If you pay the Sports equipment it increases your Total baggage (exluding hand) to 32Kg.
Recently on a trip to Italy we all fretted at getting our baggage down to 12kg as all our bike bags weighed about 20kg each.
There was no need though as even though they were placed on the scales at Luton they didn't actually check the weight and only stuck the tags on. Other side at Nice on return they didn't bother putting bike bags on the scales.
For safety try and get your baggage down to around 15kg and you should be OK
Edit:
Just to mention again, officially there is a limit on your bike and overall weight
Copied from Easyjet web site
Bicycles (1), golf equipment, and skis, surfboards, wind surfers, hang gliders, and firearms (2)
An additional non-refundable fee is charged per item per flight for the carriage of the above items as set out in our carrier’s regulations.
Payment of the additional fee increases your checked-in hold baggage allowance (including additional item) to a maximum weight of 32kg.
Where your total checked-in hold baggage weighs more than 32kgs, normal excess baggage charges as set out in our carrier’s regulations shall apply in addition to the above fee.