Bike tyre size help?

i need new tyres for my bike the current size is
700 x 40c
but i was wondering i've seen tyres of different sizes from 700 x 15 to about 70 x 50?
whats the the advantage/disadvantage of the different sizes please
what would be better for me, i only ride on the road? thanks

If you only ride the road you could go a little narrower.

As far as widths: Wider is more stable, heavier, better traction on uneven ground, dirt and gravel. They are less likely to flat as the use lower pressure and because of this they give a soft smooth ride. Wider tires also soak up more energy and have more friction making them slower.

Narrower tires use higher pressure, are quite a bit faster due to less friction, give a harsher ride and don't work as well on sand, dirt and gravel. They provide faster handling hence less stable.

You can't put any size you want as your rim is quite wide to fit 40s on, but you could go 1 to 2 sizes narrower if you like. If you ride pavement only it's the way to go.

Any 700 tyre will fit a 700 wheel as that is the designated diameter of the rim. The other size is the width of the tyre and they range from about 18 to 50 and if it has 700 stated on the side wall of the tyre it will fit your wheel. If you ride mainly on the road, as stated, I would recommend a tyre width of 25 or 28 for general commuting.

Depends on your bike, and how you ride.

Only certain tyres will fit certain wheels eg. you couldn't go from 700x50 to 700x15 tyres whilst using the same wheels. Inner tubes also come in different sizes.

Thinner tyres give you less friction, so riding fast is easier.

Big tyres give more grip, for when it's needed.