i have a stock z400 and want to put 25s on it to keep the axle off the ground. will gears be enough.

 

The Z isn't a torquer, it is a rever. It just doesn't have the low end grunt to get the bit tires moving.

You can gear it down, but it isn't going to be very satisfactory. Get a Raptor 700 if this is what you want to do.

When I need more clearance, a set of Holeshot XCT's is the way I go.....