I have a Dahon speed pro which I have had for about 1.5 years. Lately the chain started to fall of the chain ring in front when I use the 4 higher gears in the back so basically I can only use the three low gears in the back now. I don't understand how this can happen as the chain ring is in fairly good shape and the back end is in one piece. I don't think I am so strong that I manage to put that much stress on it that the flex could cause it. Not sure if my weight could be a problem (75 kg)? Any suggestions what the problems could be? Not my bike but the same model:

Do you have a chain guide that has possibly moved out of position or become damaged / worn out?

Not sure what you mean with chain guide but the "protection" outside the chain ring is in its proper position and seems ok to me. Nothing has come loose or has and play in it (I have checked the crank, chain ring, the chain guard etc). I have also looked for cracks in case the frame is about to give but none found. Looking at it when it is still nothing seems out of the ordinary but then again I did not stare at it much when it was working.

How many chain rings to you have in the front? Does the chain fall on the inside (between the chain wheel and the frame)? Do you have a chain ring protector on the inside?

I don't know what caused this problem to appear but I had in the past similar problems with a different bike (non Dahon, single chain wheel, no inside protector) and solved it successfully with a Deda Dog Fang.

Did you have any accident recently? Have you replaced any related part? Any other event that may cause it?

Kam

Dupe. Deleted.

Nah.. falling of to outside. I guess I have to find some kind of chain guide like on a mtb with single chain ring in front (I've got a single chain ring). Didn't need it when it was new though.

When chains wear, they also get more sideways freedom. Shifting gears to the outside usually happens with a very quick movement, setting up a sideways snakelike wave in the chain. This often has the effect of throwing the chain off the outside.

The cure is to arrest that sideways wave. Usually a chain guard is enough but if that chain guard is too far away from the chain, it won't have the desired effect. The cure is to move the chain guard closer to the chain, perhaps by using smaller spacers or filing the existing ones a bit shorter. Put it as close as possible with the chain on the smallest rear sprocket, without rubbing.

here is a chainguide
https://www.thorusa.com/dahon/accessories/special.htm
might do the trick ...

first check if the wheel is straight and doesnt twist the chain un necessary

thor

If the chain falls off when shifting to the smaller cogs, the rear deraileur is not applying enough tension on the chain as the cage swings back. Shift it to the smallest cog and bounce the bike up and down while observing the chain. If the chain looks really loose, you need more tension my adjusting the deraileur or taking chain links out.

I'll try to take one or two links out (or as many as possible when having it on the large cog back). The chain doesn't fall off immediately when shifting to smaller cogs but after some time when I put a bit of pressure on the pedals (could be one minute or 20 minutes). Maybe I should buy a replacement spring for the derailleur if that doesn't work. I will report back next week (this week-end is devoted to my newly built Rambouillet )

I think this makes sense. Looking at the photo, the chain is on the biggest cog and the derailleur is still hanging straight down. It should be pretty extended in that position. Looks like you can take 2 or 3 links out.

Did you check for chain stretch? If the chain is stretched, I would replace the chain rather than removing links. Here is a quote from Sheldon Brown's article on chains:Measuring Chain Wear

"The standard way to measure chain wear is with a ruler or steel tape measure. This can be done without removing the chain from the bicycle. The normal technique is to measure a one-foot length, placing an inch mark of the ruler exactly in the middle of one rivet, then looking at the corresponding rivet 12 complete links away. On a new, unworn chain, this rivet will also line up exactly with an inch mark. With a worn chain, the rivet will be past the inch mark.
This gives a direct measurement of the wear to the chain, and an indirect measurement of the wear to the sprockets:

If the rivet is less than 1/16" past the mark, all is well.
If the rivet is 1/16" past the mark, you should replace the chain, but the sprockets are probably undamaged.
If the rivet is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.
If the rivet is past the 1/8" mark, a new chain will almost certainly skip on the worn sprockets, especially the smaller ones."

This picture a Part Tool article about chain length. It shows a good derailleur position when the largest front and rear cogs are selected:


"Adequate chain length seen above in largest sprockets front and back. Note the chain bends at both pulleys."

https://www.parktool.com/repair/readhowto.asp?id=26

The largest cogs + 2 links is also a common method:

https://bicycletutor.com/calculate-chain-length/

You can take a look at the installation instruction of your derailleur. All the ones I have seen specify the recommended chain length.

Kam

Here's an easy (and cheap) way to check for "chain stretch":

https://www.performancebike.com/bikes...chTerm=40-3545

Just replaced the chains on our 2-year old custom Fridays due to recent test with this tool.

Wife's was at .75% (borderline) and mine was 1% (replace now). A worn chain can also damage your cassette and chain ring.

Looks like you may need to shorten your chain a bit, too.

Lou

I don't think removing links will solve the problem, because when shifting to the outside cogs, the derailer will become more relaxed again. (Remember the pic he posted is not of his own bike.) I have nothing at all against removing excess links, but I speak from lots of experience of chains getting thrown off the outside at the front. And my bikes don't have excess links. On my Swift, the only cure was to make a custom pipe-like guide mounted at the chainring to arrest the sideways wave. With the Yeah, Connie had endless frustrations until I fixed that with a little wheel over the chain. With the Birdy, I finally ditched the plastic useless chain guard and mounted proper aluminium guards right next to the chain. Occasionally when shifting to the outside, I hear a satisfying 'ping' and I think, "That's another chain derailment prevented."

I had the same problem with my speed p8. this is what I did:

remove chain protector
remove chain ring
flip chain ring around so that inside is now facing outside
reverse steps

check dahon fourm for more details

good luck

It's due to the short chain stays on folders, a roller kit will solve the problem (orange wheel), from here:

Sheldon suggest just using a ruler to measure chain stretch.

Myth. Most good folders have fairly normal length chain stays or only marginally shorter.

Just after posting this I won an ebay auction on a German touring bike (Nöll) and haven't been using my Dahon since (been biking all the way to work instead of cheating by train most of the way). Got a cold last week and started using the Dahon again. I cut the chain by a lot! and so far no problems at all. Very simple solution it seems after all. Almost had forgotten how fun it is to ride a good quality folder.