A lot of the UK tracks are multisurface, and for those the Minispikes are a good tyre on all surfaces, whereas the Minipin may not be so affective on the grass or dirt sections like we have at Bury, Southport and Kiddy (Just Astro and a bit of dirt).
On the full Astro tracks 9Stotfold), they are probably better, but to keep the series consistent (I presume) then the Minispike is chosen as a control tyre and the national series is easy to police, and tyre availability is easy to arrange as Schumacher know that they'll prob sell plenty of Minispikes and so mold them over the Pins. Til Winter comes.
Belgium GP Astro is ace by the way
