can a miss-aligned frame cause rear shifting issues?

Discuss light weight issues concerning road bikes & parts.
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Catagory6
Posts: 388
Joined: Thu Feb 09, 2017 2:36 am

by Catagory6

adjusting the RD for the outer sprockets causes up-shifting (into larger sprocket) on the inner sprockets
adjusting the RD for the inner sprockets causes down-shifting (into smaller sprocket) on the outer sprockets

bike shop straightened the hanger. but that only did so much.
the rear wheel doesn't sit evenly between the chain stays at the rim
and the "string around the head tube" test has the seat tube off to one side.

luckily its steel, so i can take it to be realigned... hopefully

just wondering if all of this can cause the above shifting issues

by Weenie


Wookski
Posts: 1090
Joined: Tue Feb 23, 2016 5:51 am

by Wookski

Absolutely and alignment is something that should have been checked before it was built up.

Catagory6
Posts: 388
Joined: Thu Feb 09, 2017 2:36 am

by Catagory6

Wookski wrote:
Mon Feb 11, 2019 12:41 am
Absolutely and alignment is something that should have been checked before it was built up.
yeah thanks, that was ME who built up the bike

thankfully there's a frame builder an hour away

alcatraz
Posts: 2103
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Maybe it's a problem with the derailleur or chainline.

If the hanger is aligned with the wheel the shifting should be spot on.

It also sounds like you could be running a mismatched group that can't be indexed properly.

Better give the frame a good inspection. Like dropout alignment, rear triangle alignment, dropout width. With steel you can adjust things pretty easily.

Check out “RJ the bike guy" videos on youtube. He straightens steel frames all the time, converts to newer gearing and so on. When possible he uses simple tools.

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wheelbuilder
Posts: 663
Joined: Wed Feb 08, 2017 2:10 am

by wheelbuilder

Rear section of housing too short?
Never cheer before you know who is winning

NiFTY
Posts: 1305
Joined: Sat May 26, 2012 11:26 pm

by NiFTY

Did they straighten the hanger front and back as well as up and down?
Evo 4.9kg SL3 6.64kg Slice RS 8.89kg viewtopic.php?f=10&t=110579" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

RocketRacing
Posts: 782
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

I have this problem with a scott spark premium mountain bike. High end carbon. Rear is offset. Shifting is a bit rough as a result.

Catagory6
Posts: 388
Joined: Thu Feb 09, 2017 2:36 am

by Catagory6

don't know if dropouts are properly aligned
i'm kind of thinking that might be the issue with the rim of the rear wheel being off center in the chain says

i assume that the RD hanger was aligned both on the X and Y axis

i am using a SRAM 10-speed cassette with a Campagnolo 10-speed group, but i've properly compensated the pull-ratio on the RD. i have another bicycle with the exact same setup that works flawlessly

i guess i'll swap out the RD between the two. maybe the RD is bent?

i've bent RDs in the past and they give the same symptoms as i'm having, stated above. same symptoms as a bent hanger.

is there a way to tell if its a bent RD?

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pdlpsher1
Posts: 2390
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

Every bike that leaves the factory should have the dropouts grinded so the wheels sits perfectly in between the chainstays. If the alignment of the dropouts are off substantially then a realignment of the dropouts is needed. But for most bikes the misalignment is very minor and the 'adjustment' is made by grinding some materials off the dropouts so the wheel will sit pefectly even in the frame (both the 'tilt' and the 'steering' angles). This is an easy process with the right tools. See the attached video and fast forward to 6:28. Once this is done you need to realighn the derailleur hanger to match the new alighnment of the rear wheel.

https://www.youtube.com/watch?v=xJDea5mSUJY

by Weenie


alcatraz
Posts: 2103
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

The upper pulley should (at least in the middle of the cassette) be perfectly aligned with the cog. Both planes, up/down, side/side.

Before I got an alignment tool, I used to eyeball it and it was possible to get it really close with practice. The advantage of eyeballing it is that if you have a worn derailleur, you can kind of make the best of a bad situation and get it better aligned regardless of it's internal misalignment. The alignment tool always assumes your derailleur is fine.

You can check the derailleur for play in the cage by gently feeling it for sideplay. Your upper derailleur pulley also needs to have a certain amount of play to work properly.

Don't use the cage of the derailleur to assess alignment. Some derailleurs have weird cage designs intentionally. The safe bet is to look at the upper pulley only. Flip the bike, take pictures direcly below and from the back and really determine which way the derailleur needs to be twisted to improve alignment.

It's a time consuming process.

Another thing I found helps to fine tune alignment is to take a small allen key and place it against a cog to project it's line next to the pulley. It's easier to see that way.

Also the pulley's internal play can have it shift a bit and it confuses alignment. I'm usually happy when it's straight and has equal play both ways when I wiggle it. Not just rests at an angle to become straight with the cassette.

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