Ever since my daughter keeled over on the Peugeot earlier this year (blame the clipless pedals) the gear changes have not been the same. I tried a few times to rectify the problem but the SIS gear changes were never quite as crisp as they used to be so I decided that apart from a buckled wheel which I had repaired, something must have gotten bent.
I decided to purchase a couple of tools to assist in my plight for perfectly smooth Shimano 105'ness gear changes
Firstly I bought a Park Tools derailleur hanger alignment gauge (DAG-2), this was set up and showed the hanger to be out by quite a bit, so after resetting the hanger things improved but it still wasn't perfect
I then bought a Cyclus Drop Out Alignment tool (less than half the price of the equivalent Park Tools FFG-2)
So this morning I set up the Cyclus and it showed the rear dropouts were indeed out by a few mm, after a bit of frame bending it was looking much better
So I refitted the wheel and reset the hanger again
I adjusted the derailleur and it is now working as it should, so I will have the Peugeot for a while longer