Racing road frames tend to have very short chain stays (usually about 410mm) plus they would use a short cage rear derailleur and a maximum 25t or 27t rear cog. A standard 26" Hardtail usually uses about 425mm long chainstays. A 29er or Full Suspension will use longer in addition to a med or long cage rear derailleur and a 32t or 34t large cog...pretty sure that chain will be too short for a MTB triple.