me and a friend did this and were semi-successful. what we did was use thin strips of electrical tape to build up the diameter a little on the rim, then put the pvc over it. our mistake was we used a pair of those rachet cutters to cut the pipe, these were not worth a ****. you need to make them real small so ours came out ****ty and wavy. id recommend using a hacksaw or something to that effect. also i had some clearence issues because the pipe is bigger than the origanl tires, i normaly run without the body anyway though. once we did get it working our cars would drift crazy all day long even on concrete...
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as far as the size its 1inch
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that clear scotch tape works wonders too for drifitng and only takes about 30 seconds to do