I've ordered some new wheels for the Rover.
The present ones only give about 20 mm clearance, which isn't enough really.

To improve this I've ordered 8 Inch Wheels. This should give approx 150 mm of clearance.

This wheels however don't have a 5 mm D type shaft connection. However the Roboshop also supplies the appropriate hubs which have 6 mm D shaft holes.
Amazon provides the appropriate converter and also 6 mm D Shafts.

The other advantage of this approach is that there is in theory there should be the ability to put a third set of wheels. These would have have either two inboard and one outboard or the other way round.

A couple of issues, the wheels will take time to get here and there are only three immediately available. Oh well this isn't urgent :).