I've got a '98 450ES, and soon after I put the 28" Mudzilla's on it, I had to replace the front wheel bearings. (of course this is after I rebuilt the engine, installed a K&N Power Kit, and added a 2" lift)
I had to replace the wheel bearings again just the other day (about 6 months from the first replacement).

Why is this?, I have an idea, but I'd like to hear opinions from other riders.

 

well it depends on riding conditions alot. i take it you do alot of mudding right? with the tires u have.that has some effect on how long the bearings last.

and your tire size also has a effect on them too 28" tires put more stress on them than they were designed for.just like adding bigger tires on a truck things just wear out faster when you do it.because they were not made for the added stress.