How do narrow rims affect ride?

[cupacabra]

I am looking at a set of 29er wheels with 18mm rims. Am I making a big mistake if I would like to ride 2.2 tires on these?
Thanks

[Pato]

Wider rims allow for wider tires obviously. All things being the same a wider rim will also create a slightly larger contact patch given the same tire. It will also square out the tire a little since it brings the sidewalls out. This will give you better performance when the bike is closer to vertical. I think this will make it more prone to washout when leaning the bike over though.

Another benefit of wider rims is that you can run a little lower air pressure for greater traction without the sidewalls rolling over. Of course this is mostly all theoretical on my part. I could be just talking out of my @$$.