skate berings with tyers?
i like the idea personaly, might be worth it on a large x axis.. bit bulky to impliment but if you have three way apposing wheels i imagine you could pre-load them against each other with enough force to prevent them flexing any more than your frame / gantry etc

the tyres (+ the larger diameter) would smooth out any of the smaller rail inperfections

might be a winner if your after saving the brass

its allways a gamble though when you try something new