MACinRWC

300 yards from my driveway as a accelerated up the last little hill, my chain breaks-I coasted home with it in my pocket, and threw it in the garbage when I got home. Today I go to put a new chain on it and I don't know how to measure how long the chain should be-(9 speed Dura-Ace chain) when I put it on my bike.
b/c this morning was garbage day-the chain is gone, and I have no idea how log it needs to be.
is there anything I need to measure by


does it matter?
what should I measure?

thanks
mac

well biked

Yes, very much.
Sheldon's got you covered:
https://sheldonbrown.com/derailer-adjustment.html#chain

MACinRWC

thanks a lot

Mach42

Yes, it most definitely matters.

Too short and you will rip up your derailleur if you shift into the big ring/big cog combo. And I mean, it will rip the D off, and possibly either put it into your spokes or bend the frame.

Too short and you will have issues with excess slack in the small/small combos, and that's bad too. Though not nearly as instantly destructive as having it too short.

Here's what Zinn says about finding the right length:
"Wrap the chain around the big chainring and the biggest cog without going through either derailleur. bring the two ends together until the ends overlap. One full link should be the amount of overlap."

Parktool's site will probably also have a guide to follow.