Thursday, February 12, 2009

Shaft Drive bikes

Well, Monday I encountered my first shaft drive bicycle. If you haven't at least heard of such a thing, I'd be surprised. Along with "automatic shifting" bikes that crop up every few years, the "chainless" bicycle in one form or another periodically gets trotted out as the biggest "new thing" to hit the bicycling world ever.

Okay, so that makes me sound like a luddite, or in the bicycle world a "retrogrouch", I suppose. But the fact is that both of the above ideas have been tried many times in the past, with varying degrees of success, yet the chain drive bicycle with gears operated by the rider still remains dominant. I've got some ideas why, and we'll get to those shortly. First though, some pictures:

To the left here is the business end of the bike... showing the drive train. Notice the total absence of a chain. The first thing that struck me (after "what's wrong with this picture") was how tidy it all looks. Let's face it, chains tend to be dirty, and a chain type drive train, especially on a derailleur system, looks kind of cluttered compared to this. And that in a nutshell is one of the primary selling features of shaft drive bikes... it's tidy. Read the ads, and that's what they focus on... how it does away with all the messy aspects of a chain drive. And I can't argue with that... it is a tidier setup.


To the right you can see a closer view of the front end of the system. Where you would customarily have a chain ring or multiple chain rings attached to the crank, here you have an enclosed gear box, containing what I believe is a set of bevel gears... two cogs at 90 degrees to each other, with the meshing, toothed faces angled to 45 degrees, so they convert the rotary motion of the pedals and cranks in one plane into the rotation of the drive shaft in another plane. And you can see, there is no chain or toothed chain ring to make a mess of your pants leg.


And here is the rear of the system. Obviously that is the back end of the drive shaft, and inside that housing by the axle is another set of bevel gears that convert the rotation of the shaft back into rotation in line with the wheel and cranks. It's hard to see in this picture, but the whole system basically connects to a Shimano Nexus 7 speed internally geared hub, a fairly standard bit of bicycle hardware, and very reliable and pretty efficient. And again, no messy chain or exposed sprockets back here either.


So if it's so clean and tidy, what's not to like about it? Well, first off, it's kind of heavy... heavier than a single chainring, sprocket, and chain would be, driving the exact same Shimano hub. How much heavier? Well, I don't know exactly, not having the specs, but it's probably not a huge weight penalty, and honestly, I don't stress that much over a little weight on a bike, especially if it's not a competition style bike.

A much bigger issue for me is the proprietary, or "single source" nature of some of the vital parts. I give this manufacturer bonus points for incorporating the Shimano hub, instead of using something of their own proprietary design, but the drive shafte and gear boxes and cranks ARE proprietary. Why is that a problem? Well, an awful lot of companies that come up with "innovations" in the bicycle industry don't survive, and if this company were to go out of business, you'd be hard pressed to find replacement parts. For that matter, even with the company in business, you're not going to be able to walk into your local bike shop and expect them to have the parts on hand. I'm sure the manufacturer does have provision for shops to order parts, but that's not always as easy or quick as getting more standardized parts, such as chains, cassettes, and chain rings, which are all pretty well standardized in the industry. (Okay, so there are in some cases multiple "standards", but availability of spare parts is rarely a problem.)

And finally, one thing you don't see the manufacturer touting as a virtue of this system is its efficiency. There's a good reason for this... it's not that efficient. Way back when I was in graduate school for technical theatre production, we had a couple of classes in physics and machinery for the stage, and one of the things I learned there was that for efficiency and reliability, it's hard to beat plain ol' roller chain and sprockets, of which a bicycle drive train is a prime example. In terms of energy lost in the process of transmitting power from point A to point B, few other transmissions are as efficient.

So while there are certainly some benefits to the system, all in all, I'd rather have a chain drive bike, with perhaps a good chain guard or fully enclosed "chain case" to keep me clean. That way I can walk into any bike shop and get replacement parts or have it serviced without any concerns about the shop never having worked on one before. And I'll have a lighter, more efficient bike to boot.

The maker of this particular bike is a company called Dynamic Bicycles. Look for them on the web at:

http://www.dynamicbicycles.com/

10 comments:

Teck said...

Great post – quite enjoyed it! I agree that chainless bike alternatives will not necessarily replace chain bikes. Having said that, I also believe that having different bike alternatives may bring new (or revive old) interest in riding which could only mean more "ridership".

One thing I want throw out there is that efficiency loss can also occur in chain systems especially when the components are not properly installed, maintained, tuned, and cleaned. Because the shaft drives are fixed and covered, it makes them less prone to damages due to moving parts and exposure to weather conditions.

Shaft drives may not be pro riders or racers but they make great commuter bikes! If the limitations of a shaft drive are still too daunting – the other chainless alternative is the belt drive systems.

Full disclosure – I am from Abio Bikes (makers of folding shaft drive & belt drive bikes) so I'm biased. =)

beth h said...

I loved this piece. I have seen and ridden a shaft-drive bike, and while it wasn't for me (I love the sound of my whirring freewheel and the purr of a well-aligned chain-drive) I appreciated learning something about the technology.

I think that most non-performance cyclists (read: racers and/or club riders) don't worry too much about "efficiency" in a bicycle. But lots of riders of all kinds think about weight. They want their next bike to be lighter than their last. They also want the bike to be easy to take care of. If any of them bother to educate themselves about the current state of the shaft-drive market, the difficulty in finding parts (and a shop that can service the bike) may give them pause.

Thanks for sharing.

Tim said...

Thanks to both of you for your comments! I do think there may be a place for these bikes in the market, but I think folks need to think long and hard about them before taking the leap.

Gaell said...
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Jax Rhapsody said...

I like these new shaftdrive bikes.I've not had the chance to see or ride one but. Thhere is a slight loss in power tranference(said 95% vs 98% in chain) and they wiegh about 1 or 2 lbs more than a chain driven bike. But if it works with motorcycles, why not bikes?

You want to put more power down, run two shafts, want more gears run a front hub. Sure they are heavy but power to wieght ratio depends on the rider. I want one of these to put on a trike. I think somebody makes a kit you can buy. They may slowly catch on or it may be like the VCR vs Beta Max.

Dennis said...

I heard from a mechanic that on a Motorcycle the shaft drive has an efficiency loss of about 25%. That's a huge difference, especially if you're the motor.

Ted Danielson said...

I love biking; It's a hobby, and I ride every day. I commute to work on a bike (about 12 miles a day), and in the evenings and weekends I ride in a club.

That said, I think that a "cleaner" bike is a great option for commuting. I have always hated how biking to work ruins my clothes, and would gladly trade out what seems to be a small amount of efficiency for quality. I imagine that for these to be successful, it is important that the bikes are designed for the likely target market - very low maintenance, reasonable weather and security features, as well as decent cargo options.

Anonymous said...

As for the service/parts hassle: don't the drive shafts have lifetime warranty?

Anonymous said...

As for the service/parts hassle: don't the drive shafts have lifetime warranty?

Tim said...

I don't see any mention of a lifetime warranty on the site linked in the post. It's possible there is, but it's going to vary from brand to brand. Also, if the manufacturer goes out of business, or their distribution channel runs into problems, you're stuck, as the parts are unique to that brand. Not necessarily a deal-breaker, but something to be aware of.