Rear Gear Alignment

uclown2002

Veteran
Location
Harrogate
Having a play with my new (Park Tool) rear gear alignment tool when I managed to thread the hanger. I bought 2 new hangers and they are clearly dead straight. I'm using the same reference point on the wheel, the valve, yet the 12 o'clock position is at least 1 inch adrift of the 6 o'clock position. It's identical when I swap over hangers. The wheel looks pretty true, but surely that shouldn't matter with same reference point.

The frame looks fine so what else can I do?

Shifting is ok but not perfect.
 

bpsmith

Veteran
Personally, I would use the tool for what it's supposed to be for, and bend the hanger so that all reference points match. Then set up your dérailleur and see how the shifting is.
 

bpsmith

Veteran
I have the same thing to do on my newer bike. Looks straight on the bike, but rear cage is a fair bit out when looking down from the saddle.
 
Location
Loch side.
Have another look at your wheel. Either it is true or it isn't. Don't fiddle with the hanger if the wheel isn't true. The Park hanger alignment tool doesn't have any incremental markings for you to go on and playing a compensation game isn't good enough. True that wheel or use another one that is true.

Then align again. Don't make any assumptions until you've done that. I won't suspect the frame until you've done a proper alignment. Once you've done that, let us know and I'll tell you how to see if the frame is straight.

A bent hanger present as a shifting problem - yes. However, it presents very specifically. It will shift perfectly in one direction but imperfectly in the other.
 
OP
uclown2002

uclown2002

Veteran
Location
Harrogate
Thanks I'll try another wheel. I've got a couple of others I can try. The hanger can't be bent as I've tried 2 x brand new ones which are perfectly flat.
 
Location
Loch side.
If you use the same point on the wheel, in each of the 4 positions when aligning, then that takes away any issues with a wheel being potentially out of true.
True.
 
Location
Loch side.
Not that it negates the need to true the wheel mind you.
I just didn't trust @uclown2002's reference point. Sorry friend, but the ParkTool gadget is so imprecise that I didn't want the wheel itself to also add a dimension. Remember, that the cones have to be adjusted too.
The tool has quite a bit of play, so always take out the play in the same direction i.e. by either pulling or pushing, but not randomly.
 
Last edited:
Location
Loch side.
Let's for the want of a better term, call the part where the hanger sits on the frame the hanger mount. If this part is bent, it is usually bent inwards just because that's the way bikes fall. If it is bent inwards, it thus presents the hanger with a bulge and the hanger cannot seat properly in one, guaranteed position. There will be the straight hanger that sits on top of a wobbly mount and its final position is a combination of the torque in the mounting screws and the tightness of the QR. To spot such a problem, release the wheel (don't remove) and tighten the QR whilst watching the hanger from the rear of the bike so that you can see the mount and the hanger. If the two move vis a vie one another, you have a bent mount. Just as an aside, if you see the frame and hanger move vis a vie the hub, you have a bent axle or bent frame.

To check if your frame is in alignment, do the following.

Place it on a stand. Remove the wheels and other things as they get in the way in the next step. Tie a piece of long string around the seat tube just above the BB. Now wrap the string symmetrically around the bike. For instance, go from there to the right dropout, through the left dropout, back to the bb, to the head tube, around the head tube, back to the seatstay etc etc. Now tie off the string and walk around the bike, eyeing the various distances between string and frame. An misalignment quickly shows up. Obviously you have to ignore asymmetric chainstays (Pinarello) and BBs (Cervelo) but apart from that, the string doesn't lie. You can do the fork independently with its own piece of string. If you include the fork in the frame wrapping, it messes things up because it is floppy and moves about.
 

Cyclist33

Guest
Location
Warrington
Have another look at your wheel. Either it is true or it isn't. Don't fiddle with the hanger if the wheel isn't true. The Park hanger alignment tool doesn't have any incremental markings for you to go on and playing a compensation game isn't good enough. True that wheel or use another one that is true.

Then align again. Don't make any assumptions until you've done that. I won't suspect the frame until you've done a proper alignment. Once you've done that, let us know and I'll tell you how to see if the frame is straight.

A bent hanger present as a shifting problem - yes. However, it presents very specifically. It will shift perfectly in one direction but imperfectly in the other.
Sorry to mildly hijack the thread but as you clearly know your onions, I have had two bikes where when I back-pedal the chain starts to derail down the cogs (from big to small on the cassette). On the few occasions I've tried to ask before people have gone (why are you back-pedalling lol) but as I can't board a bike in fluid forward motion, I have to back-pedal to get on-board. Do you know why it happens?
 
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