Dollars to donuts it's plain steel, not cro-mo. Clue is the chain tensioning system. All high-end frames have an eccentric bottom bracket for adjusting the transfer chain tension, not an external idler wheel.
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BICYCLE - [[I]bahy-si-kuhl] - Noun :> A medical device used to correct the common geriatric condition of OFS, (Old, Fat & Slow), in a manner that does not induce brain-decaying boredom like walking or running.
2005 Trek T2000 tandem, Giant TCR, Eddie Merckx Majestic Ti, Fuji Team, Giant Revel 29er, Windsor Clockwork (Orange) fixie, and a BikTrix Juggernaut Ultra 1000 fat tire eBike