joiiisey

I have a 2016 Fuji Track Bike, single speed fixed gear.

It has the ability to switch to a freewheel, as the other side of the hub is threaded, however the single speed freewheel is not included with the bike.

My question is:

If I purchase :

SHIMANO DX SINGLE SPEED FREEWHEEL, it has choices of 16t, 17t, 18t. I am unsure of the differences b/w the 3, and if I choose a particular one, will i need a new chain. The Fuji currently includes a :



16T fixed cog w/ lockring



KMC Z510 chain, 112 link



As I am not familiar with this , which can I install with the stock chain and which will I need a longer chain, and difference among the 3.

aniki

The difference between the three is the number of teeth; one has 16, one has 17 and one has 18.
How old is your current chain? If it's fairly new you may well get away with it (although technically it will 'work' anyway)
If you're currently using a 16t and the wheel is positioned right in the front of the dropout; we can assume the existing chain won't be long enough to accommodate a cog with a greater number of teeth.
If there is plenty of room for adjustment in the dropout you will likely get away with a freewheel with an extra 2 teeth.
If your existing chain is old and worn it would be prudent to get a new one anyway and install at the same time as the freewheel.
If you are currently happy with the gear ratio you get with a 16t then stick with it. If you want an easier gear, get the 17 or 18.

Lot's os 'Ifs' I'm afraid.....

joiiisey

its the stock chain which the bike is lightly used..

joiiisey

so if I have a lightly used stock chain, 4 year old bike. Is it safe to get a 17t freewheel, without having to change my chain?

79pmooney

Sounds like you are new to all of this so a quick crash course. (And I will forget a key point or two. Forgive me.)

One - chain and cog wear. Chains "stretch". (It's actually wear, but the pins get further apart.) As the chain stretches, it wears the cog's teeth to match. With not too much stretch, you can put a new chain on that cog. More chain stretch and cog wear and the new chain will not run well on the worn cog. If you run a stretched chain over a newer cog, you will rapidly wear the cog to the stretch of the chain.

It is easy to measure chain stretch. Use a metal ruler or tape measure. Measure 12 pairs of links from pin center to pin center, (I measure pin front to pin front. Exactly the same, but far easier to see accurately.) A new chain will measure 12" exactly. 12 1/16" - chain replacement time if you want to be able put a new chain on. More than that and you may have issues running it over a new cog plus you will be "aging" that cog fast.

Two - there are two different chain widths for single speed/fix gear bikes, 3/32" and 1/8" with cogs to match each of the widths. Likewise chainrings. Your Fuji is probably 3/32" but go look. (The dimension is the inside width of the narrow links.) You can run an 1/8" chain over 3/32" cogs and rings (I don't but many here do) BUT you cannot run a 3/32" chain on 1/8" cogs and rings.

Three - the rear hub is sitting in a horizontal slot on the bike, called a track end. The slot is roughly 1 1/2" long. You accommodate different cog sizes by sliding the hub forward and back. Each tooth you add to the cog means you have to slide the hub forward 1/4". Do you have a 1/2" of slot forward of where the hub is sitting now? That's your answer re" chain length. If you buy a new chain, give thought to whether you want to keep the old length or go a pair of links longer.

Four - chain slack (or "tension"). Fix gear/single speed chains should always have slack at all times. Meaning, if you put the bike on a stand and spin the pedals, over the next few minutes, the chain should never go tight. If it does, you are loading the bottom bracket and hub bearings with a load applied by a steel band. You may think you are strong, but compared to steel bands, we aren't ****! Beginners and hipster love to set their chains tight. Go to to the velodrome and look at the guys with elephant quads who race very expensive bikes and you will see real chain slack on every one of those bikes (from the spectator stands).

We who ride the road set our chains a little tighter. (They don't allow pavement bumps at velodromes!) Still, we always should be running some slack. Now slack is less than an 1/8" of hub movement so it really doesn't affect how many teeth you can add and stay within the track end.

There's plenty more to say but I'm calling this enough for the day. Quote me if you have questions. (I don't ride single speed but love riding fix gear and have for the past 45 years. 10 years ago I went to a fix-fix double hub. (Oh, useful fact - you can run a freewheel on the fix gear side with no issue. Exact same threads. But don't run a fix gear cog on the freewheel side because you cannot run a counterclockwise lock ring. You could spin the cog off with a hard stop.)

Welcome to Bike Forums! And yes, you are asking about a freewheel but keep riding the fix gear. They rule! But don't let that stop you from riding.

Ben

aniki

It's your call but if the chain is 4 years old, lightly used or not I would replace it anyway.

Rolla

That depends on where the axle is currently positioned in the dropout (or track end), and how long the slot is. A 17T cog will set the axle closer to the seat tube, so you need to have enough room in the slot to accommodate for that. But a singlespeed chain only costs like 12 bucks, so replace that four-year-old one anyway and you don't have to worry about it.