I posted a message earlier this week about tires for my 300ex. I know that the stock tires on a 300ex measure 22 x 10 x 9. What size do you recommend for me to get. I thought the 22 x 11 x 9 Razr's would be the right size, but I know the 400ex has a 20 inch tire size. Thanks for any responses in advance!!

 

The 20X11-9s are a good match for this quad. You lose a bit of ground clearance versus the 22", but unless that is a BIG problem concerning where you ride,... the greater handling 20" is more beneficial than the added clearance of the 22" in my opinion.
As for the specific tire tread, everyone has their favortites.

 

i got 20 by 11-9 razr's for my 300ex and they hook up great and look sweet