I'm guessing this is due to load rating required for the T6. If you look on THQ or Wheelbase, you will see the 20" tyre options with a load rating of 101, 103 or 104 are either 265 or 275.Thanks. According to the table above 265 is too wide for a 8.5" wheel. Did you find them ok?
Edit: I just realised the size was in the post above the pics. Doh!