The wheel is a type of rhythm used in hymns or narrative songs sung in European churches or gatherings from the 12th to the 16th Centuries.
The first 14 lines use a pentameter rhythm: Sithen the sege and the assut was sesed at Troye, The borgh brittened and brent to brondes and askes, The tulk that the trammes of tresoun ther wroght Was tried for his tricherie, the trewest on erthe-- Hit was Ennias the athel and highe kynde, That sithen depreced provinces and patrounes bicome Welneghe of al the wele in the west iles.
Ticius to Tuskan and teldes bigynnes, Langaberde in Lumbardie lyftes up homes, And fer over the French flod Felix Brutus On mony bonkkes ful brode Bretayn he settes with wynne, Where werre and wrake and wonder Bi sythes has wont therinne, And oft bothe blysse and blunder Ful skete has skyfted synne.
The content of the bob and wheel varies, but, generally, it functions as a refrain, or a summary, or an ironic counterpoint to the stanza that preceded it.
It is often considered as a regular metrical form as the Pearl Poet uses it, but in fact, in Middle English, there is great variation, and wheels are often used without the bob.