one complete rotation, uses up the whole circumference, and the longer the diameter, the longer the circumference.
for a bike wheel, the longer the circumference or its perimeter, the more it goes, since the tire is longer. A 27in tire will cover more ground in one-go-around than a 25in tire.
let's just check how much ground each one cover, and get their difference.
[tex]\bf \stackrel{perimeter}{circumference}\textit{ of a circle}\\\\
C=\pi d\quad
\begin{cases}
d=diameter\\
-------\\
d=27
\end{cases}\implies C=\pi (27)\implies C=\stackrel{inches}{27\pi }
\\\\\\
\stackrel{perimeter}{circumference}\textit{ of a circle}\\\\
C=\pi d\quad
\begin{cases}
d=diameter\\
-------\\
d=25
\end{cases}\implies C=\pi (25)\implies C=\stackrel{inches}{25\pi }\\\\
-------------------------------\\\\
27\pi - 25\pi = \boxed{2\pi }\qquad \qquad \approx 6.2831853[/tex]
