Typically the guys I've worked with over the years considered equal tire sizes as a square set-up without consideration of the bolt circles or wheel offsets. It is the rarity that one runs into mixed bolt circles on a vehicle. I have seen it it, but it isn't common. However, if you do have alternate bolt circles in your hubs, all you really loose is the ability to easily rotate tires to any position. In a car turning right and left, I don't see that as an issue on the same level as a car that only turns one direction that may be running alternate diameters right to left.
Are replacement hubs in a square bolt pattern more or less expensive than the wheels under consideration and which methods serves the long term goals best?
I'd price this, and having wheels wheels re-drilled if there's enough meat between the existing pattern. I know I've read about holes being welded up and then re-drilled, so maybe the voids between your existing holes could be filled if there's not enough there to drill. In the long run probably be cheaper to pay to have tires remounted and balanced each time. And don't forget to price replacement axles, but then you'd still need two new wheels!
Years ago I thought one of the circle track wheel companies sold a 15" dual bolt pattern wheel, wonder if those are still available.But for circle track use I doubt you'd find them in 20" sizes.
