The ground clearance dead centre is maybe 6". Is it possible to buy bigger tires for this quad, or put another size(brnd) rim and tire to achieve grd clearance that way?

 

yea but you can loose stability ,and raise your center of gravity ,

 

IRS. Love mine. People really look for the high rocks I go over. Sort of funny.

 

What machine we talking about here??? That makes all the difference.....

Bigger tires mean a loss of low end power (you are raising your effective gearing). If it is shaft drive, you won't be able to compensate for that with a gearing change like you could on a sport quad.