What is the difference between 1/8 and 3/32?

Why do I get the feeling I am going to regret reviving this thread?

New bike comes with 1/8 chainring, 1/8 chain and 1/8 fixed cog, and looking to put a White Industries Dos Eno double freewheel on other side (I don't ride fixed, and having a bit of flexibility in gearing suits what I want the bike to do)

Trouble is the Dos Eno freewheel is 3/32 - with switching between the two cogs chainline may never be perfect, and biggest fear is whether this will be enough to affect drive, or end up derailing chain

1/32 is a tiny difference in chain width, but is it going to screw up my plan for a simple ratio change? next best option is a custom free/free hub (Phil Woods or similar) but the tyres I plan to run are directional so not really an option

Any suggestions

It'll be fine.

Definitive answer took me by surprise there!

Looks like I need to start shopping for parts :)

It'll never work.

It might be fine, but there's a possibility of fatal failure.

It'll be fine.

lol

Why do I get the feeling I am going to regret reviving this thread?

New bike comes with 1/8 chainring, 1/8 chain and 1/8 fixed cog, and looking to put a White Industries Dos Eno double freewheel on other side (I don't ride fixed, and having a bit of flexibility in gearing suits what I want the bike to do)

Trouble is the Dos Eno freewheel is 3/32 - with switching between the two cogs chainline may never be perfect, and biggest fear is whether this will be enough to affect drive, or end up derailing chain

1/32 is a tiny difference in chain width, but is it going to screw up my plan for a simple ratio change? next best option is a custom free/free hub (Phil Woods or similar) but the tyres I plan to run are directional so not really an option

Any suggestions

A 1/8" chain is designed to work with a straight chainline.

A 3/32" chain is designed to work with derailleur gears which means an often staggered chainline. It will flex more easily than a 1/8" chain to allow this.

Given that the chainline will always be slightly off with the Dos you can see why they went for 3/32".

A 1/8" chain will happily sit over a 3/32" cog and will have some side to side play - possibly enough to allow for the difference in chainline but depending on how close together the cogs are a 1/8" chain may foul the larger cog when used on the smaller one. (Try putting a 1/8" chain onto a 9 or 10 speed cassette to see what I mean).

So, it'll probably work with an 1/8" chain, would almost certainly work better with a 3/32" chain but will never work as well as a single cog/perfectly straight chainline regardless of what chain you use anyway.

3/32 is 3/32. 1/8 is 4/32.

Those were the days when important topics were being discussed on the forum.

Dont think Ive ever seen a definitive reason to choose 1 over the other besides 1/8" having more surface contact area between chain and cogs so less deformation on the chainring teeth as the force is spread out more.
The Japanese keirin riders only ever use 1/8" but there are 3/32" dura ace chainrings available and Id have to double check but they may have njs stamps on them.

both chain types have the same side plate thickness so share same tensile strength, not sure how much lighter 3/32" is,
ill weigh equal lenghts of new kmc 510hx and 610hx some time for comparisson. The lighter weight would prob offer negligble acceleration advantage, the chainrings are same thickness up until the support ridges at the edges were the teeth begin.

Shimano had their Dura Ace 10cm pitch but overall it wasnt much of a weight saving.

in conclusion 3/32" looks funny on a fixed/track bike, it looks weak and skinny. 1/8" should always be used with the largest chainring possible

3/32 have never been approved by njs

3/32 have never been approved by njs

Absolutely this.

I've heard it said that at least at the lower end of the price scale, 3/32" chain is more actually stronger and more reliable than 1/8". This would supposedly be due to singlespeed drivetrains being somewhat outdated and thus, chain manufacturers would be investing time, effort, research etc into multispeed chains.

Pretty sure this would be invalid by the time you got to talking about NJS stamped chains.

My experience, never had a totally 1/8" drivetrain skip or jump or miss a beat but when I fitted a 3/32" cog to my otherwise 1/8" track bike's drivetrain (should be compatible) it ran like shit, catching and clicking and banging under load.

I've also had a fully 3/32" singlespeed setup drop a chain which almost put me under a transit van.

I've heard it said that at least at the lower end of the price scale, 3/32" chain is more actually stronger and more reliable than 1/8".

The conjecture held perhaps in the 1970s but no longer. 3/32" is now obsolete. The old Sedis and Regina chains that used to be so popular are no longer available--- production ended decades ago. For the past 2 decades almost all road chains are bushingless designs and all the latest and greatest are for multigear setups of 8 and beyond. By current standards the Rohloff SLT-99 (no longer in production), in its day with 7.1mm (6.8mm for the 9-speed version) the narrowest and most flexible chain on the market, is wide (Campa's 11-speed chain is 5.5mm wide).

For 3/32" track/singlespeed you want a chain with bushings and 7.8mm wide. These are now at the fringe. HIghest end chains seem to be either old school 1/8" for elite track (Izumi and friends) or super narrow chains designed for fast gear changing in multi-gear systems. In the middle are 1/8" BMX chains. With BMX still going strong, singlespeed/fix-gear become cult and road cycling drifting off into sub 6mm spheres.. the pendulum has swung back strongly for 1/8".

I think the only argument for 3/32" left is the available of old Campa NR/SR 144 chainrings. While Campa made them with 42 to 70 teeth most of the NOS chainrings one will find are limited to a few popular sizes.