From Lexicanum

A Land Speeder Squadron is made of between 1 and 3 Land Speeders of varying types.

They are made up of a mixture of any of the following:

• Land Speeders¹
• Land Speeder Tempests¹
• Land Speeder Tornados¹
• Land Speeder Typhoons²

Sources

• ¹:Codex: Space Marines (4th Edition)
• ²:Forgeworld

Space Marine Vehicles
Rhino Chassis	Rhino • Damocles Command Rhino • Razorback • Vindicator • Whirlwind • Whirlwind Hyperios • Predator Annihilator • Predator Destructor • Baal Predator
Land Raider Chassis	Land Raider • Land Raider Crusader • Land Raider Helios • Land Raider Prometheus • Land Raider Spartan
Dreadnought Chassis	Dreadnought • Furioso Dreadnought • Mortis Dreadnought • Venerable Dreadnought • Grey Knights Dreadnought
Land Speeder Chassis	Land Speeder • Land Speeder Tornado • Land Speeder Typhoon • Land Speeder Tempest