This is from DL's site concerning bikes, so say the very least it is ambiguous.
Are bicycles and golf clubs considered part of the free domestic baggage allowance for Medallions, First and Business Class passengers and SkyMiles Credit Cardholders?
Yes, non-motorized touring or racing bicycles with single seats and golf bags are accepted as checked baggage. Bicycles cannot exceed 115 linear inches, and excess weight fees will apply to bicycles greater than 70 lbs. One golf bag may be accepted as checked baggage, and overweight fees will apply to bags that exceed 50 lbs. For detailed information on traveling with sports equipment, see Sports Equipment page.
Bicycles
Non-motorized touring or racing bicycles with single seats are accepted as checked baggage on most flights with the exception of some Delta Connection® carriers and aircraft that may not accept bicycles as checked baggage, and may have different limits due to cargo constraints. Linear dimensions must not exceed 115 linear inches (292 cm); no oversized fees apply. Bicycles weighing over 70 lbs will be charged the applicable excess weight fee; bicycles weighing over 100 lbs will not be accepted.
Bicycle Transport Fees
Destination Fee
Travel to all regions (excluding Brazil) 150 USD/CAD/EUR*
Travel to/from Brazil 75 USD
*CAD amount will be charged exit Canada, and EUR amount will be charged exit Europe.
Your bike must be packaged in a cardboard or canvas container in one of the following ways:
Handlebars fixed sideways and pedals removed
Handlebars and pedals encased in plastic, Styrofoam, or other similar material