More fitting solutions

The tight armhole is a hard one.  The sleeve is a shaped two piece construction, so the typical diamond shaped gusset won't work.  (See Threads, http://www.taunton.com/threads/pdf/tootightgarment.pdf).

 I took some inspiration from an old Swedish military jacket I got thrift shopping.

The armholes have ovaloid gussets that fit between the sleeve and armhole. The gussets are also in a cotton twill for breathability.  I really liked this feature for cold-weather biking, too.