[roadbike_moron]

This is truly odd.
What would cause a SRAM rear derailleur to go out of adjustment every time I change a flat?
When I pop the wheel back onto the bike ( yes, it's positive and straight), I always have to mess with the barrel adjuster so that the chain doesn't skip.

What could be the cause - cable stretch?

 

[wim]

What would cause a SRAM rear derailleur to go out of adjustment every time I change a flat?

I've no idea, and am venturing the guess that your diagnosis is simply false. The rear derailleur doesn't go out of adjustment every time you change a flat, but something else is not lining up or seating properly after your wheel changes.

Do you shift the chain to the smallest cog before removing the wheel, put the chain on the smallest cog when replacing the wheel and let the wheel re-seat itself with the bike standing straight up on the ground?

 

[Ventruck]

If you're really sure about how you put the wheel back in, I'd suspect cable stretch - coincidentally recurring whenever you remove the wheel. This is just on the mere basis that cable stretch would yield frequent RD adjustments in my experience. That, and you didn't address the condition of your cable.

 

[natedg200202]

A cheap RD hanger that does not fit flat against the dropout and moves slightly when the wheel is removed and replaced. Look into getting a Wheels Manufacturing replacement.

http://wheelsmfg.com/content/section/4/27/

 

[Andrea138]

I 2nd the bent hanger theory.

 

[fast ferd]

If it's one of those replaceable hangers attached with tiny allen screws, sometimes those screws loosen and create a little play.

Cables don't typically stretch, although housing seats in places, giving the illusion of a stretching action. This is quite obvious just after one replaces a brake cable and clamps hard on the lever afterwards to cinch things up. For the shifting cables, you can accomplish the same thing by shifting to the bike's biggest cog or ring. Then fine tune it.

 

[roadbike_moron]

Thank you for everyone's help.
I will check the hanger. I had that replaced several months ago, and it's been doing it ever since.

 

[cxwrench]

i've noticed something that happens w/ the team bikes every now and then. the sram derailleur cable has to go over that little grooved fin before it goes under the anchor bolt. if you pull the wheel out and push in on the derailleur to make some room, sometimes the cable will be so slack that it comes off the 'fin', and then your adjustment is wayyyyyy off. the photo is how it should look...

 

[frdfandc]

Cables don't typically stretch, although housing seats in places, giving the illusion of a stretching action. This is quite obvious just after one replaces a brake cable and clamps hard on the lever afterwards to cinch things up. For the shifting cables, you can accomplish the same thing by shifting to the bike's biggest cog or ring. Then fine tune it.

Your right to a point. Cables don't stretch, but elongate. Along with housings seating, as you use the shifters/brakes the little strands get compacted together, being pulled tighter together, giving a sense of stretch or elongation. Kind of like tying something up with a nylon rope. As the weight is pulling on the rope, the strands are pulled together, then the rope elongates and the item drops lower than when you first hung it up.

 

[fast ferd]

Maybe with cheapo cables

Your right to a point. Cables don't stretch, but elongate. Along with housings seating, as you use the shifters/brakes the little strands get compacted together, being pulled tighter together, giving a sense of stretch or elongation. Kind of like tying something up with a nylon rope. As the weight is pulling on the rope, the strands are pulled together, then the rope elongates and the item drops lower than when you first hung it up.

I've used Dura-Ace cables for years. No stretch, no elongation.

So perhaps it depends.