BK268

There 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 mm, 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

Moe Zhoost

No doubt the chain angles are accentuated by the short wheelbase. Nevertheless you shouldn't be having frequent chain drops. Is the chain dropping off the chain ring or is it happening at the rear cogs? If at the chain ring then a narrow-wide may help. Another option is a chain keeper. These cage the chain like a front derailleur. Also, nsufficient tensioning by the rear derailleur cage would likely cause the chain to drop off the chain ring.

If at the rear, I'd check limit screw adjustments, chain wear, and then finally the derailleur alignment.

soyabean

Understand that foldables and small wheeled bikes are in the same category as Bicycle Shaped Objects, so it's already rather amazing they even work at all.

When a rider gets to the point where they totally depend on their ride, that's time to upgrade to a dialed bike to give them the best experience possible.

Hint: There's a reason why foldables aren't sanctioned by UCI.

mdarnton

How's your frame alignment? I bought a bike that did that. I checked the alignment and the frame wasn't straight. The middle of the chainwheel path was pointed straight at the smallest gear on the back. It was new, so it went right back where I got it from. It was an internet bike from a known company and came in a factory-packed box. Now I realize who does their quality control. Me. I went right out and bought a Trek from a reputable local shop.

tyrion

A chain guide might help.

BK268

yes it's chain is dropping on front, single front chain ring, and 8 speed Shimano cassette,

alignment is fine, and tried making small changes to the alignment, but then it drops on the front when the back is on smallest sprocket, rather than big, so its definitely just and max angle thing,

I also spoke to 2 other people with this bike, have the same problem so definitely just a design flaw rather than defect.

i thought about a chain keeper type thing too. but because its just an angle issue, i feel like it will still slip off but the chain keeper will push it back on, and it will just repeat. id rather have something a bit more smooth

BK268

Is there some way i can nominate this comment for an award for most helpful and /or useful comment?

I actually disagree with sentiment on folding bikes , iv'e just come back from a 2 month traveling trip with my foldable, done thousands of miles and numerous hills, we were relying on them to carry 20kg of shopping on a 700m climb twice a week at one stage.

Just one small problem chain sometimes comes off, I learnt how to put it back on while riding with my toes, but still would rather not have to do that, other than that there well built sturdy bikes.

Not a delight to ride i admit, but in Europe you cant take larger bikes of trains, so we didn't have a choice.

It is nice to be back on my Reynolds built road bike though, not gunna lie

FYI i don't have a car or any other mode of transport so rely 100% on my folding and road bike for all my transport along with trains, the folding bike actually gives me that reliability when combined with trains and busses. means i can get anywherein the UK within a day.

Trakhak

The list of items that employ wheels but are not used for racing and are therefore not under the jurisdiction of the UCI also includes wheelbarrows and fob watches.

alcjphil

Hey, guess what? One reason why small wheel bikes are not sanctioned tor at high level racing is that they can be much faster than bigger wheel bikes in some situations. Alec Moulton who was also famous for designing the suspension system for the original Mini automobile was a designer of small wheel bicycles. His bikes are still being produced today, but sadly unable to compete in professional bike races. His bikes were used in many races before his design was banned. Small wheel bikes can be every bit as capable as bikes with bigger wheels. There are quite a few makers of high end small wheel bikes. A US example is Bike Friday

grumpus

If you fit a double crankset you could adjust the chain line on the fly to counter chain drop. Would that be a problem for the folding?

grumpus

Weirdly they hate recumbents too - people still happily race them, but far away from the chilling influence of conservative control-freakism that is the UCI. For the UCI it's about the rider, not the bike, which is why there have been so many innovative advances over the years ... in doping.

Trakhak

Doping innovations would have, of course, occurred even if recumbents were permitted. That said, the UCI has constantly fiddled with bike design restrictions for mass-start racing, time trials, etc. Make Spinaci legal!

But in that they're no different from the sanctioning bodies that govern all other sports that incorporate machinery - motor sports being only the most obvious example.

Immaterial, anyway, since, as you pointed out, recumbent riders have their own separate racing organization, like triathletes.

mdarnton

I have noticed that sometimes a new chain doesn't always act exactly right when cross-chaining on a normal bike, then it goes away. I wonder if part of the problem is a bit too much lateral stiffness in a new chain that is quickly lost. Maybe you should get a chain guide and use it for a while until the chain loosens up?

Hvac

You might try a 9 speed chain. The tighter fitting chain will grab on to the chainring more avidly. I’m currently trying this for my daughter’s bike. As a technophobe she needs it to be perfect.

icemilkcoffee 

Do you really need all 8 gears? Get rid of the smallest cog and space the cluster outwards using cassette spacers, and adjust the derailleur to stop correctly.

BK268

yes, this is a very sensible suggestion and in fact, this is how it's being ridden currently, well I haven't changed the cassette, just set the derailleur not to go into the lowest gear. but maybe it would make sense to change it so its the highest gear it doesn't go into and probably used less, I've never respaced a casset before TBH

SJX426 

@BK268 My Tern.Link D8 came with a guide to avoid the problem you experience.
PB Tern Link D8 on Flickr

Pop N Wood

Can you get a narrow wide ring and give it a try? NW rings are a known fix for certain ebikes with chain retention problems.

the 9 speed chain idea seems like a good one, or at least just a different brand might make a difference.

Hvac

Just to clarify, make certain the derailleur hanger isn’t bent.

tcs

The Dahon Vitesse comes from the factory with an inner chain guide and an outer chainwheel disc.



IF your bike is factory stock, then your claim of tossing chains to the inside is specious. Your claim of tossing chains to the outside is physically impossible.

If you're dealing with a modified bike, then it's hardly an instance of 'design fault'.

maddog34

9 speed chains are not "tighter" on the sprockets in any way when compared to 6-7-8 sp. chains... they are only narrower on outside dimensions... same goes for 10 sp. chains... 11 and 12 sp. are "tighter", with marginally narrower rollers, 11/64", compared to 3/16" for the 6-7-8-9-10 sp. chains.

1/64" is .015", or almost .4mm

interestingly.. higher gear count chains are actually made a bit "looser" when pin shape is considered.. the pins are ground in a slight "barrel" shape to allow more side flex to accommodate the wider 10-11-12 sp. cassettes.... and chronic cross-chainers will wear the pins into the slight barrel shape sooner than other riders.....

cheapo chains installed by some factories will often exhibit the "wet noodle effect" very quickly.. every pedal stroke causes a bike to swing from side to side, and so does the chain........... modern chainrings have their teeth cut somewhat narrower at the top to reduce deraillings.from chain swing, and to accommodate the now wider cassettes people crave.

you may want to try a Shimano brand 10 sp. chainring, and a quality 6-7-8 sp. chain, on your folder bike... and do check the DERAILLEUR ALIGNMENT too, ok? a bent der or hanger can cause derails.