Friday, August 27, 2010

Thoughts On Belt Drive Systems For Bicycles: Part II

<==Gates Carbon Belt Drive on an mtb. (Image credit: "c_g")
I've been thinking a lot about belt drive mountain bikes again, and after checking into it here, I see I have not posted on the subject in almost two years. (You can read the full rant here)

Interestingly, the case of belt drive systems for mountain biking seems to be a case of "the more things change, the more they stay the same". At least, the reminders from my posting in 2008 would indicate as much. Let's take a closer look........

Back then, I wrote the following: 

The belt drive system for bicycles is being developed by the Gates Company which does all sorts of belt technologies for motorized vehicles. They were out at Interbike last year, (2007),  en force to answer any questions and to observe first hand a real world demonstration of the "Carbon Belt Drive System" performance. After a quick briefing by the Gates folks, I got on board a Spot Brand bike and took off on the Demo loop at Bootleg Canyon.

On a steep up, I heard a very loud "pop" and I thought I was going to crash because of a belt failure, but I didn't. I rolled on. At the Spot Brand tent, the Gates folks were telling me I "ratcheted" the belt. This is when you essentially get the belt to slip one tooth over on the cog or more. I did that and that was the loud "pop" I heard. With the belt tensions on the verge of being too tight for the bearings on the hubs already, Gates had to go back to the drawing board for a revision for this year.(2008)
So, as you can see, issues plagued the system from the get go. Noise was common. I heard it. Everyone within earshot of a Spot in 2007 heard them. Then there were the ratcheting problems, and worst of all, breakage. Yes- There have been revisions. In fact, I mention one back in my 2008 post:

What they did was to specify a larger "chain ring" and rear "cog" size with a slightly reduced amount of tension on the belt. The larger "cogs" would increase the number of engagement points and hopefully eliminate the "ratcheting" problems. I'm not sure if this also addressed the many complaints of noise in the system from 2007 Interbike riders, but it may have.
Okay, so they fixed the ratcheting problem and reduced pre-mature bearing failures at the same time. Great. Or wait a minute..............did they? Let's fast forward to 2010 and see where this belt drive business has progressed to.

A cursory reading of this thread on's Single Speed forum shows that in 2010 folks are still ratcheting belts, still getting noise from belts, and still having issues with hubs from high belt tensions, (which Gates seems to have re-instated since I last looked into this two years ago). Now the solutions being suggested range from "belt specific" frame designs that feature heavier, stiffer chain stays, to installing "snubbers" to keep the belt from wandering and ratcheting on the Gates specific cogs, which by the way, have increased in size yet again since 2008.

Okay. Those are the facts about belt drive on mountain bikes in 2010. It seems as though not much has changed about the actual performance aspects of belt drive mountain bikes since 2007, but a lot of solutions have been thrown at the system to remedy the problems folks are experiencing in the field. I still see and hear about failures: from belts out and out breaking, to noises, ratcheting, and being damaged. It seems as though much has changed, but the outcome remains the same.

Belt drive systems are expensive, finicky, and not proven. There are too many failures for the small number of units being actually mountain biked in comparison to chain failures per mountain bike. I don't think Gates could refute that with a straight face.

They would rather you focus on that "greasy, noisey chain". That thing that is imminently reliable, easy to maintain, cheap, adaptable, and works even to single speed your geared bike. No, they would rather have you focus on the fact that belts are lighter, and, ("if" they run a full life), will easily outlast a chain's lifespan. You know, instead of a chain that is easy to repair on the trail, strong, and can be found almost anywhere. Not to mention the fact that belt drive systems are "cool", never mind the fact that you must run certain sized cogs which are hard to obtain and may not clear your chain stays. (Ventana display at Sea Otter 2009, anyone?)  You know, not like a nasty chain drive, which has so many variations on cogs and chain ring sizes that it makes your head spin to have to choose one set. I mean, who needs that?

Who does need that? 

I'm raising my hand high. How about you?



kurisu said...


Belts belong on trousers.

Chains work fine, especially with that beautiful only-to-be-found-on-a-SS straight chainline. I barely ever have to even oil my chain, let alone clean it, and even top quality chains are (almost) dirt cheap.

This was a solution seeking a problem. Or maybe creating a problem?

Wally Kilburg said...

I'm not a bicycle belt drive guy but belts are used in motorcycles with very high torque applications. I'm sort of amazed that they can't get something to work for a bike.

Guitar Ted said...

@Wally Kilburg: Excellent point! I have to say that I too am amazed that it works there, but not on a bicycle. I theorize that it has something to do with the tooth profile. A motorcycle has no issues with the way teeth on a belt engage and disengage a cog. However; I wonder if efficiency of a bicycle rider is negatively impacted by too aggressive a profile on the belt and mating cog. That may increase the likelihood of success in terms of eliminating ratcheting, noise, and belt wandering, but may negatively impact efficiency in terms of the rider.

Causing a power loss due to belt engagement on a bicycle would not be acceptable either, so that may be the root cause of the issues they face with bicycles.

Ari said...

Let's not forget that we also need to have a special frame that "opens" between the seatstay and chainstay to allow the belt to get into the rear triangle. I think the whole thing is just too complicated.
Surly chainring, 15 dollar chain, decent cog is all we need.

Todd said...

FINALLY! Someone else who feels the same way I do about belt drives and will post it for all to see.

I have been "trying" to run a belt drive since getting a replacement frame from Spot. They sold me the entire belt system at cost, otherwise I would have just stuck with a chain. Even at cost the CDS was expensive and I couldn't find replacement parts anywhere. I started having ratcheting problems from the very beginning and tried everything possible to get the system to work properly.

Finally, after a couples months and a lot of frustration I posted a review on my blog. I tried to be as fair as possible and mentioned the pros as well as the cons. To their credit, within a couple days of my post, a representative from Gates posted a comment and suggested I contact him. I did and was treated to some impressive customer service. He warrantied my belt and had some suggestions to get the new one working. Long story short, it worked for one race and a couple rides. The ratcheting came back with a vengeance at Raystown Lake and I have gone back to my chain.

I have found very few comprehensive reviews of the Carbon Drive. Most are brief rides at trade shows and these are woefully inadequate to judge the long term reliability of the system. I imagine most people who have bought into the Carbon Drive have had problems similar to me and Guitar Ted. It would be great to hear from the rest of you.

Ari said...

Maybe,just maybe the belt system is just not intended for off-road use. The higher torque factor, mud, dust and lower gears might just over-whelm the system.

Jim said...

I use my Spot Longboard for my winter commuter. I live in Edmonton, Canada, and last winter was my first using it. It was a nightmare to get set up right, but I found a mechanic with experience with belt drives and he got it right. My biggest problem was the quick release on the back wheels being too tight which caused the hub to sieze up. Or something like that. Loosening it up a bit did the trick.

The Spot tensioners are crap, but they're working ok now.

It was a very tough winter, and extremely cold. The bike performed like a champ. I have about a ten mile commute each way with some road, some path, and some trail. In winter, even the roads can seem like a trail. And the snow and ice used to get into my chain, which made shifting gears a risky proposition, so a single speed works well.

Once you get it set up correctly, you don't have to worry about a thing. It's great. I'm actually looking forward to winter.

As far as it being quiet, it's really no quieter than a well lubricated chain on a well maintained bike in my experience. And the belt keeps on going, where I have to replace my chains every year. The belt does start to make some strange noise under heavy torque (going up a steep hill) when it gets colder than minus twenty, but all of my bikes start to get a little wonky sometimes when it's really cold.

I don't know that I needed a belt, but I'm enjoying riding this bike immensely. My customer service experience with Spot wasn't good though.