First off, this is a bad conversion to do in the first place, unless you replace the whole axle, the hardware is unreliable at best and difficult to find and purchase to boot. An extension for your wheelhub which would allow a 5 lug conversion does exist i believe, but it would extend your wheels out another inch or so severely limiting the wheel and tire sizes you can choose.

As for the notion that braking would be easier, that is pure nonsense. Once your car has stopped accelerating and begins to decelerate, you rely on the force of the brake pads on the rotors or drum to stop the vehicle.

Lets call this force F. The force F puts a torque on the spinning wheel opposite the direction that its moving. This torque has a magnitude Fr = T where r is the radial distance between the wheel hub and brake pads. This force is opposed by the angular momentum p of the spinning wheel which is given by p = Iw where I is the moment of inertia of the spinning wheel and w is the angular velocity of the wheel (which is just the speed times the radius of the wheel from hub to tire). The force which is applied to stop this rotation is related to the change in momentum over the change in time.

The moment of inertia I is determined by some integral given the shape of the wheel but the most important figure in that calculation is the wheel mass. A greater wheel mass will translate to a greater moment of inertia which will translate to a greater angular momentum given some speed. Therefore a greater force will be needed to slow the system down. Since the braking force will be more or less constant regardless of the wheel size, it will take that force a longer time to slow down a heavier wheel. Combine this with the forward motion of the vehicle chassis and you'll find that braking is indeed impaired by a bigger wheel.

Go physics :fawk: