Oh and did you know this can be done with two different ratios? (Apologies if this has been mentioned already.) Jocelyn Lovell for example used it for the '82 World Championships kilometer time trial, which is done on a track bike from a standing start, so having a lower gear to start is an advantage.
There are a couple ways of doing it but Lovell's '82 Worlds bike used a single-speed freewheel on the right side, and the higher gear (smaller rear sprocket) on the left side. The smaller left one was a regular track cog, but with the lockring not threaded on all the way. That gave him an 87" gear to start, and a 95" gear that kicked in once the left-side cog unthreaded far enough to hit the lockring. After that point, about 70m into the 1000m total of the race, the lower gear on the right simply freewheeled.
Whether the extra weight of the second chain, chainring and freewheel was worth it for the lower "hole shot" gear is debatable. He didn't win; 4 seconds off the winning ride was only good enough for 7th place. The commisaires might have had something to say about it if he'd won. UCI commisaires have been known to disallow bike innovations after the fact, if the rider wins. Some say it's politics, business considerations or just good old fashioned bribes that determine whether a particular idea is allowed.
Last edited by bulgie; 06-30-20 at 02:54 AM.