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I recently met a guy who'd just broken his belt drive, with no spare, and no bike shops anywhere near. He ended up hitchhiking and doing a 15 km walk with his bike to a railway station.

This made me wonder, is there any possibility of a (McGyver style) emergency repair for a belt drive, so that at least you don't have to walk or hitchhike?

In this particular case, there were small villages nearby, but no shops, so some household materials would be available with any luck.

Or maybe I should ask at lifehacks SE?

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    I believe this is a potentially useful question, but I have a feeling the answer may be to carry a spare belt.
    – Weiwen Ng
    Commented Sep 16 at 17:19
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    Was the belt obviously wearing, before the break? Could be periodic maintenance spotted the impending failure, and at that point replacement or at least procuring the next belt would have made this a smaller issue. I've done the same with tyres, trying to get the last wear out of one by carrying its replacement for a week or two
    – Criggie ♦
    Commented Sep 16 at 19:16
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    @Criggie I don't know, I didn't get to have a good look at the belt. He did tell me it was already an old one, and he should have taken a spare with him. (In which case not the belt but some other part would have failed ;-)
    – Berend
    Commented Sep 16 at 19:33
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    I've never done it, but a stranded bike/rider can be "towed". An inner tube is normally used as the tow cable, but the broken belt might work just as well. This assumes the dead bike can roll okay, still support weight, and brake itself.
    – Criggie ♦
    Commented Sep 16 at 22:09
  • I think if you could get hands on sewing supplies, you could sew a strip of strong fabric to the remains of the belt to return it to a useable loop shape, at least for pedaling on the flats and minor slopes instead of walking. A needle and nylon thread may be all you need, and a length of nylon strap webbing could be sacrificed from a backpack strap or similar. In some cases, the thread can be obtained from the strap itself, so, the needle is all you need. A needle, thread and a nylon dog leash can be obtained at a dollar store or you could ask for it from a house nearby.
    – Jahaziel
    Commented Sep 20 at 16:12

5 Answers 5

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There are no good easy replacements for gates-style belts other than another belt.

From the automotive world it is possible to replace a V belt with pantyhose, but that has a valley on each pulley that holds and captures the material.

A bicycle belt is toothed and needs those teeth to pull the belt, unlike a V belt where the sloped "walls" of the valley grip the belt.

Belts are relatively uncommon, so blagging a "spare" off another rider on the road is very unlikely.

The rider failed to prepare, and perhaps failed to notice the worn belt. Carrying a new belt and the tools required to swap it would be the only solution, and that requires pre-planning and preventative maintenance to spot the upcoming failure.

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    Note that carrying a spare is a very feasible solution for longer tours and/or remote areas: a properly folded belt is very light and doesn't take much room, and depending on your frame you may well not need any exotic tools (in my case: 5mm allen, 15mm wrench - things I'd be carrying anyway)
    – user4520
    Commented Sep 17 at 6:06
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    @user4520: What do you need the heavy 15mm wrench for?
    – Michael
    Commented Sep 17 at 7:55
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    @Michael 15mm would be an axle nut, so wheel removal without having a QR or similar.
    – Criggie ♦
    Commented Sep 17 at 8:28
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    The Gates belt for bicycle is much more similar to a timing belt (toothed, can't stretch) than a poly-v belt (fanbelt). It isn't really a fair comparison.
    – Noise
    Commented Sep 17 at 17:43
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If this were a self-contained tour of some sort, in practical terms the answer is usually going to be replace it all with chain drive. Most Gates bikes are IGH with either a 104, 110, or (more rarely) 130 chainring. That means all you need to convert it in many situations is a 3-notch IGH/coaster brake type cog, a 1/8" chain, and a relatively common chainring. Most shops will have all that. For Gates bikes with singlespeed cassette hubs, the more common cog sizes can usually be had, or in the worst case cut out of a cassette. They won't have the ring and cog in every size, especially since IGH cogs are normal service items in some parts of the world and not others, but usually at least a 16t cog is at hand plus various chainrings for 104/64, and it's not optimal to run a multispeed front but it doesn't really matter. Alternatively, a ring and cog in many cases could be obtained off trash bikes, and the chain needed can be found at big boxes.

When Gates belts break, the tendency is a fairly long section becomes completely shredded and unusable. Belt drive bikes might have 2-4 teeth of acceptable variance in the belt length they can take from minimum to maximum, but the damaged section is usually much longer than that. So since the broken belt in question was going to start somewhere within that range, there becomes very little possibility that it would be long enough afterward even if you somehow had the ability to cut out the damaged section and rejoin/splice the belt.

In reality when belts break, the root problem is almost always that at some point, someone kinked it by forcing it onto the front ring while reinstalling the wheel. One upshot here is that it's preventable, and another is that the kink is visible when not under tension before it breaks, so all you really have to do is bite the bullet and get a new one before you're stranded. That said, the entire conversation points to chain drive as the superior choice for riding in resource-minimal environments.

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  • Useful information, but there weren't any shops to begin with. So 'most shops will have all that' is a moot point
    – Berend
    Commented Sep 16 at 18:37
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    @Berend To that point, if this were a self/contained, low resource situation, and you made the mistake of getting into that environment with an irreparable drivetrain, here you'd probably have an out of getting a 16t 3-notch cog from a rusty kids coaster brake bike you pull out of a ditch, a 104 ring from a 90s mountain bike, and banking on 1/8" singlespeed bike chain being a common item worldwide.
    – Nathan Knutson
    Commented Sep 16 at 18:41
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    Okay, that could be an option. Would such a cog fit on a Rohloff IGH?
    – Berend
    Commented Sep 16 at 18:45
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    Rohloff is an exception, it needs its own cogs.
    – Nathan Knutson
    Commented Sep 17 at 5:51
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    "In reality when belts break, the root problem is almost always that at some point, someone kinked it by forcing it onto the front ring while reinstalling the wheel." - unsure if you mean breakage as in the belt splitting, but this statement feels too general to me. The failure mode I've experienced is belt teeth shearing off after around 5k miles/8k km on a CDX belt - I've been told by Gates customer support this is their standard failure mode and the that mileage sounds about right for how long they last.
    – user4520
    Commented Sep 17 at 5:57
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There’s not realistically an option to repair a standard Gates-style belt drive in the field short of having a spare belt. Any kind of ‘splice’ wouldn’t be able to actually reliably join the two ends of a severed belt (it would fail again very quickly due to the tension requirements for it to actually work well), and even if it could it would usually shorten things far too much to be usable (short of active sabotage, it’s really rare for a belt to just cleanly ‘snap’ at one spot, it usually loses teeth and the layers partially delaminate as well, so you end up with a long stretch of unusable length, often 5% or more of the overall length of the belt).

And spare belts are, in reality, not actually that easy to carry. They are definitely light, but they’re relatively big and you can’t bend a Gates belt beyond a certain radius without risking damaging it because of the stiffness, which makes it unwieldy to actually carry one on a bike. Imagine trying to carry a wire-bead tire with an extremely low TPI and you’ll get the general idea.

The ‘conventional’ approach is to stay on top of maintenance and get the belt replaced when you start to see the bright blue inner layer peeking through the teeth (it’s there specifically to be a highly visible wear indicator) and ensure you have proper tension on the belt every time you install the rear wheel. Almost all catastrophic failures of these belts happen because they’re either far too worn down, or the belt is way too lose (which can cause skipping, which in turn wears out the teeth super fast and can cause whole runs of teeth to just shear off).

I go a step further than this myself with my commuter that has a Gates drive, and have a (waxed) chain, sprocket, and chainring ready and waiting in case the belt fails so that I have a usable bike until I can get a new belt shipped, and I have sufficient tools to replace all of it myself, though I don’t generally carry any of it with me when riding (I rarely ride far enough from home for this to be a worry, and I very actively stay on top of maintenance so it’s unlikely I’ll ever actually be running a belt that’s sufficiently worn to be a risk, except possibly to get the bike to my LBS for a replacement). If I were going long-distance though, I would definitely include those parts in my kit, plus a chain whip and strap wrench to swap the sprocket, and appropriate Allen wrench for the chainring so that I could swap everything in the field.

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    Additionally, if there was a good way to splice a drive belt then you'd bet manufacturers would use it rather than require drive-belt compatible frames with a cutout somewhere.
    – Criggie ♦
    Commented Sep 17 at 8:27
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    The size issue is minimal. The spare belt can be triple folded into a circle of ~15cm diameter without damage to the carbon. At that point it will fit into almost any bag. Alternately tape a belt to the frame.
    – Warren Burton
    Commented Sep 17 at 12:11
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    @Criggie I don't know if it's a "good way", but at least 1 manufacturer is creating spliceable belts (no affiliation): veercycle.com/collections/all/products/split-belt-pro
    – Saaru Lindestøkke
    Commented Sep 17 at 15:31
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    @SaaruLindestøkke That belt is spliced one time only. The belt cannot then be removed until it is worn out. Further, you have not the precision or tooling to create and use a new splice on the belt to make a repair except in a specialist workshop.
    – Noise
    Commented Sep 17 at 17:51
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    Sure, I don't think this would've solved the problem at hand, but it does remove the requirement for a special frame.
    – Saaru Lindestøkke
    Commented Sep 17 at 18:43
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Belts are unfortunately not a good solution for bikes. Unlike a derailleur chain which can be repaired quite many times using lightweight parts (all you need are spare Shimano-style reinforced connecting pins if your chain requires them), belts cannot be repaired. They can be replaced, but carrying a spare belt takes lots of space in your emergency repair kit.

This is one of the reasons why chains are preferred on bikes.

Of course, there's always the solution of using a bike as a kickbike. It won't work uphills, but uphills you would be going slowly anyway. Downhills it works excellently, and at a level ground acceptably.

Walking is thus not needed, you can travel faster than walking by using the bike as a kickbike.

But still, it's better to be able to do roadside repairs to your equipment. So chains are preferrable to belts.

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    Yeah, kick biking is the obvious way, but that wasn't really my question
    – Berend
    Commented Sep 16 at 18:39
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    @Sam7919 There are two approaches here - kick biking sounds like a big balance bike where the rider is on the lowered saddle and strides forawrd with feet on the ground. That might be easier without pedals. The other way I'd move is to stand beside bike on the left side, put my right foot on the left pedal, and "scooter" the bike alone with left foot only pushing on the ground. This can be easier with saddle rotated ~90 degrees so you have somewhere to lean your hip. Right turns can be sketchy, and cleats don't help at all. Both assume the bike can roll but not "power"
    – Criggie ♦
    Commented Sep 16 at 22:05
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    @Sam7919 might be a new question here - how many ways are there to move a dead/damaged bike with limited resources.
    – Criggie ♦
    Commented Sep 16 at 22:06
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    I really don’t think common failures on a derailleur drivetrain are any easier to repair. To fix a broken chain you need a chain tool and possibly a length of spare chain. A spare gates belt only weighs 88g and is really the only thing likely to fail. With a derailleur drivetrain you also need a spare hanger and are still stuck if your derailleur breaks.
    – Michael
    Commented Sep 17 at 8:03
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    @rexkogitans all parts of the BB/crank/pedal assembly are designed to withstand the full weight of the rider. During hard pedalling by a strong rider, the leading pedal is exposed to much the same load, and the 360° crank movement makes it even more of a mechanical challenge. So "scootering" a bike is indeed a perfectly valid option, and it works much better than the balance-bike option. BTW I find it also works well with SPD cleats - having the right foot clipped into the left pedal makes the position more secure and allows swinging the whole body for a fast kickoff.
    – leftaroundabout
    Commented Sep 17 at 8:15
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The alternator belt broke while travelling in my motorhome once. As I was in the middle of nowhere and no cell service, I used shoe laces tied together and made it to the next town!

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    Hi, welcome to bicycles. Are you really suggesting that a pair of shoelaces tied together would make a substitute for a broken drive belt? I'm confident it wouldn't work.
    – DavidW
    Commented Sep 19 at 19:16
  • Welcome to the site - that's a good hack for a V-belt, but bikes with belts have drive teeth and don't use the pressure from the side-walls of the valley in the pulley.
    – Criggie ♦
    Commented Sep 20 at 0:45
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    But you have a good point - shoelaces can be tied. So it could be possible to get a small arc of pedal motion by tying two shoelaces separately from the chainring to the cog such they follow the path of the belt, one above and one below. You wouldn't get more than an eighth of a crank turn before having to reverse the crank for another "bite" but it might work for a while. Same foot would always be "forward" which could be fatiguing.
    – Criggie ♦
    Commented Sep 20 at 0:48

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