@Srida: the idea is not as illogical or impractical as it seems from the outset. Many hard core OTR fans do use this same method - highway tyres for their jeeps to drive on the highway (till the OTR point) and OTR spec tyres for the OTRs. But you have to factor in the additional efforts you have to put in before and after every highway drive. Kudos to your wife for thinking out of the box and coming up with the idea. If this idea came from my wife, I would have gifted her something nice, just for thinking like this.