Many thanks to everyone who pitched in on my computer sound thread. Here's
a more traditionally-DIY question:

I have to fix two grab rails to the walls of a walk-in shower: these are
timber and plasterboard stud walls covered with ceramic tiles. I do have
limited access to the other (non-tiled) side of the walls, so I could
probably locate the vertical studs by drilling a series of holes, but the
rails are a fixed length so even if one end can be secured into timber the
other probably could not.

Can anyone recommend the best really strong and secure hollow-wall fixings
for use through tiles? In the past (on plain walls) I've used the type with
two sprung metal arms which open up once through the hole, but I'm concerned
in this particular job that the hole has to be considerably larger than the
diameter of the bolt: isn't there a danger of the rails, however tightly
fixed, being able to slip about slightly, especially on a glossy tiled
surface?

Thanks for any thoughts.