Sy Reene

Shifting issues are often diagnosed as potentially caused by a RD hanger alignment problem. Is it a possibility that instead a hub could off by the small fraction of a degree necessary to cause shifting issues? Is this a nonsensical question? If we correct RD hanger alignment with one of those purpose-made tools in this instance, could there be potentially the same problem when we go to put on another wheelset (ie. one whose hub wasn't misaligned)?

Bill Kapaun

The hub should have the same relation to the axle which should go in the same place.

mrrabbit 

First off, before even trying to align a rear derailleur hanger...the rear wheel must first be verified as a properly dished wheel.

THEN . . . that wheel is to be installed centered between the stays.

THEN . . . the rear derailleur hanger is aligned parallel to that wheel...and by virtue of that, parallel to the center line of the bicycle.

An improperly dished wheel centered between the stays WILL result in the hub not seated properly in the dropouts.

Aligning the derailleur hanger against that will result in incorrect alignment.

=8-|

cyccommute 

Okay. Kinda. Well, now that I thing about it, it won’t matter. A derailer hanger tool aligns the hanger based on the distance of the arm to the top and bottom of the wheel. The distance of the center of that wheel is from the rim won’t matter with respect to the position of the hanger.

You could have started and stopped right there. Before checking for derailer hanger alignment, ensure that the hub is square in the frame. Full stop.

Nope. Won’t matter. As I said, the derailer hanger alignment is based on the distance of the hanger from the top and bottom of the wheel. The wheel could be feet off to one side but that wouldn’t make any difference to the alignment measurement.

Nope. Not a sausage. The only thing dishing does is center the rim between the ends of the axle. It has no bearing on how the hub will seat in the dropout unless the dish is so far off that the hub can’t be mounted in the frame. But that’s a very different problem.

Aligning a derailer hanger against a improperly seated wheel will result in an incorrect alignment. But dish doesn’t factor into the alignment process.

JohnDThompson 

Hanger alignment tools use the wheel as a reference plane, so I suspect if you use the same wheel to ride that you used to align the hanger, it won't matter.

cyccommute 

More succinctly put then I did but essentially correct. The only quibble is that it wouldn’t matter which wheel you use. The wheel is just a plane of reference. If you used a piece of cardboard, the results would be the same as long as the cardboard is aligned with the frame.

Sy Reene

I get this, but if the wheel is off, using another wheelset may require another RD alignment to work? Anyway, bad shifting stories usually get a RD alignment troubleshooting response. It never seems suggested that the wheel could be a tiny bit off, or how one checks that.

70sSanO

A bent axle can cause shifting issues. I think most qr axles are not perfectly straight, as in thousandths of an inch.

I know as I’m trying to get precise cup-cone adjustments I sometimes will feel more play at one point than at another point around 90*. Usually it doesn’t impact shifting. I attribute it, right or wrong, to axle straightness.

I did have an issue that went away when I swapped out the axle. The axle was maybe 1mm out, which I wouldn’t think would cause a problem.

I’ve only tweaked the hanger on my steel frame bikes. I have used a square to get the hanger close enough for 8 speed cassette spacing.

John

mrrabbit 

Derailleur hanger is aligned in four positions, not two. Top, bottom, and most importantly, front and back. That insures the hanger is aligned properly planar parallel to the centerline.

If you align the hanger against an off dish wheel that is otherwise centered in the chain stays, the hanger will be off alignment either at the forward reference or the rear reference depending upon which side the wheels is off dish.

=8-|

Common dude, I've known you as a smart person for a long time...you should know this.

cyccommute 

Theoretically. Functionally only 3 because the 4th one is hard to get to because of the frame. New versions have a swing arm that allows you to get past the frame but older ones don’t. But, again, that has nothing to do with the dish of the wheel.

No, it won’t. A wheel that is off-dish isn’t “off dish” on the front or back or top or bottom. It is off-dish all the ways around. Let’s assume that the valve stem is 12 o’clock. If you put an off-dish wheel in a truing stand, do you move the arms of the stand when the wheel is rotated to 3 o’clock or 9 o’clock? No, the rim is in a plane. It just happens to be in the wrong plane but the displacement is the same all the way around the wheel.

The gauge of a derailer hanger isn’t moved from the measurement top to bottom nor front to back...nor from top to 9 or 3. A wheel that is off-dish will be displaced the same amount of distance from the hanger in all dimensions. If the hub isn’t square in the dropout that would have an effect but the dish doesn’t have the same effect.

What you are describing is a tacoed wheel. The rim isn’t in the same plane depending on the position of the wheel. It would be silly to align a hanger to a tacoed wheel but I really don’t someone would do that.

I often have aligned the hanger without a gauge for various reasons. I sight to the cogs on the cassette and don’t worry about the wheel location at all. Alignment is done by drawing a line from the cog though the two jockey pulleys.

mrrabbit 

If you take a wheel that is off dish 1/2" to the non-drive side AND insert in the rear stays and CENTER it between the chainstays....the trailing point of the wheel at the rear of the bike will be approximately 1" off to the left of the bikes centerline.

If you align the derailleur hanger to that wheel in that state - the derailler hanger will have a outward bias at the forward reference and an inward bias at the rear reference.

The derailleur hanger and attached derailleur will NOT be operating in parallel to the centerline of the frame.

There's a reason why master frame builders keep a set of properly dished wheels in their work environment. It is to do exactly that - make certain the wheel will be properly centered in the frame when installed correctly AND allow proper alignment of the derailleur hanger.

They're simultaneously checking rear dropout alignment AND rear hanger alignment.

There's a free version of the Paterek Frame Building manual online...feel free to look it up.

Frame builder I've worked with since 1984 does the same.

=8-(

70sSanO

I have no dog in this, but I thought you took the 4 measurements from the same point on the rim; i.e the valve stem at 9-3 and 12-6. You just rotate the wheel. This takes wheel trueness out of the equation.

If the hub is not centered in the dropouts, that a different issue.

John

cxwrench

Rim 'dish' won't matter. If the wheel is in the frame square and it's true that's all that matters. It could be off center to the left or right, but as long as it's true and the axle is in the dropout properly it won't matter. The rim is supposed to be something to use to judge whether something else is parallel to it. The rim being centered doesn't matter at all...if it did using various wheels w/ different rim widthsto align a hanger wouldn't work. The ONLY thing(s) that matter are the plane of the rim. Doesn't matter where it is. That's why hanger alignment tools have an adjustable 'feeler'.
For the OP's question...I don't think a hub could be 'misaligned' and make into a completed wheel and on a bike. Well, I guess anything is possible but this is a helluva stretch.

cjenrick

what kind of bike? what kind of derailleur? how many teeth on rear cogs?

do not rule out a broken axle. especially if you have phantom shifting on steep hills,

cyccommute 

You are describing something that just doesn’t happen. On a properly built bike, the dropouts are the same distance from the bottom bracket and parallel. If the wheel is off dish by 12mm of center line at the front of the wheel, it is 12mm off center line at the back of the wheel. The wheel is parallel in the frame. The wheel doesn’t go off at an angle if it is off-dish.

Again, how? If we assume that the hub is square in the frame, the front and rear of the wheel will be the same distance from hanger as well as the same distance from the center line of the bicycle.

Only if the wheel isn’t parallel to the frame. If the wheel is tacoed or not square in the frame, the derailer wouldn’t be aligned properly. If the wheel is just off-set to one side, it’s still parallel.

Although I didn’t read every word in the Paterek Frame Building Guide...it’s 400+ pages...I could find no reference to aligning derailer hangers by using a wheel. There’s lots of references to use the wheel to check various others alignments but not with regards to derailer alignment.

cyccommute 

Like 70sSanO says above, a bent axle could throw the alignment off. A tacoed wheel could throw it off. A hub misaligned in the frame could throw the adjustment off. All three are somewhat unlikely to happen, however. And I doubt, with the exception of the tacoed wheel, I doubt that it would have that much of an effect on the shifting. The alignment needs to be good but there’s a bit of wiggle room.

dabac

You seem to be ignoring bikes with horizontal dropouts.
If you stick an incorrectly dished wheel in a horizontal DO frame and center the rim between the chainstays, the wheel will sit at an angle WRT the center line of the frame.
Any hanger alignment done referencing that wheel will also be off-plane.

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.

mrrabbit 

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-|

cxwrench

What exactly do you mean 'centered'? If the hub is centered in the dropouts (horizontal) or the vertical dropouts are on the ends of chainstays of the same length and the bb shell is straight...the hub will be 'straight'. If the wheel is true it doesn't matter if the rim is centered over the hub. The rim is still parallel w/ the centerline of the frame. Like I said before it would be the same as checking a hanger w/ multiple wheels and they each had a different width rim.
I will agree w/ you if there is one or more things that aren't 'correct', but rim dish or centering isn't one of them that matters.

cyccommute 

Because you didn’t explain the process very well. First, I wouldn’t just hand the tool to a new mechanic and say, essentially, “you figure it out.” That’s a good way of coming back from lunch to an expensive repair you’d have to eat.

By checking to see if the hub is centered and ignoring the rest of the wheel. The scenario you keep bringing up would require someone to be rather clueless about how the hub sits in the frame. If the dish were off by 12mm (that’s a huge amount, by the way) and the rim were centered in the frame, the hub would be visibly crooked in the dropouts. If a mechanic understands how the alignment tool works, they would look to see if the hub is square in the frame.

So have I. Others have rejected your answer as well.

More often than not, they are one and the same.

mrrabbit 

Scenario A: "Center the wheel. Here's the tool. Check top, bottom and front. Re-attach derailleur. Adjust. Good to go."

Scenario B: "Check the wheel dish OR put in and center a properly dished wheel. Check top, bottom and front. If you are curious, you can check the rear too. Re-attach derailleur. Adjust. Good to go."

One is technically correct.

One is also technically correct AND good advice. See if you figure out why.

=8-|

cxwrench

You still haven't answered my questions...why not?

cyccommute 

I’ve already figured it out. Scenario A is correct and good advice. Scenario B includes thoroughly unnecessary steps.

smashndash

I'll respond to OP. The hub doesn't even need to be misaligned. If you have a hub that uses cups + cones or thread-on end caps, it can be loose. If it's loose, the wheel can wobble when pushed laterally. If it wobbles, I believe this will lead to a poor alignment of the RD hanger. Super worn-out bearings will probably do the same even in a press-fit hub.