Thinner tires on rim

I use Continental Sportcontact slicks, 32-559, on 25mm wids rims:

http://www.conti-online.com/generator/www/de/en/continental/bicycle/themes/tires/city/sportcontact/sportcontact_en.html

I would prefer to use 25-559 on 18mm rims,
http://www.conti-online.com/generator/www/de/en/continental/bicycle/themes/tires/mtb/grand_prix_mtb/grand_prix_mtb_en.html
faster...

EDIT: However, from the information posted below, my current tyre/rim combination may not be compatible.

cheers
George

Quoted post said:

Originally posted by robcar
I need some advice. I have a Giant Mountain bike that came with 26X1.95 knobby tires. I ride the bike with the kids on the street and on bike paths. I want to put thinner road tires on the rims. What is the thinnest tire I can put on this type of MTB rim.

Thanks!🙂

Depends on how wide the rim is.
Check the information on Sheldon Brown's site:

<http://www.sheldonbrown.com/tire-sizing.html#width>

You need to un-mount a tire to measure the inside width of your rims.