The BMW R80ST is one of the few classic BMW boxers that can legitimately be called lithe (relatively speaking, at least). Derived from the famous BMW R80G/S, the R80ST borrowed its sibling’s banana tank, scrambler-like seat, offset mono-shock, and tightly-tucked banana exhaust. Compared to its 1,000 cc stablemates, it’s downright skinny?but not skinny enough for STG Tracker.
Run by Marcelo Obarrio and Germán Karp, and based in Buenos Aires, Argentina, STG Tracker has a penchant for building aggressive street bikes. So machines like this svelte BMW R80ST street tracker fall squarely within their wheelhouse. The brief called for an agile boxer with sharp lines?and STG Tracker delivered in spades.

Marcelo and Germán started with a bone stock 1983-model BMW R80ST, but most of it ended up in boxes. The main frame and drivetrain are original, but everything else is either custom, aftermarket, or scalped from another motorcycle. That said, the engine hasn’t exactly gone untouched. STG rebuilt it, gave it a fresh coat of paint, and polished the edges of its fins to add contrast. They also installed a set of classic BMW ‘peanut’ valve covers, and then trimmed the cooling fins on the cylinder heads to better complement the curves of the new covers.

The airbox has been ditched for a pair of K&N filters, with a new cover filling the space where it used to sit. STG rebuilt the carbs too, and fitted a pair of carb-mounted choke pulls, eliminating...