I started a regular tuneup on my gf's 7-speed roadbike today and out of habit checked the chain stretch. This bike has (probably less than) 400 miles since the last chain replacement. To my surprise it was obviously .75 stretched! I talked to my LBS mechanics and they told me there's almost no way this could have happened in less than 2000-3000 miles and were confused. Any ideas what's going on?

as a side note:
-the cogs and chainrings have been maintained
-rides in all weather
-live in new orleans, the roads are flat so we often ride in top gear only
-chain is lubed occasionally, but probably could be lubed more often
-chain is not rusty or dry

No benefit in going cheap, premature chain replacement is OK .. it should allow the chainwheels it wraps around to last longer..

".75" what?

The only accurate way to gauge chain wear is with a ruler. You need to remove the chain once in a while to clean and service it. My worst chain wear was with Prolink. I would simply relube the chain and wipe it down. The chain lasted 2000 miles.
Chain care, wear and skipping by Jobst Brandt

If you're using the Park chain checker, try measuring between some different links on the chain and see if you get the same reading everywhere. Since it works by squeezing the rollers together, you might just have one roller with too much slop and it's not stretched at all.

++ Chain wear indicators are a solution looking for a problem when it comes to non-shop use. Save your money and use a ruler. I cannot think of a single reason that an individual would need a chain wear gauge, aka chain selling gauge.

@fietsbob yeah I’m changing it regardless. just don’t want to change the chain every ~300 miles for an unknown reason

@AnkleWork .75% vs 1% stretched as indicated by a chain wear indicator tool similar to Park Tool Co. » CC-3.2 : Chain Wear Indicator : Chain

@davidad why wouldn’t using an actual tool designed for checking chain wear be more accurate than an eyeball estimate with a ruler?

@DiabloScott checked several times at different spots, wear indicated all around.

OK, and did you measure it when it was new?

The chainchecker is a fine tool for a quickie measurement, but it can read high; I'd always double check with a metal ruler before I'd throw away a chain.

[MENTION=68015]DiabloScott[/MENTION] heh, no didn't check when new. I'll go check with a ruler too, thanks for the heads up!

Finally!

@davidad why wouldn’t using an actual tool designed for checking chain wear be more accurate than an eyeball estimate with a ruler?

The chain checkers measure at the rollers and they don't contribute to wear. In my experience when my Rohloff gauge showed .75mm wear the chain was still in good shape. You will find a lot of BS in the bike business.

Chain checkers are bs. Don't trust us, read the experts; then use a ruler.

KMC digital chain wear gage More satisfyingly technical , perhaps ? KMC Digital Chain Checker : Fairwheel Bikes, Cycling Boutique

If you are using the Park chain checking tool with the two pins, they can be bent if you squeeze the tool too hard.

Even a brand new chain has some play in the rollers (varies with brand), so unless the chain checker is compensated for that it will show a new chain as having some wear. Also most checkers measure over a short distance so the added roller play can add significantly (in proportion) to the perceived pin wear.

This isn't to say roller play doesn't matter (it does) but the 1/2% rule of thumb (1/16" over 12") is based on pin wear only, with the roller wear imputed. Adding it then is essentially double counting.

Most people that have gone this route, use a chain checker as a screening device, then confirm with a ruler.

BTW- it is possible to properly integrate roller and pin wear, and some chain companies use their own replacement guidelines based on combined wear. However, to my knowledge, none of the gadgets sold as chain checkers are properly calibrated to factor the roller wear, and therefore read high.

Dirt can cause premature wear. Your experience sounds extreme even considering the effect of dirt however.

IME the only thing that can cause this kind of wear (not counting being used exclusively for the mt. Washington climb) is rust. If you ride an unlubed or poorly lubed chain in the rain, the water can wick in and attack the pins before it dries completely. This speeds wear, and can happen even if there's no surface rust visible.

However, I suspect that the OPs problem isn't wear as much as high readings on a gadget.

here's some images of the chain... looks like its right at 1/16th over 12inches. still seems extreme that this occurred over so few miles.

Now we're getting somewhere. Your chain appears inadequately lubed. Add some rain and dirt and there you are.

Yep, it's worn.

There's no way of knowing why, but lube or weather may be factors. Also, the chain wear rate is highest when using the smallest rear sprockets so that may also factor, though that would need a strong rider to matter.

One other thing to consider is that not all chains are made of the best materials. If this is a low end OEM chain that alone may explain it.

BTW- why would a non-skid surface be a feature on a ruler. Are slippery rulers are such a safety hazard?

Just curious, was the chain originally purchased from a shop ? Or was it bought from an acquaintance of some sort. Less than 400 miles, I just don't see it happening with a truly new chain. I guess it's possible, just not very likely.

[MENTION=158672]FBinNY[/MENTION] ha! ruler was bought for graphic design purposes, skid marks on professional artwork never looks good [MENTION=54127]Northwestrider[/MENTION] its a KMC Z51 chain bought from a LBS, I'm replacing it with sram 850 bought from an LBS and promise to be more vigilant in the future

Again it's interesting, I looked up the KMC chain on Amazon and found it rated quite well, in any case good luck with the Sram chain. I'd be happy to know how the Sram does in comparison ? Lets us know. BTW I use Sram and Shimano , both have worked well for me.

Now all derailleur chains are bushingless in design. rather than a sleeve running across the whole inner link, supporting the roller and the pin.

the surfaces bearing the load are steel, left, pushed in , when punching the hole in the inner link . its how they are made more laterally flexible..

But the surface area is less , so the weight , being the same is spread over less surface and so will wear faster
than say a 3/32" Bushing Chain (running in a straight line )

but Derailleur shifting performance requires the flexibility.

Be sure to measure with both ruler and chainchecker and create a table of values - say every 500 miles - and post results here.