Hikebikerun

So I replaced the stock 25c tires on my Trek Emonda SL5 with a pair of 28c Conti GP5000s, and after putting the rear wheel back on the rear derailleur is slightly off (it makes a clicking noise when pedaling and the pulleys are not quite lined up with the cog in the cassette, so the chain is being slightly torqued to the side).

I checked that the wheel is completely set into the dropouts several times. In fact, this is the first time I have messed with the rear wheel, and based on the witness mark on the dropout I am thinking it was not completely in the dropouts when I purchased it, and since the dérailleur was indexed with the wheel like that, now that the wheel alignment is corrected the dérailleur adjustment is now off.

Here’s a pic of the QR nut witness mark showing (to my mind) that the wheel was not fully seated before:




Does that seem plausible? Or is there something else I could have messed up? I definitely did not smack the dérailleur or bracket, I was very careful.

Assuming I’m correct about the cause of the issue, can I just turn the barrel adjuster until the dérailleur pulleys line up with the correct cog in the cassette, or do I need to mess with the set screws or something else?

trailangel

Turn the bike right side up, reset the wheel in the dropouts and adjust the DR.
Do not put the bike upside down.

Hikebikerun

What’s the reasoning behind not putting it upside down? I had to in order to coax the rear wheel out. The bike doesn’t have hydraulic brakes, an I missing something?

As for adjusting the DR, do I need to reset the set screws or just use the barrel adjuster?

trailangel

There isn't any reasoning. It's scientific. The weight of the bike pushes the wheel completely into the dropout.
You don't have to turn the bike upside down for any reason. If you cannot get the rear wheel out you don't have experience.
Yes
Yes

79pmooney

I'm guessing you are sitting the bike upside down on the floor.. Not an issue but derailleurs were intended to be operated rightside up. If you don't have a proper stand, you can fake one with a rope and a loop for the nose of the seat. Hang the bike from the garage overhead or even a tree branch. (I've been doing this by choice in the garage for decades.)

The derailleur: See to it the rear wheel is all the way in. (Looks like you are there.) Now, loosen the barrel adjust all the way, shift into high and spin the pedals to get the chain to the high gear. Spin the pedal with one hand and bush the bottom half of the derailleur in to shift to the next gear. Now adjust the outboard limit screw (t may say "H" for high) until the chain just shifts nicely into the small cog but no further. Now tighten the cable barrel adjust until the chain nicely snaps in to the second smallest cog with one click of the shifter. Shift to the next to biggest cog. Repeat the adjust, now of the other limit screw, until you get a nice positive shift into the big cog but no more. Now tweak the barrel adjust as needed to get the best shifting throughout the range.

Last, go to a steep hill and make sure you can shift into the big cog as it gets hard. Adjust as needed. (Do this with your feet ready to disengage and plant on the road!)

Throughout this process, periodically look from the back and see to it that the derailleur is nicely lining up with the cogs. Also that it lines up vertically and fore and aft with the chainrings, If you see that it doesn't, the derailleur hanger of the dropout is probably bent and needs to be straightened/ replaced. Any bike shop has the tool to both check and correct.

This is a quick and dirty of setting up a rear derailleur. Come back if you need more explanation.

Ben

dsbrantjr

79pmooney's procedure is a good one, but I prefer to set my limit screws by pulling and releasing the exposed shift cable, and adjusting the limit screws for enough clearance to allow a clean shift and no more; I do not have bikes with in-frame routing so the cables are accessible. The exception is the front low limit, which I set with the chain in the small front/big rear combination, to have 1mm or less clearance. This technique helps take shifter indexing out of the picture.
I then adjust indexing for clean shifts without reference to visual alignment of the derailleur to the cogs; good shifting and quiet running are the goal. This assumes an aligned rear derailleur and hanger.

cpach

Experienced mechanics tend to scoff a little at bikes being turned upside down. It's not mechanically necessarily terrible, but it's really easy to knock the bike over and it scuffs up your saddle and handlebar tape and pro mechanics pretty much never do it. It is not difficult to remove a rear wheel upright and lay it on the non drive side and it's safer. For real bike work it really should be suspended right side up. If you work infrequently on your bike, you can suspend it from a rope attached to the ceiling. Really if you can afford an Emonda SL5 you are likely to be well served spending a couple hundred on a real stand.

Anyhow, make triple sure the wheel is seated in the dropouts by putting it on the floor and using the weight of the bike to make sure it's seated, then if difficult to shift into lower gears thread the barrel adjuster counter clockwise a few clicks to see if it improves, or clockwise if its difficult to shift into higher gears. If you can't get it consistent, it is likely to be the alignment of the derailleur hanger, which requires a specialized tool to align, or is the result of friction in the cable/housing.

Hikebikerun

Thanks, guys. I put a hook on the ceiling so I can hang the bike from the seat rather than turn upside down. I will look into getting a real stand.

Rechecked that the wheel is in the dropouts, set H limit, indexed, and set L limit. Everything appears to be in working order with no weird noises. Gonna test out the new tires tomorrow!

Andrew R Stewart 

I might have missed someone mentioning the QR springs not being in the right arrangement. The small ends go against the axle and the big end against the QR end caps. Andy