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Carbon belt life and failure symptoms

johnmcl7johnmcl7 Posts: 158
edited June 2013 in The workshop
I've had a hunt through the forum but the only references I can find to carbon belts when people are considering new bikes and not anything about them after that point. Basically I'm having issues with mine and would be grateful for advice from anyone else who has used a carbon belt drive system for a while.

I bought a Trek Soho Deluxe in August 2011 as a daily commuter which is fitted with the Gates Carbon Belt drive system and a Nexus 8 (the cheaper one) gear hub. I chose the belt drive for its low maintenance as I wanted to cycle daily through the winter, up until now there's not been many issues bar the hub being replaced around July last year due to third and fourth gears being rough. In March this year the belt was slipping at the back under power, it was staying on the sprocket but the pedals would spin round before the belt engaged again. This was resolved by tightening the tension on the belt.

More recently the belt has started coming off at the back so the bike shop had a look and diagnosed a new sprocket due to wear on the teeth of the existing one. I went to pick it up with the new sprocket but on the first good pedal the belt came straight back off, they had another look and they think it needs a new belt.

The bike does around 6KM a day on average plus other longer runs but I'd say the total mileage is under 4,000KM so not that high. I've mailed Gates to try and get some advice from them, the first response was a fairly coherent one requesting pictures of the belt but the second one was in quite broken English and the third reply was my own text sent back to me. The first response did say that if the belt was used in wet weather and snow it would considerably reduce the life of the belt which somewhat goes against their website which claims the system is weather proof although I'm sure they've significantly revised their claims downwards as portions of their site now claim the belt only has around twice the life of a chain (I'm sure they were claiming 10,000 - 15,000 miles originally)

So I'm wondering for those that have had to replace the belt, how many miles had you covered and in what conditions? What were the symptoms of the belt needing replaced and did you have any issues after fitting a new belt?

Also I'm wondering if the Centertrack system is worth looking into, it would obviously mean forking out for another rear sprocket if the bike shop won't take the first one back and the front ring as well but it looks like it should last longer as I assume this problem with the belt coming off at the back wouldn't happen because of the guide in the middle?

I assume I could convert fairly cheaply to a chain drive with a new sprocket at the back and replacing the one at the front but while the belt has fallen well short of expectations for durability, it has done well as it's worked well up to this point.

The bike shop have been speaking to Trek but I'm not expecting much from them as the bike is well out of warranty now, if it is just a case of stumping up for a new belt then I'll just need to do that but thought it was worth seeing what other people's experiences were first before forking out a decent chunk of money (when compared to what the bike is worth).



  • dgunthordgunthor Posts: 644
    sorry to hear that, it seems the belt drive stuff has gone quiet after the initial excitement

    personally don't see any great advantage with belts over a single speed or hub geared 1/8 chain drive bike
  • andyrrandyrr Posts: 1,566
    I had a Trek District belt drive for a few months - that was a warranty replacement for the 2nd District model (chain drive)
    I liked the lack of maintenance through the winter (just gave the occasional sponge down) but I did suffer a bit from problems with it
    a) Noise that I was sure was the belt rubbing on the front 'pulley' due to slight misalignment
    b) Occasional jumping
    c) Freehub failure. The freehub was replaced by the shop F.O.C. but it seemed to be poorly greased from new.

    I got rid a few months back in the main due to me deciding that a 35 mile round trip on hilly roads, 4 times a week, required a geared bike to make life easier for my legs ( I also went to a disc-braked model)
    Anyway, I diverge, the specific problems that my belt-drive had were, I think, possibly in the main due to lack of familiarity with belt drive transmissions in comparison with the way more common chain. Most people don't have the experience to be able to identify and fix the little problems that all bikes will throw up. I think that the belt drive is sensitive to very good alignment and also tenstion and when these are not very close to perfect then the transmission generates nosies and vibrations that a chain drive bike doesn't exhibit.
    Too loose and the belt can jump off the pulley teeth, too tight and the resistance is excessive.
    My original District seemed to wear through chains - which were nice and cheap fortunately - quicker than expected and I think an inconsistant tension (due to some poor alignment somewhere to lack of perfectly concentric chainring/sprocket) influenced this and I think that similar can be the case with the belt-drive, if the belt runs loose-tight-loose-tight-loose-tight on it's run then there will be issues - short / long term. Too loose and it can jump the teeth and in doing that it could damage the belt which in turn can make it more prone to doing that again.
    Too tight and I'd imagine the bearings (bottom bracket and wheel/freehub) will suffer.

    I think the theory is great and in real life works fine but, as I say, I think that they are sensitive to things like manufacturing tolerances of frame and transmission and component wear and then not many people know how to tweek the belt transmission. I recall looking around and seeing mentions of Centretrack but if it is just belt wear then a new belt isn't all that expensive (much more than a cheap 1/8 chain obviously) and if that's all that it takes to cure your bike's ills then it isn't a huge price to pay but the issues I'd question is why has it worn that much quicker and is belt wear the only problem or are there other things at the heart of the jumping. No idea how one can determine if a belt is worn or not - compare old with new belt ?

  • johnmcl7johnmcl7 Posts: 158
    Argh...typed up a reply and got the login box on hitting submit, should know to copy the text first. Here we go again...

    Thanks Andy for taking the time to write up a detailed description of your experience with the system which is what I was looking for. I had read that the belt system could be fiddly so I've let the bike shop do any required work on it and to be fair it's been great up until now aside from needing a couple of tension adjustments. One of the guys at the bike shop has a belt drive bike (a District as well I think) and he reckons he's got about twice the miles out of his belt so far but he doesn't ride it day to day in mixed weather.

    I did ask Gates how to identify the condition of the belt but they've haven't answered that, the belt looks fine although the bike shop pointed out that the belt doesn't seem to be meshing properly with the new sprocket: ... &k=STPLTNq

    They mention on the Gates site that the belt coming off under power is the sign of a belt needing replaced so that gives me a bit of confidence that this will resolve it.

    The question about how long they last and whether mine has failed prematurely is what I'm trying to work out as well, I'm getting the impression from the Gates site and their mail responses that the belt needing replaced at this state is not unusual. The price I've been quoted for the belt is around £100-£120 which is a little less than I was expecting but obviously a lot of money for the time it's lasted which is why I'm looking into options. To be fair to the belt although it's not lasted that long it hasn't given me any issues despite cycling through the salt covered roads in winter, the mountain bike by comparison needs quite a lot of work (comparatively) to keep the chain running smoothly. Admittedly it goes through a lot more mud but that's probably not as bad as the salt during the winter.

    The Centertrack system does seem to resolve a lot of the alignment issues and it looks like it should improve the life of it as well if the problem with a worn belt is it coming off the sprocket as hopefully in the same situation the sprocket would hold the belt properly but I've seen no reference to that being a benefit.

  • andyrrandyrr Posts: 1,566
    My original response probably didn't add a huge amount of helpful info to what you already have : I did not have mine for all that long but was using it pretty heavily and my bike shop did comment that really these bikes were not really expected to have such use.
    I was doing 140 or so miles a week via a hilly 35 mile round-trip commute in all weathers with me riding at a strong pace - as the Trek was a flat-bar bike (I swapped the front-end over from my original 2nd District) I think that Trek expect the typical purchaser to be someone using it for short urban rides.
    I did many a Google for Gates carbon belt drive info whilst I had mine to see what helpful hints there were : just found this :

    I recall examining my belt and although there was visible wear it just looked like the shine having been worn of fthe teeth, no nasty rough bits or funny profiles to the teeth so the assumption that I and LBS (who were pretty good with me but I think weren't expert) was that the belt was not excessively worn. TBH as I'd only had mine for a few months and at a rough guess did <2000 miles, I'd be v. disappointed if the belt had been worn out. I think I've seen comments saying that if the belt jumps the pulleys (as I termed them since they arn't truly sprockets in the normal sense) then that can compromise the belt but without visible issues I didn't see why I should splash out on a new one. I didn't think the cost was as high as that, I though more like £50 ?
  • johnmcl7johnmcl7 Posts: 158
    Gates have got back to me and they're saying the Centretrack belt doesn't last any longer than the previous belt which I'm a bit surprised about but what's also interesting is they sent me a pricelist and the belt prices they're listing are in line with what you've said at 60 Euros for the belt. The sprocket on the price list is about the same as the one I paid for already so I'm not sure if the bike shop were giving me a price off the top of their head or if that's a fitted price but I don't think it's the latter as their labour charges are usually low.

    I'll go down and see them tomorrow to get this sorted, the mountain bike is ok as a stopgap for the hybrid but starting to really miss the hybrid for road travel.

  • johnmcl7johnmcl7 Posts: 158
    Good news - Trek have footed the bill for the replacement belt so I have the bike back now and it's running great. Aside from the belt now staying on it feels far smoother, almost like the sprocket and belt are a sealed unit so clearly the bike shop were right it was the belt that was also needing replaced. So I'll see how long this belt lasts, hopefully I'll get at least a couple of years out of it.

  • andyrrandyrr Posts: 1,566
    Very good news that Trek covered that as a drivetrain component could easily just be seen as worn out and not faulty : I also felt that, for my issue of a visible crack that could have easily been just paint as the frame material itself, Trek were very good with me/the shop so kudos to them.
    Only fly in the ointment is that although it's lasted a few years, the actual mileage you suggest is pretty low for a belt and really, one of the main attractions of these over the chain is the lifespan. Maybe more frequent cleaning than what I think Trek recommend (once a week with a sponge ?) and if possible have full mudguards fitted so that the belt is kept relatively free of grit etc.
    It may be that when used in a nice sunny US state the belt's life can be 10,000 miles but here in our frequently grotty weather and on grotty roads the life just cannot be of that scale - grit and the like is going to cause wear.
  • johnmcl7johnmcl7 Posts: 158
    I agree about it being a drivetrain component and it wearing out, I thought the shop were only speaking with them for advice as they must have a decent amount of experience with the belt system both the older style I have and the newer centretrack version (which was fitted to the MY2012 version of the bike which replaced mine). So I hadn't asked for any goodwill gesture as I was not expecting so I'm impressed Trek did so anyway.

    I have full mudguards fitted and there's a chain guard around a lot of the belt but I don't think cleaning the belt is going to make much difference as the wear seems to have occurred within the self cleaning part of the sprocket. Although the weather is part of the problem I am thinking I need to check the tension more regularly as that can potentially shorten the life of the belt as well.

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