Bicycle Driveline Efficiency, Chain vs. Shaft

[williamthorn]

I am an avid mountain biker and a mechanical engineer. Release of the internal geared rear hub has recently made shaft driven wheels possible to the biking world. It has however raised some serious questions in my mind.

We all know that chains are a very efficient means of transmitting power. In ideal conditions they will reach into the mid-upper 90 percent efficiency. However, the mountain biking operating environment is far less than ideal. The chains are constantly churning just over loose dirt and gritty sand, getting caked with mud and getting immersed directly in streams. Furthermore, most bikers only lube the chain well after it becmoes noisy. Which is obviously less than ideal. I am wondering if anyone has any sort of information about their efficiency drop operating in such environs.

An obvious alternative is shaft drive (

http://www.dynamicbicycles.com/).

All greased connections are encapsulated to eliminate much of the dirt contamination. However, the losses inherent in the system are greater.

If anyone has any information that might shed some light on this issue it is greatly appreciated.

Regards,

William Thorn

 

[ivymike]

well, it's cool looking if nothing else... I like this line from the site:

Internal gear hubs are designed to require fewer gears to cover a wide range of gearing. For instance, each gear change on our bike is like changing 2-3 gears on a chain bike - so you can transition quickly from hill climbing to cruising with a quick twist of the wrist.

My first reaction is "there's a reason my mountain bike has 21 "gears," and it's not because the chain needs help climbing from the little ones to the big ones. It's because sometimes I like using number 18, but if it gets a little steeper, I might go for number 19, or number 20, and if it's really bad then I can always fall back on number 21. If I wanted a bike with only 10 gears, I could go get one of those, and almost never have the "right gear" for the occasion.

 

[williamthorn]

Thanks for your input Mike...

I am one of those screwy guys that only has one cog and one chain ring on my only bike. Is it efficient in most situations? Absolutely not, but it gets me a great workout in less time.

Most recreational riders I know don't regularly get out of the middle ring in off-road situations in this area. Remember that most new mountain bikes now have a 9 cog rear end for 27 different gearing combinations.

I saw a bunch of shaft driven comfort bikes while in Asia this summer. Since the chainline is the single largest area of maintenance on any bike, I thought that shaft drive would be great. This is the first time I have found a geared shaft drive bike.

 

[electricpete]

I took a quick look and saw they moved all the gearing into the back hub. But there is still a chain to transmit power from the pedal to the back hub, right?

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[williamthorn]

The dynamic bike uses a shaft drive to transmit power from the cranks to the Shimano Nexus internally geared hub.

Shaft drive has been used in asia for years. There the majority of bicycles are used for daily transport. They are constantly exposed to the elements. Furthermore the majority of bicycles are only one speed. I think that shaft drive is more reliable hence its popularity in asia.

 

[electricpete]

Ah - that makes sense.
Thx William for some interesting stuff.

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[peteswift]

My understanding is that Chain is more efficient where as the shaft drive is slighlty less so.

In commparrison; the efficiency of the chain is about the same in all ratios however the planitary types engage and disengage additional stages so the efficiency changes dependent on the ratio you are using and the number of stages.

Hub gears are totaly enclosed and operate in a protected enveironmnt. Chain are open to the elements and must be cleaned re-lubed etc.

I get about 2000 miles from a chain and then change it. Using approx 3 chains for each casette. The chain doesent fail but becomes difficult to change.

 

[ivymike]

I have no idea whatsoever how many miles I get out of a chain. My bike, which I purchased used for $180 in 1994, still has the same chain on it that it had when I bought it (been through many sets of ridden-til-bald tires). I used to do 90%+ of my commuting by bicycle (probably 15 miles/day or more, 5+ days/wk), and recreational (single track paths) riding on top of that, but the bike use dropped significantly in late 1998 when I moved to the midwest. Nowadays the bike probably gets a hundred miles per year, give or take. The chain is a bit stubborn when I shift, but I don't feel like spending any more than I absolutely have to spend to keep the wheels turning.