The Lion Speeders are small transport vehicles housed within each Lion's chest, allowing their Paladins to separate from their Lions and travel at speed to other locations while still being protected from the environment. They are also part of the transportation network that allow Team Voltron to reach their Lions within the Castle, after they have used the ziplines down from the main bridge.
It is currently unknown whether the speeders have weaponry of their own, but given the way the bayards plug into the Lions to form weapons for Voltron, it is likely the same holds true for these vehicles.
The Lion Speeders look like motorcycles, with one wheel and the weight of the vehicle resting heavily in the front. Not only does this allow for movement in narrow spaces, but it also provides much more stability than a two - wheeled but even motorcycle.