Sorry it is all in french but here's how to mount 1/8 on road car tyres on your 1/10 buggy
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http://www.gaz-on.net/Monter-des-pneus-mousse-sur-un
Page takes a little while to load , but it shows how to get the foam off the wheel with acetone and then put them on the 2.2" rims of your buggy .