 5% energy loss is probably not really noticeable. It's only 1/20 of a rotation if you want to look at it that way.