kevincott

Hi all, new member.

I am a long term mountain biker turned city biker. Bought a Breezer city bike with Shimano ALFINE FC-S500 with 8 speed gears hidden in the rear hub.

Looking to upgrade the fly-wheel from stock 39t, as I find gears 1-3 all but useless.

Is there an effective/efficient way to upgrade my crank fly-wheel? Are there many options?

trailangel

What Flywheel?

CliffordK

Ok,

You apparently have an Internal gear hub (IGH) on the rear.

You need to change the chainring.

Photos would help. Go to the Advanced editor and click on the paper clip "attachments"

Upload a photo of the bike, and of the crankset, 100 to 200 kb, JPG. Oh, also a photo of the sprocket on your rear hub.

If the chainring is bolted on with 4 or 5 bolts, then it is relatively easy to replace.

If it is riveted on, then you'll have to replace the whole crankset. Probably "square taper". Fortunately new cranksets aren't that expensive.

You'll also have to replace the chain with a new 1/8" single speed chain, and may need a chain tool to do so.

If your city is pretty flat, then a 48T or 50T chainring would probably work well.

Oh, also look at the rear sprocket. It may be easier and cheaper to buy a smaller rear sprocket instead of the chainring or crankset. How many teeth does the sprocket have?

Sci-Fi

Missing a lot of information. What cog is on the rear hub? Looking for more speed? Why are gears 1-3 useless?

What crank is on the bike? If it's Shimano Nexus/Alfine, it came in 2 BCD versions, 130 and 110...can easily find bolt-on replacements. Probably need a new (longer) chain to size it for a larger chainring.

kevincott

Thanks for reply.

Did not occur to me to change the rear sprocket, good call might be more effective. Rear sprocket appears to be integral to rear hub shifting mech. Also can't count rear crank teeth (covered) and nothing in any spec sheet I can find.

My apologies, I thought fly-wheel would be self explanatory, I have ridden for years but not thought about upgrades/terminology.


Having trouble w photos, don't have 10 posts. Crank wheel has 5 bolts. Lowest my camera goes is 804 kb, can't find editing options to decrease size.

edit: I find gears 1-3 are too low and worthless.

edit2: BCD is 130mm according to specs.

Jeff Wills

OK, 130mm BCD is pretty darn common. Universal Cycles breaks out chainrings by BCD, so you can pick among different manufacturers:
https://www.universalcycles.com/shop...?category=2629

If you feel like getting fancy, the colored Pake rings would fill the bill.

CliffordK

Did you click on the paper clip attachments under the advanced editor?

Ok, 130 BCD is pretty common. As long as you have 5 nuts holding the chainring on, then you can replace with a number of chaingrings. And also replace the chain with a longer chain.

There are some single speed specific (1/8") chainrings which will be a little better than multi-speed rings, although it won't make much difference. Also "vintage" rings from E-Bay without the new shift pins/gates.

Wolftooth makes quality single speed rings, but are a bit expensive.

https://www.wolftoothcomponents.com/...oss-chainrings

Here is a 48T, 1/8" single speed ring that should work.
https://www.ebay.com/itm/48T-Fixed-G...8/122863485127

And 50T
https://www.ebay.com/itm/MOJO-Fixed-...R/122100590573

Get a new chain too (1/8")

As far as the rear sprocket. It is a wear part and must come off. Probably a circlip of sorts holding it on.

Dan Burkhart 

The rear cog is not integral to the rear shifting mech, AKA cassette joint, but it is mounted behind it. If it has the cog with integrated chain guard, it will be either a 20 or 18 tooth.If this is the case, the cog is dished inward by default, and replacing with a smaller cog like a 16 tooth should work OK.

In some applications, the cog is dished outward for correct chainline, and in these cases, smaller cogs can cause chain/cassette joint interference.

cny-bikeman

I would suggest you determine the number of teeth on the rear cog before making any changes. It would be very easy to go to the other extreme, so that you have insufficient low gears - in case you take a trip or move to a place with hills, are carrying a load on the bike, etc.

Also, you may be doing yourself no favors even if nothing changes about where you ride and what you carry. Even if I assume you have a 20 tooth rear cog, saying that even your 3rd gear is "too low" indicates to me that you are being very inefficient on the bike, and possibly setting yourself up for knee problems. Using the ratios on either the Alfine hub the 3rd gear should be good for about 10mph at 80 crank revs per minute, and would be useful for acceleration from a stop as well. Lower than 80 revs is usually not very efficient and has lower cardio benefit. Much lower means more knee stress as well. Of course if you have an 18 tooth rear cog the gearing is 11% higher. I think ramping up to a 48 tooth is inadvisable no matter what the rear cog, as your high gear(s) will then be the useless ones..

kevincott

Thanks, a lot of good info given.

I may slightly exaggerate 3rd gear being useless, I use 3rd when I start out or go across grass. Not very often. I live in Chicago suburbs where it is relatively flat.

Not sure what my crank/minute is but I shift to maintain a steady crank pace and enjoy the speed. Only issue this time of year is getting back into 'bike shape'. I run 3 miles in 21 minutes and do lots of cardio all winter, bike pumping hits the legs a bit different and gotta re-adjust.

Lotta comments about the rear cog. It appears Dan was right and I think the rear cog is behind a shifting cassette. Will do more searching and try to find the rear tooth count.

kevincott

Couple websites say my rear cog has 18t.

I am considering either a 16t rear or roughly 45t (39t stock) front, 15% upgrade either way.

Downsides: need new chain replacing front and unsure of rear cassette complexity. Keeping OEM parts I can always return to stock if desired.