When I tuned up the RD two weeks ago, it was 60 degrees F. Today, it was 40. I noticed the up shifts were instantaneous, but the down shifts were noticeably more cumbersome. Sometimes it was smooth, but other times, the chain would just rub the sprocket, and not budge unless I shift it twice. I thought that this could only mean that the cable tension increased. But then again, 20 degrees F is nothing... Is adjusting cable tension a common practice when it comes to index shifters?