Lance 1025 on 3/4 ton diesel Silverado

I switched to 285 tires from the factory 245 tires and in theory the gearing should have been 4% taller but in reality with the weight of a heavy camper in the bed the tires squat down and the speedometer is dead on accurate with the larger tires as a result. Without the camper the truck is going about 2-3 MPH faster than the speedometer indicates which is not enough to worry about.