mja024

Hi everyone, I'm looking for advice about changing a chainring sprocket. I bought a cheap folding bicycle and I love it, it suits my needs and my budget perfectly. Everything functions perfectly, gears shift nicely. It's an APEX folding bike by Shimano (or at least it has Shimano gears/derailleur).

My biggest problem/complaint is with the small 16" wheels on the bike, the gearing from the factory is not set up correctly. It has a single chainring sprocket on the front (the press-on/oldschool kind like on an old 3-speed bicycle). Size - 46T (about 7" dia).

The rear casette has the following teeth count, I could be off on the count or size slightly, but maybe this will help:
28T *, (about 4.25" dia)
24T *
21T *
18T
16T
14T, (about 2.125" dia)

The 14T gear is labelled as 6th gear on the shifter, and the 28T is 1st gear. When riding the bike, I only use the 14T gear. The other gears are useless. I've used the 16T and the 18T gear to get up severely sharp inclines, but the gears with asterisks I can't even pedal fast enough to gain momentum to keep the bike upright, even on a hill. I'm wanting to make this more of a road bike, as it's set up now I would guess it's mountain bike gearing, and there's no mountains in Houston.

I was guessing I could just press on/replace something like this (but with more teeth/same diameter than I currently have):
Robot Check

Or change the front gear to something like this:
https://images.gearjunkie.com/uploads...chainring1.jpg

I really don't know all the technical names for these things. I'm good at building things and work on cars a lot, I've worked on a few motorcycles in the past, but don't know anything about bicycle gearing/mechanics. Please help me out with some recommendations, I'm working on uploading some pictures of the gears and things. I'd like to spend less than 30-35$ if possible. Also, the pedals are fold-in ones, and I'd like to keep the pedals.

Aubergine 

Is this the bike you bought?

https://aws-app01.roadbikeoutlet.com/...APEX-SIL_3.jpg

looking at that, I can't tell if you could change the chainring (the gear on the crank) without replacing the entire crankarm. However, you may be able to find a different six-speed cogset for the wheel. If you get smaller gears on the rear (say 21-12?) it would definitely work better for you. If not, then look for another crankarm/chainring that has 52 or more teeth.

yadder

Hi! You dont change chainring. Need change cranks.You need to install replacement chainring cranks.

yadder

maybe he install road system 52-42T. And select chainring

mja024

Yes, that's the bike I bought, thanks for the link. Hmm, okay yes 21-12 would work better than what I have now. How do I know which gearset would fit this bike? Is there a common place where these types of gears are ordered?

Edit - if it's easier to change the rear gearset I may just do that. I'm trying to find a new set that would fit. 12T would at least be an improvement over the 14T that's on the bike now.

mja024

Hi Yadder, I don't understand exactly the difference between the crank and chainring. I see a few of these 'road system' sets with multiple gears on them on amazon/ebay, and I could just take out one or two of the gears? Are these types of cranksets universal for all bikes?

yadder

You have 6gear frewheel Shimano. Need buy frewheel but dont cassette!!

yadder

Your system we called the "square". You need only length cranks and for the bottom bracket "square"

dabac

Welcome to the challenges of small wheel bikes.
Going from a 46T to a 52T is a 13% increase.
Don't know if that'll be enough to satisfy you.
Don't know if the bigger chainring will clear your chainstay either.
If your bike is the one linked to by others, you can't use the chainring in your first link.
That's intended for one-piece cranks. You have a 3- piece crank.
52T is about as big as chainrings go, unless you go custom.
Shimano makes a folding bike hub called Capreo, which has a 9T smallest sprocket. 14-to-9 is a bigger difference than 46-to-52.
Or you can get a Duodrive hub, an internally geared hub with a cassette mount.
Unfortunately both will bust your budget.
There are also geared cranksets, Schlumpf, and one more I can't remember right now.
Which will also bust your budget.

But I wonder about your cadence, pedalling pace.
Many new riders prefer to pedal slow-and-hard, which isn't really how it should be done.
It's quite generally agreed that the ideal cadence is in the 80-100 RPM range.
Unless you're there, work on pedalling technique instead of bicycle technology.
Admittedly, getting some serious speed on a 16" wheeled bike with standard gearing will always be a challenge, but the situation might not be quite as bad as you think, with a good pedalling technique.

yadder

I install that. But a dont know length your cranks
https://xt.ht/phpbb/download/file.php...w/IMAG4536.jpg

mja024

Ah, thank you again. Okay, I'm looking for a threaded freewheel Shimano. I found some 7 speeds that have a 12T on them. Most of the 6 speeds have 14T as the smallest gear.

Thanks for your picture yadder, I'll look for the rear gearset for now and change it to a 12T if I can find one. If I can't find one then I'll try to take the crank off/apart and post pics of it later.

mja024

Thanks debac, you guys are a big help. What about this: the price looks right -
Shimano Capreo HG70-S 9-Speed Cassettes - Outside Outfitters

I think you're right about my pedaling pace, it definitely needs work. But I have 3 impossible gears to use on a 6 speed bike, and I actually can only use 2 gears normally. I'm pretty fit and would like to get this thing moving a little quicker than it can go now.

dabac

14T is the smallest sprocket you get on standard freewheels.

mja024

Hmm, I guess there may not be a quick/cheap fix since the hub would need to change from freewheel to cassette?

...debac could you recommend a good 52T chainring for a 3 piece crank? If it doesn't work I gave it a shot at least.

yadder

No you need change only frewheel or only cranks.

dabac

Trouble is, there is an incompatible difference between freehub wheels and freewheel wheels. On freewheel wheels the sprocket stack and the one-way clutch mechanism is treated as one unit, while on freehubs the sprocket stack - the cassette - and the clutch mechanism are treated - and replaced - as separate entities.
Your wheel can't use a cassette, and your shifter wouldn't play nice with a 9-speed cassette.
A 12T smallest freewheel and possibly a bigger chainring are probably the only fixes anywhere near your budget.

dabac

Your confusion is understandable. Cranks are available in a number of different configurations. Good cranks of your generation of cranks - 3-piece cranks - the chainring(=sprocket) is bolted to the right crank and is individually replaceable.
On cheaper cranks the chainring is riveted to the crankarm and generally not seen as replaceable.
Cranks aren't quite universal. There are several different standards of bolt circle diameters, bottom brackets etc which makes replacing parts less than self-explanatory.
Buying a double or a triple crank and simply ignoring one or two chainrings is unlikely to end well. That will most probably put the chain at a different point WRT the centreline of the bicycle than before, which can mess with shifting and chain lifelength.

mja024

Thank you for helping me understand, for the 3-piece crankset, my crank looks like it's square taper. There are two options - square taper ISO and square taper JIS. Does this make a difference in fitment?

... also, I have about 1" - 1.5" to clear the chain guard/chain arm piece? There is a notch on the frame where the crank ring/chainring would hit if the diameter goes up too high. Edit - I guess that means if I have a 7" diameter now, the biggest I could go is around 9".

mja024

Something like one of these?

50T
Track Fixed Gear Single Speed Crankset 165mm 50T Black Cranks 1 8" | eBay

52T
TMC Single Speed Fixie Bicycle Fixed Gear Bike Crankset Cranks 52T Purple | eBay

56T (a little over budget)
Robot Check

dabac

Yes.
While ISO and JIS will be close enough to engage, the taper is sufficiently different to influence how far in on the bottom bracket axle the crank will end up. End results tend to be a bit random if you mix parts.
Unless clearance or chainline issues becomes a problem, ride performance will often be just fine.

mja024

Okay thank you dabac. Ya'll have really helped a lot with this, I would've been lost without it. I'm going to splurge for the Lasco 56T and see how that works. Hopefully it'll be enough difference that I don't need to tinker with the bike any further.

dabac

Something of that general style, yes.
I wouldn't get the first one. It explicitly says 1/8" chain, and they aren't used for multi-gear rears. You need one that can use a 3/32" chain. Also the crankarms are a bit short, which isn't to everybody's liking.
Can't tell if the others would work for you or not.

mja024

Okay, I'll email the seller and see if the 56T one may work for a multi-gear application and a 3/32" chain. If it doesn't fit the bill I'll keep looking.

habilis

One of the online gear calculators (like this one: Fixed Gear Calculator - Ratio & Skid Patch for all! ) can help you predict the effect of a different chainring or gear cluster. For example, the 56T ring would let you reach 20.9mph @ 130 pedal rpm. That's with your 16" wheel and the 14T cog in back. Not too shabby.

Also, look at the answered questions at the bottom of the page for the Lasco item. One customer says it will work with a 6-speed rear cluster, so chain width is 3/32".

EDIT: Turns out Lasco is a Taiwanese company, so taper should be JIS, but you may want to ask the seller. An ISO crank on a JIS spindle (or vice versa) could cause problems. Google Sheldon Brown on this topic.

fietsbob

my 16" wheel bike has a 3 speed hub and a 15t sprocket , and a 54t chain ring . *

it puts the range of those 3 gears where its useful @ 58g" (1st 43, 3rd 77)

you need a crankset with the potential to exchange chainrings..

When I bought it, a Brompton, it had a 13t on the hub & a 50t on the crank.


if the price/quality are there you can change things once it is in your hands, thats what I Do.