Best way to attach a wheel to a DC motor with 6mm shaft

I’m building a robot driven by two 300 RPM high torque brushed motors. I’d like to use slightly larger wheels (5″+) to increase the speed of the robot, but having a hard time figuring out how to adapt the motor’s 6mm shaft to the wheels 1/2″ bore.

Any advice for attaching generic wheels (i.e., like lawnmower wheels) to a 6mm shaft would be much appreciated.

As a more fundamental question: if I were to just use smaller wheels and a higher RPM gearing, would I be making the exact same torque / speed tradeoff? (So I may as well just use smaller wheels and higher RPM instead of trying to attach larger wheels?)

Thanks!

submitted by /u/t3mp3st
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