Us older riders will remember riding out to very early morning time trials , eg on courses J13 and 14 on the East Lancs road and many others , in my case mid to late 1960s , on a set up similar to the photo .
Race wheels carried on aluminium brackets. A bigger ( more teeth )fixed rear sprocket to ride out on then a smaller sprocket to race on . Typically to give an 81″ , 84″ or 86″ gear to race on.
I always remember 100 revs per minute on a 84″” gear would result in 1 hour for 25 miles !
Get home , drop off race wheels then ride out and join the club run !
Always a very full day out !