Tires

[farseer80]

I am just wondering if standard street tires like Toyo Tires' Proxes A18, would fit a Mini?

[MiniDave]

Do they offer them in 10, 12 or 13" sizes?

[MPlayle]

Are you asking about fitting on a classic Mini (1959 - 2000) or a new MINI (2002 - present)?

If classic, then Dave's question is the first step.  There are limited sizes that will fit on a classic Mini due to the suspension and body spacing.  Too tall and the rears will rub on the swing arm and/or swing arm outer mounting bracket.  Too wide with the wrong wheel offset and you will potentially get rubbing both front and rear.
Sizes known to fit classic Mini (last number is rim diameter):
145/80/10
165/60/10
145/70/12
165/60/12
175/50/13

If new MINI, then the answer is "most likely" as long as you are going with something in the '+0' or '+1' type classes in comparison to the factory spec.  You can see tire options for new Minis on sites like Discount Tire or Tire Rack.