chaadster

Can I get some insight from the forum on what I need to know if I want to replace the crank on my Dahon Mariner?

My feeling is that the flex of the crankarms and the chainring is detracting from the ride quality and 'motivational force' of my bike. It rides okay, of course, but it's not a fast bike, and doesn't inspire spirited riding, so I can't help but think that addressing the visible flex in the drivetrain components would remedy that to some extent.

It seems to be a simple square taper BB, so could I slap any ol' square taper crank on there? It seems that a standard crank with an integrated spider would be much stiffer than the stock setup, unless there's some limitation I'm unaware of.

What's the tooth count on the stock chainring? I would also like to add a tooth or too to while I'm at it, to lower the gearing.

Anyway, what should I know before I jump into this? Thanks in advance!

smallwheeler

i've never used one , but the litepro crankset seems to be a popular and affordable upgrade- 53t single. also, driveline sets. any good track crankset would be good too. think SUGINO.. also, you are probably running a 3/32 cassette sprocket and chainring, so keep that in mind.. track bike cranksets usually use 1/8" chains and tidbits...

chaadster

Thanks for the tips, esp. regarding chain width, Smallwheeler. I'll probably just get a cheap crankset like the kind designated for fixies, so am I right to guess that those would be ready for a 3/32 width chain, too?

Thanks again!

fietsbob

Cranks for Fixies can often use a 1/8" chain ring ... ie 4 rather than 3/32"
don't guess, get dimensions.

snafu21

Which part of the crankset is 'visibly flexing'?

chaadster

Will do. Thx.

chaadster

I can see the lower part of the arms flex when I stand on them, but also it's deflecting the chainring, so I think the whole assembly is ill suited to a 220lb, 300w FTP rider like me! I also get flexing out of the cheap, folding, plastic pedals, but after those flex, then goes the crank, so the whole thing is rather vague and unresponsive. On the roll, the chainring flexes enough to rhythmically rub the chain keeper when just putting moderate power through; I don't dare sprint on this bike, because I think I'd twist it apart!

sreten

Hi,

Replacing the pedals with MTB platforms might be an idea.

After that I'd suggest your cranks are fine in that the flexing
is probably more the frame than the cranks, and updating
them will not help that much, but I'm not sure ....

Though at even odds I'd put money on stiffer
cranks not helping at all any day of the week.

So IMO very probably a waste of money.

rgds, sreten.

I have something very like these on my folder :
https://www.ebay.com/itm/New-Bike-Bic...item2ec5a18a66

But a full length spindle may be better for the heavier :
https://www.ebay.com/itm/WELLGO-PLATF...9d4c01b8f#shId

chaadster

Hmm, so do you believe that people cannot feel crank flex, that the stock Dahon crank does not flex, or that crank stiffness has no effect on the sensation of responsiveness to rider input? Something else, perhaps?

it's my experience that crank flex is perceptible; I've swapped them out and felt the difference.

sreten

Hi,

Whilst I won't disagree with your last statement, IMO compared to normal bikes,
the BB of a folder flexes more, and you seem to be discounting BB frame flex.

YMMV, but obviously stiffer cranks can't fix frame flex, though I'm not saying
you wouldn't notice stiffer cranks, I am saying the difference they would
make depends on the frame and the BB arrangement.

I am saying IMO it's simply not worth the cost for benefit to upgrade the cranks.
I am saying IMO it's likely it won't fix the fundamental issue you want to address.

I am saying IMO better pedals are a good idea.

rgds, sreten.

My budget folder will never get near my budget road bike.

FWIW I have a pair of cranks I took off my cheap road bike, styled to look
like alloy but made of steel, suitable for an elephant on a bike, and as stiff
as you could ever possibly want, but utterly crap, they are stupidly heavy.

The left crank just reminds me of an utterly vicious cosh, its so heavy.

chaadster

Ah, I see.

You may be right about the frame flex, particularly in regards to the chain keeper rub. I tend to think that when it comes to the lack of responsiveness under pedal input, however, that the tiny rear triangle and short stays are probably not flexing, and that the cranks are at fault in that case.

that said, I'm not an engineer, and you may be right. Since I'm not averse to putting some money int this bike, good process suggsts that I go after the obvious, low hanging fruit, and there's no doubt in my mind that the crank and chainring are flexy, and that pedaling would feel better if they weren't.

I think one of those $50 Lasco cranks that are often indicated for fixies would be stiffer than the stock Dahon crank, so if I can find one in the appropriate 170 length, I'll probably throw down for one of those and see. I'd try a Litepro as posted earlier, but I really just want silver.

oh, and yes, no doubt changing pedals would help, too; considering some MKS quick release types

sreten

Hi,

IMO you are simply wrong. Crank and chainring flexing for a folder is a joke.

Better pedals is a good idea. Spend your money to find the above is true.

rgds, sreten.

pacificcyclist

Lack of responsiveness has a lot to do with the stiffness of the bottom bracket. Just observe the latest race bikes and guess what they have -- ALL oversized bottom brackets; they look so extremely massive compared to anything you can find on a folding bike or the older style road bikes, like that on my Trek 5000. You will find more bang for the buck there.

Having said that and unless you are willing to pay a large sum of money, most cranks are already stiff enough. Unless you want to pay something like $500 for a pair Rene Herse cranks from Compass Cycles, you are just wasting your money on something you probably won't give you a significant benefit.

Lastly, frame design also has something to do with the stiffness involved. If you want something really stiff that promotes acceleration like sprints and in crits, then a really stiff bike that does not flex very much. However, without give the ride will be also very stiff as well. Ultimately, you need to choose between frame flex or stiffness for acceleration. There is a difference between my Mu Sl that is stiff and really rough and my Dahon Speed Duo which is slightly flexy and more comfortable. The Mu SL is fast, but the Speed is not as responsive with equal quality cranksets.

In summary, make absolutely sure that your crank bolts are tightened and the cups are torqued correctly with a tool up to correct specs and not by hand! Sometimes loose cups and bolts can attribute to pedal flexing. It's a common problem when you ride a lot especially when the previous mechanic only hand tightened them!

Hope this helps.

brakemeister

if you think the cranks are flexing and a new one ( which is cheaper than the original ) will help ... go for it ... Its a waste of money but whatever floats your boat ....
You have frame flex like in every folding bike ( and those so called regular bikes as well )
Mariners came in different ways over the years..the first ones were basically steel boardwalks, than crmo framed boardwalks, after that the Alloy frame which is currently used ....

No matter what .... foldies are best ridden when spinning in a higher cadence instead of mushed with low cadence. Maybe raise the seat a little and try to spin and the flexing will be a thing of the past ...

and free of charge

best Thor