I'm planning on using spacers to test how far out my wheels can go whilst retaining good clearance ready for the new wheels I plan to buy, just so I know what offset I should order. It's especially necessary with the SS-Tuning extended arches I plan to buy, which are themselves 20mm wide. Because it's only for a one off test fitting of my stock wheels I'm going as cheap as possible. The cheapest I could find are some second hand 20mm spacers on ebay. My guess is that with the extended arches I'm looking more at 30mm, 40mm if I choose to roll the arches. My question is, are you able to stack spacers on top of one another? Please remember, this is ONLY for wheel clearance test purposes rather than for actual driving, so safety isn't an issue.