17" set up doesn't fit within the GCR's for dirt track (max 150mm wide rear), so most run a trials tyre on the rear (18" but 19" are available) and stick to the 21" front wheel. It's hard pack and does get a blue groove throughout the day on the race line and most use from intermediate to hard fronts. Sliders run 19" speedway tyres.
Trials tyres like michies don't last long but many of the other brands do the job for the less financial.
Without wanting to detract from Australia's awesome DT history, I think one of these set up's would be the go here.