tyre size

[mark1974]

Some advice would be appreciated
Tyres on my hybrid size 700x45
Question is "what other sizes would fit if any?"
Was looking at some thicker knobbly tyres for rims not sure if it is possible to change
Also what is the 700?
what is the 45?
thanks
Mark

 

[Tanis8472]

45 is the width of the tyre.
700 is the wheel size.

There's a nice guide here http://www.cyclechat.net/threads/wheels-and-tyres-a-beginners-guide.117272/