My Gates Belt Drive Broke!
 

My wife and I just got from a cycling trip in the Netherlands. It's a great place to ride! Very flat, but really beautiful and different than anywhere else that I've ever been. The cycling culture there has to be see to be believed.

Anyway, on our last day, with 1.6 miles to go to our hotel, I passed a bunch of cyclists in the big ring and then got stuck at a light and forgot to downshift. When I went to take off at the light, I stood to really crank on the pedals and get us going while in way too high a gear and the Gates timing belt snapped!

Early in the week I noticed that the belt had an abrasion on the outside. I think I banged it into a curb or cement step. It didn't look like any real damage, just a surface scuff, so I didn't think anything more about it.

However, for the several days prior to the break, the belt had been driving us crazy making a lot of noise. I tried pouring water on it and that helped for an hour or so. Another trick someone told me was to rub a dry soap bar along the belt, so I tried that and it quieted the belt for a few hours. Gates once told me you can spray the belt with silicone, but I didn't have any.

I didn't really think the noise and the scuff had anything to do with each other. But with the break, now I think the scuff led to the break, and there must have been some internal damage that was contributing to the noise. Although why the water and soap tricks worked even briefly if the damage was causing the noise does not make sense.

The belt had about 8,300 miles on it and this is our travel bike. It's been on about 15 flights during that time, meaning that many assembly and disassembly rotations.

Anyway, we're going to be carrying a spare when we go on trips now.

Anyone have any similar stories of Gates belt breaks?

Some questions:
- CDX center track belt or older type?
- did the break happen where it was scuffed?
- when you travel, how do you pack the belt? Do you fold it?
- what sort of tension do you run on the belt?
- how old was the belt?

When you put the belt on, how do you do it? Rolling the belt on the pulley the way you would a chain on a chain ring is a major no-no.

Twisting of the belt can break the internal carbon fibers. I learned that the hard way.

• It was a center track belt.
• It was about 3 years old.
• It did break at the scuff. Meant to say that in the original post.
• I always loosen the eccentric to install or remove the belt.
• My tandem has only one set of couplers and I travel with it in an Evoc case. The belt is velcro'ed to one of the rims on the side with the disc, and that side is always facing inward, toward the bike.
• I use the Gates app on my iPhone to set the tension according to their spec.

I am sure that the scuff ultimately caused the break. I wasn't really questioning the why here, just wanted to hear if anyone else had a similar experience. And maybe what other failure modes people have had with the Gates drive.


Thanks

For those of us trying to learn from your experience, the good news is that there appears to be a fairly clear cause, and also that the belt gave you some warning by making some noise. Thanks for the post.

Never had a CDX belt fail.

On trips we have always pack a spare belt along with at least one spare tire, a few tubes, etc... common sense. For packing, I re-coil the belt in the same way that it is delivered new in 3(?) loops. The correct action for doing that is gentle enough and does not necessitate twisting the belt to any excessive degree.

However, just this last weekend a small twig flipped up into the belt and into the rear timing sprocket, derailing the belt half way on the rear sprocket. We stopped pedaling as soon as we realized what had happened and coasted to a stop. Seems like no harm, but we'll see as we continue to ride with it.

As interesting timing would have it, I had ordered a new belt to have as a spare just before we left on this trip. The new belt was waiting for me when I got back. Please note that the new belt is packed flat - it is not coiled into 3 loops as you suggest.

The Gates site FAQ says this about coiling:

For general storage, Gates does not recommend coiling. It is best to leave the belt in its original packaging until ready to use. However, if you want to carry a spare belt with you, proper coiling is an option. Care should be taken not to damage the belt, please watch this .

I've tried the Gates App with questionable results. The phone often has a difficult time picking up the vibration of the belt. Best I could determine was that our belt is at about 25 - 30 Hz (in one orientation). The recommended 60 - 65 Hz seems awfully tight to me. I doubt that a high tension has any effect on the belt breaking but I would think a higher tension would be less efficient than a lower tension.

I don't actually bring a BB wrench with me when I travel, so the belt is only tightened to as tight as I can by hand, which is about 40-45hz. Like you say, lower than their recommended amount, but 60 is really tight.

Never really understood why they want it so tight as that would introduce additional friction and wear on the BBs.

^ The original belts were prone to skipping under heavy load if not pretty tight. The center track belts in our experience are much less prone to skipping, and can be run at lower tension.

I think Gates may just not have revised their recommended tension with the new design.

And from their point of view, a little bearing wear and reduced efficiency has less risk to them than a failure from the belt skipping or derailing.

I also have trouble with the app but when it does "hear" the belt, it's right at 65.

I had the exact thing happen a couple of years ago and called Gates to get their input. The tech that I talked to recommended that I change the belt, the failure mode is catastrophe and usually does not give any warning. Some of the internal fibers could have been damaged.

I immediately put on the spare belt an ordered another spare. I did not want a catastrophic failure!

To me this is a classic example of carbon fiber. It is a great material but has drawbacks that users should consider and evaluate. Light and strong but some small danger of complete failure with only subtle warning signs. Danger that can be mitigated when the user keeps it them in mind and uses due care. Items need to be replaced if damaged or in doubt of damage. For those who want a product with a tolerance for user inattention or error it is not the best choice.

I seem to recall they did have some diagram showing the correct twist technique to recoil a belt. Funny to see that now Gates has reversed that (AFAIK) perhaps because they do not want to be on the hook for replacing belts (or liability) from people screwing up by attempting to follow a posted recommendation.

Look at 1:18 in the video you linked and observe how easy it can be to perform. Then just after that when she demonstrates bad handling. Big difference.

We have been riding with the CDX for a few years now and I have had many opportunities to pack and reinstall the Gates belt. Never a problem for us, but your mileage may vary depending on how you hand it.

Curious how your new belt was actually packaged if not coiled at all. Was it somehow wrapped and delivered as one big loop? Everybody I know has always received their belts coiled, plus we had 2 delivered this way as well. So yes, I suggest that ours were delivered that way.

It is the same method as coiling a bandsaw blade.

Our incident had a very small twig and only a 1/2 derailment which did not appear to involve a significant potential for damage. After a few more rides with this belt, there are no signs (visual or audible) of any further issue. Will keep on riding it as a test case.

The belt was no doubt stretched. I would hate to see that belt break while you are hammering our of the saddle. That might be painful! A catastrophe failure mode was enough incentive for me to change belts.

Chains break as well. So far we've managed to break one timing belt and one timing chain.


One fortunate thing is that when they do break, its usually under very high torque load, which typically corresponds with low speed.

Yup chains break as well . . .
Broke drivechain in TWO places simultaneously a month ago! Fortunately we were quarter mile home!
Some stokers (Kay is only 82 years old) can be tough on chains!!!
Pedal onl TWOgether!
Rudy and Kay/zonatandem

Reviving this old thread just in case anyone has had new failures of their Gates CDX belt.

I just purchased a bike with Gates center track carbon drive.

I'd like to hear your experiences about when / if your belt broke. Were you standing up while pedaling? Were you riding at high speed? Were there any warning signs?

How many miles or days/months had you been using the belt?

Thanks!

We've been using the CDX belt for about 3 years without any issues. We have a spare belt but it's still un-used. We prefer the belt to chain because it's quieter and cleaner. .

We also have a CDX belt. We never tighten it to the Gates spec. If we do that, our BBs have more drag than we like. We normally run it with ~1" of total up/down movement. Never had a problem with it or slipped a cog. OTOH, we're not the strongest team that ever rode a tandem.

Belts can fail suddenly. I got over 15,000 miles on my CDX belt. The time from minor fraying to a few missing teeth to falling apart was only a few weeks. I replaced it before it snapped. It's wise to carry a spare belt if getting a replacement would be a big problem.

We’ve got 55,000 miles on our original belts, now almost 8 years old on our coupled tandem and haven’t had any issues. We do a lot of overseas traveling and have packed it at least 30 or more times into the cases (including test runs of packing). We bought spare belts (still unused) when we got the tandem and have kept them coiled since then - apparently not a good idea based on what I’ve now read on the Gates FAQ site. We always take the spares on our tours. We don’t run the belts super tight - I haven’t had much success with the Gates app - and now just use my judgement on belt tension. We’ve had some squeaking occasionally, but the silicone spray cures that quickly (or some water from our bottles when on tour has been effective). We’ve also had a small twig caught in the belt a couple of years ago, but apparently it didn’t damage anything.
I’ll cross my fingers and knock on wood now.

Ferengii, 55k miles is truly astounding! Thank you for sharing some of your personal experience. Do you mind sharing some other pertinent information? Specific bike info would be great. You mentioned the plural "belts," so I assume you're using either a Pinion or Roholoff gearing? How heavy is your team? Unloaded riding, I assume? Anything else you care to share?

After reading about some of these failures and other experiences I've encountered elsewhere (Ryan van Duzer belt failure, ending his CO Trail trip), I'm not 100% convinced belts are the solution. Sure, I totally get the lube-free advantages. But with today's immersion & drip wax options, the typical "black grimy chains & components" can really be a thing of the past. (On one of our previous trips, one rider's drive train was immaculate. Yup, immersion waxing. He never had to do a thing to his chain during our 2-week trip.) So this is a "solution" looking for a problem. But with additional downsides. I really do not like the un-repairability of a belt. With a timing or main chain, spare links are a simple fix. And I've experienced all of ONE tandem chain failure in 30 years of road and off-road tandeming (after having blown up six rear hubs, I'm not exactly "gentle" on our tandems either). Stick or rock tossed up into our timing chain which broke it. Quick fix and we were back riding in no time. And since virtually all "belt drive" tandems are only timing belts, you're using a chain main drive, so you are carrying a chain tool & quick links anyway. With a belt, you're carrying an entire replacement in addition to the chain stuff anyway. Doesn't make that much sense. However, if I were specing a new tandem today, I'd be VERY tempted to opt for two belts and Pinion or Rohloff because of the cool factor.

And then when I hear someone boast 55k miles, I take notice! That's some MAJOR mileage out of belts!