Check bicycle and weight policy. I.e. emirates 300cm box limit
For tickets issued on or after 15th November 2014
Individual items with total dimensions exceeding 300cm (118 inches) cannot be transported as checked baggage, and must be sent as cargo or freight. There are no exceptions to this rule.
and weight 30 kilo, BA is not expensive to buy an extra bag around 50£ i belive for another 23 kilo. Emirates once you go over your initial 30kg 180£ each 5 kilo
SAA used to give 10 kg extra now it seems It gives the whole bike for free
The following Sporting equipment as described below (ONE additional Piece weighing not more than 23kg per passenger & maximum dimension of 158 cm unless specified) is free of charge and must be requested with a SSR SPEQ in the booking:
Cycling: 200cm – 100cm – 75cm
does not apply if flying codeshare through dubai.
So all depends if you fly heavy packed or not. Do not leave any valuables in luggage Johannesburg is a known for many bags opened and searched.