Yaris newbie, trying to find out max tire size....

[xixixi]

I live in Africa, just bought a Yaris sedan in California and shipped it out to Africa where I'm based.

The problem is, the roads here aren't that good (lots of potholes and all) and the Yaris is naturally low, so the average drive turns out into a ground-smooching spree. The tires on the Yaris right now are the default size (185/60/R15).

So I'd like to get bigger tires so as to increase the ground clearance a little (without increasing the rim size or raising the shock absorbers).

My question is, what is the biggest tire size that I can get to increase the clearance, without getting any rubbing.

Thanks a lot, would appreciate any help.