Members who say 17'' wheels fit over IS350 calipers are correct, but to relate this to upgrading the IS250 with IS350 calipers and discs is completely wrong . The IS250/220D hub is different than the IS350 hub, so although the IS350 calipers are a direct bolt on without modification, they do not have the same clearance as they have on a 350 hub. The standard 17'' wheel does not therefore fit over the IS350 caliper when it is bolted to the IS250 hub. Exdee has already stated this fact, but it appears either no one read his post or the misunderstanding continues,
I know for a fact that the 350 and 250 hubs are different because I still have a pair of new IS350 backplates/dustcovers that I purchased in the USA believing I could fit these bigger diameter plates when doing the brake mod, but they do not fit.