If I'm not mistaken, RealDrums will automatically substitute with the appropriate tempo if available. The key is 'if available'. Some, such as BossaTerryClarke^8-Shaker can only go as low as 110. If you set the tempo to 60, the 110 tempo will be used as it is the lowest available.

I would check that the 'Allow RealTracks substitution...' checkbox is selected in the RT Preferences. Perhaps that is unchecked and not allow tempo substitution. And not all RTs have substitutions available. Check yours in the RT dialog under the column labeled TS (Tempo Swaps). If it says Y it should change tempos.

R