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Chain choice(8 posts)

Chain choiceVikingbiker7
Nov 25, 2003 5:28 AM
I have just finished my fixie, but I have a concern about my chain. I have a Sram with the powerlink. My worry is that when I use the pedals to stop, the chain may come apart. Is this just neurotic thought, or a real problem. Thanks for any help.
Yes.eddie m
Nov 25, 2003 8:03 AM
Most chain failures are caused by the combination incorrect joining and the high stress caused by shifting when the chain engages two cogs simultaneously on the cassette. Chains on fixed gear bikes rarely fail IF the cogs are reasonably well aligned and the chain is joined properly. Regardless of whether you apply back pressure or forward pressure to the pedals, you will still only load the chain in tension. If you try to apply a compression load to the chain, it will just fold up.
Super narrow derailer chains are a poor choice for fixed gear use, both because they are too expensive and because of the difficulty of joining them. I use inexpensive KMC chains for my fixed gear. KMC has a website with all the chain specs, and I choose whatever 3/32" chain has the longest rivets. Longer rivets can be pressed in with an ordinary chain tool without worrying too much about perfect alignment or about peening the ends over for more strength. If I wanted to spend a lot of money for a fixed gear chain, I'd convert the whole drive train to Japanese spec track stuff, or get a NOS Regina ORO on Ebay for $45 or so.
Is it 1/8" ?Steve Young
Nov 25, 2003 9:04 AM
Just wondered if it was a 3/32": or a 1/8". IIRC the SRAM PC1 is a 1/8" chain - just wasn't sure whether it is possible to get a powerlink in 1/8"

I agree with the other post - braking only applies tension forces to the chain - there should be no risk to the powerlink on a fixie. (Opinion only - I haven't tested this:)

Steve
Is it 1/8" ?Vikingbiker7
Nov 25, 2003 9:49 AM
No, it is 3/32. Thanks for the info. I can't wait to ride it tonight!!!!
Is it 1/8" ?mr_e
Nov 25, 2003 9:53 AM
KMC (and I beleive SRAM) sell master links with most of there decent 1/8" chains. I know KMC offers them seperatly as well, in several sizes (depeding on the pn length you need). Ask your LBS about em. I beleive they are in the SBS catalog, but maybe Quality stocks them as well (both wholesale companies your LBS likely has an account with).
SRAM PC-58 for over 8 months w/out failureTig
Nov 26, 2003 8:21 PM
I liked the ease of the power link on my geared bike so much, I use a SRAM chain on my MTB and fixed gear as well. I use the 8-speed instead of the 9-speed chain on the fixed gear since it is stronger. Watch an MTB race where people brake chains and you won't see an 8-speed chain among the casualties.

SRAM products are gaining my confidence more and more over Shimano. That's one of the advantages of being an LBS mechanic... you see what works and what doesn't, but on other's bikes!
Fixed chain tension is no higher than geared!winstonc
Dec 5, 2003 12:28 AM
Everyone seems to have the impression that fixed-gear riding puts more stress on the chain. This simply isn't true.

The difference between fixed and coasting riding is stopping, and that's where people think the danger of chain breakage is. The maximum force that you will put on the drivetrain is when you lock your legs and the bike skids. The speed at which you start the skid doesn't matter; the skid is the max deceleration rate, and corresponds to the max chain tension when stopping.

I don' t have the numbers here, but I'll throw this out: there just isn't that much force in a skid. I don't think it's much more (if at all) than the amount of force in a hard acceleration. Sorry I can't back this up with any data...

Before you say my argument is half baked (which is sort of true), let's look at some numbers. Let's say you're running a 42-16 setup, with 170mm cranks. The 42T chainring has a diameter of about 21 inches, and a radius of approximately 93mm. When you pedal forward, you get a mechanical advantage (MA), relative to the chain, of 170/93, which is roughly 1.8. That means the chain tension is 1.8 times the amount of force you're putting into the pedals.

We all know of big, tall, beefy MTB riders. Let's say 250 pounds. He rides up walls with his 21T granny gear. This guy is probably riding a 180mm crank, so his MA is about 3.85. That's over twice the MA that you have. Plus he weighs 1.5 times as much as you, the scrawny roadie. So he ends up putting over 3 times as much force into the chain, on a sustained basis. Do you hear of his chain breaking? Only when he's neglected it (ie. rust or severe wear), or if he's bashed it into a rock. You would never hear of such a chain breaking from climbing a steep paved hill in his granny ring. (Keep in mind that the size of the rear cog is irrelevant here.)

All that said, having a chain break on a fixie when you're skid stopping is really bad news. So it's a good thing that you're aware of it...
Oopswinstonc
Dec 5, 2003 12:31 AM
I just realized I answered a question you weren't asking... Eddie's response is dead on.

But the stuff I wrote is still true. It's just the wrong answer here. :)