I have a city jogger mini double. Before buying it I had a Phil and Teds double but the tandem style suits me better. The steering on it needs a bit of a service and as I do a lot if off road walking I think I'd benefit from bigger wheels. Rather than buying a new GTmodel (as I can't see anything else I think better) I wondered if it would be possible and cheaper to jus upgrade the wheels? Anyone done this? Can recommend what to get where from?