[xb-60]

What about both of you buy new TKOs in the configuration that you want and sell your current 'boxes? You might not come out that much out of pocket when you consider the time/hassle/cost/sweat of reconfiguring your current setups to the setups you want.

Another thought...and only half serious.....what if you change to lower profile tyres and your dad changes to higher profile? As an example, 295/50x15 tyres are around 26.8" (680mm) OD, and 275/60x15s are 28.1" (714mm) OD. That's 5% change in your gearing (all gears though) that you could pick up or lose.

Cheers,
Glen