Originally Posted by
cyccommute
That fits in the “hub not square in the frame” scenario. This whole “out of dish wheel” thing is a red herring. How often have you used a wheel that is significantly off-dish? How often have you run across one that is out of dish even a little? And, finally, how often are you going to end up with a bent derailer hanger and have a wheel that is out of dish? There are a whole lot of stars that need to align for any of this to happen.
It's not a red herring.
Put yourself in a different pair of shoes - so to speak.
You tell the new mechanic:
"No need to check the dish of the wheel, just make sure the current wheel is centered. Attach the hanger alignment tool as such. Check the top position, check the bottom position, and check the forward position. When the comparison at the three looks about the same, done!"
Then you head out to lunch, or to talk to a customer elsewhere in the shop - never noticing the mechanic scratching his head for a few seconds before finishing up the bicycle.
Several days later, customer returns complaining about a little noise, and a little hesitation on the downshifts.
You eyeball the bike from the rear, and notice the rear derailleur is angled in the forward position slight AWAY from the centerline.
Question 1: Why did this happen?
Question 2: How is this avoided 100% of the time?
Hint: I already gave the answer.
And yes, I don't just work on wheels, about 5% of my business is working on bikes - and rear derailleur hanger aligned outward in the forward position on steel and just recently an Aluminum bike with a stainless steel dropout hanger is something I see way to often.
Another hint:
There's technically correct advise. And then's there's good advice - they're not always one and the same.
=8-|