We've started transporting our tandem inside our SUV occasionally, so I decided to replace the timing chain with a Gates carbon belt to reduce the chance of chain grime getting on things.

I bought a second belt as backup. Wondering how many of you feel the need to carry a spare belt on your bike. I'm pretty conservative when it comes to getting stranded, and usually carry a spare folding tire as well as all the other normal stuff. But Gates warns that the belt is vulnerable to damage if it gets folded or bent wrong, so I'm concerned about having it in the pannier and getting jammed by something else getting stuffed on top of it, etc. Just how likely is it that a CDX belt will fail in the field? What's the best way to carry one on the bike, if advisable?

I have no firsthand experience or knowledge of belts, but my knowledge of bike mechanics in general suggests that the probability of failure of a timing belt (or chain) is low. Very low. The chain drive to the rear wheel probably has a higher probability of failure and I'm guessing a chain breaker is not part of your field repair kit. If the belt is as susceptible to damage as is being alluded to, I for one wouldn't think it worth carrying, but if I did I would pack it last, on top of everything else in the pannier. Folded (correctly) in an appropriate size of Ziploc bag.

We have used a CDX belt for three years and have not had any problems. In the past we carried a spare belt on our long foreign tours, but this year we decided not to carry a spare due to the fact that the belts seem very reliable. I have not read any posts recently of anyone having problems with CDX belts.

We have run the CDX belt for at least 10,000 miles on our CoMo Macchiato with no problems. I inspect it at irregular intervals and have seen no signs of wear. If the teeth look dirty, which is rare, I wet it and gently brush it.

The Gates carbon belt was originally designed to replace standard chain and sprockets in industrial applications. The belt should last a very long time on a bike. The main thing to remember with a spare is not to back bend it. The tension members are likely to break if being bent backwards.

Easier/lighter to carry an extra chainlink/chaintool.
As for "clean" . . . we use the hot wax method on our tandem chains for over 40 years. No fuss, no muss, no chain tattoos.

... and back on topic...

We started using the CenterTrack belt in 2013. No problems. We only pack an extra belt on trips to Europe when our ride schedule is preset and downtime must be limited.

I looked into this when we bought our Beyond with the belt and the responses were 10K to 20K miles before replacement is needed. At 6K miles we started to carry one in the travel case just as insurance that a vacation doesn't get ruined. I guess I worry more that I may kick something up that could cut the belt, but those things are pretty tough so I don't really see that happening. If it did break I would probably move back to the stokers seat and I would guess we could make it back to the car or at least civilization where we could get a ride.

I put a belt on last year and wondered about traveling out of town without a spare. I packed the old transfer chain and chain rings in our basket of cycling stuff in case the belt would break. The only problem would be getting back to the van. Maybe my stoker/wife could pedal us back and we could find out if anyone would yell "he's not pedaling."

I am not using a tandem, my belt drive bike is my commuter. I have a spare belt; but it has been just hanging in my garage for the last three years. I have never needed it.