Did Novarro and Bushman Do Their Own Stuntwork?

I saw the 1925 Ben-Hur, recently, for the second time in 15 years and the chariot race still impresses! What really boggled my mind was how realistic it looked. NOTHING about the race seemed staged and the close-up shots of Ramon Novarro and Francis X. Bushman indicate, to me, that the two lead actors were definitely NOT holed away in a studio somewhere, on a merry-go-round with set props and photographed backgrounds, the way most pictures were made even into the 1960's.

I can't even find anything making it obvious that there are stunt substitutes for Novarro and Bushman in the longshots. Do I just have a bad eye for discerning where stuntmen have been substituted for the lead men--or, did they really do some/most of/ALL of their own stuntwork?