solving front chain drop issue on Dahoon Vitesse d8
 

This is a clear design fault on the Dahoon D8, I'm wondering if a narrow wide chainring will help.

I recently brought the bike for a bike/cycle tour through Europe, I was anticipating selling it on my return, but I've actually somewhat fallen for it, but there are two big failures in the design,

1. The break and gear cables routes are ridiculous- I've sorted that,
2. The chain comes off the front chain ring occasionally when on he biggest rear sprocket, not because of chain jump, but because the chain angle is too much.

Will a narrow wide chainring solve this? or does it just solve chain jump on rough terrain?

I've tried changing the spacing on the rear wheel by a few ml, but then it comes off on the smallest rear sprocket - it seems the chain angle range between biggest and smallest sprocket is to much for the chain ring.

any thoughts appreciated

Our Mu D8, with the same chain angle range, has never dropped its chain. Lots of 1X8 folders use a similar drivetrain without issue.

A Vitesse should be fitted with a Dahon factory chain guide.

https://cimg5.ibsrv.net/gimg/bikefor...ed0dd53c8c.png

Make sure your chainwheel is perfectly straight.

The bike should be fitted fit a quality 8-speed chain.

Have you tried moving the chainring inwards by installing it on the inside of the crank arms? If so, the next steps would be a wide-narrow chainring and/or a chain guide. Also make sure your chain is not too long or short.

Some Speed P8's had a bashguard on the inside and outside of the chain ring.
Seemed to do the job pretty well
Narrow wide may also do the trick

Some folders have chain keepers or retaining rings to keep the chain in place, my Birdy had a keeper, and when I removed it, the chain dropped a few times. Install a keeper, and that should take care of your problem. You can also tighten the tension screw on your derailleur a little, this will hold the chain more tightly against the chain ring.

And in fact, a factory-stock Dahon Vitesse is equipped with an inner chain guide and an outer chainwheel disc. As everyone can see, on an unmodified factory bike there is no way that "the chain comes off the front chain ring occasionally". I encourage our OP to jump back in and try to further explain because it sure seems like the claim of "Dahon design fault" does not hold up to scrutiny.

https://cimg3.ibsrv.net/gimg/bikefor...f9e7b08cc9.png

That is not a good solution. My Zizzo Liberte came with the same setup. I bought the bike as a second from Zizzo, meaning it was either a return or a factory second. It came equipped with the same solution shown above. From the beginning, it had a tendency to throw the chain. I think it came off on my second ride. I noticed then that the plastic chain retainer attached to the seat tube was not adjusted properly and that the chain ate into it. I adjusted it properly, which is harder to do than one might think. The chain eventually moved it and came off during a ride anyway. The plastic piece now prevented me from putting the chain back on. I had tools, but not a Philips head. I was miles from home and, without the tool needed to adjust and move it. I ended up pushing the bike a few blocks to a bike shop and borrowing a Philips head from them. I removed the piece, then put the chain back on and road home without incidence. I called Zizzo and described the problem and sent them a picture of the chewed chain retainer. They sent out a new one. This one worked for a while, but eventually the same problem developed. I removed it, never replaced it. I adjusted the chain properly and have not had the chain come off in more than a year. If it does come off, I will just put it back on. I have speculated that the chain coming off may have been why the bike was a second in the first place. I had never seen a new bike come with this device before.

If I were to continue to be a problem, I would first try to address it with a narrow-wide chainring. As it comes stock, the Zizzo is somewhat geared to low.

Sorry the Zizzo didn't work out for you. As I said in post no. 2, my Dahon has been fine for the last 15 years.

In this thread, the OP claimed the rear wheel was respaced a few millimeters to the left which caused the chain to come off the small rear sprocket to the left. This is nonsensical.

In a concurrent post on Bicycle Mechanics, the OP claimed the chain came off the front chainring to the left. This means the chain passed through the gap between the chain guide and the chainwheel disc - a gap that is smaller than the chain is wide. THEN after magically getting past this small gap, the chain climbs up over the chainwheel disc to come off. This is also nonsensical.

I again ask the OP to rejoin the thread and explain.

It is neither magic nor nonsense. The chain for whatever reason is has forces on it which makes it prone to coming off on the left side of the chain wheel. If it did not, then it would not be coming off. At first, for a period of time, the plastic piece works because it blocks the chain. However, accumulated tries either eat into it when it contacts it or causes it to rotate. If the plastic chain retainer is on tight enough that it does not rotate, then it gets eaten away slowly by the chain until there comes a point when the chain eats away at enough, and it tries to break free the rotation of the pedals forces it through the gap that the chain has eaten away. Because our legs are stronger than are arms, we will not be able to put the chain back on without moving the damn thing.