A greaseless chain, what's not to love?

[Apennine]

http://tech.fortune.cnn.com/2012/07/31/gates/

[Alan]

Yeah, belt drive has some real nice features...nearly no maintenance and they aren't greasy.

They have some downsides, though, besides price (which would get closer to chain if they were more popular). They're a little bit less efficient, though at some point chain gets worse if it's not maintained. Rumor says they can break or wear prematurely offroad, especially on sharp gravel (I haven't read an actual study of that, though). If they do break, they aren't common stock at most LBS. The variety of sprockets and belt lengths isn't anything like the variety with chain but it's probably good enough for most of us. And, of course, it takes a special frame with openable drive-side rear triangle to slip the belt into place, and the selection of those is small.

One thing that article misses on is where it mentions the gear-range limits of belt drives due to internally geared hubs. While that's partly true, one can run a two-speed bottom bracket like a Schlumpf or Metropolis Patterson to multiply the hub's range and get really quite a wide total gear range.

Cool stuff, I considered it on my dream bike for awhile, but now I'm back to plain ol' chain.

[q`Tzal]

Originally Posted by Alan

They're a little bit less efficient, though at some point chain gets worse if it's not maintained.

The 1st post on the second page of this thread sums it up best.
It seems however that most of the apocryphal "belts are worse than chains" stories eventually reference back to V-belts. A Department of Energy publication expounds upon the types of drive belts. The Gates belt, a synchronous belt, is rated around 98%. Curiously a John Hopkins study from 1999 where the researcher bench tested bike chain efficiency varying tension and both sprocket sizes showed a peak efficiency of 98.6% bottoming out at 81%; this did not include wear factors.
Further it seems that both belt and chain drive in general are more efficient with larger sprockets, to reduce angular friction losses, and higher tension.

Originally Posted by Alan

Rumor says they can break or wear prematurely offroad, especially on sharp gravel (I haven't read an actual study of that, though).

Rumor really should not be the basis of this sort of a decision. Give me a first hand account by the person that was riding it when the failure happened, not the spin from the LBS wrench with decades of pro-chain prejudice, preferably with pictures. I believe it could happen; we see bike tires taken down everyday by the most mundane of tiny sharp debris but very few swear off pneumatic tires for long.

Originally Posted by Alan

If they do break, they aren't common stock at most LBS.

Neither is any high end specialty component; it's the price of being an early adopter. On the other hand it is being stocked an several online bicycle parts stores staring around $45.

Originally Posted by Alan

The variety of sprockets and belt lengths isn't anything like the variety with chain but it's probably good enough for most of us.

True, chain links can be added or removed as needed to adjust length. Often when done without the proper equipment the user has added a new weak spot in their drive line; a "weak link in the chain" you might say.
In addition even in optimal conditions chains stretch as a component of wear; the chain length is always changing.

[canuck]

You have to allow a break in the frame to install the belt, something not required with a chain.

Either a seat stay or chain stay needs to have a removable section. This can create issues with ride quality as well as durability.

[Spiffy]

I just got a new bike a couple months ago with a belt drive... it's a Raleigh Alley Way...

I really like it... it's super quiet... with the internal hub it shifts super fast with barely a sound...

there seems to be a split second of lag as soon as you take off... as if the belt is tightening up... I don't really notice it any more though, was really only the first few rides...

but it's soft, smooth, and forgiving...

I have a belt-guard as well so I really don't have to worry about grease... greasy pant legs and maintenance were the reason I got it...

[Alan]

Originally Posted by q`Tzal

A Department of Energy publication expounds upon the types of drive belts. The Gates belt, a synchronous belt, is rated around 98%. Curiously a John Hopkins study from 1999 where the researcher bench tested bike chain efficiency varying tension and both sprocket sizes showed a peak efficiency of 98.6% bottoming out at 81%; this did not include wear factors.

Thanks for the numbers. I knew efficiency was close, but that's even closer than I thought. It's also impressive how much a chain falls off (and I don't mean off the spockets, which is a whole other issue) under less-than-perfect conditions. No wonder a freshly cleaned and oiled chain has such a nice feel!

Originally Posted by q`Tzal

Rumor really should not be the basis of this sort of a decision.

Yup, that's exactly why I said it that way. This reply was going to say something about not seeing belt-drives in MTB races and gravel-grinder endurance events, possibly due to the lack of promotion by Gates that the CNN article mentioned as well as "pro-chain prejudice." Fortunately I looked first and found this:

Gates Carbon Drive Creates a Belt Drive Mountain Bike Team
May 10, 2012
Building on the success of its singlespeed cyclocross team, Gates Carbon Drive has created a singlespeed belt-drive mountain bike team. Team Gates Carbon Drive MTB will compete primarily in Colorado, with plans to attack the Rocky Mountain Endurance Series, the Winter Park Race series, the Breckenridge 100 and the USAC Mountain Bike 24-Hour National Championships, among others.

The goal of the new team is to increase awareness in the singlespeed race community about the advantages of Carbon Drive, which is lighter than a chain drive, requires no greasy lube and sheds dirt and mud like a bad habit.

Note the link, there, to the Gates Carbon Drive Systems website.

Of course it's one thing for a sponsored racer who gets a new belt every time a nick appears in the old one, but it's something else for an unsupported soloist doing the Pacific Crest route or something even more remote. More evidence needed; time will tell.

Originally Posted by q`Tzal

Neither is any high end specialty component; it's the price of being an early adopter.

Yup, but it's still a consideration. Long-distance tourers in particular don't want to be stranded in BFE waiting for UPS, but it could be a show stopper for commuters relying on their bike to get to work every day, too. Or just carry a spare; it's lighter than chain! (but heavier than a couple spare links)

Originally Posted by q`Tzal

True, chain links can be added or removed as needed to adjust length. Often when done without the proper equipment the user has added a new weak spot in their drive line; a "weak link in the chain" you might say. In addition, even in optimal conditions, chains stretch as a component of wear; the chain length is always changing.

So, another caveat for belt-drive bikes is that they need a drivetrain length adjuster just like single-sprocket bikes; normally either a slotted rear dropout or eccentric bottom bracket (which rules out two-speed brackets). But belts don't stretch like chains so that adjustment is more 'set and forget' than routine maintenance. I wonder how a tension idler (like Surly's Singleator, only made for belt instead of chain) would work with a Gates belt drive?

(Pedant: chain elongation isn't actually "stretch," it's bushing wear, but you knew that already. I call it stretch, too.)

I also wonder how much gear wear there is on belt sprockets over time? For the belt itself, Gates website says "twice the life of bike chains." Are the sprockets still going strong at that point? It implies that they are. What about on-the-ground experience? They have some testimonials on their site, but I want to hear from some independent critics.

[lovedoctor]

Originally Posted by Alan

I also wonder how much gear wear there is on belt sprockets over time? For the belt itself, Gates website says "twice the life of bike chains." Are the sprockets still going strong at that point? It implies that they are. What about on-the-ground experience? They have some testimonials on their site, but I want to hear from some independent critics.

I would guess (a highly scientific and reliable way of making decisions) that a belted sprocket would last longer, because the contact area between each tooth and corresponding section of belt is much larger than the chain link and sprocket. The tooth on a chain drive sprocket is a tiny triangle of metal, compared to the flat, wide, almost paddle-shaped tooth for the belt cog. But, as mentioned above, this is speculation on my part so therefore be suspect of my ramblings. Perhaps Spiffy could report back this time next year?

In the next few months I'll be building up a super-commuter/light-tourer and I'd really love to jump into the belt pool. There are not a lot of non-custom frame makers building compatible frames, but I would think any decent steel frame could be modified by a competent welder to allow the pass-thru (voiding any applicable warranty, of course).

[Alan]

Originally Posted by Spiffy

I just got a new bike a couple months ago with a belt drive... it's a Raleigh Alley Way...

ooooohhh! aaawwwww! Scwheeet ride! And as far as the belt-drive topic, EcoVelo's review says: "From all reports the bugs are pretty much worked out of this system and it’s ready for prime time. My experience during the test period bears this out."

[keithwwalker]

Convincing traditional conventional wisdom cyclists on the merits of the belt will never work.

The reason it won't work, is that you are also telling them to throw away their derailleur as well. A lot of cyclists will never switch to an internal hub.

kww

[Spiffy]

Originally Posted by keithwwalker

A lot of cyclists will never switch to an internal hub.

the only problem I had with it was the loss of so many gears that I was used to... granted I only have an 8-speed internal, but it's a lot less than my 21-speed derailleur...

they're putting more and more gears inside them so once they get up to a 20-speed I think people will be willing to switch... I've only seen 11-speed ones so far...

however, I'm not sure what the weight comparison is, so for racing we'll be talking about something completely different...