Sorry Didwot - don't quite agree - When you purchase something, and this is not done with 'money or money's worth', you can still have taken the rights of this as long as you can shomw some form of detriment - this can take place in the form of a promise to pay (teh credit card thing I believe you were trying to speak of) - To make it simple, for a legally binding contract of sale, there must be a benefit and a detriment to both parties.
The old saying that 'posession is 9/10 of the law' can. in some instances be correct, on the proviso that you are a bonafide purchaser for value without notice (property law)
Although you may not have legal title to something, this does not mean that you do not have an equitable interest - and as equity prevails over all other interests, it will prevail. In other words, equity can overeach the legal title of the wheels - simple really.
Good luck, but I shouldn't worry.