I have Sugino 75 cranks, BB and 48t chainring, Surly 15t cog, Izumi chain.

First comment: I have never had a new chain 'wear-elongate' aka stretch so much. I've run out of tensioner adjustment range when I had 1/8" to spare before. Is Izumi chain known to be this bad? I tension it right and 20mi later (with zero axle slipping) its loose again. It has 700mi on it and still loosens after every ride. (to the point I can move chain up and down ~1/4" and there is feelable and visually noticable backlash on crank arms.

More importantly I have noticed a small skip or micro-jump when cranking hard up farily steep hills seated. It occurs when the left crank arm is just starting downstroke. I wonder if crank arms are tightened correctly to BB axle, or if top/botton chain tension difference could cause this. I'll swing by LBS to be sure on crank install.

I had none of these issues with my previous 3/32" drivetrain.

Al

wow. that's a lot of stretch.

Yeah, my guage says I almost need a new chain already.

The slip sounds like your lockring's a teeeeeeny bit loose. Take off your rear wheel, and remove the cog & lockring. Crank the cog back down hard, then crank the lockring down extra hard, on top of some loctite. That should eliminate the slip.

Thanks for the idea. I know my cog and lockring are tight. There is also zero loosening force when cranking up a hill.

Al

can't say for sure, and i'm not sure what you meant by skip. but i wouldn't be surprised if the chain is indeed stretched badly, that the links would grind against the teeth. maybe this phenomenon is worse at the beginning of the downstroke since that is when chain tension is highest?

pure speculation, i'd replace the chain and see. best of luck.

By skip I meant a very slight extra movement forward that can only be felt in the leg as a little 'tick' if you will. Always in the exact same crank rotation position as I begin the downstroke on the left side/leg only.

Is it possible for a chain to wear this much in 700mi of relatively clean non wet roads? My last 3/32" fixed gear chain lasted 6800mi before it measured as stretched.

Al

did you change your cog and chainring? It still seems pretty fast.

Everything was new out of box.

very strange. if a chain does stretch that fast, it's either a manufacturer defect or a piece of crap. or both.

There was another thread I started when I first got this driveline, complaining how noisy it was. That was at ~100mi.

https://www.bikeforums.net/singlespeed-fixed-gear/267247-fixed-drive-chain-noise-1-8-a.html

Now the noise is much less, but it keeps getting longer!

Note there were a couple of folks in that other thread noting that Izumi eco chain is known for its stretching.

Al