I just took three flights with my bike over the past two days, all domestic within China, where the luggage limit is two pieces of twenty kilograms total. I had two pieces of check luggage, one of which is a packed bicycle, each weighing 18 kilograms for a total of 36 kilograms. I expected to be fined for the excess weight, but all three airlines charged no handling fee for my bike, and additionally did not count my bicycle toward my total luggage weight.
Almost too good to be true isn't it? If only North American airlines are equally progressive. I have an Air Canada flight from Shanghai to Toronto this afternoon. I'll report the results when I get home.
The airlines I flew on were Air China (who last year also waived my overweight fine when I flew with a bike from Rome to Shanghai), Hainan Airline, and Shanghai Jixiang Airline.
Edit: Air Canada charged me the usual fifty dollars. I tried to get by with the standard 'sporting equipment', but the clerk asked what type, and I couldn't lie. I was within the weight allowance.