Just put one on rear of my whippet, 2.25 compared to a 2.35 High Roller on the front and it bloody dwarfs the HR!
I've got the ardent race same size, and agree. Makes my old 2.25 Nobby nics look tiny.
Think I may have acquired some HRII that are slightly bigger.
The old highroller's one of the most famously pisstaking tyres when it comes to sizes- the 2.7 measures 2.5, the 2.5 measures 2.35 and the 2.35 is around 2.2. Which is a shame, because there's a 2.1 and it would have been good to keep the pattern. Supertacky rubber's a great material for tyres, not ideal for rulers.
From memory the Ardent's actually pretty honest, we're just used to being lied to.
As above, old Maxxis tyres were a bit off in their sizing, seem to have got their act together now.
For future reference
http://www.reifenbreiten-datenbank.de/