changing to 5.50 Bias Ply = changing to 3.54 ratio

[MikeK]

One very slight problem with the above calculations- The measured diameter of a tire is not equivalent to the rolling diameter. Even for tires of the same size, this will vary between manufacturers, construction, and tread.

Many tire manufacturers list revolutions per mile for each tire they produce. That is the most accurate way to figure speed vs. RPM.